ateam - Potsdam Institute for Climate Impact Research

ATEAM final report Section 5 and 6 (2001-2004) 26
provided by the Lund-Potsdam-Jena global dynamic vegetation model (LPJ) to scale inventory based
stem growth in EFISCEN. This approach enabled us to utilize state-of-the-art information about forest
resources and forest management in Europe together with scenarios of climate and land use that were
consistent with other results of the ATEAM project.
In order to quantify the effect of forest management, climate change and land use change, we ran the
model using the four management scenarios with and without land use change (the latter separately for
current climate and the climate change scenarios). Growing stock, increment, age-class distribution, and
carbon stocks in above- and below-ground biomass were used as indicators to describe forest resource
development in the 21 st century.
For each scenario, climate change resulted in increased forest growth, especially in Northern Europe.
The adverse effect of increased summer drought in Southern Europe was mitigated by higher
precipitation in spring and increased water use efficiency in response to the rising atmospheric CO2
concentration. Figure 15 presents the development of annual net increment for current climate, climate
change, and combined climate and land use change model runs. The climate change effect of
increased forest growth was more pronounced for the A scenarios than for the B scenarios.
Management proved to be crucial for the development of increment. When wood demand was high, as
in the A1f and A2 scenarios, and therefore forests were managed intensively, increment remained
relatively stable or decreased slightly. When wood demand was low, as in the B1 and to a lesser extent
in the B2 scenario, forests were managed less intensively and annual increment decreased drastically.
The impact of land use change on increment varied substantially between the scenarios, depending on
the extent of forest area change. In A1f, forest area remained almost unaltered, and therefore increment
hardly changed when land use change was implemented. In B2, forest area increased by 32% between
2000 and 2100, and consequently increment was much higher in model runs with land use change than
in those without.
The share of increment removed from the forest increased from 59% in 2000 to 118% in 2100 for the
A1f scenario, and to about 97% in the A2 scenarios. In A1f, removals exceeded increment from the
2080s onwards. There was substantial regional variation in the share of the increment that was removed
from the forest. In most parts of central and Southern Europe, removals exceeded the increment in
2100 in the A1 and A2 scenarios. In B1 and B2, removals remained smaller than the increment in all
studied countries. In the B1 scenario, the share of increment removed from the forest decreased over
time, while it remained relatively stable in the B2 scenario. Hence, in the A1f and A2 scenarios, wood
demand exceeded potential felling, particularly in the second half of the 21 st century, while in the B1 and
B2 scenarios future wood demand can be satisfied.
Growing stock was larger in 2100 than in 2000 in all scenarios, despite the high felling levels and the
decrease in increment in some of the scenarios during the last decades of the 21 st century. The
increase was highest under the HadCM3 B1 scenario, and lowest under the HadCM3 A1f scenario. The
variation between the four GCMs was very small, while the SRES scenarios spanned a broad range,
from 24800 million cubic meters in 2100 under the A1f scenario assumptions, to 41600 million cubic
meters for the B1 scenario. For the A1f scenario, growing stock decreased from the 2080s onwards,
because felling exceeded net annual increment during that period (see above). For all A2 scenarios,
total growing stock was still slightly increasing at the end of the 21 st century.
Figure 16 compares how management, climate and land use change impact on the change in growing
stock between 2000 and 2100. As the difference between the four GCMs was very small, we included
only the HadCM3 scenarios in this analysis. The majority of variation between the level of increase was
explained by differences in forest management, caused by varying demand for wood. When climate
change was included, growing stock increased additionally by 18% (B1) to 24% (A2). Land use change
accounted for 3%, 14%, 21% and 34% of the increase in growing stock for the A1f, A2, B1 and B2
scenarios, respectively.
The amount of carbon stored in managed forests is an important part of the total amount of carbon