Determination of the world's humid tropical deforestation rates during the 1990's : methodology and results of the TREES-II research programme

In spite of the importance of the world's humid tropical forests our knowledge concerning their rates of change remains limited (IPCC, 2000). The second phase of a research programme (TREES-II) exploiting the global imaging capabilities of Earth observing satellites has just been completed to provide the latest information on the status of these forests. The results of the TREES II programme show that in 1990 (the Kyoto Protocol baseline year) there were some 1,150 ±54 million hectares of humid tropical forest. Furthermore the 1990-97 period showed a marked reduction of dense and open natural forests: the annual deforestation rate for the humid tropics is estimated at 5.8 ±1.4 million hectares with a further 2.3 ±0.7 million hectares of forest degradation visible from satellite imagery. Large non-forest areas were also re-occupied by forests. But this consists mainly of young re-growth on abandoned land and partly of new plantations, both of which are very different from natural forests in ecological, biophysical and economic terms, and therefore not appropriate in counterbalancing the loss of old growth forests. These new figures are the most consistent currently available. They show that Southeast Asia is the continent where forests are under the highest threat (0.91% annual deforestation rate). The annual area deforested in Latin America is similarly large, but the rate (0.37%) is lower, due to the vast Amazonian forest. The humid forests of Africa are being depleted at a similar rate to that of Latin America. At the global level, these figures indicate a 23% lower net forest cover change rate for the tropical humid forests than was generally accepted until now. This has major repercussions on the calculation of carbon fluxes in the global budget resulting in a terrestrial sink smaller than previously inferred.