Conservation and Sustainable Use of the Biosphere - WBGU

234 F The biosphere in the Earth System
hemisphere growth at the Northern border of the
forests is expected to be so slow that the losses at the
Southern border will not be offset. Thus, the level of
carbon absorption by forests could reduce (Hörmann
and Schmielewski, 1998). In particular, the
reactions of tropical and boreal forests have been
investigated in numerous research projects since
publication of the comprehensive report of the German
Enquete Commission on the Protection of the
Earth’s Atmosphere and more detailed findings
resulted (Enquete Commission, 1994). Due to market
incompatibility and to a high degree of complexity
no tangible global research findings have so far
been achieved with regard to the climate impacts for
functions that forests in general assume for
humankind (timber production, conservation, water
conservation, hunting, recreation) (Solomon, 1996).
Tropical forest ecosystems
Because of their comparatively small temperature
modifications and increases in carbon dioxide content,
while tropical forests will potentially demonstrate
higher growth rates, limiting factors in the
modified chemistry of tropical forest soils and water
levels will mean a minimal real increase in their net
primary production (Silver, 1998). In particular, limitation
through the nutrient phosphorus must be
researched further according to Silver (1998) in
order to understand better the structural and functional
reactions of the tropical rainforests and the
changes in the global biogeochemical cycles. Further
warming-related effects are expected, in particular a
higher incidence of droughts as a result of the El
Niño phenomenon and the associated greater frequency
of fires and heavy tropical hurricanes with
their significant local effects on forestry and biodiversity.
Tropical forests will undergo significant
changes in the composition of species as a result of
changed precipitation patterns and greater aridity
that may possibly lead to further extinctions in
exposed ecosystems (Markham, 1998). In that context,
fragmentation as a result of non-site appropriate
forestry methods (clear cutting, monoculture, etc)
and further direct human influences (conversion,
road construction, settlements, etc) will have a negative
impact on adaptability.
Boreal forest ecosystems
Boreal forests will be impacted harder by climate
change in their structure and function than other forest
types because the warming in higher latitudes will
probably be greater and boreal forests react more
sensitively to temperature changes in connection
with increased carbon dioxide concentrations (Beerling,
1999).They will spread into regions that are currently
covered by tundra if the groundwater level is
not too high. At the Southern reaches of the area
they currently cover the boreal forests will be pushed
out by pioneer species of temperate forests and
grassland because warming will probably lead to
more fires and insect blights (Kirschbaum and Fischlin,
1996). The adaptive behaviour of boreal forest
ecosystems in global change will be discussed and
researched in particular on the background of the
sink problem in the context of the Kyoto follow-up
process. In that context, the long-term experiment
CLIMEX in Southern Norway which has simulated
under real conditions the assumptions about probable
climate change scenarios and subjected a forest
area to increased temperatures (+3°C in summer and
+5°C in winter) and increased concentrations of carbon
dioxide (560ppm) over a period of nine years.
Ultimately it is clear that boreal forest areas under
those conditions become net carbon sinks (Beerling,
1999).This calculation only applies, however, to areas
in which the boreal forest remains despite warming.
A detailed presentation of the current areas covered
by forest and changes in that stand can be found in
Section G 4.1.
F 4.2.2
Tundra ecosystems
The regional form that climate change has taken thus
far in the Arctic has varied depending on the location.
Areas with warming tendencies in winter and
spring (such as Norway, Northwest Canada, northern
Russia, Western Siberia, Yakutiya) contrast with
areas that are cooling distinctly (such as north-eastern
Canada). Furthermore, the results of most model
calculations do not yet concur with the observed climate
data (Hansell et al, 1998). One thing is certain,
though, the mean warming experienced thus far of
the very varied, very sensitive Arctic is still within the
natural realms of variability (Maxwell, 1997). Several
new biome models forecast a drastic decline in tundra
acreage in favour of boreal forests in the case of
a doubling of CO 2
concentration (Neilson and
Drapek, 1998). That would not just change the local
biotope structures and water levels in peatlands completely,
above all and this is the fear, it would lead to
feedback effects on the global climate in the form of
large-scale thawing of the permafrost soils and the
release of large amounts of the greenhouse gases carbon
dioxide and methane, even though there are contradictory
results on this question (Siegert and Hubberten,
1998; Section F 5).The indigenous population
in Arctic regions (eg Inuit, Lapps) have to expect
changes in the snow and ice coverage and new erosionary
processes and adapt their already jeopardized
lifestyle and economic livelihoods accordingly