Areas deforested in Brazil increased from 152 000 km_ in 1976 to 517 000 km_ in 1996. That figure is the equivalent of the surface area of France. Deforestation is a complex process and involves a host of changing and widely differing situations. The factors behind it are many and varied. They include rising demand for agricultural land, international trade needs for timber and political decisions regarding strategic planning and development.
Researchers of the IRD Space Unit conducted an investigation from January 2000 to December 2002, on deforestation in the Amazon Basin. Their overall procedure is based on the use of remote-sensing data obtained from satellites and aircraft. The approach adopted, termed “descending hierarchical”, often used by geographers, was first applied in French Guiana. It consists in analysing the Amazonian forest cover making the most of a full range of remote-sensing tools which provide means of taking into account the different scales involved. These scales are: the regional scale, studied using satellite images of NOAA-AVHRR and Spot 4 VEGETATION sensors which give coverage of terrains of surface area of 2000 km_; the sub-regional scale, with Landsat and Spot images which provide more detailed data on areas of 185 and 60 km_ respectively; local scale (a few tens of kilometres square observed using aerial photography). Together these tools enabled the researchers were therefore able to demonstrate the size diversity of cleared plots in the Amazon forest, from extensive areas of deforestation like the pioneer fronts of Brazil to the small 1-ha plots epitomized by brushwood plots in French Guiana.
In parallel, the team processed a mass of field measurements and socio-economic data, for French Guiana in particular, in order to calibrate the available aerial or satellite observations, interpret them and place them in the prevailing context. Such socio-economic data take particular account of the land-ownership situation and strategic planning and redevelopment problems. The untimbered areas in Guiana correspond to spontaneous land-take for agriculture often liable to change rapidly and shift geographically, whereas the pioneer fronts in Brazil mark rather government intentions to enhance agricultural potential, expressed as a plan which indeed prompts the clearances and permanent occupation for pastoral purposes.
Marie-Lise Sabrie | alfa
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