Vegetation Gradient Analysis of Two Sites in Southeast Alaska

Abstract

Abstract Two study sites in Southeast Alaska, one on the mainland and one on Etolin Island, were compared for tree, shrub, and herbvegetation cover in summer, 1983. For the tree stratum, detrended correspondence analysis (DCA) indicated that soil moisturedrainage and study site were the first two factors related to composition differences among samples. DCA indicated that, forthe shrub stratum, study site and soil moisture drainage were the first two factors. For the herb layer, the first three factorsfrom DCA were interpreted as soil moisture drainage, elevation, and study site respectively. Direct gradient analysis ofspeciesdistributions revealed clear patterns for many species with respect to soil drainage and elevation gradients. Even though DCAdid not identify elevation as a factor for the tree and shrub strata, individual species within these strata did show responsesto elevation. Many species abundances were also clearly differentiated between study sites. IntroductionThe coastal forests that extend from southeasternAlaska to northern California are part of the co­niferous forests ofPacific Northwest North Amer­ica (Waring and Franklin 1979). Cool, maritimeclimates with winter rains predominate in theregion. The climate, topography, and vegetationof Southeast Alaska limit the frequency and ex­tent of natural fires, and extensive areas havebeen free from large-scaledisturbances for greatperiods oftime (Harris and Farr 1974). The mostcommon natural disturbances, windfall (Ruth andHarris 1979) and slope failure (Swanston 1969),occur on a local scale.Vegetation studies in Southeast Alaska andthe nearby coastal conifer forests of British Co­lumbia, Canada, have consisted of broad classi­fications and descriptions ofmajor environmen­tal gradients. Heusser (1960) and Neiland (1971)reviewed earlier literature. Alaback (1980),Godman (1952), Palmer (1942), Viereck andDyrness (1980), and Worley (1974, 1975, 1977)provided various classification schemes forSoutheast Alaska vegetation. Forest understoryassociations were described by Neiland (1971),Schoen