Biodiversity in 2010
Tropical forests continue to be lost at a rapid rate, although deforestation has recently slowed in some countries. Net loss of forests has slowed substantially in the past decade, largely due to forest expansion in temperate regions.
The best information on terrestrial habitats relates to forests, which currently occupy approximately 31 per cent of the Earth's land surface. Forests are estimated to contain more than half of terrestrial animal and plant species, the great majority of them in the tropics, and account for more than two-thirds of net primary production on land - the conversion of solar energy into plant matter.
Deforestation, mainly conversion of forests to agricultural land, is showing signs of decreasing in several tropical countries [See Box 5 and Figure 7], but continues at an alarmingly high rate. Just under 130,000 square kilometres of forest were converted to other uses or lost through natural causes each year from 2000 to 2010, compared to nearly 160,000 square kilometres per year in the 1990s. The net loss of forests has slowed substantially, from approximately 83,000 square kilometres per year in the 1990s to just over 50,000 square kilometres per year from 2000-2010. This is mainly due to large-scale planting of forests in temperate regions and to natural expansion of forests. Since newly-planted forests often have low biodiversity value and may only include a single tree species, a slowing of net forest loss does not necessarily imply a slowing in the loss of global forest biodiversity. Between 2000 and 2010, the global extent of primary forest (that is, substantially undisturbed) declined by more than 400,000 square kilometres, an area larger than Zimbabwe.
South America and Africa continued to have the largest net loss of forests in 2000-2010. Oceania also reported a net loss of forests, while the area of forest in North and Central America (treated as a single region) was estimated to be almost the same in 2010 as in 2000. The forest area in Europe continued to expand, although at a slower rate than in the 1990s. Asia, which had a net loss in the 1990s, reported a net gain of forests in the period 2000-2010, primarily due to large-scale afforestation reported by China, and despite continued high rates of net loss of forests in many countries in South and Southeast Asia.
The conifer-dominated boreal forests of high Northern latitudes have remained broadly stable in extent in recent years. However, there are signs in some regions that they have become degraded. In addition, both temperate and boreal forests have become more vulnerable to outbreaks of pests and diseases, due in part to an increase in winter temperatures. For example an unprecedented outbreak of the mountain pine beetle has devastated more than 110,000 square kilometres of forest in Canada and the Western United States since the late 1990s.
Savannas and grasslands, while less well documented, have also suffered severe declines.
The extent of other terrestrial habitats is less well documented. It is estimated that more than 95 per cent of North American grasslands have been lost. Cropland and pasture have replaced nearly half of the cerrado, the woodlandsavanna biome of Central Brazil which has an exceptionally rich variety of endemic plant species. Between 2002 and 2008, the cerrado was estimated to have lost more than 14,000 square kilometres per year, or 0.7% of its original extent annually, well above the current rate of loss in the Amazon.
The Miombo woodlands of Southern Africa, another savanna region with significant plant diversity, are also experiencing continued deforestation. Stretching from Angola to Tanzania and covering an area of 2.4 million square kilometres (the size of Algeria), the Miombo provide firewood, building material and extensive supplies of wild food and medicinal plants to local communities across the region. The woodlands are threatened by clearing land for agriculture, extraction of wood to make charcoal, and uncontrolled bush fires.
Abandonment of traditional agricultural practices may cause loss of cultural landscapes and associated biodiversity.
Traditional techniques of managing land for agriculture, some dating back thousands of years, have served an important function in keeping human settlements in harmony with the natural resources on which people depend [See Box 6]. In many parts of the world, these systems are being lost, due partly to the intensification of production, and partly to abandonment linked to migration from rural to urban areas. In some cases, this trend may create opportunities for biodiversity through the re-establishment of natural ecosystems on abandoned farmland. However, the changes may also involve important losses of distinctive biodiversity, among both domesticated and wild species, and of ecosystem services provided by managed landscapes.
Terrestrial habitats have become highly fragmented, threatening the viability of species and their ability to adapt to climate change.
Ecosystems across the planet, including some with exceptionally high levels of biodiversity, have become severely fragmented, threatening the long-term viability of many species and ecosystem services. Global data regarding this process are hard to obtain, but some well-studied ecosystems provide illustrations of the scale of fragmentation and its impacts. For example, the remaining South American Atlantic Forest, estimated to contain up to eight per cent of all terrestrial species, is largely composed of fragments less than one square kilometre in size. More than 50 per cent lies within 100 metres of the forest edge.
When ecosystems become fragmented they may be too small for some animals to establish a breeding territory, or force plants and animals to breed with close relatives. The in-breeding of species can increase vulnerability to disease by reducing the genetic diversity of populations. A study in the central Amazon region of Brazil found that forest fragments of less than one square kilometre lost half of their bird species in less than fifteen years. In addition, isolated fragments of habitat make species vulnerable to climate change, as their ability to migrate to areas with more favourable conditions is limited.
One-quarter of the world's land is becoming degraded.
The condition of many terrestrial habitats is deteriorating. The Global Analysis of Land Degradation and Improvement estimated that nearly one quarter (24%) of the world's land area was undergoing degradation, as measured by a decline in primary productivity, over the period 1980-2003. Degrading areas included around 30% of all forests, 20% of cultivated areas and 10% of grasslands. Geographically they were found mainly in Africa south of the Equator, South-East Asia and southern China, north-central Australia, the Pampas grasslands in South America, and parts of the Siberian and North American boreal forests. Around 16 per cent of land was found to be improving in productivity, the largest proportion (43%) being in rangelands.
The areas where a degrading trend was observed barely overlapped with the 15% of land identified as degraded in 1991, indicating that new areas are being affected and that some regions of historical degradation remain at stubbornly low levels of productivity. About 1.5 billion people directly depend on ecosystem services provided by areas that are undergoing degradation. The decline in fixation of carbon from the atmosphere associated with this degradation is estimated at nearly a billion tonnes from 1980 to 2003, (almost the equivalent of annual carbon dioxide emissions from the European Union) and emissions from the loss of soil carbon are likely to have been many times greater.
Despite more than 12 per cent of land now being covered by protected areas, nearly half (44%) of terrestrial eco-regions fall below 10 per cent protection, and many of the most critical sites for biodiversity lie outside protected areas. Of those protected areas where effectiveness of management has been assessed, 13% were judged to be clearly inadequate, while more than one fifth demonstrated sound management, and the remainder were classed as "basic".
An increasing proportion of global land surface has been designated as protected areas [See Box 7 and Figure 8]. In total, some 12.2% enjoys legal protection, made up of more than 120,000 protected areas. However, the target of protecting at least 10% of each the world's ecological regions - aimed at conserving a representative sample of biodiversity - is very far from being met. Of the 825 terrestrial ecoregions, areas containing a large proportion of shared species and distinct habitat types, only 56% have 10% or more of their area protected [See Figure 10].
The existing protected area network also excludes many locations of special importance to biodiversity. For example, complete legal protection is given to only 26% of Important Bird Areas (IBAs), sites with significant populations of species that are threatened, have restricted geographical ranges, are confined to a single biome, or congregate in large numbers to feed or breed. Of nearly 11,000 IBAs in 218 countries, on average some 39% of their area is included in protected areas. Similarly, only 35% of sites holding the entire population of one or more highly threatened species are fully covered by protected areas [See Box 8 and Figure 9]. However, the proportion of both of these categories of sites under legal protection has increased significantly in recent years.
Clearly, the benefit to biodiversity from protected areas depends critically on how well they are managed. A recent global assessment of management effectiveness has found that of 3,080 protected areas surveyed, only 22% were judged "sound", 13% "clearly inadequate", and 65% demonstrated "basic" management. Common weaknesses identified in the assessment were lack of staff and resources, inadequate community engagement and programmes for research, monitoring and evaluation. Aspects relating to basic establishment of the reserves and maintaining the values of the protected area were found to be quite strong.
Indigenous and local communities play a significant role in conserving very substantial areas of high biodiversity and cultural value.
In addition to officially-designated protected areas, there are many thousand Community Conserved Areas (CCAs) across the world, including sacred forests, wetlands, and landscapes, village lakes, catchment forests, river and coastal stretches and marine areas [See Box 9]. These are natural and/or modified ecosystems of significant value in terms of their biodiversity, cultural significance and ecological services. They are voluntarily conserved by indigenous and local communities, through customary laws or other effective means, and are not usually included in official protected area statistics.
Globally, four to eight million square kilometres (the larger estimate is an area bigger than Australia) are owned or administered by communities. In 18 developing countries with the largest forest cover, over 22% of forests are owned by or reserved for communities. In some of these countries (for example Mexico and Papua New Guinea) the community forests cover 80% of the total. By no means all areas under community control effectively conserved, but a substantial portion are. In fact, some studies show that levels of protection are actually higher under community or indigenous management than under government management alone.