The ELAwatersheds are dominated by tree species typical of boreal subclimax forests (Rowe 1959), with jack pine, black spruce, trembling aspen and white birch dominating.
Jack pine stands are found both on some sandy, well-drained, glacial drift on the dry bedrock ridges and well-drained slopes. In the deeper soils, these stands may be closed such that their canopy shades out other tree species, leaving mosses, lichens and Lycopodium spp. to dominate the understorey vegetation. On the dry ridges, the jack pine canopy is typically open and juniper (Juniperus communis L.) forms the understorey. On intermediate slope areas, the semi-open canopy is often formed by a mixture of jack pine and black spruce, with an understorey of balsam fir, speckled alder (Alnus rugosa (Du Roi) Spreng.), hazel nut (Corylus americana Walt.), and Vaccinium spp. (Schindler and Brunskill 1971). Jack pine is a fire succession species and its distribution is dictated by fire frequency and intensity. Thus it will be found in areas where fires have burned with sufficient intensity to kill other tree species. Following the fires of 1974 and 1980 in the ELA, young jack pine naturally reseeded, often at high density, in many parts of the burned watersheds.
Black spruce occurs mainly in lower areas where soils are deeper and conditions are usually more moist. It often forms dense stands whose canopies shade out other trees. In more exposed areas, it intermixes with jack pine and other species. In wet areas, including the mats of Sphagnum bogs, it typically is found in a mixture with alder and tamarack, and with the shrubs Labrador tea (Ledum groenlandicum Oeder.), swamp laurel (Kalmia polifolia Wang), leather leaf (Andromeda glaucophylla Link.), Betula glandulosa Michx., and bog rosemary (Chamaedaphne calycutata (L.) Moench).