Vegetation, soils, and forest productivity in selected forest types in interior Alaska

Abstract

Vegetation, forest productivity and soils of 23 forest stands in the taiga of interior Alaska are described. The stands are arranged on an environmental gradient from an aspen (Populus tremuloides Michx.) stand on a dry, steep south-facing bluff, to open black spruce (Picea mariana (Mill.) B.S.P.) stands underlain by permafrost on north-facing slopes. The coldest site is a mixed white spruce (Picea glauca (Moench) Voss) and black spruce woodland at the treeline. Mesic upland sites are represented by successional stands of paper birch (Betula papyrifera Marsh.) and aspen, and highly productive stands of white spruce. Several floodplain stands represent the successional sequence from productive balsam poplar (Populus balsamifera L.) and white spruce to black spruce stands underlain by permafrost on the older terraces. The environmental gradient is described by using 2 soil factors: soil moisture and annual accumulated soil degree days (SDD), which range 2217 SSDD for the warmest aspen stand to 480 SDD for the coldest permafrost-dominated block spruce site. Soils vary from Alfic Cryochrepts on most of the mesic sites to Histic Pergelic Cryochrepts on the colder sites underlain by permafrost. A typical soil profile is described for each major forest type. A black spruce stand on permafrost has the lowest troe standing crop (1586 g .times. m-2) and annual productivity (56 g .cntdot. m-2 .times. yr-1) whereas a mature white spruce stand has the largest tree standing crop (24,577 g .cntdot. m-2) and an annual productivity of 540 g .cntdot. m-2 .cntdot. yr-1, but the successional balsam poplar stand on flood plain alluvium has the highest annual tree increment (952 g .cntdot. m-2 .times. yr-1). Possibly, black spruce is a nutrient poor, unproductive forest type and that its low productivity is primarily the result of the low soil temperature and high soil moisture.