Conservation and Sustainable Use of the Biosphere - WBGU

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Conservation and Sustainable Use of the Biosphere - WBGU

102 E Diversity of landscapes and ecosystems

stitute only some 3 per cent of the rainforest, they

make a great contribution to biodiversity (Goulding,

1990, 1993). Fig. E 2.2-1 shows a schematic cross-section

through the lower Amazon, indicating the various,

site-specific vegetation types and crops.

E 2.2.2

Emergence of biological diversity in the Amazon

basin

The Amazon rainforest is considered to be one of the

most complex and species-rich ecosystems on Earth.

The remarks above show that some of the complexity

and diversity results from the locational diversity.

With the exception of the nutrient-rich Várzeas, this

biodiversity has developed on mostly nutrient-poor

and acidic soil, upon which humus layers developed

as a refuge for decomposers. Very high ecosystem

productivity is achieved by the formation of almost

self-contained, internal nutrient cycles, involving a

large number of organisms. This depends on the

maintenance of the geochemical cycles. Disruptions

to these cycles can have catastrophic consequences

that can only be balanced out over extremely long

periods.

For a long time it was assumed that this diversity

was the result of a process of adaptation that had

been going on for millions of years. However, this

idea has been revised in recent years, because the climate

was not constant and there were repeated local

or regional disasters. For example, during the Ice Age

the climate was colder in the Tropics as well; occasional

fires and floods led to temporary, locally limited

destruction of the forests. However, these phenomena

did not destroy the flora and fauna, as the

Ice Ages did in Europe or North America; through

the destruction they led to an increase in biodiversity.

The entire ecosystem is, as was shown, by no means

uniform. Differences in the soils, precipitation, floods

and geochemical inputs, linked to differing dry periods,

caused evolution that varied greatly from place

to place. All of this meant that the Amazon basin is a

colourful mosaic of the most varied ecotopes with living

communities in varying stages of succession, but

which has hardly been researched to date in terms of

its multifaceted structures and functions.

The question as to why there is such high diversity

in the Tropics has not been completely answered.

This fact makes its difficult to develop strategies to

conserve diversity.The ecological factor of ‘diversity’

not only contains the number of species in an ecotope,

but also their relative frequency. This diversity

is called α-diversity. Here, a distinction is made

between β-diversity, a measure of the differences of

species compositions in living communities in neighbouring

and similar habitats and the γ-diversity of

large regions with very different habitats and ecosystems.

The prevailing opinion is that in the Tropics, in

addition to favourable conditions for the formation

of species, there are also, above all, favourable conditions

for the conservation of species. The question is

why the many species, which are mostly extremely

rare, do not become extinct or why individual species

do not become superior in terms of competition at

the expense of others.

In this respect, two basic hypotheses are discussed

(König and Linsenmair, 1996). In the deterministic

equilibrium models it is assumed that the available

resources are partitioned by means of competition

between species with similar demands. In the stochastic

models it is assumed that the occurrence and

frequency of individual species is determined by random

processes. Gaps in the ecosystems come about

through disruptions that cannot be spatially and temporally

foreseen. The latter models expand the spectrum

for explanation, but the former models also

appear justified. The factors that promote diversity

definitely include habitat richness and heterogeneity

in the ecosystems. The various storeys of the forests

and soil diversity offer many structurally and microclimatically

differentiated niches.The size of the area

and the age of the system also correlate positively

with biodiversity. But diversity is also characterized

by the establishment of varied relation between the

species. There are many examples of this in the tropics.

The nutrient-poor status of many tropical soils

promotes diversity of primary producers, ie green

plants. In turn, this diversity promotes diversity of

consumers and decomposers in the subsequent

trophic levels. There are many factors that promote

the great diversity in tropical ecosystems. Nevertheless,

it is currently not possible to satisfactorily

explain the diversity that occurs in the various

ecosystems.

E 2.2.3

Human intervention

The Amazon basin is an ecosystem that was subjected

to continuous change. However, the disruptions

always took such a form that large parts of the

ecotopes remained because of the geographical differentiation

and subsequently interlinked with the

developing systems in the disturbed zones. The

appearance of the forest Indians around 8,000 years

ago is an example of disruptions in history that

remained within the sphere of internal ‘scope for

repair’. Cultivation techniques and hunting possibilities

were of such limited extent that the original

inhabitants did not pose a threat to the viability of

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