Conservation and Sustainable Use of the Biosphere - WBGU

242 F The biosphere in the Earth System
(Bonan et al, 1992). It is, however, more probable to
assume that adapted forestry management methods
will now be applied more consistently and as a result
of the CO 2
related global warming, a renewed northwards
migration with self-reinforcing feedbacks for
the global climate will set in.
F 5.3
Biogeographical criticality
In the previous section certain regions were
described whose biosphere has an important metabolic
and physiological significance within the Earth
System. The selection was unsystematic and based
simply on expert assessment (Nisbet, 1994). In the
following section we have attempted to list individual
indicators which when linked demonstrate the
regional significance of the biosphere for the Earth
System. This approach also gives the first points of
reference for performing a criticality evaluation in
the case of existing or potential degradation and, at
the same time, shows the particular protection merited
by the biogeographical regions.
F 5.3.1
Evaluating the importance of the biosphere for
the Earth System
A possible strategy for developing a criticality index
for the biosphere is presented in the following. This
index characterizes the importance of the regional
biosphere for the Earth System. Here, therefore, features
are identified that possess a function within the
global ecosystem which is the Earth. Of course, such
an approach is not clear a priori and the selection is
certainly not complete. The Council emphasizes
therefore explicitly that the following concept can
only be the first step towards such an evaluation and
indicates a possible approach.
The following parameters of the biosphere were
selected: robustness or sensitivity (R) vis-à-vis a
change in environmental conditions and a combination
of important metabolic functions of the biosphere
for the overall system which are characterized
by the integral value F. The criticality indicator K is
therefore derived from the quotient of these features,
that is:
K = F R .
It thus represents a simple, geographically explicit
evaluation function into which suitable base indicators
for the named characteristics (R, F) may be
inserted. The global functions of the biosphere for
the Earth System are subsumed under F.
For the sample evaluation in this section the primary
energy uptake P, the distribution of the annual
albedo of biosphere and the contribution that the
biosphere makes to the global hydrological cycle
were considered. Function P may be represented as
productivity of the biosphere on the biome scale and
as required may be defined more closely. As a suitable
measure for P, the net primary production
(NPP) may be used since it can be formulated as
energy flux density (energy intake per unit area) and
there is a relatively complete set of base data. By
NPP we understand the amount of plant material
that is formed by photosynthesis during a given year
per unit area. The level of NPP describes the system
in balance with its environment. Both for semi-natural
and agricultural or silvicultural terrestrial
ecosystems, plant primary production plays a crucial
role. In the semi-natural ecosystem this plant material
serves above all to promote the growth of the living
biomass; furthermore, it replaces dead or eaten
plant parts and forms reproductive organs. In ecosystems
under agricultural use, the NPP forms the upper
limit of the harvest yield, a level which is hardly ever
reached because of the non-usable parts (root systems,
stalks). In a global representation, the NPP distribution
is a suitable measure for the regional
energy intake of the biosphere and thus is immensely
important for the Earth System. Through linkage
with the worldwide representation of primary production
in the marine biosphere – an important outcome
of the Joint Global Ocean Flux Study (JGOFS)
of the International Geosphere Biosphere Programme
(Ducklow and Fasham, 1999) – this aspect
can be identified worldwide.
Comparison of seasonal albedo distribution
(Matthews, 1983) allows identification of regions
where the albedo of the biosphere over the course of
a year shows negative feedback if at times of lower
solar irradiation in the winter months less is diffused.
Of course, there is no complete compensation; however,
foliage coloration and drop and the darker
background of the soil soften the transition to the
winter months in energy terms.
Also, the contribution of the biosphere to the
hydrological cycle (Section C 2) can be understood as
an important function of the global ecosystem. The
transpiration output of plants exceeds the evaporation
output from abiotic processes by far and thus
makes a decisive contribution to the energy and
nutrient transfer within the Earth System (Section
F 1). This aspect can be demonstrated by linking
global datasets on evapotranspiration and leaf area
index. Both figures are necessary to be able to repre-