A number of habitats exist on the island, the primary being
boreal forest, similar to neighboring Ontario and Minnesota. Upland areas along some of the ridges are effectively "balds" with exposed bedrock and a few scrubby trees, blueberry bushes, and hardy grasses. Occasional marshes exist, which are typically the by-product of
beaver activities. There are also several lakes, often with wooded or marshy shores. The climate, especially in lowland areas, is heavily influenced by the cold waters of
Lake Superior.
Flora According to the
A. W. Kuchler U.S.
Potential natural vegetation Types, Isle Royale National Park has a Great Lakes
Spruce/
Fir (
93) potential vegetation type and a Northern
Conifer Forest (
22) potential vegetation form. The predominant floral habitats of Isle Royale are within the
Laurentian Mixed Forest Province. The area is a
temperate broadleaf and mixed forests biome transition zone between the true
boreal forest to the north and
Big Woods to the south, with characteristics of each. It has areas of both broadleaf and
conifer forest cover, and bodies of water ranging from conifer bogs to swamps. Conifers include
jack pines (
Pinus banksiana),
black and
white spruces (
Picea mariana and
Picea glauca),
balsam firs (
Abies balsamea), and
eastern redcedars (
Juniperus virginiana).
Deciduous trees include
quaking aspens (
Populus tremuloides),
red oaks (
Quercus rubra),
paper birches (
Betula papyrifera),
American mountain ash (
Sorbus americana),
red maples (
Acer rubrum),
sugar maples (
Acer saccharum), and
mountain maples (
Acer spicatum). There are over 600 species of flowering plants found in Isle Royale National Park such as wild sarsaparilla, marsh-marigold, wood lily and prickly wild rose.
Fauna Isle Royale National Park is known for its
timber wolf and
moose populations, which are studied by scientists investigating
predator-prey relationships in a closed environment. There is a cyclical relationship between the two animals: as the moose increase in population, so do the wolves. Eventually, the wolves kill too many moose and begin to starve and lower their reproductive rates. This is made easier because Isle Royale has been colonized by roughly just one third of the mainland mammal species, because it is so remote. In addition, the environment is unique in that it is the only known place where wolves and moose coexist without the presence of bears. Other common mammals are
red foxes,
beavers, and
red squirrels. Some foxes are accustomed to human contact and can be seen prowling the campgrounds at dawn, looking for stray scraps left by unwary campers. For its part, the
wolf is an elusive species which avoids human interaction. Few documented cases of direct wolf/human contact existed for most of the island's history. In the 2024 season dozens of wolf sightings were reported around the Rock Harbor area.
Ermine have been periodically sighted around docks. Other mammals that can be seen include
mink along the various lake shores and
muskrats (occasionally) at beaver ponds. Several species of
bat also exist on the island. Reptiles include the
eastern garter snake,
painted turtle, and
northern redbelly snake. Six species of
frogs and three species of
salamander also live on the island. Historically neither moose nor wolves inhabited Isle Royale. Just prior to becoming a national park the large mammals on Isle Royale were
Canada lynx and the
boreal woodland caribou. Archeological evidence indicates both of these species were present on Isle Royale for 3,500 years prior to being removed by direct human actions (hunting, trapping, mining, logging, fires, competition for resources from exotic species and possibly disease due to the introduction of invasive species). The last caribou documented on Isle Royale was in 1925. Though lynx were removed by the 1930s, some have periodically crossed the ice bridge from neighboring
Ontario, Canada, the most recent being an individual sighting in 1980. Although lynx are no longer present on the island, their primary prey,
snowshoe hares, remain. Before the appearance of wolves,
coyotes were also predators on the island. Coyotes appeared around 1905 and disappeared shortly after wolves arrived in the 1950s. Four wolves were brought from Minnesota in 2018 after some debate as to whether or not the introduction was an unnatural intervention. Moose are believed to have colonized Isle Royale sometime between 1905 and 1912. It was initially believed that a small herd of moose (moose typically do not travel in herds) colonized the islands by crossing the ice from the adjacent mainland; later this theory was modified to a herd of moose swimming 20 miles across
Lake Superior from the nearest mainland. The improbability of these theories received little scrutiny until recent years. Although no thorough scientific investigation to determine how moose arrived on Isle Royale has been carried out to date, both cultural and genetic evidence indicates they were likely introduced by humans to create a private hunting preserve in the early 1900s. The cultural evidence that moose were trapped in northwestern
Minnesota and transported to Isle Royale seemed unlikely until decades later when genetic evidence revealed the moose on Isle Royale were more closely related to moose in the far northwestern Minnesota/Manitoba border area than the mainland adjacent to Isle Royale in far northeastern Minnesota bordering Ontario. Further evidence has also shown that the
Washington Harbor Club, a group of well-to-do businessmen, owned various buildings on Isle Royale in addition to railroads that ran from
Baudette to
Duluth and
Two Harbors and so had the means to transport moose from northwestern Minnesota to Two Harbors. There are usually around 25 wolves and 1000 moose on the island, but the numbers change greatly year to year. In the 2006–2007 winter, a survey found 385 moose and 21 wolves in 3 packs. In spring 2008, 23 wolves and approximately 650 moose were counted. However, recent reductions in winter pack ice had ended replenishment of the wolf population from the mainland. Due to genetic inbreeding, the wolf population had declined to two individuals in 2016, causing researchers to expect that the island's wolf population would eventually become extinct. At the same time, the island's moose population had exploded to an estimated 1600. By November 2017, the wolf population was down to one, a female. The decision to relocate 20–30 wolves to the island was approved and from September 2018 to September 2019, 19 wolves were relocated to Isle Royale from various locations in Minnesota, Michigan, and Ontario. As of April 14, 2020, there were an estimated 14 wolves remaining on the island.
Geology The island is composed largely of ridges, running roughly southwest-to-northeast. The main ridge, Greenstone Ridge, is over in many places.
Greenstone belts are exposed, with rounded stones of
chlorastrolite, also known as greenstone, near and in the lake. The two main rock assemblages found on the island include the Portage Lake
Volcanics and the Copper Harbor
Conglomerate, both
Precambrian in age. The volcanics are mainly
ophitic flood basalts, some 100 individual flows over an accumulated thickness of at least 10,000 feet. The conglomerate
outcrops on the southwestern portion of the island and consists of
sedimentary rock derived from volcanic rocks in present-day Minnesota.
Glacial erosion accentuated the ridge and valley topography from pre-glacial stream erosion.
Glacial striations indicate a generally westward movement of the glaciers as do the
recessional moraines west of Lake Desor.
Drumlins are found west of Siskiwit Lake. Recent analyses by the USGS of both unmineralized basalt and copper-mineralized rock show that a small amount of naturally occurring mercury is associated with mineralization.
Native copper and
chlorastrolite, the official state
gem of Michigan, are
secondary minerals filling
pore spaces formed by
vesicles and
fractures within the volcanic rocks.
Prehnite and
agate amygdules are also plentiful island gemstones. ==Recreation==