Geoscience Reference
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Fig. 8.4 Expert estimates of the levels of anthropogenic forcings on ecosystems and their
consequences
functions (
↗
), a reduced ability (
ₘ
), mixed trends (
ₑₓ
), unknown trends (?). The
figures characterize the levels of the ecosystems
'
functioning as life-supporting
compared with the situation 20
30 years ago: 1
—
excellent, 2
—
good, 3
—
satis-
-
factory, 4
no estimate. The results of the expert
assessments shown in Fig.
8.4
testify, on the whole, to considerable anthropogenic
forcings on ecosystems (especially during the 20th century) that have led to con-
siderable changes in their ability to perform the life-supporting functions. Though
in some cases (e.g., food production) the ecosystems
—
weak, 5
—
unsatisfactory, 6
—
productivity has substantially
increased, providing thereby the needed level of production, nevertheless, in other
cases (drinking water quality, preserving the biomass, etc.) there was a degradation
of the ecosystems
'
functioning.
The biodiversity losses during the last century have acquired the threatening
scales and concern practically all ecosystems (mainly
'
as a result of the loss of
habitats). So, for instance, the area of forests has decreased at least by 20 % and
probably (on global scales) by 50 %. Some forest ecosystems (like the dry tropical
forests of Central America) have disappeared at all. In many countries up to 50 % of
mangrove plantations have been lost, the area of wetlands has almost halved, and in
some regions the size of territories covered with grass has decreased by 90 %. Only
the tundra, arctic, and marine deep-water systems have little changed though in
these cases substantial anthropogenic impacts also occur sometimes.
Even when the initial areas of the ecosystems have been preserved, many species
are threatened with pollution, over-exploitation, intrusion of
—
species, and
degradation of habitats. From the viewpoint of biodiversity, the fresh-water eco-
systems have suffered most. For instance, about 20 % of the fresh-water
“
alien
”
fish species
have been exterminated, and many other species are in a very dangerous condition.
The forest, grass, and coastal ecosystems face serious problems of survival. The
biodiversity is threatened with frequented diseases of marine organisms, intensive
fl
florescence of water bodies, and a considerable reduction of the population of
amphibians. Apart from the respective losses for medicine (due to a decreasing
volume of raw materials for drugs), banks of genes, and eco-tourism, a reduction of
biodiversity means also a threat to the ecosystems
'
productivity, their integrity and
resistance to various external forcings.
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