Assessing farmland dynamics and land degradation on Sahelian landscapes using remotely sensed and socioeconomic data

Through the integration of SPOT HRV, biophysical and socioeconomic informat ion, the study identified population carrying capacities and their vulnerab ility to land degradation. Land use intensification on the landscapes was q uantified into expansion, early and late phases based on the Ruthenberg ind ex calculated using a biennial series of SPOT images for the period 1986-96 . Subsequently, farmland dynamic on different landscapes was calculated whi le observed patterns were linked with agricultural intensification and popu lation carrying capacity. Results show a pattern of agricultural land degra dation due to increasing pressure of population and agricultural intensific ation within a system characterised by little or no use of inputs. Fifty-si x percent of the study area supports a population density higher than the c arrying capacity (less than or equal to 15 pers/km(-2)). Sixty-three percen t of the study area is under early to late phases of agricultural intensifi cation. Between 1986-96, cultivation declined 2-3% annually on landscapes w ith Low risk of degradation but increased by 1-2% on those with Average/Ext reme risks. This emphasises the process of land abandonment as farmers move on to cultivating marginal lands despite above normal seasonal rainfalls o bserved during most of the period. By 1996, cultivation tended to include f ields much farther away from the vicinity of villages, compared with 10 yea rs earlier. Furthermore, by 1996, farmlands in the zones of late intensific ation declined from 12 to 4% and increased from 6 to 11% in the zone under the expansion phase. Indicating that by 1996 substantial amount of the land area required increasing lengths of fallowing. The spatial GIS modelling a pproach allowed not only identification of zones but synthesis of the obser ved pattern of landscape degradation. The paper highlights the need for com bining remote sensing, biophysical and socio-economic data in environmental degradation studies in developing countries with their poor data availabil ity. The role of developing countries scientists is stressed in taking the forefront to tackle environmental problems, which affect their region. The paper calls for increased co-operation between these scientists and regiona l and international data providers to overcome data availability problems a nd pave the way for better local and regional studies on environmental degr adation.