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