Beringia as a glacial refugium for boreal trees and shrubs: new perspectives from mapped pollen data


Brubaker, Linda B., Anderson, Patricia A., Edwards, Mary E. and Lozhkin, Anatoly V. (2005) Beringia as a glacial refugium for boreal trees and shrubs: new perspectives from mapped pollen data. Journal of Biogeography, 32, (5), 833-848. (doi:10.1111/j.1365-2699.2004.01203.x).

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Description/Abstract

Aim Beringia, far north-eastern Siberia and north-western North America, was
largely unglaciated during the Pleistocene. Although this region has long been
considered an ice-age refugium for arctic herbs and shrubs, little is known about
its role as a refugium for boreal trees and shrubs during the last glacial maximum
(LGM, c. 28,000–15,000 calibrated years before present). We examine mapped
patterns of pollen percentages to infer whether six boreal tree and shrub taxa
(Populus, Larix, Picea, Pinus, Betula, Alnus/Duschekia) survived the harsh glacial
conditions within Beringia.
Methods Extensive networks of pollen records have the potential to reveal
distinctive temporal–spatial patterns that discriminate between local- and longdistance
sources of pollen. We assembled pollen records for 149 lake, peat and
alluvial sites from the Palaeoenvironmental Arctic Sciences database, plotting
pollen percentages at 1000-year time intervals from 21,000 to 6000 calibrated
years before present. Pollen percentages are interpreted with an understanding of
modern pollen representation and potential sources of long-distance pollen
during the glacial maximum. Inferences from pollen data are supplemented by
published radiocarbon dates of identified macrofossils, where available.
Results Pollen maps for individual taxa show unique temporal-spatial patterns,
but the data for each taxon argue more strongly for survival within Beringia than
for immigration from outside regions. The first increase of Populus pollen
percentages in the western Brooks Ranges is evidence that Populus trees survived
the LGM in central Beringia. Both pollen and macrofossil evidence support Larix
survival in western Beringia (WB), but data for Larix in eastern Beringia (EB) are
unclear. Given the similar distances of WB and EB to glacial-age boreal forests in
temperate latitudes of Asia and North America, the widespread presence of Picea
pollen in EB and Pinus pollen in WB indicates that Picea and Pinus survived
within these respective regions. Betula pollen is broadly distributed but highly
variable in glacial-maximum samples, suggesting that Betula trees or shrubs
survived in restricted populations throughout Beringia. Alnus/Duschekia
percentages show complex patterns, but generally support a glacial refugium in
WB.
Main conclusions Our interpretations have several implications, including: (1)
the rapid post-glacial migration rate reported for Picea in western Canada may be
over estimated, (2) the expansion of trees and shrubs within Beringia should have
been nearly contemporaneous with climatic change, (3) boreal trees and shrubs
are capable of surviving long periods in relatively small populations (at the lower
limit of detection in pollen data) and (4) long-distance migration may not have
been the predominant mode of vegetation response to climatic change in
Beringia.

Item Type: Article
ISSNs: 0305-0270 (print)
Related URLs:
Keywords: Beringian pollen data, boreal shrubs, boreal trees, climatic change, cryptic refugia, glacial refugia, post-glacial migration patterns
Subjects: G Geography. Anthropology. Recreation > G Geography (General)
G Geography. Anthropology. Recreation > GE Environmental Sciences
G Geography. Anthropology. Recreation > GB Physical geography
Divisions: University Structure - Pre August 2011 > School of Geography > Environmental Processes and Change
ePrint ID: 55293
Date Deposited: 01 Aug 2008
Last Modified: 27 Mar 2014 18:38
URI: http://eprints.soton.ac.uk/id/eprint/55293

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