Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUB-SUBSECTION IX.7.3. Isle Royale
DISCUSSION: The bedrock ridges of the Keweenaw Peninsula and of Isle Royale are both part of the Lake Superior syncline, which extends from northern Wisconsin to the tip of the Keweenaw Peninsula of Michigan. Isle Royale, located at the northern end of the syncline, is treated as a separate sub-subsection because of its climate, which is even more strongly influenced by surrounding Lake Superior than that of Sub-subsections IX.7.1 and IX.7.2.
ELEVATION: 602 to 1,362 feet (184 to 415 m).
AREA: 230 square miles (595 sq km).
STATES: Michigan.
CLIMATE: Climatic data are not available for Isle Royale. Lake Superior has a strong climatic influence on the island; even in the middle of the summer, temperatures are low. Fog occurs commonly.
BEDROCK GEOLOGY: Erosion-resistant conglomerates and amygdaloidal basalt form the ridges of the sub-subsection, between which veins of more easily eroded lavas are sites for lakes and wetlands (Dorr and Eschman 1984, Reed and Daniels 1987). The Lake Superior shoreline consists of rugged volcanic bedrock. Copper-rich lava flows were extensively mined.
LANDFORM: Linear bedrock ridges and narrow wetlands characterize most of the island, while thin, rocky till covers the southwestern end. There are several steep bedrock peaks, including Sugar Mountain (1,362 feet), Mount Ojibway (1,136 feet), and Mount Siskiwit (1,205 feet).
LAKES AND STREAMS: Several linear, inland lakes: Siskiwit, Desor, Feldtmann, and Sargent; numerous narrow embayments connected to Lake Superior. Streams on the island are small.
SOILS: Soils are thin and sandy or loamy; boulders are common. Bedrock is at the surface over most of the island. Depressions in the bedrock contain organic soils.
PRESETTLEMENT VEGETATION: The thin, rocky soils of Isle Royale supported trembling aspen, white spruce, and balsam poplar. Sugar maple grew on areas with deeper soils.
NATURAL DISTURBANCE: Both windthrows and fires noted.
PRESENT VEGETATION AND LAND USE: Copper was mined by Native Americans and by early European settlers. The entire island is now a National Park.
RARE PLANT COMMUNITIES: Bedrock balds and bedrock beaches support a diverse flora of boreal and disjunct northwestern montaine species.
RARE PLANTS: Carex atratiformis (sedge), Carex media (sedge), Castilleja septentrionalis (pale Indian paintbrush), Clematis occidentalis (purple clematis), Collinsia parviflora (small blue-eyed Mary), Cryptogramma acrostichoides (American rock-brake), Draba arabisans (rock whitlow-grass), Draba incana (twisted whitlow-grass), Dryopteris expansa (expanded woodfern), Empetrum nigrum (crowberry), Euphrasia arctica (American eyebright), Lactuca pulchella (blue lettuce), Lonicera involucrata (fly honeysuckle), Luzula parviflora (small-flowered woodrush), Nymphaea tetragona (pygmy water-lily), Oplopanax horridus (devil's club), Osmorhiza depauperata (sweet cicely), Parnassia palustris (marsh grass-of-Parnassus), Phacelia franklinii (Franklin's phacelia), Phleum alpinum (mountain timothy), Poa alpina (alpine bluegrass), Polygonum viviparum (alpine bistort), Potentilla pensylvanica (prairie cinquefoil), Ranunculus macounii (Macoun's buttercup), Ranunculus rhomboideus (prairie buttercup), Ribes oxyacanthoides (northern gooseberry), Sagina nodosa (pearlwort), Salix planifolia (tea-leaved willow), Saxifraga paniculata (encrusted saxifrage), Saxifraga tricuspidata (prickly saxifrage), Senecio indecorus (rayless mountain-ragwort), Tofieldia pusilla (false asphodel), Trisetum spicatum (downy oat-grass), Vaccinium uliginosum (alpine blueberry), Vaccinium vitis-idaea (mountain-cranberry), Viburnum edule (squashberry or mooseberry).
RARE ANIMALS: Alces alces (moose), Canis lupis (gray wolf), Falco columbarius (merlin), Falco peregrinus (peregrine falcon), Felis lynx (lynx), Lycaeides idas nobokovi (northern blue butterfly).
NATURAL AREAS: Wilderness Natural Parks: Isle Royale; Research Natural Areas: Passage Island.
PUBLIC LAND MANAGERS: National Park Service: Isle Royale.
CONSERVATION CONCERNS: The combination of remoteness and wilderness status makes this a secure landscape.
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| Figure 27.—Sub-subsection IX.7.3: Isle Royale Wilderness Natural Park, Michigan. Isle Royale was formed from the extensive Keweenawan-age lava flows. The lava flows more resistant to erosion by waves and ice remain as small islands off the coast of Isle Royale; the less resistant flows have been eroded away. The lava, which was laid down as numerous, thin horizontal layers on land, has been greatly deformed; the layers now slope at 30 to 40 degrees from the horizontal. Photo by P. Melhop. |
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