The assessment consisted of the following three steps: (1) establishment of a computerized database; (2) development of a deforestation model (or an adjustment function); and (3) computation of results for the standard reference years.
The source data consisted of two categories:
Tabular data including forest resources, population and socio-economic variables at the sub-national level (province, state).
The Guidelines for assessment based on existing data were prepared in the three official FAO languages to compile the country statistics and bring them in a framework of common concepts and classifications. Using the guidelines, the available country reports were reviewed and reliable information extracted, edited and stored as part of the Project database: “FORIS” which stands for Forest Resources Information System.
At present the FORIS database contains data for tropical and non-tropical developing countries using a common classification system. In future also the data for developed countries will be integrated in FORIS in order to build a time-series of a global forest resources information.
Map data including vegetation types, ecofloristic zones and country and sub-national boundaries
Realizing that deforestation is a location-specific process driven by, among others, population pressure and environmental conditions (particularly the population carrying capacity of the area), demographic and ecological parameters were included in the database and integrated with the statistical data in the form of a GIS.
Presently the FAO GIS database contains vegetation and ecological zone maps of the Northern, Southern Africa and Southern America Sub-regions. Data for the Middle East and Temperate Asia sub-regions were obtained through area calculation using existing bio-climatic maps. No GIS database is available for these subregions.
The forest cover area contained in FORIS refer to different periods and need to be brought for reporting purposes to the standard years, namely 1980 and 1990. This was done with the help of a forest area adjustment function (syn. deforestation model) which correlates forest cover change in time with other variables including population density and population growth for the corresponding period, initial forest cover area and the ecological zone under consideration. Ideally, time-series provide the basis for developing the model data at the sub-national level.
For the non-tropical zone, as pointed out earlier, multi-date data were available only for 4 countries and it was not possible to derive a general equation based on existing information. It was, therefore, decided to use a cross-sectional analysis using forest cover as dependent variable and population density and ecological conditions as independent variables. The available observations were used to build 5 sub-regional regression models, one for each sub-region. Annex 2 gives a detailed description of the technique used and results obtained.
Deforestation in the non-tropical zone, in general, follows the pattern of relation between forest cover and population, as observed for dry and very dry areas of the tropics (see figure 1)
Figure 1
Illustration of model curves for different ecological zones
The FORIS, in conjunction with the model, is used: (i) to adjust forest cover area data of the sub-national units to the standard reference year 1990; and (ii) to produce estimates of the forest cover area change over the period 1981 to 1990. For these purposes the most recent forest inventory data of a national/sub-national unit are used as baseline, and forest cover area in 1980 and 1990 (standardized results) estimated using the model coefficients computed for each sub region.
The estimated values at sub-national level are aggregated at national, regional and global levels. Keeping in view the law of propagation of errors the global estimates are expected to be more precise than the sub-regional; and the sub-regional estimates more precise than the national and sub-national estimates.
