An interesting story has been depicted by Ren and Beug
(2002) in the northern half of China (north of Yangtze river)
for the whole Holocene.
Forests generally expanded in the early Holocene times, reaching their maximum at 6 or
4 ka BP, with a maximum in Central China, and then re-
gressed during the late Holocene. An exception was found
for northeast China where the maximum development of for-
est occurred during the last 4000 or 2000 years. They con-
cluded that, if the EAM enhancement seems to be responsi-
ble of the forest expansion at the beginning of the Holocene,
disturbance by human activities may be responsible of the
forest decline after 6 ka BP.
This picture was completed by the study of Yu et al.
(1998) who analysed the vegetation variations at the biome
level for the whole China, but restricted at the 6 ka BP pe-
riod. In eastern China at 6 ka BP, forest shifted northwards,
with broadleaved evergreen forest extended about 300 km
and temperate deciduous forest about 500600 km beyond
their present northern limit. In northwestern China, the area
of desert and steppe vegetation was reduced as compared to
present. They concluded that these shifts were likely a re-
sponse to enhanced Asian monsoon.
Lake levels data are less susceptible to be influenced by
human disturbances. Yu et al. (2003) proposed a story of the
lake levels since the Last Glacial Maximum (LGM, about
21 ka BP). This compilation showed LGM conditions much
drier than today in eastern China but somewhat wetter in
western China. These east-west differential patterns of cli-
mate conditions were completely different from the modern
dry-wet conditions with a north-south opposition. During
the Holocene, at the mid-Holocene, both regions were wetter
than present. Modern dry conditions returned after 54 ka BP
depending on the region. Then if humans played a role in
the forest decline in the Late Holocene, they simply accentu-
ated a climatic trend. Atmopheric general circulation models
(AGCM) coupled with land surface process model showed
that the dry conditions in eastern China resulted from less
summer precipitation due to the Pacific Subtropical High oc-
cupying eastern China and the decline in the summer mon-
soon.
More at north, in Mongolia, Tarasov et al. (1999) recon-
structed, from pollen, warmer and wetter at 6 ka BP condi-
tions for the northern part of the country, in agreement with
higher lake levels. In the central part of the country, warmer
and drier conditions prevailed (inferred from pollen, no lake
data being available). But these dry conditions are likely due
to more evapotranspiration and not necessarily to less precip-
itation.
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