ulation pressure. Thus, state subsidies were used to clear enormous areas for "ranching" establishments during the inland colonisation of Brazil (Kohlhepp 1991). At that time grass seed was sown from planes, but subsequent grazing was mostly given up after a few years as replacement communities with hard grasses (sclerophyllic grasses, e.g. Imperata cylindrica, and others) developed which were not suitable species for animal fodder. The practice of shifting cultivation with slash and burn used commonly in all moist, tropical areas was previously regarded as damaging. Today this form of land use is regarded as less damaging, particularly if fallow periods last long enough. However, almost allover the tropical regions the fallow periods were shortened because of pressure from fast-growing populations. Regeneration, particularly of my-corrhizae, is no longer guaranteed. Bruenig (1991) compared the consequences of mild intervention with "modern" intervention and assessed the consequences with the help of two profiles (Fig. 4.1.27). In Fig. 4.1.28A-C typical phases of the development of land use from the natural forest to unproductive fallow areas are shown.
Worrying numbers showing the loss of tropical moist forests have been published. The FAO documents a faster rate of decrease in rain forests from the 1980s onwards and estimates for the year 1991 alone indicate a loss of 2% of tropical forest area. Klotzli (1993) quotes 0.3 million ha/year, Bruenig (1991) calculated more than 7 million ha/year. Even if starting from the assumption of a relatively low //-diversify (differences of diversity between different sites), these area losses affect complete plant communities with highly endemic species, and particularly the specialists amongst plants and animals. Genetic material for breeding, species for medical use, food and various commodeties are lost (WBGU 2000). Erosion on the cleared areas increases manifold, changes in water relations occur. There are local climatic changes at the micro- and mesoscale range. Because of the increased atmospheric C02 content global climate change is expected, with increased greenhouse effect with rising temperature and changed precipitation (IPCC-WGI 2001).
Linked to the destruction of tropical rain forests, the establishment of more protected areas than so far established has been demanded. However, many millions of people live in these areas, so concepts for sustainable management must be developed. It is often overlooked that such concepts already exist, and that there are examples of sustainable land use. The earlier hunters and gatherers, and the first settled agriculturists, independent of each other, developed well-adapted forms of land use in most tropical regions. Low population density allowed long fallow periods. The population was less mobile, stimulating a closed cover of several "storeys" from different crop plants. The original land use simulated (intuitively?) the structure and biodiversity of a natural rainforest with useful plants.
Figure 4.1.29 A-C shows forms of sustainable land use in the permanent rain forest, and in the seasonally moist rain forests of the tropics.
Wood extraction by foresters cannot be sustainable in the continuously moist tropical rain forests because of the imbalanced nutrient supply. Integrated forms of use, with crop plants adapted to - and supplementing - the conditions (e.g. supply with nutrients and water) and affecting the site (e.g. creation of particular microclimatic conditions) must be developed or taken over from indigenous populations. However, in doing this, the expectations of high yields often linked to land use in the tropics must be revised. Sustainability must be considered more than mere technologies and rates of production; the ultimate aim is maintenance of the cultural heritage in particular environments. Some elements of sustainable use are generally valid. These are agroforestry, mixed cropping, mulching, biological pest control, etc. (Furley 1993).
Examples of recent attempts to protect the environment exist but almost everywhere a creeping loss of protected areas can be observed. Many questions are also open about the scientific basis for nature protection in the tropics. It is, for example, assumed that a suitable number of individual plants, able to reproduce, must be available to maintain a species. Assuming this number to be 500, this would require, in the rain forest ecosystem, probably several 100 ha per species. This does not (only) concern the protection of species, but the protection of plant communities in an area. Little is known about the protection of communities in environments, about the minimum size of such spaces required and the bordering buffer zones. The borders of national parks and biosphere reserves were
I Fig. 4.1.28. The three photographs show the typical processes and sequences in exploitation of tropical rainforest (example from central Sulawesi, Indonesia). A Uncontrolled clearing (slash and burn) of primary forest, done often by groups of people without knowledge of methods appropriate for the environment. B Agricultural use of the cleared forests for only a few years (without fertiliser application) until the fertility of the land is exhausted by the cultivated plants grown to fulfil the people's needs. C The unproductive area is abandoned and quickly invaded by alang-alang grass (Imperata cylindrica) and bracken (Pteri-dium aquilinum). (Photos K. Müller-Hohenstein)
usually roughly estimated, even if not determined according to political and economic criteria. These are important tasks for ecology which is concerned with the protection of tropical ecosystems.
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