Vegetation–soil relationships along a spruce forest transect in interior Alaska

Abstract

Five distinct forest communities were recognized along a 3-km transect. These are, listed in order of decreasing elevation: (i) open black spruce/feathermoss - Cladonia, (ii) closed black spruce/feathermoss, (iii) open black spruce/Sphagnum, (iv) black spruce woodland/Eriophorum, and (v) white spruce/alder/Calamagrostis (restricted to a narrow band adjacent to a stream). Several techniques of ordination were used to recognize these five forest communities plus two intergrades: (open black spruce/feathermoss - Cladonia) - (Sphagnum) and open black spruce/Sphagnum - woodland/Eriophorum.The distribution of two-thirds of the plant species was highly correlated with vegetation–slope zones. Results of the fit of Gaussian curves also suggest that vegetation boundaries were well placed. The distribution of the four soil series in the area was well correlated with vegetation–slope zones: three were limited to one zone each. Permafrost, absent from the soil on the ridgetop and upper slope, was generally within 40 to 50 cm of the surface elsewhere and tended to be at shallower depths as elevation decreased. The most striking differences in forest floor properties were found in the white spruce zone compared with the six black spruce dominated zones. The white spruce forest floor was markedly thinner and had higher levels of nutrients. In the six black spruce dominated zones, forest floor thickness and concentrations of N and Mg tended to increase with distance downslope, and P and K decreased.