Vegetation Chronosequence Near Exit Glacier, Kenai Fjords National Park, Alaska

Helm, D; Allen, E; Ahlstrand, G

The vegetation chronosequence near Exit Glacier in Kenai Fjords National Park has developed on an outwash plain deglaciated in the last 200 yr but which still actively floods much of the area deglaciated within the last 40 yr. This glacier is at the northern edge of the Harding Icefield and is the least isolated glacier within the Park. Vegetation cover, diversity, density, and plant sizes in several stands in each of seven successional stages were sampled using systematic points along line transects and belt transects. Seedlings were smaIl, < 0.5 em taIl during their first year, and were subject to flooding during late summer and fall. Populus trichocarpa (black cottonwood) was an important species through the first 100 to 150 years after deglaciation and was the dominant early colonizer. The most extensive stands of Alnus sinuata (Sitka aider) occurred primarily in areas of repeated avalanche and rock slides and was also in the understory of Cottonwood stands. Although Picea sitchensis (Sitka spruce) and Tsuga mertensiana (mountain hemlock) seedlings were found on the outwash plain, these individuals probably did not survive to be mature trees. Although P. sitchensis established in the understory of Populus trichocarpa stands, and T. mertensiana colonized dead logs and organic soils in the Spruce - Cottonwood stage. In contrast, A. sinuata was the first colonizer near other glaciers that were more isolated from vegetation during the Little Ice Age.