Forest Ecosystem Distribution in the Taiga Environment

The vegetation of interior Alaska is a mosaic of forest, grassland, shrubs, bog, and tundra types that have formed primarily as a result of slope, aspect, elevation, parent material, and succession after wildfire. Because of the dry continental climate and low sun angle, there is a great contrast in the vegetation of north-facing vs. south-facing slopes. Presence or absence of permafrost, closely correlated with slope and aspect, is also a dominant factor in the distribution of vegetation types. Because of the high fire frequency, most forest stands tend to be in successional stages, masking the factors that control the distribution of mature or climax forest types. In interior Alaska, upland forest types vary from highly productive aspen (Populus tremuloides Michx.), birch (Betula papyrifera Marsh.), and white spruce (Picea glauca [Moench] Voss) stands on south-facing, well-drained slopes to permafrost and moss-dominated black spruce (Picea mariana [Mill.] B.S.P.) forests of low productivity on north-facing slopes (Viereck 1975), lowlands, and lower slopes. Floodplain forests of balsam poplar (Populus balsamifera L.) and white spruce are productive on recently formed river alluvium where permafrost is absent, but slow-growing black spruce and bogs occupy the older terraces that are underlain by permafrost. Permafrost underlies as much as 75–80% of the area, including almost all terrain except south-facing slopes and floodplains adjacent to major rivers.