Air
Aerial habitat: The only aerial mammals are the bats, of which four species were taken during the summer. The flying squirrel is not considered to be a true aerial form.
Burns and Clearings
Fires have been numerous throughout northern Michigan and a large part of the region is covered by various stages in the succession following fires or clearings. The areas studied were selected as representative of the natural conditions of the peninsula, but even in these districts there are many burned areas.
Many large areas have been heavily logged over, sometimes followed by fire, with a result similar to that of a fire. In the region studied there are numerous small clearings, some of which are in use as the residences of settlers, but most have been allowed to revert to a wild condition. The stages in succession on an abandoned clearing seem to be similar to those following a fire, and they are here considered together.
Herbaceous stage: After a fire in a forest in this region the first vegetation to spring up seems to be the herbs, of which the fireweed (Chamaenerion angustifolium) is most prominent. A number of areas dominated by this type of vegetation were seen, but the type seems to be short-lived, and is probably quickly replaced by shrubs and tree seedlings. The stages in succession following a fire in swampy areas may be somewhat different from that in a hardwood region, but no data was obtained. No opportunity presented itself to study the mammals of the herbaceous stage, and I have no records for the species found there.
Shrub stage: Following a fire or clearing in a hardwood area the herbaceous stage is apparently quickly followed by a thick growth of shrubs and young trees. The characters of the shrub growth vary considerably with the texture of the soil, amount of soil moisture, slope, and completeness of burning. The growth is usually quite thick, though in some clearings where the growth has been kept down for some time there may be open grassy patches. In small clearings near Fish-hawk Lake the raspberry (Rubus strigosus) is a characteristic species, but near Little Girl's Point it is much less common. A large area of shrub studied near Little Girl's Point is on a rather steep slope facing to the north, though part is at the bottom of the hill on a very gentle slope. There are no large trees, but saplings up to 2-1/2-inch trunks occur; most, however, are smaller. The quaking and large-toothed aspens (Populus tremuloides and P. grandidentata), paper and yellow birches (Betula papyrifera and B. lutea), sugar maple, and linden are common seedlings. Shrubs, such as the sumac (Rhus hirta), wild cherry (Prunus pennsylvanica), raspberry, willows (Salix spp.), mountain maple, red-berried elder (Sambucus racemosa), and hazel are common. A few herbs, like the fireweed, golden-rod, and pearly everlasting, occur in open places.
A number of mammals are found in the shrub stage, but they are far less abundant than in mature hardwood forest.
Paper birch—aspen stage: The continued growth of the young trees in the shrub stage leads to the production of a sapling forest of the more quickly growing species, the paper birches and aspens. Often one or other of these species becomes dominant to the practical exclusion of the other, but sometimes both occur together. On the slopes near the lakes of the Cisco Lake chain aspens are rare, and the sapling forests on the clearings and burns are almost a pure stand of paper birch. Near Watersmeet, however, the aspen seems to be the dominant form, and few paper birches were seen. Near Gogebic Lake, also, the quaking aspen is the dominant form, though paper birches are common in the sapling forests. The growth in these sapling forests is very thick, and the ground is nearly bare of vegetation, though it is heavily covered with dead sticks and small logs. In a thick growth of quaking aspens, on wet ground studied near Gogebic Lake, a number of alders and paper birches, a few young trees of sugar maple and arbor-vitae, and a rare elm occur. A scanty undergrowth of mountain maple and numerous sugar maple seedlings is present. Few mammals are found in this stage of the forest.
On the western slope of Birch Point on Cisco Lake there is a good stand of paper birches, growing in an open stand with much grass in the spaces between the trees. This place has been much used for camping and it may be that the development of the grass is the result of opening the forest by clearing out some of the trees. Among the birches are numerous young firs and white pines, with a few young sugar maples, and a rare arbor-vitae. The birches show many signs of age, and would evidently, if undisturbed, soon give way to a forest dominated by the pines and firs. In the grass among these trees deer-mice, red-backed voles, and jumping mice (Zapus) were taken. Signs of snowshoe hare were seen.