Sustainable land use E 3.3 149 Table E 3.3-5 Regional change in forest cover. Source: Abramowitz, 1998 Region Original Remaining Annual Proportion of forests forests net change primary forest [10 3 km 2 ] [10 3 km 2 ] (1990–1995) [%] [% year -1 ] Africa 6,799 2,302 -0.7 23 Asia 15,132 4,275 -0.7 20 North America 10,877 8,483 0.2 44 Central America 1,779 970 -1.2 18 South America 9,736 6,800 -0.5 65 Europe 4,690 1,521 0.3 1 Russia 11,759 8,083 0.1 43 Oceania 1,431 929 -0.1 34 World 62,203 33,363 -0.3 40 Today the mean annual change in the forest acreage in the species-rich tropical forests is especially large. It is extreme in Brazil and Indonesia. Both countries together have annual forest losses of over 3.6 million ha, that is a third ofthe forest acreage of Germany for each country. With deforestation rates of over 0.4 million ha each, the losses in countries such as Zaire, Mexico, Bolivia, Venezuela and Malaysia are also considerable. In Russia, which does not provide any official figures, experts estimate that approx 4 million ha of taiga are cleared per year. These figures do not include the insidious changes resulting, for example, from small, repeated fires that escape detection by satellites over a long period (Cochrane and Schulze, 1999). The relationship of forest acreage to population figures is influenced both by the development of deforestation and by population growth. In 1950 around 2.55 thousand million people lived on the Earth; the figure had more than doubled to 5.7 thousand million by 1995. In 1950 there was an average of 1.6 ha forest available per inhabitant ofthe world; this figure had fallen to 0.6 ha by 1995. The forecasts predict another halving to 0.3 ha per inhabitant for 2025. However, it is not only the conversion ofthe forests that is changing biodiversity (Box E 3.3-6), but also the increasing conversion of primary forests into secondary forests or plantations. Here, the uncontrolled exploitation of primary forests, in particular, has a negative impact. The further destruction ofthe forests can only be stopped by: – ceasing uncontrolled conversion ofthe forests into arable and grazing landand into areas for transport infrastructure and settlement; – regulating forest use, in a manner incorporating existing knowledge and geared to sustaining timber increment (sustainability principle); – establishing segments of regulated, highly productive plantations in order to produce the required quantities of certain wood qualities while protecting natural forests; – halting the use-related degradation ofthe biotic and abiotic components of forest ecosystems; – reducing the deposition-related stresses upon forests from acids, nitrogen and contaminants. E 184.108.40.206 Substitution of land-use products Nutritional statistics show that in North America today the food supply per head of population is 15,181 kJ per day, 34 per cent of which comes from animal production. The figures for western Europe are 14,424 kJ, 33 per cent of animal origin. In the developing countries of Latin America 11,438 kJ are available to every inhabitant per day, 17 per cent of animal origin. In the Far East the figures are 9,285 kJ, 7 per cent from animal production, and in the developing countries of Africa 8,872 kJ, only 5 per cent of which is of animal origin. The oversupply of food in the industrialized countries, coupled with a surplus of animal protein, holds the potential to relieve shortages in the global food supply. However, because ofthe relatively small proportion ofthe world’s population that is oversupplied in this way, the relief that can be achieved by reducing the proportion of animal foods should not be overestimated, especially when we remember that the world’s population is growing by over 80 million per year. Substitution is also limited because only feedstuffs that are also suitable for human consumption can be considered. Moreover, it must also be considered that ruminants sometimes graze grasslands which cannot be used for any other purpose. Animal production and its rapid growth in recent years (Table E 3.3-6) exerts an enormous influence on the biodiversity of our world.This influence is not only due to the fact that 22 million km 2 are used as grazing land, but also that animal feed is produced on 21 per cent of arable land. If, on the one hand, the demand for food from animal sources is to be met and, on the other hand, ecological side effects are to
150 E Diversity of landscapes and ecosystems Box E 3.3-6 Forests and biological diversity The loss of forest biodiversity results both from the loss of forest land (Section E 220.127.116.11) and from the degradation of existing forests. Both processes continue apace and, after centuries of forest destruction in temperate and boreal areas, since the mid-twentieth century they have taken place particularly actively in the tropics. With regard to the loss of biological diversity, special importance is attached to the loss of tropical forests and forest degradation because the tropical forests are disproportionately richer in species than temperate and boreal forests andthe agro-ecosystems that result from the conversion are much more fragile. The best contribution to the conservation of forest biological diversity can be made by the biodiversity of forests being understood as a carrier of biological resources. The value ofthese biological resources comes to bear at various levels, ranging from the household level (firewood, food, medicine), local (food, firewood, medicine, building materials), national (wood products, water, firewood, etc) and international markets (wood products, resins, oils, tourism, etc) (Section H 5). Forest biodiversity gains global significance as an important carrier of information for future options on technological or medical developments (Section D 3.3). Further importance may be attached to the biodiversity of forests regarding their stabilising effect on the global climate (Section F 2). The importance of forests as biological carbon sinks is currently the subject of international discussion (WBGU, 1998b). The information on the number of species in forests is highly unreliable and fluctuates between 2 and 80 million species. The mean value ofthe estimates is around 10 million species, and it is assumed that the vast majority ofthese are arthropods (WCMC, 1992; Heywood and Watson, 1995). In turn, around 50–90 per cent of arthropods are to be found in the tropical forests and this emphasizes their high fauna diversity. With respect to plant biodiversity the much quoted example form Borneo can be used, where 700 tree species have been identified on 10 ha of forestland, in other words more species than occur in the whole of North America (Rodgers, 1996). In light ofthe pressure on land use described above, further losses of forests in the tropics will be inevitable (Chapter G). The majority ofthe conversion will continue to be for agricultural use. It is therefore all the more important to integrate the land use changes into comprehensive concepts that are anchored at regional level (Section E 3.9). The maintenance ofthe agricultural productivity ofthe converted forestland or increasing the productivity on existing agricultural land must be an important objective (Section E 18.104.22.168). Although most national policies emphasize that the remaining forestland should be protected, deforestation continues on a global level. From this, it can be seen that the causes of forest destruction are multi-faceted and differ from region to region. Not only direct reasons, such as the spread of slash and burn, but also indirect reasons due to the failure of policies, such as rural poverty, lead to the continuing destruction of forests (NNA, 1998; Jepma 1995; Pearce and Moran, 1998; Chapter G). Since the existing biological diversity ofthe forests cannot be preserved as a whole and species are becoming extinct more quickly than all the existing species can be recorded (Pimm et al, 1995; Section D 1), special significance is attached to the functional evaluation of biodiversity alongside recording habitats. Two questions can be asked: • How much biodiversity is needed to conserve multifunctional forests (Section E 3.3.9)? • Can this question be answered on time? The first steps along this route have been made with the identification of hotspots of biodiversity, the designation of indicator taxa andthe mapping ofthe usage pressure on existing forest ecosystems (Global Forest Watch; WRI, 1999).An accompanying measure that could help to reduce the predatory exploitation of forest resources is the certification of wood products and forms of management (Box E 3.3). A legally binding regulation for forest protection is long overdue (Section I 3.4.4). The instruments and means of implementation currently available are, however, so limited that it is extremely doubtful whether the dynamics ofthe current trend can be decisively influenced. be minimized, far-reaching changes in eating habits and in the way we keep and use animals will have to be effected. • Overnutrition with foods of animal origin must be reduced because it is inefficient on the one handand has a negative impact on health on the other. • The productivity of domesticated animals should be optimized because large unproductive stocks have a disproportionate negative impact on biodiversity. This should also include ‘improvement’ of traditional livestock breeds. • Grazing practices should be more oriented towards the carrying capacity ofthe grasslands in order to prevent the degradation ofthe grazing areas. Switching to animal foodstuffs from the sea is also limited because some natural fish populations are already being overexploited. Although aquaculture is a possible alternative, high-quality feed must be used, which – in turn – mostly comes from terrestrial ecosystems. Also, establishing cultures of this kind in lakes and shallow seas is problematic from the point of view of environmental pollution andthe impact on the biodiversity of aquatic ecosystems (Section E 3.4). The production of food using biotechnological methods has not yet progressed to a level where it can relieve shortages. Although there is great potential for the biological conversion of plant wastes or residues into feedstuffs and foods, only a few approaches have so far proved to be economically sustainable. New information and conversion methods should be developed for the better use of plant biomass (such as wood or straw) as feed and food. In this respect, molecular biological methods could open up new opportunities.