Global Change Abstracts The Swiss Contribution - SCNAT

158 Global Change Abstracts – The Swiss Contribution | Past Global Changes
cover) and pollen for the Juniperus site (eg, r(2) =
0.76 between crown cover and arboreal pollen, AP)
and the Picea site (r(2) = 0.85), whereas the linkage
is weaker at the Juglans site (r(2) = 0.35) and
in mixed forests (r(2) = 0.32). The results of the
surface samples of moss polsters are compared
and discussed with surface samples of lake sediments
that were taken at the same locations. We
use vegetational maps from around the lakes to
discuss the link between vegetation and pollen at
extra-local scales (800 m around the sites). These
comparisons show that AP underestimates the effective
tree cover around all sites, with in extreme
cases densely forested areas corresponding to AP
values as low as < 60; 30%. We explain this finding
by the prevalent background pollen load that
derives from the dry lowland and slope steppes
(Artemisia, Chenopodiaceae, Poaceae). Our investigation
may improve the reconstruction of
Quaternary vegetation and climate history of
these forest belts in Kyrgyzstan (Central Asia) on
the basis of fossil pollen assemblages from mire
and lake sediments. It provides new insights into
the pollen reflection of forest isles (eg, on humid
slopes or mountain tops) that are surrounded by
continental steppes; a vegetational situation that
may be used as an analogue for the conditions
during the full glacial in Eurasia and Northern
America.
Holocene, 2007, V17, N5, JUL, pp 599-611.
08.1-313
Surface-exposure ages of Front Range moraines
that may have formed during the
Younger Dryas, 8.2cal ka, and Little Ice Age
events
Benson L, Madole R, Kubik P W, Mcdonald R
USA, Switzerland
Paleontology , Meteorology & Atmospheric Sciences
, Geomorphology , Geology
Surface-exposure (Be-10) ages have been obtained
on boulders from three post-Pinedale end-moraine
complexes in the Front Range, Colorado. Boulder
rounding appears related to the cirque-to-moraine
transport distance at each site with subrounded
boulders being typical of the 2-km-long Chicago
Lakes Glacier, subangular boulders being typical
of the 1-km-long Butler Gulch Glacier, and angular
boulders being typical of the few-hundred-mlong
Isabelle Glacier. Surface-exposure ages of angular
boulders from the Isabelle Glacier moraine,
which formed during the Little Ice Age (LIA) according
to previous lichenometric dating, indicate
cosmogenic inheritance values ranging from
0 to similar to 3.0 Be-10 ka. (1) Subangular boulders
from the Butler Gulch end moraine yielded
surface-exposure ages ranging from 5 to 10.2 Be-10
ka. We suggest that this moraine was deposited
during the 8.2 cal ka event, which has been associated
with outburst floods from Lake Agassiz and
Lake Ojibway, and that the large age range associated
with the Butler Gulch end moraine is caused
by cosmogenic shielding of and(or) spalling from
boulders that have ages in the younger part of the
range and by cosmogenic inheritance in boulders
that have ages in the older part of the range. The
surface-exposure ages of eight of nine subrounded
boulders from the Chicago Lakes area fall within
the 13.0-11.7 Be-10 ka age range, and appear to
have been deposited during the Younger Dryas
interval. The general lack of inheritance in the
eight samples probably stems from the fact that
only a few thousand years intervened between the
retreat of the Pinedale glacier and the advance of
the Chicago Lakes glacier; in addition, bedrock in
the Chicago Lakes cirque area may have remained
covered with snow and ice during that interval,
thus partially shielding the bedrock from cosmogenic
radiation.
Quaternary Science Reviews, 2007, V26, N11-12,
JUN, pp 1638-1649.
08.1-314
Palaeoclimate-induced range shifts may explain
current patterns of spatial genetic variation
in renosterbos (Elytropappus rhinocerotis,
Asteraceae)
Bergh N G, Hedderson T A, Linder H P, Bond W J
South Africa, Switzerland
Paleontology , Microbiology , Plant Sciences , Meteorology
& Atmospheric Sciences
The impact of Pleistocene climatic fluctuations on
the distributions of plant species in the Greater
Cape Floristic Region is largely unknown. We used
a molecular fingerprinting tool, inter-simple sequence
repeat (ISSR) PCR to examine the spatial
distribution of genetic variation in the common
and widespread shrub Elytropoppus rhinocerotis.
We wished to test the hypothesis that refugia
for the species were located in areas which were
buffered from marked variations in precipitation
between glacial and interglacial periods. Populations
from less protected areas, in contrast, should
have suffered size reductions or extinctions during
the dry Holocene optimum. We detected a
large amount of genetic variation in the species,
which was apportioned largely amongst individuals
within populations rather than amongst populations
or regions, as expected for an outcrossing
and well-dispersed plant species. However, there
was significant spatial structure and an uneven
distribution of diversity across the range. Geo-