Conservation and Sustainable Use of the Biosphere - WBGU

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Conservation and Sustainable Use of the Biosphere - WBGU

104 E Diversity of landscapes and ecosystems

if the necessary development were to concentrate on

the more fertile ‘favourable areas’ of Amazonia and

if the existing knowledge concerning sustainable,

multifunctional land use (Section E 3.3.4) were used.

E 2.2.4

Comparison of intervention in tropical and

temperate forests

Now what is the cause for the different behaviour of

tropical and temperate forests after human intervention?

If we ignore the soils in the flooded areas,

whose sediments mainly come from the western

mountainous regions – these are, as outlined above,

frequently old and heavily weathered soils that are

barely capable of storing nutrients or supplying them

from minerals. The nutrients needed for the plant

populations come from the humus, which is decomposed

over relatively short periods of time at high

temperatures and high soil humidity, but is constantly

regenerated from the population waste. The biodiversity

of the ecosystems has meant that an internal

nutrient cycle has been able to develop, although the

very high and intensive precipitation, the high

turnover speeds and the extreme shallowness of the

soils counteract the maintenance of the biogeochemical

cycles. If humankind intervenes in this complex

process chain, it breaks up the biogeochemical cycles,

nutrients are washed out quickly and there is a dramatic

increase in soil erosion and loss of living communities.

The much younger soils of the temperate zone are,

by contrast, generally much less sensitive to interventions.

They have weatherable minerals, which can

supply nutrients in the event of disruptions, and thus

have stronger buffers against external pollution.As a

result of the seasons, the lower winter temperatures

lead to slackened vegetation growth and phases with

greatly reduced conversion rates. During this time

human interventions are largely harmless. Furthermore,

the level and the intensity of the precipitation

are much lower, causing less nutrient leaching and

erosion.

As shown in the previous case study for Central

Europe (Section E 2.1), human interventions have

extended over a period of 6,000 years, whereas the

large-scale intervention in Amazonia has only been

taking place for 50 years. Nevertheless, the origins of

the phase currently being undergone there can certainly

be compared to the clearance phase of the

Middle Ages in Europe, even though the intensity of

the change is much greater today. The consequences

for biodiversity are, however, completely different. In

Central Europe the use of land in young, speciespoor

ecosystems led to an increase in diversity

because of the creation of zones of disruption and

nutrient depletion. In the old Amazon region with its

great diversity and rare species, the opposite effect is

being achieved (Box E 2.2-1)

Many scientists see no future for the rainforest.

Even before the biological wealth of this region has

been recorded, the majority of it will have disappeared.

The fact that we are particularly worried

about the forests of Amazonia is because this is the

region with the highest species diversity in the world

and ‘only’ 15 per cent of the area has been destroyed,

meaning that it may be possible to conserve it. In a

country with rapid population growth, however, an

attempt to save nature will certainly fail if the economic

and social situation of the people is not

improved at the same time. To do this, appropriate

land use strategies will have to be developed and put

into practice (Section E 3.3).

The sooner a start is made on linking use to the

protection of the ecosystems by means of bioregional

management (Section E 3.9), the greater are the

chances to conserve large parts of this irreplaceable

region that is so important for the world’s climate.

E 2.3

Introduction of the Nile perch into Lake Victoria: a

Pyrrhic victory in economic terms?

Around 35 years ago a bucketful of Nile perch from

nearby Lake Albert was tipped into Lake Victoria in

order to give the local population a new source of

food. This was successful, at least in the short term.

However, the contents of this bucket had the effect of

releasing a genie from a bottle, because it was enough

to extinguish well over half of the approx 400 tilapia

(cichlid) species only present here (endemic) within

just two decades (Goldschmidt, 1997). Their biomass

fell by 99 per cent to below 1 per cent of the entire

fish biomass in Lake Victoria (Stiasny and Meyer,

1999).The Nile perch (Lates niloticus) became one of

the most important sources of food and income for

the populations of Kenya, Uganda and Tanzania. In

1994 almost 400,000 tonnes Nile perch were fished

and sold – probably even more. However, since this

record year yields have been falling and the water

quality of Lake Victoria has deteriorated drastically.

The recent history of Lake Victoria is a lesson in the

conflict between the needs of the local population to

survive and the conservation of the world’s natural

heritage.

The changes to the Lake Victoria ecosystem can

be ascribed to natural and anthropogenic effects,

with no agreement on the relative importance of the

individual factors:

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