Environmental Engineering Reference
In-Depth Information
Table 2.2
Environmental change at Lake Siles, Segura, southern Spain, during the period
20 300 to 7400 years BP (based on Carri on, 2002)
Age (cal.
years BP)
Pollen and vegetation
Other
11 900-7400
Early Holocene expansion of pine, probably
Pinus nigra.
A sudden expansion
indicates a rapidly rising treeline as
temperatures ameliorate. Increases in the
pollen of thermophilous species, e.g.
Phillyrea, Olea,
Ericaceae and evergreen
oak (
Quercus)
Between 10 100 and 7400 years BP pine
continues to dominate but
P. pinaster
replaces
P. nigra.
There are slight
increases in
Juniperus
, Poaceae,
Artemisia, Ephedra nebrodensis
,
Chenopodiaceae and other heliophytes.
After 8100 years BP
Betula, Fraxinus
,
deciduous
Quercus, Corylus
and
Acer
begin to increase
10 100-8100 years BP
shallowing of the lake
occurred with two
periods of drying. This
also reflects warming
20 300-11 900
Steppe grassland comprising Poaceae with
Artemisia, Ephedra nebrodensis
and a
scattering of pine and juniper (
Juniperus).
Other open-habitat species include
Chenopodiaceae, Caryophyllaceae,
Brassicaceae and
Helianthemum
By 12 000 years BP
Artemisia,
E. nebrodensis
and Chenopodiaceae had
declined as juniper expanded gradually
within the steppe grassland.
P. pinaster
and evergreen
Quercus
expanded
Persistent occurrences of the
warmth-demanding
Acer, Taxus, Arbutus,
Buxus, Salix, Ulmus, Phillyrea, Pistaci
a
and
Olea
indicate the proximity of glacial
refugia of temperate and Mediterranean
trees
Until 10 100 years BP
colonization by
thermophilous
microphytes (e.g.
Closterium-Zygnema,
Debarya-Potamogeton
)
coincided with a
reduction in cryoclastic
scree content and
particle size. This may
have been due to slope
stabilization as
vegetation colonised
Productivity was low
during the earlier stage
but increased with
ameliorating
temperatures
Bulgaria, Stefanova and Ammann (2003) have shown that the vegetation during the
period 11 000-10 200
14
C years BP (radiocarbon age before present) was open and
dominated by
Artemisia
and Chenopodiaceae and that soil erosion was occurring in
the lake catchment. Relatively harsh conditions thus prevailed in these mountains
prior to Holocene amelioration. What these records do not reveal is whether the pre-
11 000-year period experienced higher temperatures and that there was a late-glacial
climatic regression following an amelioration as was the case in many other regions.
