Reproducing the tree cover changes throughout the Holocene is a challenge for
land surface–atmosphere models. Here, results of a transient Holocene
simulation of the coupled climate–carbon cycle model, CLIMBER2-LPJ, driven by
changes in orbital forcing, are compared with pollen data and pollen-based
reconstructions for several regions of Eurasia in terms of changes in tree
fraction. The decline in tree fraction in the high latitudes suggested by data
and model simulations is driven by a decrease in summer temperature over the
Holocene. The cooler and drier trend at the eastern side of the Eurasian
continent, in Mongolia and China, also led to a decrease in tree cover in both
model and data. In contrast, the Holocene trend towards a cooler climate in
the continental interior (Kazakhstan) is accompanied by an increase in woody
cover. There a relatively small reduction in precipitation was likely
compensated by lower evapotranspiration in comparison to the monsoon-affected
regions. In general the model-data comparison demonstrates that climate-driven
changes during the Holocene result in a non-homogeneous pattern of tree cover
change across the Eurasian continent. For the Eifel region in Germany, the
model suggests a relatively moist and cool climate and dense tree cover. The
Holzmaar pollen record agrees with the model for the intervals 8–3 ka and
1.7–1.3 ka BP, but suggests great reduction of the tree cover 3–2 ka and after
1.3 ka BP, when highly developed settlements and agriculture spread in the
region
