The Alaska Vegetation Classification - Alaska Geobotany Center ...

Because of the dense tree canopy, the tall shrub layer of alders and willows is onlysparsely developed and generally contributes little cover. Low shrubs and dwatishrubs, such as Vaccinium uliginosurn, Ledurngroenlandicum, Vaccinium vitis-idaea,Ernpetrum nigrum, and Betula nana, become common in older stands as the canopybegins to open.A well-developed moss layer consisting primarily of the feathermosses Hylocomiurnsplendens, Pleuroziurn schreberi, and less commonly, Rhytidialdelphus tfiquefrusis characteristic of these stands. Herbaceous grtswth is usually sparse but horsetails,primarily Equisetum sylvaticum and €. arvense. may provide as much as 50 percentcover in flood-plain stands. Other forbs include Pyrola spp., Linnaea borealis,Geocaulon lividurn, Merfensia paniculata, and Goodyera repens.Phases-A phase of this type, with lichens dominating the ground cover, has beenreported from southwestern Alaska (Wibbenmeyer and others 1982). In the PorcupineRiver area of northeastern Alaska, Shephefdia canadensis and Arctostaphylosrubra are important shrubs and subshrubs in this type on dryer sites.Distribution and site characteristics-This type is found on the most productivesites throughout the Alaska taiga. It occurs on young river terraces, especially wherepermafrost is lacking, and on low-elevation slopes with well-drained soils on south,west, or east aspects. The type is most extensive in central Alaska but occurs inisolated small stands along rivers and in warm upland sites nearly to the northernand western tree lines. The soils are usually moderately well drained and lackpermafrost or have a deep active layer.Successional status-The closed white spruce type is considered by many to bethe climax vegetation on the well-drained upland and flood-plain sites in much of theAlaska taiga. In the upland, white spruce stands occasionally may regenerate directlyafter fire, but more commonly white spruce replaces successional hardwood standsof aspen or birch. On the flood plain, white spruce stands usually develop after shruband balsam poplar stages, and there is considerable evidence that over long periods,perhaps one to two generations, the white spruce stands are replaced by blackspruce as permafrost develops on the site.Closely related types-The closed white spruce forest is similar to the open whitespruce type, except that the latter has more shrub cover and the moss layer maybe partially replaced by lichens. On some transitional sites in the upland and on theflood plain, a mixture of white and black spruce occurs but with much the sameunderstory vegetation as in the closed white spruce stands. In most publications,the type is referred to as the closed white spruce forest type or the white spruceforest type.Photographs-Figure 7, this publication.Primary references-Drury 1956, Foote 1983, Lutz 1956, Viereck and others 1983,Wibbenmeyer and others 1982, Yarie 1983.