Conservation and Sustainable Use of the Biosphere - WBGU

16 C The biosphere-centred network of interrelations
Continent Area Undisturbed Partially Dominated
disturbed by man
[km 2 ] [%]
Europe 5,759,321 15.6 19.6 64.9
Asia 53,311,557 42.2 29.1 28.7
Africa 33,985,316 48.9 35.8 15.4
North America 26,179,907 56.3 18.8 24.9
South America 20,120,346 62.5 22.5 15.1
Australasia 9,487,262 62.3 25.8 12.0
Antarctica 13,208,983 100.0 0.0 0.0
World as a whole 162,052,691 51.9 24.2 23.9
World as a whole 134,904,471 27.0 36.7 36.3
(without rocky and ice
regions and infertile land)
Table C 1.1-1
Human influence on
ecosystems worldwide. The
following criteria were
considered: vegetation
(primary, secondary, type of
agriculture and forestry),
population density, human
settlement and land
degradation (eg
desertification).
Source: after Hannah et al,
1994
pastureland or plantations, and natural watercourses
into canals. This form of change in land use is a key
factor in global change and possibly the most important
reason for the loss of biological diversity (UNEP,
1995). For example, the loss of land through conversion
is cited at 68 per cent for the Indo-Malay countries
and 65 per cent for the tropical countries in
Africa (MacKinnon and MacKinnon, 1986). Today,
only 27 per cent of the Earth’s surface covered by
vegetation is classed as undisturbed by humans
(Table C 1.1-1).
This trend can be differentiated from the trend of
degradation of natural ecosystems, in which there is
no direct destruction of natural structures but a
mostly slow, anthropogenic influence that is marked
by a gradual loss of structures or functions (UNEP,
1995). In order to allow an exact differentiation the
trend degradation of natural ecosystems has been
sub-divided into the three trends below.
Fragmentation of natural ecosystems
Fragmentation means the spatial breakdown of formerly
coherent natural ecosystems into smaller, isolated
partial areas, which, for example, arise through
the construction of transport infrastructure or
through conversion (Noss and Csuti, 1997). As a
result of this, the habitats of individual species are
made smaller and the populations are isolated from
each other. Fragmentation slows down the genetic
exchange between populations or can even bring it to
a standstill, with the result that there is a gradual loss
of species in the fragments. Fragmentation can frequently
be seen after a large-scale conversion, eg the
areas excluded from the clearance of primary forest
form individual ‘islands’ in the midst of arable land,
pastureland or secondary vegetation that are often
too small to ensure the long-term functioning of the
partial ecosystems. Both globally and regionally, fragmentation
is one of the major threats to biological
diversity (WRI et al, 1992).
Damage to ecosystem structure and
functions
This addresses the loss of functional units in an
ecosystem, which, for example, can be triggered by
the extinction of dominant species or keystone
species (Section D 2), by immigration of alien species
(Section E 3.6) or by substance overload (Section
E 3.2). As a result, the functional interactions
between the species (eg food webs) are modified in
such a way that the ecosystem changes greatly (triggering
succession) or the original ecological services
can only be performed to a limited extent (UNEP,
1995).
Substance overload of natural ecosystems
There are a large number of substances that exert
negative influences on ecosystems. Excessive loading
with organic (degradable) substances and nutrient
salts (eg nitrate, phosphate) can trigger eutrophication
in lakes, rivers and streams and coastal waters
and put the groundwater at risk. Inputs of pollutants
from the air (eg SO 2
,NO x
) and the resultant acid rain
damage forests and lakes. Organochlorine pesticides
(eg DDT or lindane) from agriculture and forestry
that biodegrade slowly (persistent) can cause direct
damage, but also have an indirect effect via accumulation
in food chains. Not least, a wide variety of toxic
substances reach the biosphere from many sources:
eg mercury pollutes South American rivers and
streams as a result of gold mining, cyanides are used
for fisheries in southeast Asian reefs (Section E 2.4),
dioxin is released into the environment from industrial
processes or radioactive waste is disposed of at
sea (radiation). The consequence of this substance
deposition is that today no spot on Earth can be considered
to be free of anthropogenic pollution.
Genetic and species loss
Genetic and species loss is a major consequence of
the above-mentioned ecosystem trends (WBGU,