Satellite technology yields new forest loss estimates

FAO uses remote sensing survey to track changes

30 November 2011, Rome - A new, satellite-based survey released by the UN Food and Agriculture Organization (FAO) provides a more accurate picture of changes in the world's forests, showing forest land use declined between 1990 and 2005.

The findings of a global remote sensing survey show the world's total forest area in 2005 was 3.69 billion hectares, or 30 percent of the global land area. 

The new findings suggest that the rate of world deforestation averaged 14.5 million hectares per year between 1990 and 2005, which is consistent with previous estimates. Deforestation largely occurred in the tropics, likely attributable to the conversion of tropical forests to agricultural land.

On the other hand, the survey shows that worldwide, the net loss in forest area between 1990 and 2005 was not as great as previously believed, since gains in forest areas are larger than previously estimated.

Net loss — in which losses of forest cover are partially offset by afforestation or natural expansion — totalled 72.9 million hectares, or 32 percent less than the previous figure of 107.4 million hectares, according to the survey. In other words, the planet lost an average of 4.9 million hectares of forest per year, or nearly 10 hectares of forest per minute over the 15-year period.

The new data also show that the net loss of forests increased  from 4.1 million hectares per year between 1990 and 2000 to 6.4 million hectares between 2000 and 2005.

The figures are based on the most comprehensive use yet of high-resolution satellite data to provide a sample of forests worldwide. They differ from previous FAO findings in the Global Forest Resources Assessment 2010 (FRA 2010), which were based on a compilation of country reports that used a wide variety of sources.

"Deforestation is depriving millions of people of forest goods and services that are crucial to rural livelihoods, economic well-being and environmental health," said Eduardo Rojas-Briales, FAO Assistant Director-General for Forestry.

"The new, satellite-based figures give us a more consistent, global picture, over time, of the world's forests. Together with the broad range of information supplied by the country reports, they offer decision-makers at every level more accurate information, and underscore the need for countries and organizations to urgently address and halt the loss of valuable forest ecosystems," Rojas-Briales added.

The remote sensing survey was based on a single source of data for all three points in time — 1990, 2000 and 2005 — and used the same input data and methodology for all countries.

"In terms of change in forest area, the new results update our knowledge for Africa, where previous data for some countries was old or of low quality. Here the remote sensing survey shows a much smaller rate of forest loss than previously estimated based on national reports," Adam Gerrand, an FAO Forestry Officer, said.

Regional losses and gains

There were notable regional differences in forest losses and gains.

Between 1990 and 2005 the loss of forests was highest in the tropics, where just under half of the world's forests are located. Net losses in this region averaged 6.9 million ha/yr between 1990 and 2005. The highest rate of conversion of forest land use to other, unspecified, land uses for both periods was in South America, followed by Africa.

Asia was the only region to show net gains in forest land-use area in both periods.

Deforestation occurred in all regions, including Asia, but the extensive planting that has been reported by several countries in Asia (mainly China) exceeded the forest areas that were lost.

Slight net increases in forest area were registered in subtropical, temperate and boreal zones over the full 15 year period.

Further remote sensing studies are expected to reveal changes occurring since 2005, including any progress which may have been made in the protection of existing forests and the establishment of new forests since 2005.

Global view

The new results provide important input into national and international reporting processes which require information on forest area and land-use change statistics. This includes the Convention for Biodiversity and the emerging initiative for Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD+), under the UN Framework Convention on Climate Change (UNFCCC), currently being discussed at the 17th Conference of the Parties being held in Durban, South Africa (28 November-9 December 2011).

To develop the survey, FAO worked over four years with technical partners in the European Commission Joint Research Centre and more than 200 researchers from 102 countries to analyze satellite imagery from the United States National Aeronautics and Space Administration (NASA) and the United States Geological Survey (USGS).

Funding for the study was provided by the European Commission, the Heinz Center, the governments of Australia, Finland and France and FAO.

Photo: ©FAO/H. Wagner
The world lost nearly ten hectares of forest per minute between 1990 and 2005.