Convention on biological diversity
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I.Status and trends of forest biological diversityForest biological diversity should be quantified and described on a multiplicity of scales, from large forest landscapes of several thousand square kilometres, to the genetic level within individual organisms. The present report refers to forest landscapes, ecosystems, species, and genes, and considers the diversity of structure, function, and composition existing at each level. Scale is also considered in a second sense, including global, regional and local (or national), required to report activities and outcomes that address the issue of maintenance of biological diversity in forests. Determining the current global status of forest biological diversity is somewhat problematic because of difficulties in quantifying biological diversity in a meaningful fashion. Describing biological diversity on the local or national scale for most countries may not be entirely possible, and even in countries that attempt to report on biological diversity, data on indicators are usually not well developed. Further, the extent and rate of change of the world’s forests are still unclear, especially at the national level, and long-term trends are distorted by the lack of solid baseline data and inconsistent use of terms. Where forest inventory data do exist, in both the developed and developing world, the information is often outdated, of poor quality and is especially difficult to compare among regions because the data sources, as well as the definitions of forests and forest types, differ. The present report uses the Food and Agriculture Organization of the United Nations (FAO) definition of forests, which has been set for the monitoring of global changes in forest cover and allows comparison between countries. Although there is not complete global agreement with the FAO definition of “forest”, based on those FAO data 3,869 million ha of global forest remain in 2000, but there has been decline in the forest area by ca. 9.4 million ha (0.22 per cent) annually since 1990, of which most was natural forest in the tropics. Preliminary estimates show that net deforestation rates have slightly increased in tropical Africa, remained constant in Central America, and declined slightly in tropical Asia and South America. The establishment of plantation forests and reforestation activities in temperate and boreal forests of some industrialized countries have increased and led to a decline in deforestation rates in those biomes. In the tropical biome, the rate of plantation establishment has increased dramatically during the last decade. However, the Group noted that plantation forestry cannot fully compensate for deforestation of primary forest in terms of biological diversity, especially in the tropics or in temperate regions, where exotic, rapidly growing tree species have most often replaced the original stands. FAO’s assessments do not encompass forest quality aspects (e.g. no clear distinction between primary and secondary forests, nor among different types of plantations), making an assessment of the quality of global forests difficult.
At the broadest level, forests need to be better categorized to enable a proper global assessment of change in forest biological diversity. At the very least, it is important to distinguish between primary forests, that have not been directly influenced by humans and thus have most of their original biological diversity, and various types of secondary forests, which have regenerated following cutting or clearing and may support only a portion of the original biological diversity. Plantations are best described as a class of secondary forests, where often the major objective is wood production, although many countries are also using plantation forestry to try to recover previously degraded woodlands. Agroforests should also be considered as a distinct class of forests because, while supporting a portion of local biological diversity, they lack full species complements. Care must be taken in reporting forest cover, relative to biological diversity, by distinguishing among these broad classes of forests, because biological diversity differs in each. There is a need to harmonize forest reporting on the national, regional, and global scales to improve understanding of forest quality change, and also to include within these reports aspects relevant to assessing biological diversity. A key enabling feature required for reporting is the use of comparable forest classification systems that can be aggregated to higher scales, from local or national scales, and that will accurately correlate to changes in forest biological diversity. Essential improvements in collecting and reporting forest data would be, for example, to distinguish between various numerical classes of canopy cover by forest type, and between primary forests, secondary forests, plantation forests and preferably, also between young forests and older forests. On very large scales, there is clear evidence that forest biological diversity is related to total forest area, and small forest fragments retain only a small portion of the normal species complement. Globally, many primary forests have become degraded or deforested, so it is clear that forest biological diversity is rapidly declining, especially in the tropics. The capability of forests to maintain biological diversity has changed over large areas, as primary forests have been deforested or replaced by secondary forests of various qualities as a result of activities such as cutting, land-clearing, deliberate forest fires, fragmentation caused by forest road networks and conversion to agricultural lands, and the homogenization of forest stands. Far fewer intact larger blocks of primary forests now occur, compared to earlier, in all forest biomes. Generally, species richness increases with decreasing latitude, with the highest levels of endemism in the tropics for flora and fauna. Unfortunately, knowledge and documentation of species follow the opposite trend, and many tropical species and processes remain unidentified. An important difference between tropical forests and temperate or boreal forests is the high local richness per unit of area (alpha diversity) in tropical forests and the high endemism, compared to lower alpha diversity in the other two biomes at the stand level. Temperate and boreal forests tend to have greater landscape diversity than tropical forests. Yet in all forest biomes there are areas with very high local diversity, and forest sites with high primary productivity maintain greater diversity than those with low primary productivity. These facts have important implications, which differ among the biomes, for landscape management strategies, including protected area placement and research needs for forests. The number of threatened and endangered forest species seems to correlate with the size and quality of forest habitats, temporal and spatial continuity in the forest landscape, and with the history of forest use. The current extinction rate is far higher (1,000 to 10 000 times) than the rate at which species evolve and is at a historically high level. The majority of animal and plant species that are becoming extinct come from forest ecosystems. Current estimated rates of extinction for most higher life-forms in tropical rainforests are 1-10 per cent of those species in the next 25 years. The main direct causes of extinctions are habitat loss, due to land conversion and fragmentation of habitats, alien species invasions, and over-harvesting of forest resources, including logging. In future, climate change may be a further major factor, interacting with existing problems and contributing to extinctions (see sub-section D, below ‘Causes of forest biological diversity loss”). The number of endangered species, as well as local extinctions of rare species, can be expected to rise because of the time delays (”extinction debt”) associated with fragmentation effects, forest loss, and declines in habitat quality. In particular, species requiring specific habitats that may be limiting, or which have large home-ranges, will become increasingly endangered. Some well-known species, such as great apes and large carnivores, are expected to become extinct due to habitat loss, over-exploitation, genetic effects of small populations and illegal hunting, in spite of the general positive attitude towards their conservation and the considerable conservation efforts. While there is information on the genetic diversity of a few animal species and important trees, in general few such data exist. However, it is evident, that genetic diversity will be severely eroded due to forest decline (e.g. local extinctions of small, often unique populations) and that the effects of forest fragmentation and deforestation on genetic diversity have been overlooked. Protected forest areas have increased in recent years, both in number and in area. However, globally forests are neither well protected, nor well represented in protected areas, with less than 8 per cent of the world’s forest afforded some kind of protected status. Furthermore, particularly in tropical areas, only a minor portion of all the so-called protected area is actually secure. Most protected areas are small and insufficient to serve as source populations for large vertebrate species; nor do they fully protect regional species or local genetic diversity. The lack of small-scale forest classifications for all countries precludes an assessment of the representativeness of forest types in protected areas. Nevertheless, biological diversity will never be maintained by a network of protected areas alone, and sustainable management of large associated areas will also be required. Protected areas must be considered as part of a continuum of managed areas, from primary protected forest to fibre plantations. Regardless of forest type, various characteristics develop or accumulate with forest age. Different animal and non-woody plant species associate with various stages of forest development because of these features, and so forest communities change over time in the same location. Old forests are an important category of forests, because certain species are optimally or solely associated with such forests. Key indicators for old forests are known for boreal zones and, to a lesser extent, in temperate forests, but are poorly known in tropical forests. A body of scientific theory helps to understand biological diversity, but much remains to be understood. In particular, while biodiversity is clearly related to forest goods and services, the exact mechanistic relationships are not well understood. Further, little testing of indicators has been carried out in terms of their capability as predictors of broader changes in biological diversity, or defining the concept of forest quality and how well it can be predicted by indicators. Finally, there is a clear need to understand critical thresholds of forest change that will produce substantial losses in biological diversity, particularly among key or keystone species. One source of information that has largely been overlooked is the traditional knowledge of indigenous peoples. Indigenous peoples have knowledge that has developed over many generations, but this knowledge has not yet been fully understood nor recognized, because the origin, nature, ways of use and transfer of this knowledge are different from Western “formal” science and scientific practices. In addition, there is often little mutual trust for sharing traditional knowledge, due to the absence of recognition of indigenous peoples and their rights. Total forest cover is a coarse predictor of biological diversity, and much better indicators are needed to properly report status and trends of biological diversity on scales ranging from national to global. Most local forest inventories are conducted to monitor harvestable volumes, rather than to monitor biological diversity. Monitoring of biological diversity and of changes caused by forestry practices is important in order to assess the effectiveness of management and cumulative change through forest use. Adaptive management, based on consistent monitoring and comparison of biological diversity between primary and secondary forests, is an important part of the ecosystem management protocol. Surrogates for high levels of biological diversity, such as umbrella species, indicator species, key habitats and structural indicators, may help to assess and predict the effectiveness of conservation and forest management programmes. Such surrogates must be carefully selected, based on sound scientific understanding of their properties. Data on rare and threatened forest species alone are insufficient to provide a reliable picture of broader trends in biological diversity. Species that are naturally rare, or have declining populations, represent a special case for knowledge needs and management. Such species must be identified and understood in terms of the processes which affect their populations. Often, national biological diversity databases do not exist and the availability of long-term benchmark data for trends in possible indicators is rare. Aside from the lack of useful indicators, the incomplete and non-standard forest classifications, and the need for improved science, many countries lack the necessary infrastructure to report on biological diversity. An important prerequisite in assessing the status of biological diversity is technology transfer to developing nations, along with equipment and training in the methods required to evaluate biological diversity and natural resources, and to map their distribution.
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