During the years 1991 – 1995, in the framework of the Forest resources Assessment 1990, FAO carried out a pan-tropical survey for an independent assessment of forest cover, deforestation rates and to study the associated processes of change1. This survey covered, with 10 percent intensity, all tropical forests in wet, moist and dry conditions. The survey was based on a statistical sample composed by multi-temporal satellite images over 117 sampling units (Figure 1). For each unit the study included the analysis of one entire Landsat image close to year 1990 and one (or more) close to year 1980.
The results of this survey confirmed the pan-tropical estimates of forest cover and deforestation rates produced by the complementary component of FRA 1990 that used all reliable forest information produced by countries.
For what purpose has FAO undertaken the remote sensing survey of tropical regions?
The need for an independent survey was felt for the first time during FRA 1990, as a consequence of the experience gained during the collection, harmonization and standardization of existing country data. The global concern on the faith of world’s forests called for new, deeper knowledge on the processes of depletion, but the global synthesis of the heterogeneous mass of existing information could only lead to much needed albeit crude estimates of national forest area and deforestation rate. Statistics that are unable to inform, alone, on the processes and cause-effect mechanisms associated to forest depletion.
In this context, an independent forest/land cover survey was seen as an essential input of consistent information over the entire tropical regions to complement the country data already produced. Consistent in space, all regions analyzed following a standard method and classification scheme, and consistent in time, focused on the reliable assessment of land cover changes. The need was not to produce a new estimation of tropical deforestation but rather to describe the processes, inside and outside the forest, associated to deforestation, forest degradation, fragmentation, etc. Monitoring as a tool to understand on-going land cover change processes rather than a pure estimation of deforestation rates.
The main contribution of the remote sensing survey has been the first consistent description of the processes of change, at pan-tropical, regional and ecological level, in form of transition matrices and flux diagrams. From these matrices and diagrams several forms of depletion could be differentiated (deforestation, degradation, fragmentation, shifting cultivation, etc.), and important elements of cause-effect could be disclosed. A step forward toward the understanding of a complex phenomenon rather than a simple estimation of deforestation rates.
Figure 1: Pan-tropical forest survey. Distribution of Sampling Units
In the framework of FRA 2000 the scope of the remote sensing survey has grown in ambition. In fact, by adding one series of new observations the survey will update the 1980-1990 information produced during FRA 1990 to the period 1990-2000 and, through the comparison of the two periods, produce the first assessment of trends. Trends of deforestation, degradation, fragmentation rates as well as trends in the associated/causal processes.
In consideration of FRA 1990 experience and the resulting recommendations, and in view of time and cost implications related to the immediate FRA 2000 needs, a two-phase approach for the implementation of the remote sensing component of FRA Programme have been adopted. This approach takes into consideration the needs of FRA2000, as well as future global assessments. The phases are the following:
Since 1996, FAO has worked toward the development of a global continuous monitoring programme, now called World Forest Survey (WFS). This programme follows the same principles of the FRA 1990 survey but it is intended to extend a statistical sample over the entire world following new stratification criteria to improve its efficiency. At present, due to several technical and financial considerations oriented to satisfy both the immediate FRA 2000 requirements as well as the need to meet the global challenge beyond 2000, a phase-in of the long-term World Forest Survey is being envisioned along with the implementation of the 2000 Update for the year 2000 assessment.
1 This activity was a multi-donor trust fund and a major global cooperative effort coordinated by the Forest Resources Assessment 1990 Project. Methodology, activities and results of the survey are published in Forestry Paper 130 “Forest Resources Assessment 1990 – Survey of Tropical Forest Cover and Study of Change Processes”, FAO, 1996.
