The Alaska Vegetation Classification - Alaska Geobotany Center ...

I.A.2.g. Open Black Spruce-White Spruce ForestDescription-These open stands are made up of black spruce and white spruce ascodominants. Total arboreal cover is between 25 and 60 percent. Paper birch andquaking aspen may be present in small amounts. The trees tend to be small; thelargest trees are about 5 to 10 centimeters (2 to 4 in) d.b.h. and 6 to 10 meters(18 to 30 R) tall. Tree reproduction may be either black spruce or white spruce,or a mixture. A welldeveloped tall shrub layer dominated by Befula glandulosa1 to 2 meters (3 to 6 ft) high often is present, especially at sites near treeline. Othertall shrubs locally important on moist sites include Alnus crispa, A. sinuafa, Salixspp., and Rosa acicularis. A low shrub layer usually is present and consists primarilyof some combination of Vaccinium uliginosum, V. vitis-idaea. Potentilla fruticosa,Arctostaphylos rubra, Empetrum nigruum, and Ledum spp. Grasses and sedges maybe common, especially in young stands, but in other stands herbs may be scarce.The moss layer is continuous or nearly so and dominated by a combination ofHylocomium splendens, Pleurozium schreberi, Polyfricbum spp., and Dicranum spp.Lichens such as Cladonia spp. are important on some sites.Distribution and site characteristics-Open black spruce-white spruce forestsare found at tree line, especially in the Yukon-Tanana uplands and on the northernslopes of the Alaska Range. These tree-line stands are similar to the more commontree-line stands of open white spruce forest but have a significant admixture of blackspruce. Open black spruce-white spruce forests are occasionally found at lowerelevations and have been reported from the Porcupine Plateau in northeasternAlaska. Soils are Pergelic Cryaquepts and Pergelic Cryochrepts. Permafrost usuallyis present at depths of 60 centimeters or more but is absent from some soils.Successional status-Many stands, particularly those near tree line, may be climaxor at least stable. Others may be in the process of changing from closed white spruceforests to black spruce forests in response to increasing organic layer thickness, arising permafrost table, decreasing soil temperature, and decreasing soil drainage.Succession after disturbance on these sites has not been adequately described.Closely related types-Open black spruce-white spruce forests may resembleclosed black spruce-white spruce forests and black spruce-white spruce woodlandsbut have roughly 25 to 60 percent tree cover. They also may be similar to open whitespruce forests and open black spruce forests, but have significant amounts of bothspecies.Primary references-Viereck 1979, Yarie 1983.Communities-Picea glauca-P. mariandLedum groenlandicum-Vacciniumvifis-idaea/Pleufozium schreberi (Viereck 1989). Picea mariana-P. glauca/Befulaglandulosa (Viereck 1979). Picea glauca-P. mariana/Vaccinium uliginosudArctostaphylos rubrdDicranum spp. (Yarie 1983). Picea mariana-P. glaucdBetulanandArcfostaphylos rubra-Vaccinium uliginosum (Yarie 1983). Picea mariana-P.glaucdLedum decumbens/Pefasifes spp./Dicranum spp. (Yarie 1983). Piceamariana-P. glauca/Shepherdia canadensis/Epilobium spp./Pelfigera spp. (Yarie1983). PiCea glauca-P. mariandVaccinium uliginosum-Carex bigelowii (Craigheadand others 1988). Picea mariana-P. glaucdRubus chamaemorus-Ledumdecumbens-Vacciniumspp. (Craighead and others 1988).76