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Biodiversity A Global Outlook

4. At what pace is biodiversity lost?

  • 4.1 How is the extent of forests and other ecosystems changing?
  • 4.2 How is the abundance and distribution of selected species changing?
  • 4.3 What proportion of species is threatened?
  • 4.4 How is genetic diversity of cultivated and domesticated species changing?
  • 4.5 How large are protected areas?

The first focal area of the 2010 framework consists in reducing the rate of loss of the various components of biodiversity at ecosystem, species, and genetic levels. Indicators under this focal area also include trends in protected area coverage and status of threatened species. More...

4.1 How is the extent of forests and other ecosystems changing?

Over the past 50 years, humans have changed ecosystems more rapidly and extensively than in any comparable period of time in human history. For most of the world’s main habitats and ecosystems, the current global extent and rates of change are not known with high certainty, due partly to measuring difficulties. Forests are the exception since they often have direct commercial and/or scientific value. They are thus regularly inventoried and assessed in most countries.

Forests currently cover about 30% of total land area, compared to about 50% before human influences became so extensive. This figure continues to decline due to deforestation, mainly conversion of forests to agricultural land and pasture, which continues at an alarmingly high rate, especially in the tropics. Tree planting, landscape restoration and natural expansion of forests have significantly offset the loss of primary forest area, especially in the temperate parts of the world, but the biodiversity value of forest plantations and secondary forests is generally much lower than that of primary forests. Over the last 15 years, primary forest has been lost or modified at a rate of approximately six million hectares a year and currently make up only one third of total forest area.

General patterns of change in the extent of ecosystems across other biomes besides forests show similar negative trends. For instance, almost 70% of Mediterranean forests, woodlands and scrub, 50% of tropical and sub-tropical grasslands, savannas and shrublands and 30% of desert ecosystems had already been lost by 1990. Coastal and marine ecosystems have also been heavily affected by human activities, with degradation leading to a reduced coverage of kelp forests, seagrasses, mangroves and corals. In the Caribbean, for example, average hard coral cover declined from about 50% to 10% in the last three decades. In addition, there has been a widespread retreat of mountain glaciers in non-polar regions during the 20th century, and decreases of about 10% in the extent of snow cover since the late 1960s. In the Arctic, the average annual sea ice extent has declined by about 8% in the past 30 years.

Achievement of the 2010 Biodiversity Target requires significant slowing of the current rate of reduction of the extent of ecosystems. With regard to forests, a reduction in the current rate of net loss of forest extent would imply increased efforts in re-establishing forests, along with a reduction in the harvesting of forests. At the same time, efforts would need to focus on conserving natural forest area, rather than replacing natural forests with plantations of low biodiversity value. More...

4.2 How is the abundance and distribution of selected species changing?

Trends in abundance and distribution of selected species is an indicator of ecosystem quality and complements information on ecosystem extent. Several assessments have revealed that the population size and/or geographic range of the majority of species assessed is declining.

Trends in some 3,000 wild populations of species show a consistent decline in average species abundance of about 40% between 1970 and 2000; inland water species declined by 50%, while marine and terrestrial species both declined by around 30%. Studies of amphibians globally, African mammals, birds in agricultural lands, British butterflies, Caribbean and Indo-Pacific corals, and commonly harvested fish species show population declines in the majority of species assessed. Exceptions include species that have been protected through specific measures, those that have had their specific threats reduced, and those that tend to thrive in modified landscapes.

Wild populations of species declined on average by about 1.7% per year between 1970 and 2000, and similar trends have been observed for abundant and widespread farmland and forest-dependent bird species throughout Europe.

These studies focus on well-studied groups, mainly vertebrates, and tropical areas, which are rich in species, tend to be underrepresented. Efforts are underway to expand the dataset to include a greater variety of species, especially of plants. More...

4.3 What proportion of species is threatened?

Over the past few hundred years, it is estimated that humans have increased the extinction rate of species by as much as a 1000-fold over the natural rate. Between 12% and 52% of species within well-studied groups such as birds or mammals are threatened with extinction, according to the IUCN Red List of Threatened Species. From this list, an index can be calculated to evaluate the number of species that would remain if no further conservation actions are taken. This index shows a continuing deterioration in the status of bird species, the group for which the most data are available. Preliminary data show that the situation is likely even worse for other major groups, such as amphibians and mammals. More...

4.4 How is genetic diversity of cultivated and domesticated species changing?

The genetic diversity of cultivated and domesticated species is of great importance from a human perspective. Humans use only a very small number of species, and the continuing survival and adaptation of these species to new and changing environmental conditions depends in part on their genetic diversity. In turn human well-being and food security depend on those few species, and failure of a single crop through a plant disease, for example, can have dramatic consequences. Loss of genetic diversity is difficult to quantify, but it is estimated that one third of the 6,500 recognized domesticated animal breeds are threatened with extinction.

In non-cultivated systems, the harvesting of wild species, through logging, fishing, or hunting, can contribute to the loss of genetic diversity. Generally, however, loss of genetic diversity is associated with the decline in population abundance and distribution brought about by habitat destruction and fragmentation. More...

4.5 How large are protected areas?

A key tool to counter the continuing loss of ecosystems and species is the establishment of protected areas. They currently cover about 12% of the Earth’s land surface. There are substantial differences in coverage between different biomes, ecosystems and habitats. For instance, the total surface of protected areas covers only 5% of needle-leaf forests and woodlands, 4.4% of temperate grasslands, 2.2% of lake systems, 1.4% of coastal shelves and 0.6% of oceans.

In about 475 of the planet’s 825 terrestrial ecoregions, less than 10% of the surface is protected. In about 140 ecoregions, it is even less than 1%.

The growth in number and area of protected areas is a fairly crude indicator in itself, and needs to be complemented by further information on the level of protection afforded to biodiversity and the effectiveness of management. The role of protected areas in reducing the rate of loss of biodiversity is not yet fully understood because systematic data are lacking. More...

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