Convention on biological diversity
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Natural HazardsNatural hazards, such as storms and hurricane damage, forest fires, floods and pests are natural disturbance regimes in forests. They can often have a positive impact on biological diversity. These disturbances, on a small or large scale, can create specific habitats that are important for the survival of a plethora of flora and fauna; they should, therefore, be mimicked or maintained in forest management (Angelstam, 1998). However, many human induced activities exacerbate these disturbances in a way that makes them an increasing threat to forest biodiversity. Climate ChangeGlobal climate change represents a particularly disturbing threat to FBD for several reasons. Firstly, because its impact will potentially be felt in most forest areas. Secondly, the nature and scale of its impact will be complex and require a comprehensive and co-ordinated response at both the regional level and globally. Climate change can affect biodiversity either directly through altering physiological responses or indirectly through altering interspecific relationships (Peters and Lovejoy, 1992, Kirschbaum et al., 1996). The capacity of forest associations and individual component species/populations to adapt to changed climatic conditions has been greatly diminished by fragmentation, with reduced gene flow and migration options. Climate change in combination with increasing fragmentation of forests is likely to cause extinction of many species (Reid, 1992, Botkin and Nisbet, 1992, Kirschbaum et al., 1996). More mobile, widespread, genetically variable species with short generation times will be best able to adapt and survive accelerated climate change. Forest tree species with restricted distributions, especially slow-growing, late successional species or those with restricted seed dispersal are especially vulnerable to climate change (Kirschbaum et al., 1996). It is worth noting that any form of new disturbance or environmental perturbation is likely to have major adverse effects on forests which are rich in restricted-range endemic species (Lovett et al., 2000). Forest FiresLack of fire in habitats where fire is part of the ecological process of regeneration (e.g. savannah woodlands or boreal forests) can have a deleterious effect on biological diversity and its processes in the longer term. However, extreme climatic events generating fire can have devastating impacts on FBD. For example, a prolonged or abnormally severe drought can be followed by uncontrolled fire, which can destroy sensitive forest communities and species. In recent years (1997, 1998 and 2000) forest fires have been particularly severe and very widespread (in, for instance, Australia, Brazil, Central America, Colombia, Indonesia, Kenya, Mexico, Mongolia, Papua New Guinea, Peru, Russia, Rwanda, Spain, USA and western Canada). Fires devastated large forest areas that normally do not get burnt. Such unprecedented frequency and unusual occurrences of fires may be attributed to climate change. Fragmentation may prevent or inhibit recolonisation of burnt forest patches by fire-sensitive animal and plant species, thereby aggravating the negative impacts of increased fire frequency and intensity on FBD. In Samoa, two severe tropical cyclones in the early 1990s ravaged the remaining lowland rain forests, which had been opened up to greater destruction through heavy logging. These “secondary” forests are now in a state of arrested regeneration, mostly smothered by the rampant native climber (Merremia peltata) and increasingly subject to periodic wildfire during El Niño drought years. This example illustrates the point that FBD is especially vulnerable to the interactions of multiple threat factors. [last example requests reference] Increasing atmospheric pollution, for example so-called acid rain, has had a major degrading impact on forests, mainly in parts of Europe and around the Great Lakes in United States and Canada, lowering biodiversity values and adversely affecting forest ecosystem functioning. Results of the monitoring of forest condition in Europe show that atmospheric nitrogen and sulphur deposition affects nutrient status and tree vitality. In 30% of the plots surveyed, the nutrient status is insufficient or unbalanced. Although sulphur deposition has decreased in the last decade, nitrogen depositions originating in emissions have increased. On about 50% of the plots, N-deposition is over the critical load of 14 kg nitrogen per ha/yr, above which adverse effects are very probable, specifically on the ground vegetation. Increased pollution has also lead to changes in soil properties, which are also likely to affect biodiversity (UN/ECE and EU 2000, Forest condition report). D. Underlying causes of loss of forest biodiversity The underlying causes of human impact on forest degradation and deforestation and, consequently, on biodiversity loss are both numerous and interdependent and the approaches to deal with them are country specific and will therefore vary among countries (IFF, 2000; WWF et al., 2000; Contreras-Hermosilla, 2000; Mc Neely et al., 1995; WRI et al., 1992). Some of the proximate causes discussed in the previous section, such as climate change or agricultural development, can also act as underlying causes. Among underlying causes are broader macroeconomic, political and social causes such as population growth and density, globalisation, poverty, unsustainable production and consumption patterns, structural adjustment, political unrest and war; institutional and social weaknesses such as lack of good governance, illegal logging, lack of secure land tenure and uneven distribution of ownership, loss of cultural identity and spiritual values, lack of institutional, technical and scientific capacity, lack of information, insufficient scientific knowledge and inadequate use of local knowledge; market and economic failures such as under-valuation of FBD goods and services; policy failures such as wrong incentives and subsidies and ill-defined development programmes, ill-defined or unenforced regulatory mechanisms and lack of environmental impact assessments. |