Alpine and subalpine vegetation chronosequences following deglaciation in coastal Alaska

摘要

Glacial recession is a major process in terrestrial ecosystems of the world and an obvious result of global warming. Here we describe the alpine (above tree line) and subalpine forested and wetland/peatland vegetation chronosequences in Glacier Bay National Park and Preserve, Alaska. We derived the results from three products: (1) deglaciation map of 50,000-, 13,000-, and 1- to 246-year-old (Neoglacial) surfaces; (2) a landcover map; and (3) a plant association classification. For the alpine chronosequence, Neoglacial surfaces are dominated by the tall shrub (>1.5 m) (Alnus and Salix), dwarf shrub (<0.1 m) (Salix and Dryas), and mesic herbaceous landcover classes. These landcover classes also dominate the 13,000- and 50,000-year-old surfaces but dwarf shrub dominance changes to ericaceous. The subalpine forested chronosequence consists of Populus balsamifera ssp. trichocarpa and Picea sitchensis classes dominating the mid- and late-seral Neoglacial surfaces, then Tsuga mertensiana and Picea sitchensis classes dominating the 13,000- and 50,000-year-old surfaces. Wetlands/peatlands are rare on the Neoglacial and 13,000-year-old surfaces but common on the 50,000-year-old surface. Alnus is rare on the 50,000-year-old surface yet common on the 13,000-year-old surface and, we speculate, is a relict from the end of the Pleistocene.