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View repeat photography of the stations
By Mark E. Miller, National Park Service
Never grazed area.
Latitude: 38° 005.681'
Longitude: 109° 50.399'
Elevation: 5630 ft (1716 m)
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CLIM-MET Site #2 is located in Virginia Park, a 100-ha grassland basin encircled by tall Cedar Mesa sandstone walls in the backcountry of the Needles District. The Virginia Park basin is geomorphologically varied, with coarse-textured aeolian deposits interspersed with flat to gently sloping alluvial surfaces characterized by relatively silty soils. A simple ephemeral-drainage network dissects the basin, exposing cut-bank soil profiles up to 2-m deep in some locations. Elevation of the site is approximately 1716 m.
Virginia Park is inaccessible to livestock, has never been grazed by domestic animals, and thus has a disturbance history that sets it apart from other grassland basins in the Needles area. In contrast with areas accessible to livestock, soil-surface disturbances in Virginia Park are minimal. Historically, sources of surface disturbances were limited to infrequent visits by an occasional bighorn sheep (Ovis canadensis) and relatively low numbers of human visitors. Mule deer (Odocoileus hemionus) probably are unable to access the site. For several years, human access to Virginia Park has been restricted to researchers, and research activities currently represent the greatest source of surface disturbances. Also unlike most grassland basins with histories of livestock disturbance, complex systems of rodent burrows are uncommon in grasslands of Virginia Park.
Vegetation of Virginia Park is a reflection both of this unique disturbance history as well as the basin's natural geomorphological heterogeneity. Because of the absence of livestock grazing and trampling, Virginia Park has been the focus of numerous ecological studies over the past 30 years (for example, Kleiner and Harper 1972, 1977a,b). Research indicates that the composition and distribution of plant and cryptobiotic communities in Virginia Park are strongly related to geomorphologically and pedogenically driven spatial variations in soil texture and chemical composition, depth and maturity of subsurface calcic horizons, as well as to slope angle and aspect. Further, the correlation of biotic ecosystem components with these abiotic conditions is much stronger in Virginia Park than in environmentally similar areas with long histories of livestock disturbance (Kleiner and Harper 1972, 1977a).
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Figure 1. Hilaria jamseii (galleta) |
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Figure 2. Stipa comata (needle-and-thread) |
In Virginia Park, grassland communities differentiate into two major types representing endpoints of a gradient (Kleiner and Harper 1972, 1977a). The perennial rhizomatous grass Hilaria jamesii (fig. 1) dominates one community type. The second major type is dominated by the perennial bunchgrass Stipa comata (needle-and-thread) (fig. 2). In comparison with Stipa-dominated communities, Hilaria-dominated communities occur on relatively fine-textured silty soils possessing higher levels of potassium and phosphorous as well as shallower, better developed calcic horizons. Hilaria-dominated communities also are characterized by more diverse assemblages of vascular plants. Cryptobiotic communities are better developed and more diverse on silty soils where Hilaria is the dominant vascular plant (Kleiner and Harper 1977b). The native shrubs Atriplex canescens (four-wing saltbush) and Ceratoides lanata (winterfat) are more common in communities dominated by Hilaria, whereas the native bunchgrasses Stipa hymenoides (Indian ricegrass) (fig. 3) and Sporobolus cryptandrus (sand dropseed) are more common in communities dominated by Stipa comata.
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Figure 3. Native bunchgrasses- Stipa hymenoides (Indian ricegrass) |
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Figure 4. Cheatgrass-dominated patch |
Due primarily to the absence of livestock trampling and grazing, cover and density of cheatgrass (fig. 4) in Virginia Park was until recently very low in comparison with accessible and heavily grazed grassland basins in the area. Cheatgrass was present in Virginia Park when the first vegetation surveys were conducted in 1967, but cover of the species was only 0.4 percent in Hilaria-dominated communities where it was most common (Kleiner and Harper, 1972). (In comparison, average cover of Hilaria in the same communities was 18.3 percent). In Stipa-dominated communities, cheatgrass was present only at trace levels in 1967.
It is significant that cheatgrass in 1967 was more common in Virginia Park than in Chesler Park, a nearby grassland basin with a history of light winter grazing by livestock (Kleiner and Harper, 1972). Compared to Virginia Park, Chesler Park has sandier soils and lower cover and diversity of cryptobiotic soil-crust species. Hilaria-dominated communities are more common in Virginia Park, whereas communities dominated by Stipa comata are more common in Chesler Park. These observations suggest that, in the absence of heavy grazing and trampling by livestock, physicochemical soil characteristics and interspecific competition are important factors influencing the spatial distribution of cheatgrass at two scales: (1) among soil-vegetation patches in Virginia Park, and (2) between Virginia Park and Chesler Park. Above-average levels of fall 1994 and spring 1995 precipitation resulted in large increases in the cheatgrass populations both in Virginia Park and Chesler Park. Within the two grassland areas, spatial variations in the cheatgrass increases were consistent with the observed distribution of the grass in 1967; cheatgrass increases were greatest in Hilaria-dominated communities with relatively silty soils. Cover of cheatgrass in this soil-vegetation type now varies from 25 to 50 percent. Experimental research currently is being conducted to investigate the effects of physicochemical soil characteristics and interspecific competition on cheatgrass performance at Canyonlands.
Vegetation immediately surrounding the CLIM-MET station in Virginia Park is a mosaic of the two major grassland types found in the basin. The site primarily is dominated by the two native bunchgrasses Stipa comata and S. hymenoides. The native grass Hilaria jamesii occurs in small numbers in sandy soils dominated by Stipa spp., but it is the native dominant in adjacent patches with relatively silty soils. Cheatgrass is common at the site, but it is most abundant in Hilaria-dominated patches. Average cover of cheatgrass in the immediate vicinity of the CLIM-MET station is about 25 percent. Other common species near the station include the native shrubs Atriplex canescens, Ceratoides lanata, and Ephedra viridis (Mormon tea), the native annual broad-leafed plant Plantago patagonica (woolly plantain), the native annual grass Festuca octoflora (sixweeks fescue), and Opuntia sp. (prickly pear). Juniperus osteosperma and Pinus edulis dominate washes and lithic soils near rock outcrops. In contrast with cheatgrass, the exotic weed Salsola iberica does not occur in Virginia Park. Cryptobiotic soil crusts in Virginia Park are very well developed and are characterized by a diverse assemblage of lichens, mosses, and cyanobacteria.
Kleiner, E.F., and K.T. Harper, 1972, Environment and community organization in grasslands of Canyonlands National Park: Ecology, v. 53, no. 2, p. 299-309.
Kleiner, E.F., and K.T. Harper, 1977a, Soil properties in relation to cryptogamic groundcover in Canyonlands National Park: Journal of Range Management, v. 30, no. 4, p. 202-205.
Kleiner, E.F., and K.T. Harper, 1977b, Occurrence of four major perennial grasses in relation to edaphic factors in a pristine community: Journal of Range Management, v. 30, no. 4, p. 286-289.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://esp.cr.usgs.gov/info/sw/clim-met/virginia.html
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Page Last Modified: Thu 11-May-2006 14:15:06 MDT
