VEGETATIVE SUCCESSION OF FORESTED GLACIAL ICE AT THE MATANUSKA GLACIER, ALASKA

This study evaluates spatial changes in vegetation on forested glacial ice along a 1400m transect near the terminus of the Matanuska Glacier. The transect originates at the southern boundary of the forest and continues north to the Matanuska River. From south to north, the transect crossed five environments consisting of actively flowing ice, unvegetated debris-covered ice, alder-bearing debris-covered ice, alders mixed with spruce, and an old growth spruce forest, which is apparently developed on stagnant ice. This region of stagnant ice lies to the south and west of of Lionshead, a peak that serves as a barrier to ice flow as the glacier enters the Matanuska River valley. The supraglacial debris thickness in the vegetated areas was determined with the use of a Pulse Ekko 100 ground penetrating radar (GPR) and ground truthed by hand-dug pits. The depth to buried ice in the region ranged from 1.3m to 5.6m. Also, the thickness of the O-horizon of the supraglacial debris was measured, and thicknesses ranged from 0cm to 18cm. Tree-coring was used to determine the age of the spruce forest. The sampled trees ranged in age from 37 to 165 years. These ages correlate strongly with the O-horizon thicknesses; the O-horizon is thicker and the spruce trees are older toward the northern end of the transect. Therefore, we interpret that the forest invaded from the northern edge of the stagnant part of the glacier and has since spread southward toward the actively-flowing ice. The vegetation follows the ideal successional sequence of an alpine forest with alders colonizing first and then being replaced by spruce and willow, which is followed by the establishment of dense understory vegetation. Further work includes (a) pollen analysis of sediment cores taken from kettle lakes along the transect and (b) an attempt at reconstructing late Quaternary history of the terminus region.