Bcs. Hansen et Dr. Engstrom, VEGETATION HISTORY OF PLEASANT ISLAND, SOUTHEASTERN ALASKA, SINCE 13,000 YR BP, Quaternary research, 46(2), 1996, pp. 161-175
A 13,000-year history of late-quaternary vegetational and climatic cha
nge has been derived from lacustrine sediments from Pleasant Island in
the Glacier Bay region of southeastern Alaska. Early arrival of lodge
pole pine and mountain hemlock, indicated by the presence of pollen an
d conifer stomata, suggests expansion from refugia in the Alexander Ar
chipelago. A short-term climatic reversal, possibly correlated with th
e European Younger Dryas, is inferred from the expansion of tundra ele
ments and deposition of inorganic sediments between 10,600 and 9900 C-
14 yr B.P. Two peat cores from the lake catchment verify Holocene vege
tation changes and aid in the separation of biogenic from climatic for
ces affecting vegetation history. Differences in pollen representation
among the three cores illustrate the variation among pollen-collectin
g substrates, as well as the spatial heterogeneity of peatland develop
ment and its dependence on local hydrology. Initial peat accumulation
and soil paludification, occasioned by increases in temperature and pr
ecipitation in the early Holocene, allowed western and mountain hemloc
k to replace sitka spruce 8500-8000 yr B. P. Open muskeg became widesp
read about 7000 yr B. P. and allowed lodgepole pine to reinvade the re
gion after a 2000-yr absence. The extensive replacement of fen element
s by bog taxa at 3400 yr B. P. suggests increased paludification due t
o changing hydrologic conditions; its correlation with the upland expa
nsion of Tsuga heterophylla suggests the onset of a cooler/wetter Neog
lacial climate in southeastern Alaska. (C) 1996 University of Washingt
on.