Updated July 1999
The association between human population dynamics and deforestation has been studied at various geographic levels and in various ecological and human contexts. We refer here to the Forest Resources Assessment (FRA) 1990 project conducted by FAO, the purposes of which were:
At an elementary level, it is obvious that there must be an inverse correlation between population density and forest cover: as soon as humans build shelters and housing, they need to clear the wooded areas if these are present. If in addition they engage in agricultural activities, they need even more land per caput. In a dynamic perspective, this implies a relationship between population growth and deforestation. However, the intensity of that relationship can vary considerably, because it is mediated by a series of socio-cultural, economic and ecological factors. Hence the differences among populations as to the response to population growth in terms of extension (versus densification) of human settlements, extension (versus intensification) of agriculture, etc.
Better understanding the connection between population expansion and other factors in the process of deforestation in Brazil is important because that country holds a key position in the global picture of forest resources. In fact, the forest area lost annually in Brazil accounts for approximately one fourth of total tropical deforestation. However, population data available to FRA 1990 for matching with forest resources data were compiled at the state level, which is too broad to help describe in detail and better understand the population-forest interactions . Therefore a separate effort was made in co-operation with Brazilian institutions to collect, and match, population data and forest cover data at the lowest administrative level (municipio). Building a detailed data set was of great relevance also in view of the rapid changes in forest cover that affect these regions, which may go virtually unnoticed in large-scale statistics.
New demographic time series and population maps were established for 138 spatial units. Inside Legal Amazon those units were municipios, the smallest administrative unit (groups of municipios, in high population density areas). Outside Legal Amazon the state level was maintained. At the same time an adequate data set and related maps of forest cover and forest change for the same units was undertaken; this required a considerable amount of GIS work using all available statistical and spatial information. The two sets of data were integrated into the Forest Resources Spatial and Statistical Information System (FORESSIS) of the FRA 1990 Project.
The deforestation model was then applied to the new data sets. The model in its general form is used to estimate forest area change at pan-tropical level. In this case, local observations of forest area and population change were used as to the inputs with the local value of the b1 parameter calculated for each unit. This enabled the interpolation of forest cover data for 1980 and 1990, and subsequently extrapolating them to 2000 using population projections.
Figure 2 shows the scattergram of the 138 units for forest cover and population density in 1991. There is a strong similarity between this distribution and the curve shown in Figure 1 for wet ecological zones.
The results consisted of time series of forest area change for each of the 138 units of the new data set. These results are illustrated by Figure 3. The maps show for each unit [a] the observed and projected deforestation rates for the periods 1980-1990 and 1990-2000, and [b] the deforestation trend (acceleration or deceleration) resulting from the comparison of the two decennial rates.
The information thus generated enables a more precise identification of the areas most at risk of deforestation - taking into account projected population growth - hence a better targeting of policy interventions. Without going into details here, the above maps show for instance that central Amazon - which was relatively unaffected during the 1980-1990 decade - is now undergoing an acceleration of the deforestation process.
The work done can serve also as a basis for adequately stratifying area samples in future studies where the pace of deforestation, or/and the rate of population growth, are relevant factors.