Résumé
In a context of fast land changes due to human activity, the old 'Malthus vs. Boserup' debate about human pressure on natural resources is more than ever a prevalent subject. We illustrate this debate with an example based on the Tuy Province in West Burkina Faso, which has known an important development these last fifteen years, as mainly observable in the major regression of its natural vegetation. The objective of this article is to question the possible future scenarios of this region, by using a spatial model to understand past land change mechanisms and prospect plausible future ways of development. In particular, the spatial model describes the vegetation clearance processes identified during field campaigns, which we used to draw prospective scenarios and assess their possible effect on natural vegetation evolution. The processing of remote sensing images helped us reveal that one quarter of the total study area was cleared during the last fourteen years. Surveys carried out in the field enabled the identification of the three main processes responsible for these changes: farm size expansion, creation of new farms due to family nuclearization and migrant settlement. The model was then built to reproduce these three processes, and was validated by comparison with the land use classification of remote sensing images. Our model was also used to explore past clearance mechanisms: we found that 90% of the clearance was shared equally between farm size expansion and nuclearization processes, the settlement of migrants being responsible for less than 10% of the clearance. Model outputs also showed a shift in the clearance schemes compared to ancient practices: land characteristics are no longer considered when land is cleared and now clearance also occurs in neighbouring villages with available lands. These results suggest that the region has finally evolved similarly to a Malthusian rationale, even if the past dynamics resulted from a complex combination of factors. Finally, we analysed several prospective scenarios to assess the impacts of i) different population evolutions (normal demographic growth, emigrations and demographic regulation), ii) the implementation of protected areas in each village, iii) an intensification of farming systems. Two possible solutions for reducing natural vegetation clearance in the region are discussed: Emigration to other regions or a demographic regulation accompanied with an intensification of agricultural systems. However, the question remains whether such changes can be accomplished rapidly enough to abate the pressing natural vegetation decrease threat and to maintain an acceptable livelihood in the region.