The Alaska Vegetation Classification - Alaska Geobotany Center ...

Distribution and Site characteristlcs-Birch-aspen communities are found onmoderately warm sites, primarily upland slopes, in interior and south-central Alaska.Permafrost is absent or more than a meter below the surface.Successional status-Most stands originate after fire and most likely, in theabsence of fire, will be replaced eventually by white spruce or black spruce.Closely related types-Birch-aspen communities are related to paper birch communitiesand aspen communities but have both species well represented in the canopy.If a spruce understory is beginning to enter the canopy, this community mayresemble a spruce-birch-aspen mixed forest.Primary reference-Yarie 1983.Communities-Populus tremuloides-Betula papyrifera/Rosa acicularis/Arctostaphylosuva-urssPlichens (Yarie 1983).I.B. 1.g. Closed Quaking Aspen-Balsam Poplar ForestDescription-These forest communities are dominated by aspen and balsam poplarand have a total tree cover of 60 percent or more. Scattered white sptuce also maybe present in the overstory. Regeneration of aspen and balsam poplar usually ispresent, and frequently white spruce regeneration is as well. Annual productivityaverages about 113 grams per square meter (1,000 Ib/acre) per year.Willows commonly form a tall shrub layer, especially in young stands. Characteristiclow shrubs include Rosa acicularis and Shepherdia canadensis. Common herbsinclude Mertensia paniculafa, Calamagrostis canadensis, Equisetum spp., fpilobiumangustifolium, and Galium spp. Mosses and lichens are sparse: Dicranum spp. areperhaps the most common mosses.Distribution and site characteristlcs-Aspen-balsam poplar communities havebeen reported only from the Yukon Flats but are thought to be more widespread onflood plains in interior Alaska. They commonly occur on moderately well-drained soils(Cryofluvents). These tend to be young soils with circumneutral to slightly acidic soilreaction and only a few centimeters of organic matter on the mineral soil surface.Permafrost is at least 50 centimeters (20 in) below the surface at sites in the YukonFlats and probably is lacking from many sites farther south.Successional status-Flood-plain stands generally develop after alder and willowthickets. Usually the aspen and balsam poplar establish at the same time as thealder and willows but are overtopped for a few years by the faster growing shrubs.Most of these stands, if left undisturbed, would be expected to be replaced by whitespruce. After a still longer time, the white spruce theoretically may give way to blackspruce.Closely related types-Aspen-balsam poplar stands are similar to aspen standsand balsam poplar stands, but dominance is shared by both species. Young stands,where the tree canopy has recently emerged above the alder and willows, are similarto tall alder, tall willow, and tall alder-willow shrub communities. Older stands wherespruce is beginning to enter the canopy may resemble aspen-spruce or balsampoplar-spruce stands.Primary reference-Yarie 1983.Communities-Populus tremuloides-P. ba/samifera/Rosa acicularis (Yarie 1983).91