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CHAPTER 3 (Part 1)

AFFECTED ENVIRONMENT

INTRODUCTION

This chapter describes the existing environment that could be affected by actions proposed in this Final Yosemite Valley Plan/Supplemental Environmental Impact Statement (SEIS). This chapter begins with a list of the specific topics that are analyzed to determine the environmental impacts of the alternatives. These topics were selected based on federal law, regulations, executive orders, NPS Management Policies, National Park Service subject-matter expertise, and concerns expressed by other agencies or members of the public during scoping and comment periods. The conditions described establish the baseline for the analyses of effects found in Vol. Ib, Chapter 4, Environmental Consequences.

IMPACT TOPICS CONSIDERED

Water Resources

Actions, such as new development, may affect water resources in the park. The Clean Water Act requires the National Park Service, in implementing its management activities, to comply with all federal, state, interstate, and local requirements; administrative authority; and processes and sanctions regarding the control and abatement of water pollution in the same manner and to the same extent as any non-governmental entity, including the payment of reasonable service charges (33 USC 1323). Hydrology and water quality are also discussed under this topic.

Floodplains

The Floodplains section defines the extent and condition of the Merced River floodplain and the potential risks involved in constructing facilities within the floodplain. It also summarizes the laws, regulations, and guidelines that govern development within the floodplain, including the Wild and Scenic Rivers Act, Executive Order 11988 (Floodplain Management), and the NPS Floodplain Management Guideline (NPS 1993c).

Wetlands

Wetlands are important for the preservation of natural habitats and processes. Executive Order 11990 (Protection of Wetlands) requires the examination of impacts on wetlands and options for the placement of structures in wetland areas. Wetlands are considered a highly valued natural resource (see Vol. Ic, plate D).

Soils

Many of the soil types in Yosemite Valley and surrounding areas place limitations on construction or development. Many rich soil areas are considered highly valued natural resources and have the potential to support highly valued vegetative communities, such as meadows or wetlands (see Vol. Ic, plate D).

Vegetation

The vegetation of Yosemite is diverse and complex and is a significant part of the beauty and biological diversity of the park. Vegetation plays a vital role in maintaining ecosystem health and environmental quality. Plants recycle nutrients, provide wildlife habitat and food, contribute to regulation of microclimate, regulate stream discharge, maintain water quality, and prevent soil erosion. The vegetation communities are also character-defining features of the parkís cultural landscapes, reflecting the effects of human occupation (both prehistoric and historic) in many areas of the park, and most obviously in Yosemite Valley. Riparian, meadow, and California black oak communities in Yosemite Valley are highly valued resources (see Vol. Ic, plate D).

Wildlife

Wildlife and their habitats are extremely important in the park and serve as conspicuous indicators of ecosystem condition. This section also addresses wildlife species that do not naturally occur in the parkís ecosystems. Sensitive wildlife habitat is considered a highly valued natural resource (see Vol. Ic, plate D), based partially on its value to special-status species.

Special-Status Species

The Federal Endangered Species Act requires an examination of impacts on all federally listed threatened or endangered species. National Park Service policy requires examination of the impacts on state-listed rare, threatened, or endangered species, as well as federal species of concern, and state species of special concern. The National Park Service has identified additional plant species that are rare within the park or are particularly sensitive to human disturbance.

Air Quality

The Clean Air Act requires federal land managers to protect air quality. Yosemite National Park is classified as a Class I area under the Clean Air Act (42 USC 740 et seq.). National Park Service Management Policies address the need to analyze air quality during park planning and to ensure that air pollution sources in national parks comply with all federal, state, and local air quality regulations.

 

Geologic Hazards

Rockfalls and rock avalanches continue to occur within Yosemite Valley, posing potential risk to life and property. The National Park Service and the U.S. Geological Survey have documented potential geologic hazards in Yosemite Valley (see Vol. Ic, plate E). This information was used to develop the Yosemite Valley Geologic Hazard Guidelines to assess risk to life and property (see Vol. II, Appendix C).

Scenic Resources

Conserving the scenery of national parks was one of the fundamental purposes of the National Park Service 1916 Organic Act. Yosemite National Parkís enabling legislation also expressed the importance of protecting park scenery (see Vol. Ic, plate F).

Cultural Resources

The National Historic Preservation Act, the Archeological Resources Protection Act, the Native American Graves Protection and Repatriation Act, and the National Environmental Policy Act require that the effects of any federal undertaking on cultural resources be examined. In addition, NPS Management Policies, expressed in Directorís Order (DO) 2: Park Planning; NPS-28 Cultural Resources Management Guidelines; and NPS Museum Collections Management Guideline (DO-24, final draft), call for the consideration of cultural resources in planning proposals. During the planning process, significant historic and archeological sites, historic buildings and structures, cultural landscape resources, traditional cultural properties, and museum collections that could be affected by the alternatives were identified.

ARCHEOLOGICAL RESOURCES

Past and ongoing studies have indicated that Yosemite National Park is rich in archeological resources. Yosemite Valley has been designated as an archeological district, with more than 100 sites containing evidence of human occupation and land use over several millennia. Archeological sites with high data potential are considered highly valued cultural resources (see Vol. Ic, plate D)

ETHNOGRAPHIC RESOURCES

Proposed actions could affect properties that are associated with cultural practices or beliefs of culturally associated American Indian people (traditional cultural properties). These include plant-gathering areas, spiritual places, places that figure in oral traditions, and historic village locations. The protection of ancestral burial areas is also an important concern of Indian people. Known human burials in Yosemite Valley are considered highly valued cultural resources (see Vol. Ic, plate D).

CULTURAL LANDSCAPE RESOURCES

As described in the 1994 Yosemite Valley Cultural Landscape Report, the cultural landscape of Yosemite Valley is composed of both natural and human-made elements, including historic structures, buildings, districts, and sites. Any alternative that would affect the natural or human-made environment could also affect the cultural landscape. Cultural landscape resources are considered highly valued resources.

HISTORIC SITES AND STRUCTURES

Many of the historic resources identified in the park are listed on, or are eligible for listing on, the National Register of Historic Places. These places reflect important eras or the influence of individuals important in the human history of the park. Three National Historic Landmarks are located in Yosemite Valley: The Ahwahnee, the Rangers' Club, and LeConte Memorial Lodge. These reflect the highest level of historic significance and are considered highly valued resources (see Vol. Ic, plate D).

MUSEUM COLLECTION

The location, management, and long-term preservation of the museum collection, including the archives and research library, could be affected by the proposed actions. These resources are important for documenting and understanding the natural and human history of the park and interpreting that understanding to the public.

Merced Wild and Scenic River

In 1987, Congress designated the main stem and the South Fork of the Merced River as a Wild and Scenic River under the Wild and Scenic Rivers Act of 1968, as amended. This section outlines the Wild and Scenic River values associated with the main stem of the Merced River where it flows through Yosemite Valley and the El Portal Administrative Site, and of the South Fork where it flows through Wawona (see Vol. Ic, plates G-1, G-2, and G-3).

Visitor Experience

Providing for visitor enjoyment, understanding, and stewardship is one of the fundamental purposes of the National Park Service. Many actions considered in this Final Yosemite Valley Plan/SEIS could affect patterns of visitor use and the type and quality of visitor experiences. Visitor access, orientation and interpretation, recreation, visitor services (including camping and lodging), and night sky are specific elements of the visitor experience; however, the impacts in other topic areas could also directly affect visitor experience. For example, enhancement or degradation of visual resources would also enhance or degrade the visitor experience.

Transportation

Traffic volume, including both private and transit vehicles, could be affected. Alternative travel modes, including bicycling and hiking, would also be affected.

Noise

Changes in noise, primarily from traffic, is an issue of concern. Reduced vehicle traffic, increased bus service, road relocations and closures, and changes in parking locations could affect noise levels.

Social and Economic Environments

The National Environmental Policy Act requires an examination of social and economic impacts caused by federal actions.

SOCIAL ENVIRONMENT OF AFFECTED COMMUNITIES

Five local communities—Yosemite Valley, El Portal, Foresta, Wawona, and Yosemite West—could be affected by relocation of employees, construction of new housing, and changes in commuting patterns.

REGIONAL ECONOMIES

The surrounding counties that provide services to visitors and employees and receive tax revenue or benefits through retail and other trade could be affected. These counties are Merced, Mariposa, Madera, Mono, and Tuolumne.

ENVIRONMENTAL JUSTICE

Executive Order 12898 (Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations) requires all federal agencies to incorporate environmental justice into their missions. This is accomplished by identifying and addressing disproportionately high and adverse human health or environmental effects of federal programs and policies on minorities and low-income populations. This executive order also requires that the programs and policies of federal agencies do not discriminate against persons (including populations) because of race, color, or national origin.

Park Operations

The alternatives being considered have the potential to affect National Park Service, concessioner, and other park partner operations and facilities available for public or administrative use.

Energy Consumption

The National Environmental Protection Act requires a discussion of the energy requirements of the alternatives.

IMPACT TOPICS DISMISSED FROM FURTHER ANALYSIS

Wilderness

Approximately 704,624 acres (94%) of the 747,969 acres that comprise Yosemite National Park have been designated as Wilderness under the California Wilderness Act of 1984 (Public Law 98-425). Five major hiking trails enter the Yosemite Wilderness from Yosemite Valley, including the renowned John Muir Trail. Yosemite Valley is also an international destination for world-class rock climbing, much of which occurs within the designated Wilderness.

The Valley floor is roughly 4,000 feet above sea level. The designated Wilderness in the vicinity of the Valley starts at approximately 4,200 feet above sea level. The Valley floor, where the majority of park infrastructure and facilities are located, is not within or directly adjacent to the designated Wilderness. Activities proposed by the action alternatives would not encroach upon or otherwise physically disturb any portion of the designated Wilderness. In addition, any changes in activities that may occur as a result of implementation of the action alternatives would not discernibly change visitor use of the designated Wilderness from current levels. Therefore, no impacts to the designated Wilderness would occur.

In 1982, the McCauley Ranch (185 acres), located a half mile southwest of Foresta, was added to Yosemite National Park. In 1984, the California Wilderness Act required the Secretary of the Interior to study this addition to determine the suitability or nonsuitability of its designation as Wilderness. To date, a Wilderness suitability assessment has not been completed.

Geology

The geology of Yosemite Valley, El Portal, and adjacent areas is a distinctive element of the parkís scenic character. None of the actions proposed in the alternatives considered in this Final Yosemite Valley Plan/SEIS would appreciably affect the geology of the area. Short-term incidental effects to soils and underlying rock formations may occur in localized areas from the construction or removal of facilities, but no permanent changes to the areaís geologic resources are anticipated.

Implementation of the alternatives would not discernibly affect the Valley's rock formations, walls, or glacial moraines. Actions proposed in the alternatives would occur some distance from these and other important geologic features. Impacts related to soils and geologic hazards are presented in Vol. Ib, Chapter 4, Environmental Consequences.

The Sierra Nevada range in the vicinity of Yosemite National Park is not considered an area of particularly high seismic activity. No active or potentially active faults have been identified in the mountain region of the park (CDMG 1990). However, the possibility still exists that Yosemite could undergo seismic shaking associated with earthquakes on fault zones to the east and west margins of the Sierra Nevada. These fault zones include the Foothills fault zone, the volcanically active Mono Craters–Long Valley Caldera area, and the various faults within the Owens Valley fault zone (CDMG 1996).

REGIONAL SETTING

Yosemite National Park lies on the western slope of the Sierra Nevada, a massive mountain range dividing central and northern California from more arid lands to the east. The Sierra Nevada ecoregion (which extends through the foothill zone on the west side and the base of the escarpment on the east side) is about 450 miles long and 100 miles wide. Elevations in the park range from approximately 2,000 feet to 13,114 feet. Most of the 747,969 acres of the park is designated Wilderness (94%, or 704,624 acres). National forest lands surround the park (see Vol. Ic, plates B and C).

Yosemite National Park lies about 200 miles east and four hours by car from San Francisco, and about 320 miles northeast and six hours from Los Angeles (see Vol. Ic, plate A). The park has four main entrances. South Entrance on the Wawona Road (Highway 41), Arch Rock Entrance on the El Portal Road (Highway 140), and Big Oak Flat Entrance on the Big Oak Flat Road (Highway 120 West) offer year-round access on the west side of the Sierra Nevada (see Vol. Ic, plate C). Tioga Pass Entrance on the Tioga Road (Highway 120 East) offers seasonal access on the east side of the Sierra Nevada.

The geologic environment of Yosemite National Park is characterized by granitic rocks and remnants of older rock (Huber 1989). In the early Tertiary period, 40 to 60 million years ago, the geologic environment of the Sierra Nevada region was lower in elevation, with a gently rolling upland surface. The Merced River flowed at a gentle gradient westward through a broad river valley. About 10 million years ago, the Sierra Nevada was uplifted and then tilted to form its relatively gentle western slopes and the more dramatic, steep eastern slopes. The uplift increased the flow gradients, resulting in deep, narrow canyons.

About 1 million years ago, snow and ice accumulated, forming glaciers at the higher alpine elevations that began to move westward down the river valleys. Ice thickness within Yosemite Valley may have reached 4,000 feet during the early glacial episode. The downslope movement of the ice masses cut and sculpted the U-shaped valley evident today. After the last glacier left the valley about 15,000 years ago, a lake referred to as Lake Yosemite was formed behind the materials deposited by the glaciers. More than 1,000 feet of glacial and stream sediment now underlies the floor of Yosemite Valley and cover glacially disturbed granitic rock (Huber 1989).

The Sierra Nevada range contains the headwaters of 24 major river basins, two of which are in the park: the Merced River and the Tuolumne River. The California Wilderness Act of 1984 established portions of the Tuolumne River (including the Dana and Lyell Forks) as part of the Wild and Scenic Rivers System. In 1987, Congress also designated the main stem and the South Fork of the Merced River as part of the Wild and Scenic Rivers System.

About one-third of the Sierra Nevada is privately owned, and about two-thirds publicly owned. The U.S. Forest Service manages most of the public land; the Bureau of Land Management and National Park Service manage most of the remainder. The majority of the land at high elevations throughout the Sierra Nevada is public, as are large proportions of the eastern Sierra Nevada. Private lands are predominately below 3,000 feet in elevation in the western Sierra Nevada (UC Davis 1996e).

The population in the Sierra Nevada doubled between 1970 and 1990; 40% of the population growth occurred north of Yosemite National Park. Official projections indicate that the 1990 Sierra Nevada population of 650,000 will triple by the year 2040. The foothill regions south of El Dorado County are likely to see a three- to five-fold population increase. Communities in the Sierra Nevada are dependent on the ecosystem for a combination of natural resource benefits, including non-economic benefits associated with aesthetics and scenery (UC Davis 1996e).

The major vegetation zones of the Sierra Nevada form readily apparent, large-scale north-south elevational bands along the axis of the mountain range. Major east-west watersheds that dissect the Sierra Nevada with steep canyons form a secondary pattern of vegetation. On the west side, forest types change with increasing elevation from ponderosa pine to mixed conifer to firs. Straddling the crest of the Sierra Nevada is a zone of subalpine and alpine vegetation. Fire suppression, in concert with changing land-use practices, has changed natural fire regimes of the Sierra Nevada dramatically. This has altered ecological structures and functions in Sierra Nevada plant communities (UC Davis 1996e).

Four Sierra Nevada national parks—Lassen Volcanic, Yosemite, Sequoia, and Kings Canyon—make up most of the remaining large contiguous areas of late successional forest in middle-elevation conifer types. While the national parks contain large blocks of high-quality late successional forest, similar but considerably smaller patches are relatively well distributed throughout the Sierra Nevada. However, these forest patches have been compromised in many areas by the effects of fire suppression and grazing (UC Davis 1996e).

The Sierra Nevada is rich in plant diversity. Of Californiaís 7,000 plant species, about 50% occur in the Sierra Nevada. Of these, more than 400 are found only in the Sierra Nevada, and 200 are rare. As a group, Sierra Nevada plants are most at risk where habitat has been reduced or altered. However, rare local geologic formations and the unique soils derived from them have led to the evolution of ensembles of plant species restricted to these habitats. This is true in the El Portal area, where a number of state-listed rare species are sustained in a unique contact zone of metamorphic and granitic rock.

About 300 terrestrial vertebrate species (including mammals, birds, reptiles, and amphibians) use the Sierra Nevada as a significant part of their range. Three vertebrate species once well distributed in the range are now extinct from the Sierra Nevada: Bellís vireo, California condor, and grizzly bear. Sixty-nine species of terrestrial vertebrates (17% of the Sierra Nevada fauna) are considered at risk by state or federal agencies. These species include Sierra Nevada bighorn sheep, Yosemite toad, foothill yellow-legged frog, mountain yellow-legged frog, and western pond turtle. The most important identified cause of the decline of Sierra Nevada vertebrates has been the loss of habitat, especially foothill and riparian habitats and late successional forests.

Aquatic and riparian systems are the most altered and impaired habitats of the Sierra Nevada. Dams and diversions throughout the Sierra Nevada have altered streamflow patterns and water temperatures. Foothill areas below about 3,300 feet appear to have the greatest loss of riparian vegetation of any region in the Sierra Nevada (UC Davis 1996a).

Humans have lived and sustained themselves in the region for at least 10,000 years and are part of the Sierra Nevada ecosystem. Indigenous populations were widely distributed throughout the range at the time of Euro-American immigrations. Archeological evidence indicates that for more than 3,000 years American Indians practiced localized harvesting, pruning, irrigation, and vegetation thinning. Immigration of Euro-American settlers in the early 1800s began a period of increasingly intense resource use and settlement (UC Davis 1996e).

The Sierra Nevada region is a popular destination, containing some of the worldís outstanding natural features. Residents and nonresidents, including visitors from around the country and the world, are drawn to the recreational resources in Yosemite Valley, Lake Tahoe, Mono Lake, and sequoia groves, which attract millions of visitors each year. Among the larger public agencies, 57-67% of recreational activity takes place on land administered by the U.S. Forest Service, while lands of the California Department of Parks and Recreation (15-27%), the Bureau of Reclamation (7-8%), the National Park Service (6-7%), and the U.S. Bureau of Land Management (3%) provide additional recreational opportunities. Other public lands, utility-owned properties, and private lands account for substantial additional recreational opportunities in the Sierra Nevada (UC Davis 1996b).

Within Yosemite National Park, diverse recreational opportunities and experiences are available. Three principle destinations—Yosemite Valley, Tuolumne Meadows, and Wawona— provide a wealth of opportunities for walking and hiking, stock use, fishing, natural and cultural sightseeing, interpretive centers and programs, camping, and lodging. Approximately 95% of Yosemite National Park is designated Wilderness and provides opportunities for solitude, extensive hiking, backpacking, and stock use. Camping is also available at several campgrounds along the Tioga and Glacier Point Roads, and near the Big Oak Flat Entrance. Three sequoia groves provide opportunities for hiking among these giants. Popular short and long hiking trails also originate along the Glacier Point Road. While climbing is popular in many park areas, the most unique opportunities are found in Yosemite Valley. Other recreational opportunities are available as well: downhill and cross-country skiing, snowshoeing, bicycling, and rafting, as well as golf, ice-skating, and tennis.

WATER RESOURCES

This section provides an overview and description of water resources, including hydrology and water quality. Additional information regarding the relationship of water resources, flora, fauna, and soils is contained in the Floodplains, Merced Wild and Scenic River, and Wetlands sections of this chapter.

Hydrology

Yosemite has a variety of surface water features, some of which are a major attraction for park visitors. Some of the tallest waterfalls in the world are found in Yosemite Valley, including Yosemite Falls (with a total drop of 2,425 feet) and Ribbon Fall (1,612 feet). The Tuolumne and Merced River systems originate along the crest of the Sierra Nevada in the park and have carved river canyons 3,000 to 4,000 feet deep. The Tuolumne River drains the entire northern portion of the park, an area of approximately 680 square miles. The Merced River begins in the parkís southern peaks, primarily the Cathedral and Clark Ranges, and drains an area of approximately 511 square miles. Hydrologic processes, including glaciation, flooding, and fluvial geomorphic response, have been fundamental in creating landforms in the park.

The main stem of the Merced River flows from the crest of the Sierra Nevada through Yosemite Valley and down to the San Joaquin Valley of California. The upper watershed is entirely within the boundaries of the park. Principal tributaries of the Merced River in Yosemite Valley include Tenaya Creek, Yosemite Creek, and Bridalveil Creek. Historic discharge in the river, measured at the Pohono Bridge gauging station in the west Valley, has ranged from a high of about 25,000 cubic feet per second to a low of less than 10 cubic feet per second. The mean daily discharge is about 600 cubic feet per second.

Glaciation in Yosemite Valley carved a wide, U-shaped valley that extends westward to a location near the Pohono Bridge. Following glacial retreat, a prehistoric lake known as Lake Yosemite developed and eventually filled with sediment from the El Capitan moraine upstream to Happy Isles. The resulting valley floor had a very mild slope and is responsible for the meandering pattern of the present-day river. The Merced River is an alluvial river through most of Yosemite Valley, and the bed and banks of the channel are comprised of fine-grained sediments, cobbles, and soil layers. This condition makes for a dynamic river that alters its course periodically by eroding and depositing bed and bank materials.

In El Portal, the Merced River has a steeper gradient than in Yosemite Valley and consists mostly of continuous rapids. The riverbed and banks are largely comprised of bedrock, with boulders and cobbles ranging in size from a few inches to several feet in diameter. The steeper river gradient and its contact with bedrock prevents the river from meandering as extensively as it does in Yosemite Valley. Additionally, riverbank areas in many locations have been developed and strengthened for road and facility protection. Because of the gradient and development at El Portal, shifting of the river channel usually occurs only during large floods.

In Wawona, the river meanders through a large alluvial floodplain with substantial gravel bars within the channel.

Surface water and groundwater function together in Yosemite and El Portal. In the Wawona area, the groundwater flows through upper unconsolidated fills and lower fractured rock aquifers that have not been defined. Recharge of the shallow groundwater aquifers reaches a peak during the spring snowmelt. In Yosemite Valley, the entire meadow system may be saturated to the forest edge, resulting in restricted tree growth that defines the forest/meadow boundaries and extensive Valley wetlands. In El Portal and Wawona, the steeper terrain and resulting river gradient have played a role in limiting the extent of wetlands. Wawona Meadow is a 200-acre, low-elevation wetland that is not directly influenced by the Merced River.

Groundwater is used in Yosemite Valley, Wawona, and El Portal for domestic water supplies. Four groundwater production wells in Yosemite Valley produce approximately 1,400 gallons per minute. In El Portal six wells support a capacity of approximately 240 gallons per minute. In Wawona, approximately 100 groundwater wells support about 260 residents and a store. The South Fork of the Merced River is the source for the communal water system supporting the remaining residents and all government and concessioner facilities in Wawona.

Eleven bridges cross the Merced River in Yosemite Valley between Happy Isles at the east end and Pohono Bridge at the western end. Many of these bridges influence the width, location, and velocity of the Merced River. The National Park Service (1991b) and Milestone (1978) found constriction of the river at all of these bridge sites.

The Merced River in eastern Yosemite Valley is an alluvial river, where the bed and banks are made up of the same materials that are transported by the river. Natural erosion and deposition processes cause the river channel to migrate, often over an extensive area. In addition, alluvial rivers create and use large floodplain areas.

The inherent dynamic nature of this alluvial river makes its coexistence with stationary bridges problematic; bridges can alter the morphology of the river by changing the rate, depth, and velocity of flow in the vicinity of the structure. Bridges rarely span the entire floodplain width of alluvial rivers and do not generally even span the entire natural channel width and, therefore, constrict flow area. During floods, portions of the river that would normally flow into floodplain areas are forced under the structure, increasing the amount of channel discharge. The effect of these seemingly minor, flow-related changes can be profound, both upstream and downstream of the bridge. The higher discharge and reduced flow area cause a backwater effect (a deep, slow-velocity area) to form upstream and high velocities to occur near and under the bridge opening.

The reach upstream of the bridge (in the backwater zone) often develops a sand and gravel bar in the middle of the channel caused by sediments deposited by slower-moving water. The development of this mid-channel bar can lead to bank instability as the force of the river is directed away from the bar and into the riverbank. If this lateral erosion occurs, riverbanks will eventually fail, causing rapid movement of large quantities of sediment and vegetative debris. This can even occur on banks that have been stabilized by riparian vegetation.

At Sugar Pine Bridge, water flows are dammed by the structure, forcing the river to move laterally, which in turn has encouraged development of a new channel that cuts off the natural meander of the river. Prior to the construction of the bridge and its western approach road, there were several small, natural, flood-overflow channels at this river meander. Constriction of water at the bridge, coupled with the influence of Tenaya Creek (which deflects water toward the left bank at the upstream end of the bridge), has resulted in a single, large cutoff channel immediately adjacent to the road.

In the reaches immediately upstream and downstream of the Sugar Pine Bridge, flow velocity is high. This causes bank scouring where the river meets the bridge opening. Directly beneath the bridge, velocities are at a maximum, causing a deep scour pool. Downstream of the bridge, a mid-channel bar is likely to develop as this scoured sediment drops out in the slower-moving water. As with development of a mid-channel bar upstream of a bridge, lateral channel instability and loss of riparian vegetation can occur.

At Stoneman Bridge, the channel width is also constricted, causing increased velocities during high flow, resulting in the formation of a downstream scour pool and mid-channel bar. The presence of the downstream bar has caused erosion to increase unnaturally along the right bank. The constricted channel width has also led to impacts upstream, with flood waters backing up behind the bridge and causing erosion on both banks.

Ahwahnee Bridge constricts flood flows to a lesser degree, but has two center piers in the river channel that trap logs at high flows. The trapped logs threaten the structure, but are also important components of the hydrologic and biologic processes of the Merced River.

Water Quality

Water quality throughout Yosemite National Park is considered to be good and is generally above state and federal standards. An inventory of water quality performed by the National Park Service indicated pristine conditions in many parts of the park, but some water quality degradation in areas of high visitor use (NPS 1994c). The surface water quality of most park waters is considered by the State of California to be beneficial for wildlife habitat, freshwater habitat, and for canoeing, rafting, and other recreation, as indicated in the 1998 Central Valley Regional Water Quality Control Board's Water Quality Control Plan (Basin Plan).

SURFACE WATER

Surface water draining granitic bedrock in the park exhibits considerable variability in chemical composition, despite the relative homogeneity of bedrock chemistry (Clow et al. 1996). Surface water in most of the Merced River basin is diluted (lacking in dissolved solids), making the ecosystem sensitive to human disturbances and pollution (Clow et al. 1996). Studies have indicated a presence of Giardia lamblia and fecal coliform in various surface waters throughout the park, thereby limiting direct consumption of surface water by humans (Williamson et al. 1996b).

High water quality is critical for the survival and health of species associated with riparian and aquatic ecosystems. Water quality elements that affect aquatic ecosystems include water temperature, dissolved oxygen, suspended sediment, nutrients, and chemical pollutants. These elements interact in complex ways within aquatic systems to directly and indirectly influence patterns of growth, reproduction, and mobility of aquatic organisms. For example, sediment may not be directly lethal to fish, but sediment deposited on the streambed may disrupt the productivity and life cycles of fish and aquatic insects.

Surface water quality of the main stem and South Fork of the Merced River is characterized by near excellent conditions in most areas and some water quality stresses near human development. Surface water chemistry exhibits low electrical conductivity (limited ions due to a lack of dissolved solids), near-neutral pH, low alkalinity, and low nutrient concentrations (NPS 1994c). Calcium and bicarbonate are the predominant ions in the water. Within the Merced River, major ion concentrations slightly increase downstream, but levels remain relatively low, and no significant changes have been observed in pH, alkalinity, or nutrient concentrations (NPS 1994c). Due to the low alkalinity of the stream water, the buffering capacity (ability to absorb water chemistry changes or additions) of the Merced River and its tributaries is limited. Occasional concentrations of lead, cadmium, and mercury above drinking water and freshwater criteria have been noted within the Merced River main stem (NPS 1994c). Potential sources of these metals include leaded gasoline, stormwater runoff from developed surfaces (such as parking lots), wastewater discharge, campsites, and fuel storage facilities.

GROUNDWATER QUALITY CHARACTERISTICS

Groundwater quality is generally good in the Merced River basin; groundwater is the sole source of potable water for Yosemite Valley and El Portal. In Wawona, the primary source of potable water is surface water, although some private residences maintain private wells. There are locations in Yosemite Valley where relatively high iron concentrations in groundwater result in reddish deposits on the ground surface (e.g., springs near lower Tenaya Creek and several locations on the Merced River) (Williamson et al. 1996a). These iron concentrations are naturally occurring and are not a threat to water quality. Federal regulations require that potable water systems that rely on groundwater be continually monitored and operated within set levels for turbidity, waterborne pathogens, and other potential pollutants.

BANK EROSION

Water quality in the popular areas along the Merced River has been affected by extensive and concentrated visitor use. Heavy use along streambanks induces bank erosion through the loss of vegetative cover and soil compaction. Bank erosion can result in widening of the river channel and loss of riparian and meadow floodplain areas. Water quality is then altered through increased suspended sediments due to erosion, higher water temperatures from a lack of shade once provided by riparian vegetation, and lower dissolved oxygen levels due to elevated temperatures and shallower river depths.

NON-POINT POLLUTION SOURCES

Human activities and the use of motor vehicles can distribute potential water pollutants that may collect on land surfaces and later be transported into the river or its tributaries by stormwater runoff and sediment erosion. Recreational activities such as horseback riding, swimming, and hiking can lead to the introduction of organic, physical, and chemical pollutants into aquatic systems. These sources have the potential to affect water quality in all segments of the Merced River.

Non-point source runoff from roads and parking lots may potentially affect water quality by introducing organic chemicals and heavy metals. Areas of concentrated livestock use, including stock trails used for concessioner-led trail rides, introduce nutrients and sediments contributed through erosion, while the developed areas introduce various pollutants associated with human waste and debris. The Wawona Golf Course presents a potential non-point pollution source due to the occasional use of fertilizers and pesticides (including herbicides) to maintain the golf course green, although the kinds of pesticides used and their application and disposal are strictly controlled.

Stormwater runoff from developed surfaces in the park is managed in different ways. For example, a small portion of runoff from parking lots in Yosemite Valley is diverted into the wastewater drains and treated at the El Portal Wastewater Treatment Plant. Direct runoff of oil, grease, rubber particles, metals, and other road deposits occurs from most roadways, which discharge directly or indirectly to streams and lakes throughout the park. Water resources in the park can also be affected by regional air quality pollution through particulate deposition and polluted precipitation. The entire Sierra Nevada range is sensitive to acid precipitation due to its granitic substrate and the resulting low buffering capacity of its water resources. Ongoing studies are examining the effects of air pollutants generated outside the park and inside the park on natural resources, including surface water resources.

UNDERGROUND TANKS AND ABANDONED LANDFILLS

A variety of potentially hazardous materials has been stored in the park over the last century, often in underground storage vessels. Since 1986, more than 100 underground tanks have been located and removed. The park has more than 30 known contamination sites from leaking underground storage tanks. Currently, 12 underground storage tank sites are being cleaned up. Once clean, these sites will be closed. There are also a number of old landfills and surface dump sites in the park (NPS 1999b). These underground non-point pollution sources present potential impacts to water quality.

POINT SOURCES OF POLLUTION

Point sources of pollution are discharges that can be traced to a single point or location, such as a pipe or other device. Facilities in Yosemite Valley and El Portal are connected to a wastewater collection system that terminates at a wastewater treatment plant. Treated wastewater is discharged to percolation and evaporation ponds at the treatment facility. Water quality impacts from wastewater may occasionally occur as a result of sewer line blockage and wastewater backup and overflow. A tertiary wastewater treatment plant serves most of the public and private sources in Wawona; the treated wastewater is augmented by surface water draws from the South Fork of the Merced River (up to 500,000 gallons per day in August) used to irrigate the Wawona Golf Course. During winter months, the treated wastewater is discharged into the South Fork when storage capacity is insufficient and disposal to the golf course is not feasible due to snow cover.

FIRES

Fire is a natural process of the Sierra Nevada and Yosemite National Park. The recurrence of fire shapes the ecosystems of the park, with many common plants exhibiting specific fire-adapted traits.

The National Park Service has adopted a Fire Management Plan (NPS 1990b), which has clear guidelines about when and where to allow natural and prescribed fires to burn. The effects of fire on water quality are important; fires are a disturbance that can increase sediment contributions to aquatic systems, alter runoff patterns, and thereby influence concentrations of chemical and biological constituents in water bodies.

FLOODPLAINS

The Merced River watershed has had 11 winter floods since 1916 that have caused substantial damage to property. All of these floods took place between November 1 and January 30. The largest floods occurred in 1937, 1950, 1955, and 1997 and were in the range of 22,000 to 25,000 cubic feet per second, as measured at the Pohono Bridge gauging station in Yosemite Valley. These floods were caused by warm winter rains falling on snow at elevations up to 8,600 feet (e.g., Tuolumne Meadows), partially melting the accumulated snowpack.

The 100-year floodplain is the area that is inundated by a 100-year flood, or the annual peak flow that has a 1% chance of being equaled or exceeded in any given year (see Vol. Ic, plate E). Prediction of the 100-year floodplain is necessary in order to comply with Executive Order 11988 (Floodplain Management) and with the NPS Floodplain Management Guideline. In order to predict the 100-year floodplain, it is necessary to perform a flood frequency analysis of the nearest gauging station data to determine the flow rate of a 100-year flood. This flow rate, along with topographic cross sections, is used by models to predict the inundation (or floodplain), flow velocities, and inundation depths of a 100-year flood event. The accuracy of these predictions is higher for areas near gauging stations, for areas with gauging stations that have been operating for many years, and for areas with more precise topographic cross-section data.

Following the January 1997 flood, National Park Service staff mapped the actual extent of the flood inundation in Yosemite Valley and El Portal, and the U.S. Geological Survey determined actual flood flow rates at the Pohono and Happy Isles gauging stations. These data were used to calibrate the flood frequency analysis (i.e., the predicted flow rate of a 100-year flood) and the flood inundation models (i.e., the predicted area that will be inundated by a 100-year flood) for Yosemite Valley and El Portal and are discussed below.

ABOVE HAPPY ISLES

The 100-year floodplain has not been mapped above Happy Isles. With a few minor exceptions, the floodplain is not well developed between Happy Isles and the Merced River headwaters.

HAPPY ISLES TO HOUSEKEEPING BRIDGE

The predicted 100-year floodplain in this area was mapped by Cella Barr Associates (1998), using the flood frequency analysis performed by the U.S. Geological Survey. Flow rates and inundation depths were also calculated. Flood waters associated with the Merced River use Tenaya Creek as a backwater area.

HOUSEKEEPING BRIDGE TO SWINGING BRIDGE

The 100-year floodplain in this area was mapped by Stantec Consulting, Inc. (2000). Formerly known as Cella Barr Associates, Stantec continued the work done in 1998 and used the same techniques and flood frequency analysis. Flood waters associated with the Merced River use Indian Creek and Yosemite Creek as backwater areas.

SWINGING BRIDGE TO POHONO BRIDGE

The extent of the January 1997 flood, as mapped by National Park Service staff, is considered the best available data for the 100-year floodplain in this area.

POHONO BRIDGE TO PARK BOUNDARY

The 100-year floodplain has not been mapped in this area. With a few minor exceptions, the floodplain is not well developed.

EL PORTAL ADMINISTRATION SITE

Following the January 1997 flood, the U.S. Army Corps of Engineers calculated the flood frequency for El Portal and used the predicted flow rate for a 100-year flood to determine the 100-year floodplain. This effort was hampered by the lack of stream gauge data in El Portal. The Army Corps of Engineers determined that the January 1997 flood had a lower flow rate than the predicted 100-year flood.

SOUTH FORK MERCED RIVER AT WAWONA

The 100-year floodplain for this area was mapped by the Corps of Engineers in 1981.

Floodplain Characteristics

The floodplain of the Merced River in Yosemite Valley is well-developed in some sections, such as in meadow areas in Yosemite Valley. In other areas the floodplain is lacking due to narrowing of canyon/valley walls, such as the gorge, or incision of the channel into moraine deposits, such as west Yosemite Valley moraines (NPS 1997g).

In Yosemite Valley, the character of the floodplain varies in different locations because of local hydraulic controls. From Clark's Bridge to Housekeeping Camp in the east Valley, the Merced River floods areas outside the main river channel with shallow swift flows that cut across meander bends. Near Yosemite Lodge and downstream to the El Capitan moraine, flood waters back up against the dense vegetation and tend to be deep and slow (low velocity). From the El Capitan moraine downstream, the river channel is steeper and confined in the narrow river canyon, the floodplain is narrow, and flow velocities are high.

The broad, well-developed floodplain that occurs in Yosemite Valley between Housekeeping Camp and the El Capitan moraine serves many hydrologic functions, including dissipation of flood water energy as water spreads out over the flat, expansive plain. The meadows in Yosemite Valley occur primarily in the floodplain and are maintained and rejuvenated by periodic flood waters. The roads across Stoneman, Ahwahnee, Cook's, Sentinel, and El Capitan Meadows have varying degrees of influence on the function of the floodplain.

The river channel in El Portal is narrow and steep, though less steep than in the gorge segment immediately upstream, and flow velocities are very high. The river channel can shift laterally during large floods.

In Wawona, an elongated alluvial valley, the river meanders less than in Yosemite Valley, but the river channel can shift laterally during large floods. Development in Wawona has altered the floodplain. Surface water diversions affect the Wawona floodplain through reduction of the water table during dry periods such as drought and in the fall before the onset of winter rains. Water diversion is governed by the Wawona Water Conservation Plan, which includes provisions for reduction and/or cessation of withdrawals when stream flow drops to critical levels (NPS 1987b).

Frazil Ice Flooding

Waterfalls in the park occasionally produce a late winter and early spring phenomenon called frazil ice at the base of the fall. Small ice crystals develop in turbulent super-cooled stream water when the air temperature suddenly drops below freezing. These ice crystals join into slush and become pressed together as more crystals form. Frazil ice lacks the erosional force of regular stream ice, but it can cause streams to overflow their banks and change course. Frazil ice sometimes reaches a depth of more than 20 feet along Yosemite Creek at the Lower Yosemite Fall Bridge. A 1954 flow of frazil ice completely filled the streambed of the creek and covered the footbridge near Lower Yosemite Fall with many feet of ice (Hubbard and Brockman 1961). More recently, a frazil ice event covered the Yosemite Falls footbridge on February 27, 1996.

Non-Flood Alterations of the Floodplain

Although floods are significant to ecosystems because they can induce large changes in channel morphology and the floodplain landscape, low stream-flow characteristics are also important. Low stream flow during the summer can affect the surrounding floodplain as riparian and wetland communities undergo a drying phase. Diversion of river flows for human consumption can upset this normal balance and induce further reduction of riparian communities and destabilization of stream banks. Prior to 1985, potable water in Yosemite Valley was produced almost entirely from surface water diverted from the Merced River upstream of Happy Isles. It is estimated that up to 54% of the low stream-flow discharge may have been diverted for park facilities (NPS 1991b). This practice has been terminated in Yosemite Valley, and all potable water is now taken from groundwater wells; however, water continues to be drawn from the South Fork in Wawona to augment groundwater supplies.

Development in Floodplains

Executive Order 11988 (Floodplain Management) and the NPS Floodplain Management Guideline (NPS 1993e) provide guidance for the protection of life and property in conjunction with natural floodplain values in the National Park System. This guidance applies to both existing facilities and proposed facilities, and requires the National Park Service to avoid locating facilities in floodplains if alternative locations are feasible. Where no alternative exists, and with a formal statement of findings (see Volume II, Appendix N), properly mitigated facilities can be located in floodplains.

Each action (or facility) is assigned to one of three classes, depending on its use, and each class has a different regulatory floodplain. Actions of a given class can occur within the regulatory floodplain if properly mitigated. The regulatory floodplain for Class I actions, such as administrative facilities, residential areas, warehouses, and maintenance buildings, is the 100-year floodplain. The regulatory floodplain for Class II actions, such as medical facilities, emergency services, schools, irreplaceable records, museums, and fuel storage areas, is the 500-year floodplain.

Excepted actions are exempt from the NPS Floodplain Management Guideline if risks to human life and property are studied and then minimized or mitigated through design. Examples of excepted actions are bridges, flood control facilities, picnic areas, trails, roads, day-visitor parking facilities, and campgrounds.

If a non-exempted action is proposed, a formal statement of findings is required (see Volume II, Appendix N). The statement of findings includes a description of the site-specific flood risk, describes why the action must be located in the floodplain, and describes how the action will be designed or modified to minimize harm to floodplain values or risk to life or property.

Existing facilities in Yosemite Valley, El Portal, and Wawona that are within the 100-year floodplain are listed below.

YOSEMITE VALLEY

EL PORTAL

WAWONA

WETLANDS

Wetlands have many distinguishing features, the most notable of which are the presence of standing water, unique soils, and vegetation adapted to or tolerant of saturated soils (Mitsch and Gosselink 1993). Wetlands are considered highly valued resources, as they perform a variety of hydrological and ecological functions vital to ecosystem integrity. These functions include flood abatement, sediment retention, groundwater recharge, nutrient capture, and high levels of plant and animal diversity (USFS 1996). Since the mid-1800s, more than half of the nationís original wetlands have been drained (Mitsch and Gosselink 1993).

Historically, California wetlands were much more extensive than they are today. The state has lost more than 85% of its original wetland acreage (USGS 1996). Early settlers drained wetlands to improve forage and facilitate agriculture (UC Davis 1996a). In the Sierra Nevada, broad, flat valleys with vast wetlands were often converted to reservoir sites. The most common causes of wetland loss are: (1) draining, dredging, and filling of wetlands; (2) modification of hydrologic regimes; (3) road construction; (4) mining and mineral extraction; and (5) water pollution.

Probably the earliest major impact to wetlands in Yosemite Valley occurred in the late 1800s when a portion of the El Capitan moraine was blasted to lower the water level that backed up behind it. The moraine, a band of unconsolidated boulders and sediments deposited by glaciers, spanned the Merced River and served as a natural dam to annual high water flows. The moraine was believed to be 4 to 9 feet higher before it was blasted. Recent studies show that the blasting lowered some water tables that sustained meadow vegetation and wildlife, and accelerated erosion of the river base level in adjacent areas between El Capitan Meadow and Yosemite Lodge. Other historic impacts to wetlands include farming, roads, placement of structures, and ditching.

Wetland Classification

The National Park Service classifies and maps wetlands using a system created by the U.S. Fish and Wildlife Service that is often referred to as the Cowardin classification system (USFWS 1979). This system classifies wetlands based on vegetative life form, flooding regime, and substrate material. Wetlands, as defined by the U.S. Fish and Wildlife Service and adopted by the National Park Service, are lands transitional between terrestrial and aquatic systems, where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification, wetlands must have at least one of the following attributes:

Under Section 404 of the Clean Water Act, the U.S. Army Corps of Engineers issues permits for the discharge of dredged or fill material into waters of the United States (33 CFR 323.3). Wetlands are defined under the Clean Water Act as: "Those areas that are inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions (33 CFR 328.3)."

The Cowardin system and the Corps of Engineers both use the three wetland parameters to define wetlands: hydrophytic vegetation, hydric soil, and wetland hydrology. However, Cowardin and the National Park Service require only one of the parameters be present to be wetland, where as the Corps of Engineers requires all three parameters be present. Therefore, the Cowardin definition identifies more habitat types as wetlands than the definition used by the Corps. The Cowardin wetland definition also recognizes that many unvegetated sites (e.g., mudflats, stream shallows, saline lakeshores, playas) or sites lacking soil (e.g., rocky shores, gravel beaches) are wetland habitats. The reason these wetlands lack hydrophytic vegetation or hydric soil is due to natural chemical or physical factors. These additional aquatic environments are still regulated by the Corps of Engineers under the Section 404 permit program as other "waters of the United States."

Wetland Types in Yosemite

RIVERINE

The riverine classification includes all the wetland and deepwater habitats contained within a river channel, except wetlands dominated by trees, shrubs, persistent emergent mosses, or lichens. A channel is"an open conduit either naturally or artificially created which periodically or continuously contains moving water, or which forms a connecting link between two bodies of standing water" (USGS 1960).

RIVERINE LOWER PERENNIAL

The gradient is low, and water velocity is slow. The substrate consists mainly of sand and mud. Floodplains are well developed.

RIVERINE UPPER PERENNIAL

The gradient is steep, with fast water velocities. Some water flows throughout the year. The substrate consists of rock, cobbles, or gravel with occasional patches of sand. Algae concentrations are typically low, and there is little floodplain development.

LACUSTRINE

Lacustrine habitat is characterized by the presence of standing water in ponds and other shallow depressions. In Yosemite Valley, such habitats are found in association with fresh emergent wetlands and wet meadows, and are mostly found in cutoff channels of streams and rivers. Lacustrine habitats are the most scarce type in Yosemite Valley, making up only 0.03% of the Valley's total area. Water levels in the ponds vary throughout the year, with the highest levels occurring during peak spring runoff and declining through summer and fall. This fluctuation in water level provides a rich organic food base from seasonally inundated vegetation that decomposes, supporting an abundance of zooplankton and aquatic insects. Also, water in lacustrine habitats tends to be warmer than adjacent flowing streams, especially during summer and fall. Lacustrine habitats are important feeding, roosting, and brood-rearing areas for mallards that nest in Yosemite Valley. They were also the prime habitat for California red-legged frogs that are now probably extinct in the park. The likely cause of this extinction was predation by bullfrogs that were probably introduced in the late 1960s. Lacustrine habitats, especially those that contain water year-round, are important breeding areas for bullfrogs, and recent efforts to eradicate bullfrogs have focused on these areas.

PALUSTRINE

The palustrine classification includes vegetated wetlands, but can also include nonvegetated wetlands that are less than 20 acres, less than 6.5 feet in the deepest part at low water, and do not have a wave-formed or bedrock shoreline. Palustrine wetlands can occur as isolated wetlands, on river floodplains, and along lake or pond shores. Palustrine wetlands include riparian corridors, marshes, and ponds.

PALUSTRINE EMERGENT

This wetland type includes meadows, marshes, and vegetatedponds. Emergent wetlands are characterized by erect, rooted,herbaceous hydrophytes that are usually present for most of the
growing season.

PALUSTRINE FOREST

These riparian forest habitats are regularly inundated by normal high-water flows or flood flows. The dominant woody vegetation is at least 20 feet tall.

PALUSTRINE SCRUB SHRUB

This wetland type includes areas dominated by woody vegetation less than 20 feet tall, such as willows.

Wetland Extent

The U.S. Fish and Wildlife Service mapped wetlands in Yosemite in 1995 as part of the National Wetlands Inventory. Wetlands were mapped on a U.S. Geological Survey topographic base map (1:24,000) from an analysis of color, infrared photographs taken in 1984 (1:58,000). Wetlands were identified and classified based on vegetation, visible hydrology, and geography in accordance with the Cowardin classification system. Some areas in Yosemite, such as campgrounds, have had more specific on-the-ground surveys to provide wetland delineations (Kleinfelder 1998).

Yosemite Valley

The wetland extent in Yosemite Valley was estimated using the National Wetlands Inventory information, supplemented with the 1994 Yosemite Valley vegetation map (NPS 1994e), which contains more detailed information on hydrophytic vegetation in Yosemite Valley. This map was developed using SPOT satellite imagery and color, infrared, aerial photographs (1:12,000), and has a spatial accuracy of 30 to 65 feet. For the purposes of the Final Yosemite Valley Plan/SEIS, all meadow and riparian communities (as identified on the Yosemite Valley vegetation map) were classified as palustrine wetlands and were evaluated throughout the document as wetlands. Table 3-1 shows a total for all the palustrine and riverine wetland acreage identified on the Yosemite Valley vegetation map (NPS 1994e).

OUT-OF-VALLEY LOCATIONS

El Portal

Wetland occurrences and types in El Portal vary by slope, aspect, and water availability. The extent of wetlands was estimated from National Wetlands Inventory maps. Drainages that flow through the El Portal community and adjacent nondeveloped slopes, such as Crane Creek, are inhabited by riverine upper perennial and intermittently flooded wetlands.

Low-lying areas and areas with low to flat gradients on older river terraces have palustrine scrub shrub and palustrine forest wetlands. Both types are found in the vicinity of the Trailer Village and Abbieville (Hennessey's Ranch).

Some areas have remnant river channels surrounded by development. These sites were not designated as wetlands by the National Wetlands Inventory maps due to their small size and isolated nature. Water flows in these historic channels, including one near the Village Center (El Portal), have been altered, and the understory vegetation is dominated by non-native plant species. Overstory species support classification of these sites as remnant palustrine forest.

Foresta

Drainages throughout Foresta are inhabited by palustrine scrub shrub wetlands, including those flowing through Big Meadow. An artificial palustrine emergent wetland occurs near the Foresta wood yard where earthmoving equipment has created a pond.

South Landing

A palustrine emergent wetland occurs east of the existing road along a small drainage.

Henness Ridge

No wetlands are located within areas of proposed development.

Badger Pass

An extensive palustrine scrub shrub wetland occurs in the drainage exiting the developed Badger Pass area. A large palustrine emergent wetland inhabits the open meadow at the base of the winter-use ski area.

Hazel Green

An artificial palustrine scrub shrub wetland occurs on National Park Service land immediately adjacent to the Big Oak Flat Road. This wetland results from the interception of slope drainage by the road, where water is concentrated into an inboard ditch that is directed under the road through a culvert. Additional wetlands occur in the riparian and meadow areas traversing the Hazel Green Ranch site.

Wawona

No wetlands are located within areas of proposed development.

Big Oak Flat Road

No wetlands are located within areas of proposed development.

South Entrance

Palustrine scrub shrub and forest wetlands occur along drainages adjacent to the Wawona Road corridor.

Tioga Pass

Extensive wetlands characterize this area, in the form of subalpine meadows and a network of tarns.

SOILS

General Soil Properties

All soils form from the combined effect on geologic parent material of climate, biologic activity, topographic position and relief, and time. Within the park, topography is the most important factor contributing to soil differentiation. Topography influences surface water runoff, groundwater, distribution of stony soils, and the separation of alluvial soils of various ages (Zinke and Alexander 1963). More than 50 soil types exist within the park; general or local variations depend on glacial history and the ongoing influences of weathering and stream erosion and deposition. Local variations also result from differences in microclimates due to aspect and major vegetation types.

Soils of the Yosemite region are primarily derived from underlying granitic bedrock and are of a similar chemical and mineralogical composition. Except for meadow soils, most soils at high elevations were developed from glacial material (glacial soils) or developed in place from bedrock (residual soils). Extensive areas above 6,000 feet are covered by glacial moraine material, a mixture of fine sand, glacial flour, pebbles, cobbles, and boulders of various sizes. Alluvial soils develop along streams through erosion and deposition. Alluvial soils tend to have sorted horizons (layers) of sandy material. Colluvial soils have developed along the edges of the Valley in areas where landslides and rockslides have occurred. Colluvial soils are composed of variously sized particles and rocks and have high rates of infiltration and permeability.

Organic content within the upper soil profile varies with the local influences of moisture and drainage. Thick sedges and grasses have contributed to the organic content of soils near ponds, lakes, and streams. Coniferous forest soils have a relatively high organic content and are relatively acidic. Soils lacking organic accumulations are frequently a result of granitic weathering, consist largely of sand, and support only scattered plants tolerant to drought-like conditions.

Certain soil types have been identified in Yosemite as highly valued resources (see Vol. Ic, plate D, and Chapter 2, Alternatives, Development Considerations, Highly Valued Resources). The criteria used to designate highly valued resource soils include the potential for restoring highly valued vegetation communities, protection by federal laws, and significance as a sensitive area (such as soils that take an inordinately long time to recover from disturbance). Highly valued resource soils are found in or adjacent to meadows and riparian areas, hydric soils, and soils associated with lateral or terminal moraines. Soils in and along riparian and meadow areas are often in ecotones—areas where ecosystems overlap—and are especially rich with vegetative and wildlife diversity. Highly valued resource soils are typically more susceptible to development impacts; they lack the structure to readily support building weight and erode more easily than a resilient soil type. Therefore, a highly valued resource soil is suitable for restoration. The Leidig fine sandy loam found in and around Leidig Meadow is an example of a highly valued resource soil.

Hydric soils are legally protected because they form in wetlands, which are protected by federal law. Hydric soils form under sufficiently wet conditions to develop anaerobic conditions and can usually support a predominance of hydrophytic vegetation. Hydric soils are found primarily in the river valleys of the Merced River and Tenaya Creek and in low meadows.

The 1980 General Management Plan identifies areas with development limitations based on frequent flooding, seasonally high water tables, poor drainage, steep slopes, high rock concentration, and a sandy structure that will not readily support weight. Each area is rated to show the degree of limitation that restricts the use of a site for a specific purpose. For example, a rating of "slight" is given for soils that have properties favorable for use. A rating of "severe" is given to soils that have one or more property unfavorable for the rated use. A soil with a severe rating generally requires intensive maintenance, major soil reclamation, engineering controls, or other mitigation measures.

Soils that are more suitable for use are identified as resilient. Resilient soils are those that are capable of withstanding alteration without permanent deformation, or recover more easily from alteration. Generally, resilient soils do not have major development limitations or restrictive physical attributes.

Other soils are not considered highly valued resources or resilient soils. Generally, these soils place more limitations on use because of steep slopes or other physical attributes. They may require more intensive management or engineered mitigation measures for development compared to resilient soils. Other soils do not fit into the highly valued resource soil resource category because they are generally more abundant and do not support plant communities that are rare or especially diverse. The Half Dome soil complex is an example of such a soil resource.

Soil Properties by Area

YOSEMITE VALLEY

The Yosemite Valley soils were intensively investigated by Zinke and Alexander in 1963 and were mapped by the Natural Resource Conservation Service in 1991. During flood events, alluvial soils are formed and removed as flood waters deposit and erode material over the floodplain. The active flooding builds river terraces of fine- to coarse-textured sands. Older riverbeds made up of boulders and gravel may be buried under the terrace soils. Residual soils are scattered throughout the Valley where bedrock weathering has occurred. Glacial soils are principally associated with terminal moraines. Colluvial soils have developed on the talus slopes along the edge of the Valley floor. Yosemite Valley soil depths range from nonexistent on the Valley rim to estimated depths of 1,960 feet near the Valley center. Valley soil textures vary from fine clay to fine gravel. Most soils have a relatively undeveloped profile, indicating their relatively recent origin and young geologic age.

The Natural Resource Conservation Service identified 21 soil series/types in Yosemite Valley. Each soil type has specific characteristics that influence factors such as plant growth, water movement, and land-use capabilities. El Capitan fine sandy loam, found in and around El Capitan Meadow, is an example of a Yosemite Valley soil with physical constraints that limit land use due to occasional flooding. Limitations on specific types of use associated with the various soil types are shown in table 3-2.

EL PORTAL

Most soil data for El Portal have been collected on steep slopes by the National Resource Conservation Service for the current Yosemite soil survey or extrapolated from Stanislaus National Forest and Mariposa County soil surveys.

Most El Portal soils are metamorphosed sedimentary and granitic in origin. Soils that formed in old river channels consist of alluvial boulders, cobbles, riverwash, and loamy sands. El Portal soils, for the most part, have moderate to severe development limitations. Hence, these soils require engineering and mitigation measures. Major soil types found in the area and their limitations are summarized in table 3-3.

WAWONA

Wawona area soils are primarily residual on slopes and alluvial in the Valley. Soil depth varies from 2 to 4 feet above bedrock; these soils are moderately to strongly acidic. Most soils are subject to erosion after disturbance or loss of vegetative cover. The six major soil types are distinguished by their textures and the amount and type of rock fragments they contain. Limitations on use associated with these soil types are presented in table 3-4.

FORESTA

Soils of the Foresta/Big Meadow area are primarily derived from alluvial materials, with a predominance of unconsolidated, gray to brown soils containing some clays. Some of the clay soils are moderately expansive (swell when wet and shrink when dry), but most other types are well drained and stable. Expansive soils limit building and road construction due to the potential for shifting. Isolated pockets of soils formed in glacial outwash also occur in this area. Due to limited soils data, land-use limitations are not known for this area.

HENNESS RIDGE

Most current soil data for Henness Ridge were extrapolated from soils collected in nearby and similar environments by the National Resource Conservation Service for the current Yosemite soil survey. The soil environment at Henness Ridge is characterized by fairly thin soils that were formed from igneous granodiorite material. The main limitations of the soils are their thin horizons and high erosion potential. Water tends to flow over rather than drain into the soils. Area soils are also susceptible to erosion when the surface organic layer is lost. Land-use limitations are not available for this area due to limited soils data.

SOUTH LANDING AND BADGER PASS

Most soil data for South Landing and Badger Pass have been collected on steep slopes by the National Resource Conservation Service for the Yosemite Valley soil survey or extrapolated from information in the Stanislaus National Forest and Mariposa County soil surveys.

Soils of the South Landing area are primarily derived from alluvial materials, with a predominance of unconsolidated, gray to brown soils containing some clays. Some of the clay soils are moderately expansive, but most other types are well drained and stable. Isolated pockets of glacial outwash, and possibly ash, also occur in this area. Due to limited soils data, land-use limitations are not known for this area.

SOUTH ENTRANCE

Soils at the South Entrance are similar to those found in the Wawona area. The Chiax series/family is likely the most dominant. These soils tend to be coarse textured, somewhat excessively drained, and gently to steeply sloping. Due to liminted soils data, land-use limitations are not known for this area.

HAZEL GREEN

Information for the Hazel Green area has been extrapolated from similar and nearby soil descriptions, as evaluated in the 1996 Soil Handbook for the Soil Survey of Yosemite National Park (Taskey 1996) and the 1993 Soil Survey of Sierra National Forest Area, California (USFS 1993). The landscape positions within the area include backslopes, mountainsides, and broad ridges. A narrow band of alluvial soils is likely present along the Hazel Green Creek; otherwise, soils have formed in residual materials. Due to limited soils data, land-use limitations are not known for this area.

BIG OAK FLAT

Big Oak Flat is close to Hazel Green and has a similar geomorphology. Thus, the soils at Big Oak Flat are similar to those at Hazel Green. Due to limited soils data, land-use limitations are not known for this area.

TIOGA PASS

Descriptions of soil data for Tioga Pass have been extrapolated from similar and nearby descriptions from previously referenced sources as well as the Soil Survey of Tuolumne Meadows (NRCS 1995a). Due to limited soils data, land-use limitations are not known for this area data.

Soils at Tioga Pass formed in granitic glacial till/moraine, colluvium, and alluvium. The slopes range from gently sloping near the Tuolumne River to steep along the mountainsides. Soil textures tend to be coarse and loamy to sandy.

VEGETATION

Yosemite National Park supports five major vegetation zones: chaparral/oak woodland, lower montane, upper montane, subalpine, and alpine. Yosemite Valley is in the lower montane mixed conifer zone, where 41 vegetation types have been identified (NPS 1994e). These have been loosely lumped into five groupings: upland, California black oak, meadow, riparian, and other. El Portal is in the chaparral/oak woodland zone, and other areas outside of Yosemite Valley that are being evaluated are in the lower montane, upper montane, and subalpine zones (Sawyer and Keeler-Wolf 1995). Root rot diseases primarily affect upland and California black oak communities, and they are discussed within the context of those two categories. Non-native plant species occur to some extent in each of the communities and areas listed below; they are described within each section where pertinent.

Yosemite Valley

UPLAND COMMUNITIES

Upland plant communities are found where soil moisture conditions are average to dry and where soils are not periodically flooded or saturated. In Yosemite Valley these communities fall into the categories of mixed conifer, California black oak, live oak, and cliff. Due to the ecological and cultural value as well as the sensitivity of California black oak communities, this community has been removed from the upland category and evaluated separately throughout the document. Upland plant communities dominate about 75% of Yosemite Valley. Upland communities are much more common, widespread, and vegetatively intact than California black oak, riparian, or meadow communities in Yosemite Valley as well as throughout the Sierra Nevada (NPS 1994e; UC Davis 1996e). However, they have undergone alterations through changes in fire frequency, spread of native root rot, and establishment of non-native species.

Mixed conifer communities are normally dominated by ponderosa pine, sugar pine, and/or incense-cedar and generally grow at elevations of 3,000 feet to 5,000 feet. This community also contains Douglas-fir and California black oak. The most common understory shrubs are Mariposa manzanita and deerbrush. The mixed conifer community is adapted to low-intensity, frequent fires. Nearly 100 years of fire suppression has resulted in a change from open forest to dense thickets of shade-tolerant tree species (including incense-cedar, white fir, and Douglas-fir) in many areas. Under natural conditions, the return interval for fire is estimated at 8 to 12 years (NPS 1990b). Existing conditions, however, often generate fires of much greater intensity than under a natural fire regime. Most undeveloped mixed conifer areas of the Valley are now managed through a combination of mechanical removal of hazardous fuel and prescribed burning. These treatments simulate the natural and anthropogenic fire regimes of the Valley and help decrease stand densities to more natural levels.

Canyon live oak communities grow on both north- and south-facing talus slopes and often form pure or almost pure stands. Fires in this community are infrequent but intense, with a fire return interval of 20 to 50 years on south-facing slopes. Most trees and shrubs in this community are adapted to resprout after fire.

Annosus root disease is a widespread native fungus occurring throughout northern Europe and western North America in coniferous forests. In pines the fungus first spreads through the root system, attacking and eventually killing the inner bark and sapwood. Within two to six years after initial infection, the tree can die with the fungus remaining active as a saprophytic, wood-decaying organism within roots and the butt of the dead tree. Pines weakened by annosus root disease are often killed by bark beetles. Incense-cedars, however, are not affected by beetles and will stand green for many years until the disease finally weakens the structure enough to cause failure. Cedars are thought to act as reservoirs for annosus root disease (NPS 1998h).

In Yosemite Valley, the large size of annosus root disease centers is unusual; only a few other large population centers of this species occur on the western side of the Sierra Nevada. The Valley has dense stands of large trees on a sandy floor, a high water table, and frequent flooding. The conifer forest in Yosemite Valley may not be sustainable because of these large centers of annosus that have developed within the unnaturally dense stands of conifers in former California black oak, meadow, and riparian areas. Several centers of significant annosus infestation are present in the Valley today, including former Upper and Lower River Campgrounds, Yellow Pine Campground, Sentinel Beach Picnic Area, portions of Yosemite Lodge, and most of the Taft Toe area. Existing annosus centers in developed areas can be mitigated by landscaping with native species that are not susceptible to infection, such as California black oak, live oak, and big-leaf maple.

Non-native plant species have become established in the mixed conifer zone, although not to the same extent as in meadows and California black oak stands. These species are the result of either deliberate or accidental introductions and are not part of the naturally evolved community. Many of these species are indicators of past agricultural activities that occurred throughout the area. Approximately 180 non-native plant species have been identified in the park, primarily in the chaparral/oak and mid-elevation forests (Fritzke and Moore 1998). In the upland plant communities of Yosemite Valley, non-native species are generally herbaceous and associated with ground disturbance (one-time or recurring). Typical species include European annual grasses. Bull thistle is an example of one of the more troublesome species, because it out-competes native herbaceous perennials and annuals for soil moisture and light (especially in seep and spring areas) and, with sufficient moisture and time, can convert some areas to near monocultures.

CALIFORNIA BLACK OAK COMMUNITIES

California black oaks on the floor of Yosemite Valley form pure, open stands of large, stately trees with an herbaceous understory. These pure stands—unique to the Valley due to thousands of years of anthropogenic activities, such as annual burning and removal of young conifers—are found at the change in slope between upland colluvial deposits and lower, water-driven alluvial areas. They form a band of oaks around the Valley floor between the upland plant communities and the lower-lying meadow and riparian communities. The California black oak acorn was a primary food source of American Indians in Yosemite Valley, and most of the large groves continue to be used as traditional gathering areas today. California black oak stands mixed with ponderosa pine are found throughout the Valley, and additional areas of California black oak that have buildings and other development are found in the east Valley. California black oaks also grow in dense stands on talus slopes near drainages, but for the purposes of this analysis, talus black oaks are grouped with the other upland communities. California black oak communities are considered a highly valued natural and cultural resource in Yosemite Valley.

California black oak communities in Yosemite Valley are identified as sensitive due to declines in population size, vigor, and recruitment rates, and have been included in the highly valued resources map (Vol. Ic, plate D). Changes in natural or cultural fire processes, encroachment by conifers, browsing by deer and rodents, impacts from development, and unmanaged visitor use have all caused a significant decline in density and stand structure (Fritzke 1997). Oak woodlands are also some of the most ecologically transformed terrestrial ecosystems in the Sierra Nevada due to alterations of natural processes, development, and the introduction of non-native species. The conversion of California black oak woodlands has also had a substantial effect on wildlife species (UC Davis 1996c).

Armillaria species are fungi that attack the root and crown of hardwoods and conifers of all ages. These fungi can be found on nearly every California black oak in Yosemite Valley. Armillaria mellea can kill disturbed or severely stressed oaks and is apparently favored by high levels of soil moisture during the summer. Summer watering of California black oaks in landscaped areas has contributed to the overall decline of this community in Yosemite Valley.

California black oak communities are also adapted to frequent, low-intensity fires, similar to upland mixed-conifer communities. Under natural conditions, the return interval for fire is estimated at eight to 12 years (NPS 1990b). Non-native plant species have also become established in California black oak communities. Due to past and current levels of disturbance in this community, non-native species have become more widespread than in upland forests. These non-native species include annual grasses, black locust, American elm, and extensive ground-covering stands of Himalayan blackberry.

MEADOW/FLOODPLAIN COMMUNITIES

The meadow/floodplain communities support a wide range of vegetation. Sedges and rushes dominate wet meadows, shallow backwater areas, and ponds; flood-tolerant woody species dominate other areas. Upland species are present on natural terraces that are less frequently flooded or are flooded for only short durations. Floodplains and their associated wetlands are regarded as among the most productive and diverse ecosystems in the world (Lieth and Whittaker 1975; Brinson et al. 1981; USFS 1977a). The diversity of floodplain areas is largely due to dynamic processes associated with erosion and sediment deposition, channel migration, and flood duration.

The meadow/floodplains in Yosemite Valley play a particularly critical role in the Merced River ecosystem. High spring flows create wet areas in side channels, low-lying wetlands, meadows, and cutoff channels. These areas support concentrations of organic matter, nutrients, microorganisms, and aquatic invertebrates throughout the relatively dry summer. When the flush of winter or spring flooding occurs, this stored aquatic biomass is washed into the main river channel. Nutrients flushed from the meadow/floodplain areas form the base of the aquatic food chain in the main river channel.

LOWER MONTANE

Lower montane meadows on the Merced River floodplain are hydrologically controlled communities. The maintenance of these communities depends on sustaining river processes, including the frequency, duration, and magnitude of flooding, and frequent, low-intensity fires. The meadows in Yosemite Valley are transition zones from drier upland and California black oak communities to wetter riparian communities. The meadows themselves have water tables that vary seasonally and link the Merced River and tributaries to seasonally dry land. Meadow communities in Yosemite Valley are considered highly valued resources.

Yosemite Valley meadows are classified into three general types: (1) wet meadow, dominated by native hydrophilic vegetation; (2) grass meadow, dominated by non-native grasses (introduced in turn-of-the-century agriculture); and (3) native hydrophytic forbs (NPS 1994e). Meadow acreage in the Valley has substantially diminished since the mid-1800s, from 745 acres in 1866 (as mapped by state geologist J.D. Whitney) to less than half that today, primarily through human-caused conversion from meadow to upland communities. Contributing factors have been a change in prehistoric fire frequency maintained by American Indians and more recent manipulations of hydrological patterns, including intentional draining of meadows to facilitate grazing and agricultural use, road and trail building with drainage diversions, and channelization of surface and subsurface water runoff.

As a result of these changes, many non-native species have become established in these meadows. Non-native grasses, planted intentionally at the turn of the century for agricultural purposes, remain the dominant species in the drier portions of most meadows. Bull thistle and Himalayan blackberry are other examples of non-native species that have proven their ability to invade and out-compete native vegetation. Non-native species alter the composition of Valley meadows, out-compete native species, and could reduce regional species diversity. Control and preventive measures are in place for many of these species.

RIPARIAN COMMUNITIES

The riparian communities are vegetative communities adjacent to the main river channel and tributaries. These plant communities serve as the interface between the river and the surrounding meadow and upland communities. Riparian plants in Yosemite tend to share the following characteristics: broad leaves, winter-deciduous, fast growth, short-lived, high soil moisture requirements, high rates of transpiration, ability to tolerate seasonal flooding and low-oxygen root environments, and ability to produce sprouts, suckers, and new root systems. Large trees within the riparian zone provide shade to keep water cooler in the summer. The thick vegetation along the river channel helps stabilize soils, which tend to be easily eroded because of their coarse texture.

Riparian zones extend outward from the Merced River and its tributaries into the canopy of riverside vegetation. These communities provide specialized habitat and important nutrients to the meadow and river systems. For example, leaves dropping into the river support a complex succession of microorganisms and invertebrates involved in decomposition. Riparian zones also moderate riverine microclimates by influencing light, temperature, and shade. They are included in the highly valued resource category due to their relatively limited distribution along watercourses, the current level of impact they are experiencing, their importance ecologically, and their overall decline both in Yosemite Valley and throughout the Sierra Nevada.

Riparian zones in Yosemite Valley are characterized by broad-leaved deciduous trees such as white alder, black cottonwood, and willow species. Vegetation along moving water is regularly disturbed by the deposition and removal of soil and the force of flood waters. Vegetation in this zone readily colonizes newly formed river-edge deposits. Big-leaf maple riparian forests grow on moist, gravelly soils in protected spots at the base of cliffs and on alluvial soils bordering streams. They are dominated by big-leaf maples, white alder, white fir, and mountain dogwood (NPS 1994e).

Riparian communities are among the most productive, sensitive, and biologically diverse in Yosemite Valley. They also are among the most impacted resources due to their proximity to water and the effects of trampling and above- and below-ground infrastructure, including impacts from lift stations, bridges, and underground sewer lines. The National Park Service has initiated ecological restoration projects designed to protect these sensitive communities and riverbanks from unnaturally high rates of erosion and to encourage the re-establishment of vegetative cover. Visitors are directed to areas that can accommodate heavy use without long-term impacts, such as point bars and gravel bars along meandering river segments.

Out-of-Valley Areas

EL PORTAL

In the Merced River canyon, the river is lined with a narrow band of riparian vegetation. Farther up the canyon walls is a dense mosaic of chaparral and foothill woodland communities. These communities include blue oak woodland, interior live oak woodland, foothill pine/oak woodland, interior live oak/chaparral, and riparian woodland.

All of the vegetation communities in the El Portal area are adapted to regular, frequent natural fires sparked by lightning. Fire suppression has led to increased vegetative density, especially on north-facing slopes. Natural fires probably burned every five to 10 years in grassy areas, and 25 to 40 years in chaparral areas (van Wagtendonk 1994).

Flooding has also been an important aspect of the development of riparian communities along the Merced River and along tributaries intersecting drier adjacent vegetation types of El Portal. Localized, seasonal flooding creates debris flows in tributary channels, creating a diversity of scoured areas and depositional soils for riparian species. On the Merced River, natural flooding patterns have been influenced by the construction of levees and application of riprap to confine the river. In some places, these structures have limited the development of riparian vegetation.

Oak Communities

El Portal supports numerous stately mature oak trees. Of the eight tree-like species of oak in California, six grow in El Portal. Generally, existing development in El Portal has been built to retain an overstory of native mature oaks, including valley oak, blue oak, and California black oak. This oak canopy provides indispensable shade, scenery, and wildlife habitat. The shrub layer also retains many native elements, such as redbud, buckeye, Mariposa manzanita, and yerba santa. Undeveloped areas retain a grassy understory that consists of mostly non-native grasses along with native wildflowers. Yellow star-thistle, tocalote, and other invasive species have recently become established in these sites. Historic and current development and landscaping have introduced many non-native species into this community, including the invasive tree-of-heaven, French broom, numerous herbaceous lawn grasses, and yellow star-thistle. Fruit trees and other landscape trees are also common.

Riparian Communities

Riparian communities occur along tributaries of the Merced River; on flat, shaded terraces above the Merced River; and in areas where runoff from upland sites collects in natural depressions. Black cottonwood, red willow, white alder, big-leaf maple, and ash trees occur in the wetter areas; historic fruit trees also occur in some of these locations. The drier terraces adjacent to riparian areas are dominated by a mix of valley and live oaks and foothill pines.

FORESTA

In the area being considered for development in Foresta, more than half of the site is dominated by a dry Mariposa manzanita/deerbrush/cheatgrass association. The area is undergoing secondary succession following the 1990 A-Rock Fire, with redeveloping stands of lower montane mixed conifer forests, including seedling- to sapling-sized ponderosa and knobcone pine, and resprouting California black oaks. Mesic red willow/deerbrush/Mariposa manzanita association, cattail/velvet grass wetland area, and red willow occur within and adjacent to this area. Non-native species such as annual grasses, yellow star-thistle and tocalote, and a small population of spotted knapweed, have also become established in this area and are being managed by the National Park Service.

SOUTH LANDING

Vegetation at South Landing is dominated by a moderately aged stand of ponderosa pine/ incense-cedar/sugar pine with shade-tolerant white fir and incense-cedar in the subcanopy. Understory shrub cover is dominated by greenleaf manzanita. The area has been disturbed by historic railroad logging and by construction of the Big Oak Flat Road. A small opening within the site is dominated by native perennials, including blue wildrye grass and lupines. North of the access road loop is a ponderosa pine/incense-cedar vegetation type with large, emergent sugar pine, ponderosa pine, white fir, and incense-cedar in the subcanopy, and an understory of greenleaf manzanita. A small drainage east of the access road is dominated by bracken fern, yarrow, and sedges.

HENNESS RIDGE

Vegetation consists of a fairly intact overstory canopy of montane mixed conifer in the white fir/incense-cedar/sugar pine vegetation type, with a typical understory of snowberry and kelloggia. Small patches of greenleaf manzanita and bear clover with native herbaceous plants occur in gaps in the understory.

BADGER PASS

The Badger Pass developed area straddles a small north-facing drainage that is densely vegetated by upper montane forests. Predominant species adjacent to the parking area and ski lodge are red fir and white fir, with a whitethorn understory. A montane wet meadow community south of the ski lodge has a diverse flora of native herbaceous and wetland species, including creek dogwood, sedges, willows, and alder. Lodgepole pines occur in the vegetated islands within the parking lot and along stream courses above and below the meadow. Non-native species have become established in heavily used portions of the site, including the base of the ski slopes and the parking area. These non-native species include common mullein, European annual grasses, and bull thistle.

HAZEL GREEN

Vegetation at the Hazel Green area adjacent to the Big Oak Flat Road is dominated by a white fir/sugar pine/red fir association. Large white fir and sugar pine form a partially closed canopy, with an open subcanopy and minimal ground cover on the westernmost portions of the site. Average trees range from 30 inches to more than 100 inches in diameter, indicating a mixed-aged stand that has been in existence for some time. A majority of this area was burned at a low intensity by the 1987 Stanislaus Complex Fire. A ponderosa pine/incense-cedar vegetation type occurs in the central portion of the site, which is located on a knoll straddling the Hazel Green and Bull Creek headwaters. Emergent sugar pine is dominant in the subcanopy, which was logged in the early 1920s. A small stand of red willow occurs along the artificial drainage ditches adjacent to the Big Oak Flat Road, where the headwaters of Hazel Green Creek are concentrated into one large culvert beneath the road. Hazel, ocean-spray, and white alder with sedges and rushes grow within and immediately adjacent to the drainage ditch. A small open stand of ponderosa pine occurs around the edges of the meadow at the headwaters of Bull Creek's subcanopy; it has a high proportion of California black oaks. The meadow is dominated by non-native grasses, including Kentucky bluegrass and various forbs.

TIOGA PASS

Tioga Pass vegetation is characterized by a mosaic of both wet and dry subalpine meadows dominated by native perennial grasses, sedges, rushes, and forbs, and lodgepole pine forests. In dry meadows, vegetative cover is sparse and is dominated by mat-forming, short-hair sedge. A short growing season and moisture are the limiting factors in these meadows, and plants take years to become established in newly disturbed areas or to recover from trampling and construction damage. Wet meadow vegetation is found within the treeless drainages near the pass, as well as surrounding the tarns to the south. The species mix in this community is variable, but all plants remain fairly low to the ground, forming dense, matted vegetation. These areas remain saturated throughout the growing season and are more resilient to impacts due to this increased moisture availability. However, saturated soils also increase the likelihood of impacts from trampling, with the potential for increased sedimentation into streams and water bodies, as well as damage to willows and other woody perennial species.

Lodgepole pine forests in the vicinity of Tioga Pass form open to moderately dense stands on rocky, well-drained sites and east-facing slopes above the entrance station. Herbaceous vegetation forms a sparse ground cover intermixed with dead-and-down woody material. Lodgepole seedlings are readily established in disturbed soils, often forming linear stands over utility lines and along road edges; they are an indicator of past disturbance in many subalpine areas of the park. Due to the short growing season and harsh conditions, non-native plants have not yet become a problem in this area. Yellow star-thistle has been sighted in the area, and the potential exists for this and other non-native species to become established in the future.

SOUTH ENTRANCE

Vegetation at the South Entrance is characterized by dense montane mixed coniferous forests on the drier, upland sites and riparian vegetation along ephemeral and perennial stream channels. The forests are dominated by a white fir overstory with subordinant sugar pine, Douglas-fir, and ponderosa and Jeffrey pine. Most of this area was logged by the Sugar Pine Lumber Company (railroad logging), and remnants of these practices are visible at the site. As a result, sugar pine remains a minor component of the stand structure, although it should be codominant. The understory is fairly sparse due to the dense, overgrown nature of the subcanopy and canopy. Fire has been excluded from much of the area for over a century, and fuel loads have built up to the point that normal ground cover species, such as whitethorn ceanothus and greenleaf manzanita, are nearly absent. Perennial herbaceous species such as trail plant, wood orchid, and rattlesnake plantain are common.

The leach field (for the residence and restrooms at the entrance station) is an unnatural opening in the canopy and has a variety of native and non-native plant species, including sedges, horsetail rush, bull thistle, and rabbits-ear. Riparian vegetation in the South Entrance area is found in and around low-lying areas and along stream courses. These areas are dominated by an overstory of cottonwood, Sierra dogwood, and alder, with a mix of willow, Sierra sweet-bay, and western azalea in the understory. Ground cover consists of horsetail, bracken fern, and other moisture-dependent species. Non-native species such as bull thistle and cut-leaved blackberry have become established in these riparian corridors, but remain a minor component.

BIG OAK FLAT ENTRANCE

Vegetation in the vicinity of the Big Oak Flat Entrance is dominated by two types: a white fir/sugar pine/red fir vegetation type, and a ponderosa pine/incense-cedar vegetation type with emergent sugar pine. The fir association, found along the west side of the parking area and along drainages in the area, is characterized by trees of variable sizes with diameters up to 40 inches. Most of this site was logged in the early 1920s, prior to inclusion in Yosemite National Park. The subcanopy is dominated by shade-tolerant white fir with little shrub or ground cover. The ponderosa pine vegetation type occurs on drier sites to the east of the current parking area and has a more open canopy. The subcanopy is dominated by young incense-cedar and a sparse understory of whitethorn ceanothus and greenleaf manzanita.

WAWONA

The proposed site for new housing in Wawona (Alternatives 2 and 5) occurs on a gentle, north-facing slope above the South Fork of the Merced River. The site is dominated by a lower montane mixed conifer forest of ponderosa pine, incense-cedar, sugar pine, white fir,
and Douglas-fir. The subcanopy is dominated by shade-tolerant incense-cedar and white fir. Natural openings and rock outcrops within the site are characterized by small stands of California black oak, with an understory of native perennial grasses, including blue wildrye and California brome.

 

Wildlife

Wildlife in Yosemite National Park is diverse and abundant, reflecting the wide range of Sierra Nevada habitats in relatively intact condition. Concentrated areas of human use in Yosemite have affected wildlife and their habitats, especially in the east end of Yosemite Valley. Some of the most valuable and sensitive habitats are also located or once existed in the east Valley. Montane meadow and riparian areas are highly productive, structurally diverse habitats that support a high level of species diversity and provide important linkages between terrestrial and aquatic communities. The long history of development and human use in the Valley has resulted in fragmentation and reduction of these habitats, affecting their quality to wildlife.

Habitat

Habitat fragmentation is a factor affecting Yosemiteís wildlife species. For wildlife populations to be viable, resources and environmental conditions must be sufficient for foraging, nesting or denning, cover, and dispersal of animals. Distribution, types, and amounts of resources must be sufficient for the needs of reproductive individuals daily, seasonally, and annually. Habitat must also be well distributed over a broad geographic area to allow breeding individuals to interact spatially and temporally within and among populations.

Some habitat types in the park may be affected by implementation of actions in the proposed alternatives. These habitat types and wildlife species typical of each are discussed in this section. Table 3-5 shows relationships between the vegetative communities discussed in the Vegetation section of this chapter and the wildlife habitat types discussed below.

UPLAND HABITATS

Lodgepole Pine

This habitat type, found at the Tioga Pass Entrance, is dominated by lodgepole pine, which forms open stands with sparse understory vegetation. Seedlings and saplings of lodgepole pine can, however, be abundant under the canopy of mature trees. At meadow edges, stands of lodgepole pines can contain rich herbaceous layers of grasses, forbs, and sedges. Because of the low structural diversity of this habitat type, the diversity of wildlife species it contains is relatively low. Species likely to be present include northern alligator lizard, northern goshawk, Williamsonís sapsucker, mountain chickadee, and red crossbill.

Montane Hardwood

This habitat type is found in Yosemite Valley, Wawona, and El Portal. Typically, this habitat is composed of a definite hardwood tree layer, made up primarily of California black oak and canyon live oak, with a poorly developed shrub layer. Some scattered conifers, such as Douglas-fir and ponderosa pine, may rise above the hardwood canopy. Acorns produced by the dense oaks provide an abundant food source for wildlife such as gray squirrel, acorn woodpecker, band-tailed pigeon, mule deer, and black bear. Snags and mature trees provide roosting and nesting cavities.

Montane Hardwood Conifer

This habitat is found in Yosemite Valley, Wawona, and El Portal, and is in early succession stages in Foresta. This habitat contains about equal components of hardwoods and conifers, often occurring in mosaic-like distributions of small, pure stands of each type. The degree of canopy closure is high, with conifers such as ponderosa pine often forming the upper canopy, and broad-leaved trees such as California black oaks and canyon live oaks forming the lower canopy. The dense canopy generally allows only sparse vegetation on the forest floor, but edges and openings can have considerable ground and shrub cover. Variability in canopy cover and understory vegetation make the habitat suitable for a wide variety of wildlife species, such as black bear, acorn woodpecker, and band-tailed pigeon. Denser stands are a favored habitat of California spotted owls. Mast crops produced by trees are an important source of food to wildlife in this habitat, and mature forests provide cavities for nesting birds.

Ponderosa Pine

This habitat type is found in Yosemite Valley and Wawona. Stands of coniferous trees dominated by ponderosa pines characterize this habitat. Understory vegetation varies inversely with canopy closure; openings and fire-disturbed areas can support dense stands of shrubs, such as manzanita, dogwood, ceanothus, and buckthorn. A mosaic of areas with trees of different ages and different canopy closure provides a wide variety of habitat layers for wildlife, such as Douglas squirrel, long-eared chipmunk, western wood pewee, red-breasted nuthatch, and Stellerís jay. Large snags and lightning-scarred trees can be important roosts for several bat species. Ponderosa pine habitat can be an important holding area for migratory mule deer, providing forage and thermal cover.

Sierra Mixed Conifer

This habitat type is found in Yosemite Valley, Henness Ridge, South Landing, Hazel Green, Big Oak Flat, Badger Pass, Wawona, and South Entrance. This habitat is a mixed assemblage of conifer and hardwood species that forms multiple forest layers. Such diversity within the habitat results in numerous ecological niches for wildlife. Acorns from scattered California black oaks are an important wildlife food source, but seeds from the more abundant conifers are also a substantial source. Shrubs under canopy openings, such as manzanita, bitter cherry, and gooseberry, provide food and cover on the forest floor. Pileated woodpeckers favor this habitat, as do brown creepers, white-headed woodpeckers, Hammond's flycatcher, flammulated owl, and hermit thrush. At higher elevations, Sierra mixed conifer is the habitat of species such as marten and northern goshawk.

CALIFORNIA BLACK OAK HABITAT

California Black Oak Woodland

This habitat type is found in Yosemite Valley, El Portal, and Wawona. Stands of trees dominated by California black oaks characterize this habitat type. Acorns provided by California black oak in Yosemite Valley are an important source of food to a variety of wildlife. Mule deer and black bears forage extensively in this habitat in years of good acorn production. Acorn woodpeckers, as their name suggests, are highly dependent on this food source. Gray squirrels, ground squirrels, deer mice, and band-tailed pigeons also feed heavily on acorns. The large, mature California black oaks also provide cover and nesting habitat for species such as great-horned owls. Pallid bats favor mature oaks as roost sites. Many small birds such as ruby-crowned kinglets, yellow-rumped warblers, and western bluebirds glean the foliage for insects or hawk them in the understory.

MEADOW HABITATS

Fresh Emergent Wetland

This habitat type is found in Yosemite Valley, Foresta, El Portal, and Badger Pass. It is found in areas that are flooded frequently by streams and runoff, resulting in vegetation dominated by water-loving plants (hydrophytes). The cycle of flooding and drying in these areas causes much plant decomposition, supporting a rich nutrient cycle. Fresh emergent wetland is the second scarcest habitat type in Yosemite Valley, occupying just 0.43% of the Valley. The shallow waters in this habitat are important breeding areas for western toads and Pacific tree frogs, and they are used in spring by foraging mallards. Red-winged blackbirds nest in the taller vegetation.

Wet Meadow

This habitat type is found in Yosemite Valley, Foresta, and Badger Pass. These habitats generally have a simple structure composed of a layer of herbaceous plants and occur in places where water is at or near the surface during most of the growing season. While shrubs and trees are usually absent or sparse, they can be an important habitat component in the meadow and around its edge. Willow flycatchers depend on willow thickets for nesting habitat. Within the herbaceous plant community, habitat layers are often present on a smaller scale, with different plant species growing to different heights. Wet meadows are generally too wet for small mammals during periods of high water, but they are an important source of green vegetation in summer for herbivores such as mule deer. Birds such as mallards and red-winged blackbirds nest in wet meadows, where the water and tall vegetation can be barriers to predators. Pacific tree frogs and western toads breed in the shallow waters found in this habitat.

RIPARIAN HABITATS

Riverine

This habitat type is found in Yosemite Valley, Wawona, and El Portal. Intermittent or continually flowing water in rivers and streams distinguishes this habitat. The rate of flow varies with stream gradient; faster reaches tend to have rock or gravel bottoms, and slower reaches tend to have mud or sand bottoms. Algae and decomposing leaves from trees along the river or stream form the basis of the food chain. Nymphs of caddisflies, mayflies, and stoneflies live on the undersides of rocks and gravel, and they provide food for species such as rainbow trout and American dippers. Seasonal hatches of these aquatic insects provide important food sources for insectivorous birds and many bat species. Boulders and fallen trees in the water provide habitat diversity and substrates for organisms. Belted kingfishers dive for small fish, and mallards feed and raise broods in slower-flowing reaches. Rainbow trout, California roach, riffle sculpin, and Sacramento sucker are the native fish species in the Merced River and its tributaries. Brown trout have been introduced in these same waters, and they compete with and prey on the native species.

Montane Riparian

This habitat type is found in Yosemite Valley, El Portal, Wawona, Badger Pass, and South Entrance. Vegetation in this habitat type is structurally diverse, composed of narrow bands of dense, deciduous trees associated with lakes, ponds, springs, meadows, rivers, and streams where water may be permanent or ephemeral. Such habitats are of high value to wildlife, providing water, migration corridors, thermal cover, and diverse feeding and nesting opportunities. The linear nature of montane riparian habitat along streams is highly valuable to wildlife. Insects that feed on the trees provide abundant food for bats and insectivorous birds. Cavities in trees and snags provide nesting habitat for bird species such as swallows and woodpeckers. Leaves from deciduous trees that fall into the water are important sources of nutrients in the aquatic food chain.

The diversity and structural complexity of riparian vegetation creates a wide variety of habitats for wildlife. Additionally, the riparian habitat provides a cool/moist microclimate, further adding to habitat diversity. More species and greater numbers of wildlife are found in riparian habitats than in any other Sierra Nevada habitat type (USFS 1977b). For example, the density and diversity of bird species (breeding and migratory) tend to be much greater in riparian areas than adjacent areas (Gaines 1988). Some of these species, and most amphibians, are completely dependent on riparian and adjoining aquatic environments. The riparian vegetation along the river channel provides a continuous corridor for wildlife movement.

OTHER HABITATS

Urban

This habitat type is found in Yosemite Valley and El Portal. Development is also found in the Foresta, Wawona, Big Oak Flat, South Entrance, and Tioga Pass areas. This habitat is composed primarily of stands of native vegetation interspersed with areas of development, such as campgrounds, parking areas, lodging, and housing areas. Vegetation can be similar in complexity to less-disturbed habitats, with California black oak, ponderosa pine, and incense-cedar as canopy species, and a shrub understory. The quality of these habitats for wildlife is limited by their small sizes and their proximity to human activity. Structures in developed areas can, however, provide nesting or roosting habitat for species such as cliff swallows and several species of bats. Urban habitats also contain non-native plant species that have been planted as ornamentals or for agriculture. Fruit-bearing species provide sources of food to wildlife in some urban habitats, such as El Portal and the east end of Yosemite Valley.

Mammals

Approximately 85 native mammal species in six families inhabit Yosemite. Of the insectivore family, five shrews and one mole are present. There are 17 species of bats, nine of which are either California species of special concern or federal species of concern (see table 3-6, following this section). Many of these bat species depend on riparian and meadow habitats for foraging, and large trees or snags for roosting. Carnivores include black bears, bobcats, coyotes, raccoons, weasels, grey foxes, mountain lions, and ringtails. Six species of squirrels, eight species of chipmunks, eight species of mice, and other species of rodents, including wood rats, voles, gophers, and porcupines, inhabit the park. Yosemite's largest mammal, the grizzly bear, was extirpated from the region and from the state in the 1920s. There are two native species of hoofed mammals in Yosemite: the Sierra Nevada bighorn sheep and mule deer. Other mammal species that occur, but are extremely rare, are the fisher, wolverine, and Sierra Nevada red fox.

Heavy visitation to Yosemite Valley, along with the relatively large number of resident employees, has led to many human/wildlife conflicts involving mammal species such as raccoons, mule deer, and especially black bears. The basis of most of these problems is the availability of human food. Improperly stored food and garbage and deliberate feeding alter the natural behavior of wildlife and lead to property damage and threats to human safety. In 1999, more than $225,000 in property damage (746 incidents) was caused by black bears in the park.

Sightings of mountain lions in Yosemite Valley have increased in recent years. Lions are attracted to developed areas by unnaturally large prey populations that are supported by human food sources.

Birds

Yosemiteís wide range of elevations and habitats support diverse bird species; 150 species regularly occur in the park, and approximately 80% of these are known or suspected to breed there. Most of these species begin to migrate to lower elevations or latitudes in the late summer and fall. Of the 84 species that are known to nest in Yosemite Valley, 54% are rare or absent in winter.

Noticeable population declines have been detected in numerous bird species in the Sierra Nevada, including Yosemite. Possible causes for these declines include grazing, logging, fire suppression, development, recreational use, pesticides, habitat destruction on wintering grounds, and large-scale climate changes. Brown-headed cowbird nest parasitism has also been identified as a possible significant factor in population declines of certain species (see Non-Native Wildlife Species, below).

Human activity has been the suspected cause in reducing several bird species in Yosemite Valley. Valley meadows are a suitable habitat for great gray owls, but sightings of this species in Yosemite Valley are rare. Willow flycatchers no longer nest in the Valley, probably due to the loss of riparian and meadow habitat and nest parasitism by brown-headed cowbirds. Warbling and solitary vireos are also vulnerable to cowbird parasitism; for this reason, reduction of these vireo species in the park is also likely. Harlequin ducks are now rarely seen in Yosemite Valley, although a pair was observed in April 2000 on the Merced River in the Valley. The next most recent observation was in 1980.

Reptiles and Amphibians

Compared to most mountain regions of the west, Yosemite has a particularly large number of native reptiles and amphibians: 14 snakes (one poisonous), seven lizards, one turtle, two toads, one tree frog, three true frogs, and five salamanders (including newt and ensatina). Most of these species have been found in Yosemite Valley.

Amphibians in Yosemite have suffered population declines similar to those seen in the rest of the Sierra Nevada (Drost and Fellers 1996). Only a few remnant populations of California red-legged frogs and foothill yellow-legged frogs are left in the entire Sierra Nevada. At higher elevations, mountain yellow-legged frogs and Yosemite toads are still present in a number of areas; however, they are severely reduced in population and range. Research continues to identify the causes of decline in Sierra Nevada amphibians, but possible causes include habitat destruction, non-native fish and frogs, pesticides, and diseases. Two of the species of true frogs once found in Yosemite Valley are now apparently extinct: foothill yellow-legged frog and California red-legged frog. Possible factors in their disappearance include a reduction in perennial ponds and wetlands, and predation by bullfrogs, a non-native species found throughout Yosemite Valley.

Fish

Most fish in Yosemite have been introduced. Prior to trout stocking for sport fishing, native fish were limited in both range and number of species. The last period of glaciation eliminated all fish from the high country. After the glaciers retreated, the waterfalls remaining on the rivers prevented repopulation by upstream migration. Only the lower systems of the Tuolumne and Merced Rivers were populated with fish when Euro-Americans first arrived. Rainbow trout and Sacramento sucker were abundant, while the Sacramento pike-minnow, hardhead, California roach, and riffle sculpin were less common.

Because of severe climatic conditions, low nutrient availability associated with snowmelt over granitic watersheds, and a lack of spawning habitat, fish introduced in the majority of Yosemiteís lakes have not survived. Fishery surveys conducted in the mid-1970s found 62 lakes with self-supporting fish populations, and 195 with little or no natural reproduction. Approximately 550 miles of streams in Yosemite National Park are thought to support fish (NPS 1977).

Beginning in 1978, a park policy was implemented that by 1991 had ended almost 100 years of fish stocking in Yosemite. Human activity has undoubtedly altered fish populations in Yosemite Valley. Non-native brown trout now outnumber rainbow trout in many stretches of the Merced River, and introductions of non-native rainbow trout have altered the genetics of Yosemite Valleyís native strain.

Until recently, trees that fell into the Merced River were considered hazardous to bridges and humans and were removed. Removing fallen trees from the river, however, deprived fish and other aquatic organisms of important habitat and altered natural river dynamics. Fallen trees are now allowed to remain in the river because of their value to aquatic and riparian ecosystems.

The elimination of riparian vegetation by human trampling and placement of bank stabilization devices in many areas along the Merced River has reduced nutrients from fallen leaves in aquatic ecosystems, which has affected the food chain. The loss of soil from riverbanks caused by the lack of riparian vegetation has also led to the creation of broad, shallow stretches of the river that support few fish (CDFG 1990; USFWS 1992). Roads, ditches, utilities, and other structures in meadows have likely altered meadow hydrology, affecting water and nutrient flows into aquatic ecosystems.

Non-Native Wildlife Species

Non-native wildlife in Yosemite include several species of trout, white-tailed ptarmigan, wild turkey, brown-headed cowbird, European starling, house sparrow, and the bullfrog. Feral pigs have recently been sighted near the park and could establish ranges in park ecosystems. All of these species have some effect on native wildlife.

Rainbow trout are native to the Merced River and its tributaries in Yosemite Valley. Brown trout and non-native strains of rainbow trout were introduced, and this has altered the aquatic ecosystem of the Merced River and its tributaries in Yosemite Valley. Introducing brown, rainbow, and brook trout in higher-elevation lakes and streams, all of which were naturally fishless, has likely altered those ecosystems as well. Such introductions of fish are suspected of being the primary factor in declines of native amphibian species in the Sierra Nevada (NPS 1994f; Drost and Fellers 1996).

The sensitive balance of aquatic ecosystems in Yosemite Valley has been disrupted by the presence of bullfrogs, which are voracious, non-native predators. The full impact of bullfrogs on native species in the park is unknown, but studies in other areas of California have concluded that bullfrogs prey on a wide variety of animals, including insects, fish, other amphibians, birds, reptiles, and small mammals. Bullfrog predation was probably a factor in the disappearance of California red-legged frogs and foothill yellow-legged frogs from Yosemite Valley. It is not known when bullfrogs were introduced, but recent observations suggest that they currently occupy standing and slow-moving water throughout the Valley.

Brown-headed cowbird populations in the Sierra Nevada have recently increased (Verner and Ritter 1983), threatening native bird species. Cowbirds are nest parasites that lay their eggs in the nests of other birds, usually songbirds. Cowbird eggs hatch before the eggs of host species, and the larger, more vigorous cowbird young eject the eggs or young of the host species or out-compete the hostís young for food. This parasitism can have a devastating effect on the populations of some songbird species. Cowbirds have been implicated as a factor in the disappearance of willow flycatchers from Yosemite Valley. The spread of cowbirds into the Sierra Nevada has been associated with human disturbance and activities. Currently, brown-headed cowbirds are common in Yosemite and can be found in large numbers at the parkís stables and corrals, campgrounds, and residential areas. A 1995-1996 study found relatively low rates of parasitism, but also found evidence that parasitism, based on the abundance of cowbirds in Yosemite Valley, may soon increase (Laymon and Halterman 1997).

The European starling and house sparrow are two non-native species found in El Portal that affect native bird species through competition for nest cavities, a limited resource. Both species are known to aggressively evict native bird species from occupied cavities. The existing development in El Portal has likely increased the abundance of both species by providing additional nesting sites and food sources.

SPECIAL-STATUS SPECIES

Some species of plants and animals have undergone local, state, or national declines, which has raised concerns about their possible extinction if protective measures are not implemented. As a result, the U.S. Fish and Wildlife Service, California Department of Fish and Game, and Yosemite National Park have established categories of these species that reflect the urgency of their status, and the need for monitoring, protection, and implementation of recovery actions. Collectively, species in these categories are referred to in this document as ìspecial-status species.î

The Federal Endangered Species Act of 1973, as amended, requires federal agencies to consult with the U.S. Fish and Wildlife Service before taking actions that could jeopardize the continued existence of any listed plant or animal species (e.g., listed as threatened or endangered) or species proposed for listing, or that could result in the destruction or adverse modification of critical or proposed critical habitat. The first step in the consultation process is to obtain a list of protected species from the U.S. Fish and Wildlife Service.

In addition, Council of Environmental Quality Regulations for Implementing the National Environmental Policy Act (Section 1508.27) also requires considering whether an action may violate federal, state, or local law or requirements imposed for the protection of the environment. For this reason, species listed under the California Endangered Species Act (i.e., those considered endangered, threatened, rare, or of special concern) by the California Department of Fish and Game are included in this analysis.

The various federal, state, and National Park Service categories for special-status species are defined below:

Tables 3-6 and 3-7 present federally listed threatened or endangered species and species of concern (former federal category 2 species); state-listed threatened, endangered, and rare species, and species of special concern; and species that are locally rare or threatened. These species are known to be or could be present in Yosemite Valley, El Portal, or in proposed out-of-Valley parking areas at South Landing near Crane Flat, Foresta, Henness Ridge near Chinquapin, Hazel Green, and Badger Pass. Species that could occur in the areas surrounding entrance stations at South Entrance, Tioga Pass, and Big Oak Flat are also included. Species listed in the tables are those that could be affected directly, as well as species that could be affected by radiating impacts associated with changes in human activity. A Biological Assessment has been prepared, in accordance with Section 7 of the Endangered Species Act, that further details habitat requirements for the 52 special-status plant species (see Vol. II, Appendix K).

Wildlife

A total of 46 wildlife species that could be found in areas potentially affected by the proposed actions have special federal or state status. Only one species in Yosemite is listed as federally endangered: Sierra Nevada bighorn sheep. Three of these species are listed as federally threatened (bald eagle, Valley elderberry longhorn beetle, and California red-legged frog). Four species are state listed as endangered (peregrine falcon, bald eagle, willow flycatcher, and great gray owl). Three species are state threatened (limestone salamander, Sierra Nevada red fox, and California wolverine). Those listed as state or federal threatened or endangered are protected under the state and federal Endangered Species Acts. These and other species of concern are described, with current status and habitat types, in table 3-6.

The following species accounts give a brief overview of state and federal endangered and threatened species in Yosemite. More detailed information on these species is included in the Biological Assessment (see Vol. II, Appendix K).

Bald Eagle

The bald eagle suffered steep population declines from the effects of pesticides in its food chain; however, bald eagle populations rebounded after DDT was banned. This resulted in the recent federal reclassification from endangered to threatened, and the bald eagle is currently being considered for de-listing. The bald eagle is also state endangered.

Most bald eagles seen in the park are transients, seasonally hunting over lakes, rivers, and open terrain. Bald eagle sightings are rare in Yosemite, but most often occur in Yosemite Valley, El Portal, and Foresta. No bald eagles are known to have nested in Yosemite recently, but a pair regularly nests near the park border at Cherry Lake in Stanislaus National Forest and uses nearby Lake Eleanor inside the park for foraging.

Valley Elderberry Longhorn Beetle

The Valley elderberry longhorn beetle is an insect subspecies endemic to the San Joaquin Valley of California. It is found in riparian habitats and associated upland habitats where elderberry plants grow.

The Valley elderberry longhorn beetle is found in California up to elevations of 3,000 feet. It is most commonly found along the margins of rivers and streams in the lower Sacramento River and upper San Joaquin Valley, particularly in riparian elderberry savannah or moist valley oak woodlands. The species has also been observed in the Sierra foothills, particularly in Fresno, Madera, and Placer Counties, as well as the eastern Coast Ranges foothills. The Valley elderberry longhorn beetle is completely dependent on its host plant, the elderberry. Threats to the beetle arise from the loss or alteration of elderberry habitat through urbanization and agricultural use, the use of insecticides and herbicides, and fluctuations in streamwater levels. Grazing by domestic or wild herbivores and pruning or burning by humans are additional persistent threats to elderberry plants and the continued survival of the Valley elderberry longhorn beetle.

Because the Valley elderberry longhorn beetle is not known to occur above 3,000 feet in elevation, the only location within the areas considered in this Final Yosemite Valley Plan/SEIS where these insects are likely to occur is El Portal and its surrounding habitat in the Merced River canyon.

California Red-Legged Frog

This species has virtually disappeared from the Sierra Nevada, remaining in only a few locations. Possible causes for this disappearance include pesticides, and predation and competition from bullfrogs.

Records of California red-legged frogs are fragmentary, but the species is believed to have occurred in at least several locations in the park, including Yosemite Valley. The only recent records for Yosemite come from a lake at 6,000 feet in elevation in the northern portion of the park. Surveys at this location within the last five years have found no red-legged frogs remaining, only bullfrogs. California red-legged frogs are also a state species of special concern.

Peregrine Falcon

This species, recently removed from the federal endangered species list, is still listed by the state as endangered. The falcon disappeared from much of its North American range, including Yosemite, during the 1950s and 1960s, primarily due to pesticide contamination. Populations of peregrine falcons began to rebound after the use of DDT was banned in the United States in 1972. In 1978, a pair of peregrine falcons was discovered nesting on El Capitan in Yosemite Valley. This discovery was followed by intensive efforts by the National Park Service and other organizations to increase the number of peregrines in the park through introduction of captive-hatched birds. There are now four active peregrine falcon nest sites in the park, three of which occur in Yosemite Valley: Lower Cathedral Rock, Rhombus Wall (east of Indian Canyon), and on the northeast face of Glacier Point. (A fourth nest site is at Hetch Hetchy Reservoir.)

Peregrine falcons feed primarily on other birds that they catch along cliff faces, such as white-throated swifts and violet-green swallows. Prey remains recovered from nest sites, however, indicate that the falcons also prey on birds from forest, meadow, and riparian habitats, such as northern flickers, Steller's jays, band-tailed pigeons, and gulls.

Factors affecting peregrine falcons in Yosemite include disturbance from climbers and aircraft, and continued pesticide contamination from residual sources outside the park.

Great Gray Owl

The global range of the great gray owl reaches its furthest southern extent in the Sierra Nevada, with the total population in California estimated to be between 100 and 200 birds. Declines of great gray owls in California may be due to habitat degradation from logging, grazing, and development. Yosemite has the highest concentration of this species, probably because the park contains the most intact habitats.

Preferred breeding habitat of great gray owls is pine and fir forests near montane meadows. Nests are established in the tops of large-diameter broken snags. At the latitude of Yosemite, high summer temperatures are an important factor affecting nesting success, so suitable nest snags must have abundant shade. Hunting occurs in meadows where small mammals such as voles and gophers are taken. In winter the great gray owls descend to meadows as low as 2,000 feet in elevation.

Areas in Yosemite of known great gray owl breeding include Crane Flat and meadows along Glacier Point Road. Known wintering areas include Big Meadow in Foresta, and Wawona. Yosemite Valley appears to contain good wintering habitat, but observations of great gray owls in this location are rare. This may be due to the high level of human disturbance in the Valley.

Willow Flycatcher

The total population of willow flycatchers in California is estimated at around 200 pairs. This tenuous status is believed to be caused by destruction of the preferred habitat—willow thickets in meadow and riparian areas—from grazing and development. Other contributing factors could include nest parasitism by brown-headed cowbirds, nest disturbance by grazing stock, and degradation of neotropical wintering grounds.

Willow flycatchers have not been observed nesting in Yosemite Valley for nearly 35 years, with habitat destruction, human disturbance, and cowbird parasitism likely factors. A greater factor, however, has probably been the Sierrawide decline of the species, which has limited the ability of park habitats to sustain a viable population.

Recent records of willow flycatchers in Yosemite include Wawona Meadow, Hodgdon Meadow near the Big Oak Flat Entrance Station, and Westfall Meadow near Badger Pass.

STATE THREATENED

Limestone Salamander

The limestone salamander is found in a highly restricted range near Briceburg, Mariposa County. This area is protected by the 129-acre Limestone Salamander Ecological Reserve and the Bureau of Land Managementís 1,600-acre Limestone Salamander Area of Critical Environmental Concern. The limited range of this species is natural, but Highway 140, running through potential habitat, has likely had a localized detrimental effect on limestone salamanders.

The species is found in limestone substrates in mixed chaparral habitats along the Merced River and its tributaries from 1,100 to 2,500 feet in elevation. It frequents limestone cliffs and ledges in talus, especially in areas overgrown with moss. During periods of surface activity (November to March), limestone salamanders may be found on steep north- and east-facing slopes. California buckeye may be an indicator species for optimal habitat.

No limestone salamanders have been seen in the park, with its closest occurrence 30 miles west of El Portal. Although the project area in El Portal lies within the elevation range of this species, and suitable vegetative habitat appears to exist, limestone salamanders are not expected to occur in this area due to the lack of limestone substrate.

Sierra Nevada Red Fox

The Sierra Nevada red fox prefers forests interspersed with meadows and alpine fell-fields between 3,900 and 11,900 feet in elevation, although a vast majority of records of this species are from above 7,000 feet in elevation. The low end of the elevation range is based on the historic collection of a pair of red foxes at Big Meadow near Foresta. All other specimens in the Museum of Vertebrate Zoology (10) were collected near Tioga Pass. Near the end of the 19th century, intensive fur trapping in the Sierra Nevada greatly reduced numbers of Sierra Nevada red fox. Today, the species is exceedingly rare. A photograph was taken of a red fox at Tioga Pass Resort in January 1991, but it could not be determined whether this individual was a Sierra Nevada red fox or an introduced eastern red fox.

Extensive suitable habitat for Sierra Nevada red foxes exists around Tioga Pass. If the identification of the red foxes collected at Big Meadow is valid, the species may have also existed down to relatively low elevations.

California Wolverine

The wolverine is exceeding rare in California, with its distribution scattered over wide areas. Optimal habitat for this species is in forests with large trees and moderate to dense canopy cover, in red fir, lodgepole pine forests, and in alpine meadows. Special habitat requirements are low human disturbance, and rocky areas, caves, logs, or snags as den sites. Prey includes a variety of rodents, birds, insects, and occasionally ungulates. Wolverines will also eat fruits.

Wolverines probably always occurred in low numbers in the Sierra Nevada, but trapping and human disturbance have likely reduced their population. Tioga Pass lies within the historical range of optimal habitat for wolverines, based upon the collection of specimens from nearby locations.

The remaining special-status species, federal species of concern and state species of special concern, are described in table 3-6 and in the Biological Assessment (Vol. II, Appendix K).

Table 3-6 a, Table 3-6 b, Table 3-6 c, Table 3-6 d, Table 3-6 e

Vegetation

A total of 52 plant species that have special federal, state, or park status has been evaluated in this Final Yosemite Valley Plan/SEIS. Four of these species are classified as federal species of concern, four are listed as rare by the State of California, and the remaining 44 are listed by the park as rare.

The four federal species of concern (Congdon's lomatium, Tiehm's rock-cress, slender-stemmed monkeyflower, and Bolander's clover) are former category 2 species (species for which listing might be appropriate) under the Federal Endangered Species Act. The category was abolished in 1996; however, it continues to be evaluated and managed by the National Park Service.

Four state-listed rare species (Yosemite onion, Tompkin's sedge, Congdon's woolly-sunflower, and Congdon's lewisia) are evaluated. These are species that are considered restricted and limited throughout all or a significant portion of their range, and may represent disjunct populations at the extreme of their range. The NPS-28 Natural Resources Management Guidelines (NPS 1991a) state that the management of these species should, to the extent possible, parallel the management of federally listed species.

The remaining 44 species on this list are classified by the park as rare. These species are rare in the park but have no other status (either state or federal). They are included on this list because they could be affected (due to proximity to human use zones, or susceptibility of individual plants or populations to loss from natural or unnatural events), and their existence is considered by the National Park Service when evaluating consequences for any proposed management action. Many of these species have extremely limited distributions in the park and may represent relict populations from past climatic or topographic conditions, while other species may be at the extreme extent of their range in the park or represent changes in species genetics.

Table 3-7a, Table 3-7b, Table 3-7c

AIR QUALITY

Regulatory Overview

Yosemite National Park is classified as a mandatory Class I area under the Clean Air Act (42 USC 7401 et seq.). This most stringent air quality classification protects national parks and wilderness areas from air quality degradation. The Clean Air Act gives federal land managers the responsibility for protecting air quality and related values, including visibility, plants, animals, soils, water quality, cultural resources, and public health, from adverse air pollution impacts. Yosemite National Park is located in three California counties: Tuolumne, Mariposa, and Madera (see Vol. Ic, plate B). Tuolumne and Mariposa Counties are within the Mountain Counties Air Basin, and Madera County is within the San Joaquin Valley Air Basin of the San Joaquin Valley Unified Air Pollution Control District. Yosemite Valley is in Mariposa County, which is regulated by the Mariposa County Air Pollution Control District.

NATIONAL AMBIENT AIR QUALITY STANDARDS

The federal Clean Air Act, as amended in 1990, requires the U.S. Environmental Protection Agency to identify national ambient air quality standards to protect public health and welfare. Standards have been set for six pollutants: ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, lead, and particulate matter less than 10 microns (PM₁₀). The U.S. Environmental Protection Agency also promulgated a revised standard for ozone and a new standard for particulate matter less than 2.5 microns (PM_2.5). However, in the spring of 1999, a U.S. Court of Appeals panel remanded the standard to the U.S. Environmental Protection Agency for further consideration. These pollutants are called criteria pollutants because the standards satisfy criteria specified in the Clean Air Act. An area where a standard is exceeded more than three times in three years can be considered a nonattainment area. Nonattainment areas are subject to planning and pollution control requirements that are more stringent than in those areas where standards are met.

While air quality in an air basin is usually determined by emission sources within the basin, pollutants blown from upwind air basins may also affect air quality. For example, the California Environmental Protection Agency concluded that the ozone exceedances in 1995 in the southern portion of the Mountain Counties Air Basin (i.e., Tuolumne and Mariposa Counties) were caused by transport of ozone and ozone precursors from the San Joaquin Air Basin. Air Quality in the Mountain Counties Air Basin also is affected by pollutant transport from the metropolitan Sacramento and San Francisco Bay areas.

CALIFORNIA AMBIENT AIR QUALITY STANDARDS

The California Air Resources Board has set ambient air quality standards to protect public health and welfare that are more strict than the national standards. Under the 1988 California Clean Air Act, air basins were designated as attainment, nonattainment, or unclassified.
Table 3-8 shows the California and federal air quality standards attainment designation for the counties containing portions of Yosemite National Park. Of the pollutants noted, only carbon monoxide and nitrogen dioxide are regulated from mobile sources. In addition, hydrocarbons, or volatile organic compounds, are regulated to address ozone emissions because volatile organic compounds, along with nitrogen dioxide emissions, are precursors to the formation of ozone.

Table 3-8

STATE IMPLEMENTATION PLAN

The Mariposa County Air Pollution Control District is responsible for developing a state implementation plan for federal and state nonattainment pollutants in its jurisdiction (table 3-9). State implementation plans define control measures designed to bring areas into attainment. Basic components of a state implementation plan include legal authority, emissions inventory, air quality monitoring network, control strategy demonstration modeling, rules and emission-limiting regulations, new source review provisions, enforcement and surveillance, and other programs, as necessary, to attain standards. Currently, Mariposa County is in attainment or is unclassified for all national ambient air quality standards. Mariposa County exceeds two California ambient standards: ozone throughout the county and PM₁₀ in Yosemite Valley.

CONFORMITY RULE

In 1993, the U.S. Environmental Protection Agency adopted regulations implementing Section 176 of the Clean Air Act, as amended. Section 176 requires that federal actions conform to state implementation plans for achieving and maintaining the national standards. Federal actions must not cause or contribute to new violations of any standard, increase the frequency or severity of any existing violation, interfere with timely attainment or maintenance of any standard, delay emission reduction milestones, or contradict state implementation plan requirements. This requirement applies only in federal nonattainment areas. Conformity does not apply to activities in Yosemite Valley because Mariposa County meets all federal air quality standards at this time and is an attainment area. However, activities in Madera County must conform to state implementation plans. In addition, the California Air Resources Board indicates that Mariposa County, which includes the Valley, is likely to be declared a nonattainment area for ozone in the summer of 2000, at which time conformity with state implementation plans must be demonstrated.

AIR QUALITY MONITORING

A number of air quality monitoring stations are located in and near the park. Monitors in the park include an ozone monitor and Interagency Monitoring of Protected Visual Environments (IMPROVE) site at Turtleback Dome, and a particulate monitor at the park headquarters near the visitor center in Yosemite Valley. Table 3-10 lists air quality monitors in and around the park.

According to the latest California Air Resources Board air monitoring data, summarized in table 3-11, ambient air quality at the Turtleback Dome monitoring station exceeded the state 1-hour ozone standard during three days in 1997, as compared to 11 days in 1995. In 1997, at the park headquarters station, the state 24-hour PM₁₀ standard was exceeded on only one day, compared to five days in 1995. However, no exceedances of the federal 24-hour PM₁₀ standard or state and federal annual standards were recorded that year at this station.

Yosemite Valley Inventory of Air Pollution Emission Sources

Air quality in the park is affected by internal and external air pollution sources. Internal air pollution sources include stationary sources such as furnaces, boilers, woodstoves, campfires, generators, barbecues, and emissions from prescribed fires. Motor vehicles are mobile sources, and emissions primarily include carbon monoxide, nitrogen oxides, and hydrocarbons (or volatile organic compounds). Estimates of criteria air pollutants from stationary, area, and mobile sources in the Valley for 1998 are summarized in table 3-12. Most of the stationary and area sources are associated with park operations (National Park Service and concessioner). Campfires and associated emissions, however, are typically generated by visitors. Vehicles and tour buses constitute the largest sources of mobile-source emissions in Yosemite Valley.

Table 3-13 lists major external stationary air pollution sources within 60 miles of the boundary of Yosemite National Park.

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