Geoscience Reference
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historical climate records. The technique was applied to two late Pleistocene sites
in South Australia. The first site at Kangaroo Island showed higher precipita-
tion levels compared to present, around 14 000--10 000 years BP. The second site,
Dempseys Lake, also showed higher rainfall during the late Pleistocene (39 000--
33 000 years BP) compared to present. While it has not been widely used as yet,
this technique holds considerable promise for identifying periods of drought
and higher rainfall regimes for a wide variety of regions.
Pollen and palaeobiology
Pollen is often preserved in sediments that have not experienced pro-
longed aerobic conditions. It can also be preserved in dung and in various car-
bonates such as speleothems within caves. Pollen records provide an indication
of the types of vegetation previously growing in a region. Vegetation is of course a
reflection of climatic conditions in any area and the preserved pollen species are
indicative of the rainfall regimes prevalent at the time the pollen was released
from plants and deposited.
On a global scale one can assume that vegetation regimes and their distribu-
tion are mainly dependent on climate. Vegetation is, therefore, likely to respond
to climate change if the change exceeds the physiological tolerance limits of
that vegetation. High vegetation mortality due to climatic factors such as frost
or drought, leads to a shift in species composition. The climatic influence on
vegetation is complex though. If the change in climatic conditions does not
exceed the physiological limits, any response by the vegetation to that change
is likely to be a result of inter-specific competition and interference. In some
areas, vegetation species that are normally better adapted to the new climate,
and which are found in other areas of the same climatic region, may be absent
due to physical barriers to, or insufficient rates of, spread or dispersal. Although
all this points to a complex vegetation response to climate change, pollen and
other palaeobiological indicators are still assumed to be reliable indicators of
palaeoclimates.
Pollen analysis (palynology) can also be used in combination with ecology
to provide information on past climatic events (Davies, 1999). Extreme events,
such as droughts and wind storms can have a marked impact upon the floristic
and structural characteristics of forests. The structure of tropical rainforests for
example is often composed of small juxtaposed units of vegetation that are in
different stages of regeneration. Regeneration is a cyclic process starting with
the fallofalargetreeexposingtheunderstorey of the forest to increased light
levels. This results in the growth of pioneer species that are light demanding and
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