Sphagnum Invasion beneath an Evergreen Forest Canopy in Southeastern Alaska

Abstract

The first detailed observations of Sphagnum colonization on the floor of a coniferous forest are used to evaluate the process of forest paludification. The forest, which is dominated by Picea sitchensis, is situated on a Neoglacial terminal moraine near the mouth of Glacier Bay in southeastern Alaska. The observations span a period of 14 years and have shown that (a) Sphagnum girgensohnii is the first peat moss to colonize the thick moss carpet on the floor of this forest, (b) establishment occurs only where the moss carpet has been disturbed by tree falls, (c) the number of Sphagnum patches in this forest is increasing with time, and (d) the patches are enlarging in surface area about 2% per year. As these changes occur on the forest floor, S. mendocinum and S. squarrosum are invading wet depressions and ponds in this forest. These events seem to result from soil-formation processes that are causing the water table to rise. The rate of local paludification will be affected directly, through the rise in the water table, as a water-tight seal forms within the stratified drift, and indirectly, as Sphagnum growth is stimulated by proximity to water. Investigations in this forest, at other places in Glacier Bay National Park, and elsewhere in southeastern Alaska suggest that colonization by Sphagnum takes place from 175 to 600 or more years following the initiation ofprimary succession. The development of muskeg vegetation through autogenic processes may take from 800 to several thousand years, or possibly much less if allogenic factors contribute to the paludification process.