VEGETATION CHRONOSEQUENCE NEAR EXIT GLACIER, KENAI-FJORDS-NATIONAL-PARK, ALASKA, USA

A vegetation chronosequence has developed on an outwash plain formed a s Exit Glacier (Kenai Fjords National Park, Alaska, U.S.A.) retreated, beginning in the late 1700s. However, much of the area deglaciated si nce 1950 is partly flooded most years; this has slowed succession comp ared to other chronosequences on glacial till. Vegetation cover, diver sity, density, and plant sizes in several stands of each of seven succ essional stages (Barren, Isolated Plant, Patchy, Alder, Cottonwood, Sp ruce-Cottonwood, Spruce-Hemlock) were sampled by systematic points alo ng line transects and belt transects. All major species were found in the Barren stage, but they differed in timing of importance in the rem ainder of the chronosequence. Populus balsamifera ssp. trichocarpa (bl ack cottonwood) was the most abundant colonizer and dominated many sit es up to 150 yr after deglaciation. Picea sitchensis (Sitka spruce) wa s present throughout the chronosequence, but not in significant number s until the Cottonwood stage. Tsuga mertensiana (mountain hemlock) was not common until it colonized dead logs and organic soils in the Spru ce-Cottonwood stage. Forested sites on hillslopes above the outwash pl ain were dominated by P. sitchensis and T., mertensiana. Cover of Alnu s sinuata (Sitka alder) and Populus balsamifera separated the three yo ungest stages from the middle two while Picea sitchensis cover disting uished the oldest two stages from the others.