Monitoring land-cover changes in semi-arid regions: remote sensing data and field observations in the Ferlo, Senegal

Dryland degradation rarely translates into linear, declining trends in vege tation cover due to interannual climatic variability. Appropriate indicator s of land-cover modifications need to be defined for semi-arid regions. Our hypothesis is that degradation can be measured by: (1) a decrease in the r esilience of vegetation to droughts; (2) a decrease in rain-use efficiency; and (3) a modification of floristic composition. The objective of this pap er is to test the relationships between a remotely sensed indicator of vege tation, rainfall data and field measurements of biomass and floristic compo sition. The study was based on field measurements of vegetation conditions covering a period of 10 years, in the semi-arid region of the Ferlo in Sene gal. Our results indicate that land-cover modifications in the Ferlo are be st measured by changes in rain-use efficiency. No consistent trend in the r elative abundance of grass species was visible at the scale of the decade, even on the two sites affected by degradation. Just after a drought, a give n increase in rainfall results in less biomass production than is the case for normal years. (C) 2001 Academic Press.