Fauna Series No. 7

Fauna of the National Parks — No. 7 The Wolves of Isle Royale

STUDY AREA

Flora

Isle Royale is in the Canadian biotic province (Dice 1943:Map I), just south of the arbitrary boundary of the Hudsonian province. Thus, it is actually in the transition zone between the two, and characteristics of both are evident.

In the cooler, damper regions close to the lake, and in the narrow northeast section of the island, balsam fir (Abies balsamea) and white spruce (Picea glauca) comprise the climax forest; white birch (Betula papyrifera) forms small pockets in this type. According to Krefting (1951) the spruce-fir forest composes 29 percent of the island's cover. This climax is characteristic of the Hudsonian biotic province.

Typical of the Canadian province is the climax consisting of sugar maple (Acer saccharum) and yellow birch (Betula lutea), which predominates on the warmer, more mesic sites in the southwest third of the park. About 10 percent of the island's forest consists of this type (Krefting, 1951). Small local stands of northern red oak (Quercus rubra), white pine (Pinus strobus), red pine (P. resinosa), or jack pine (P. banksiana) occupy the most xeric ridges.

Swamps and lowlands support black spruce (Picea mariana), white cedar (Thuja occidentalis), and balsam fir.

About 56 percent of the forest cover is subclimax aspen (Populus tremuloides) and white birch, interspersed with conifer reproduction (Krefting, 1951). This type results from fires, and since most of Isle Royale has been burned over (Brown, n.d.), these subclimax stands are widespread. According to Hickie (n.d.), extensive fires occurred between 1870 and 1900. In 1936, fire swept approximately one-fourth of the island (Aldous and Krefting, 1946), and this area now supports predominantly white birch and some aspen. Willow (Salix spp.), fire cherry (Prunus pennsylvania), and choke-cherry (P. virginiana) also are scattered throughout the burn (figures 7 and 8).

Figure 7—Lush, second-growth hardwoods in the 1936 burn.

Figure 8—The 1936 burn in winter.

Figure 9—Heavily browsed birch and aspen.

Figure 10—Major forest cover types.

Figure 10 shows the location and extent of the major cover types.

Shrubs and lesser trees are represented primarily by speckled alder (Alnus incana) along streams and in old beaver meadows; mountain alder (A. crispa) around lakes, bays, and rock openings; beaked hazelnut (Corylus cornuta) in rock openings and old burns; mountain maple (Acer spicatum) in mixed woods and on rocky cliffs; mountain ash (Pyrus americana) on islands and in rock openings; black ash (Fraxinus nigra) in damp upland areas; serviceberry (Amelanchier spp.), blueberry (Vaccinium spp.), bearberry (Arctostaphylos uva-ursi) and wood rose (Rosa acicularis) on open ridges; red osier (Cornus stolonifera) along shores, bogs, and swamps; red raspberry (Rubus idaeus) in forest clearings, rock openings, and old beaver meadows; hush honeysuckle (Diervilla lonicera) and thimbleberry (Rubus parviflorus) in rock openings, mixed woods, and old burns. The latter probably is the most abundant and widespread shrub on Isle Royale.

Figure 11—American yew, a favorite moose food, on Passage Island, one of the islands surrounding isle Royale. Since there are no moose on this island, yew grow profusely, but on Isle Royale this species is now very scarce.

Figure 12—Lush stand of young aspen making a return in the Washington Harbor area.

Figure 13—Moose browse in winter.

One of the most common herbs is large-leaved aster (Aster macrophyllus), which grows in old burns, mixed woods, and rock openings in all parts of the park. Cow parsnip (Heracleum maximum) is widespread, in clearings and lightly shaded areas. Bunchberry (Cornus canadensis), twinfiower (Linnaea borealis), yellow clintonia (Clintonia borealis), and wild sarsaparilla (Aralia nudicaulis) are also conspicuous in the understory. Open ridges support wood lily (Lilium philadelphicum), fireweed (Epilobium angustifolium), columbine (Aquilegia canadensis), bluebell (Campanula rotundifolia), self-heal (Prunella vulgaris), pearly everlasting (Anaphalis margaritacea), strawberry (Fragaria virginiana), goldenrod (Solidago spp.), and others.

Skunk cabbage (Symplocarpus foetidus), marsh marigold (Caltha palustris), sedges (Carex spp.), and rushes (Juncus spp.) are typical herbs of Isle Royale swamps. The common aquatics are Nuphar, Nymphaea, Brasenia, Potamogeton, and Utricularia.

The most abundant and wide spread fern appears to be bracken (Pteridium aquilinum), which grows in old burns, along trails, on ridges, and in birch-aspen stands. Interrupted fern (Osmunda claytoniana) and several species of Dryopteris occupy the more shaded sites, and polypody (Polypodium virginianum) is widely distributed in shaded rocky areas.

C. A. Brown (n.d.) listed 671 ferns and flowering plants present on Isle Royale.

Last Modified: Thurs, Jul 4 2002 10:00:00 pm PDT
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