The most significant change in Senegal is the evolving extent of cultivated areas. The overall expansion of cropland is relatively small, from 32,600 sq km in 1975 to 32,900 sq km in 2000 and 41,000 sq km in 2013, or a 26 percent increase between 1975 and 2013. However, the recent pattern and extent of cropland is profoundly modifying Senegal’s landscapes. Agricultural expansion has resulted in fragmentation of the savannas and woodlands, replacing unbroken expanses of natural habitat with a mosaic of tilled fields and natural landscapes, eroding the quality of remaining natural ecosystems. Furthermore, the speed of agricultural expansion has increased between 2000 and 2013 compared to the previous 25 years. While the average annual increase of cultivated areas was modest between 1975 and 2000 (about 10 sq km per year), it rose dramatically between 2000 and 2013, to 630 sq km on average per year. This trend, however, masks much of the internal variation within the agricultural class.
In contrast to other regions of Senegal, the Peanut Basin experienced abandonment of agricultural lands in the 1980s. In the Peanut Basin, land devoted to rainfed crops remained fairly stable between 1975 and 2000. While agricultural expansion continued to make inroads in the east, in the west cropland was being abandoned, reverting to grasslands that were mapped as savannas in 2013. This conversion of cropland back to grassland in the Peanut Basin hides the actual magnitude of rapid agricultural land increases in central Senegal. The very low price of peanuts forced many farmers to abandon their fields and turn to other economic activities, which often meant moving to Dakar, Touba, or other cities.
As in central Senegal, most of the south experienced major gains in agricultural area at the expense of savannas and woodlands, especially in the Casamance. As a result of agricultural expansion, Sahelian and Sudanian savannas have decreased by 8,200 sq km, or a 6.3 percent reduction of their 1975 area. Woodlands decreased by 42 percent, or 3,160 sq km. Gallery forests, which are found along much of Senegal’s drainage network and known for their biodiversity, registered a decrease of o19 percent. However, most of the reduction of gallery forests appears to have occurred before 1975 (Tappan and others, 2004).
Wetlands and floodplain increased by 17 percent, due mainly to the recovery of wetlands from the severe drought of the 1970s, which dried out many wetlands. Since the end of the 1990s, rainfall continues to fluctuate annually, but it has returned to levels more consistent with the longer term norm.
In the north, there are many local instances of savannas taking on steppe-like characteristics as years of drought, intensive grazing, and loss of topsoil combine to degrade the savanna structure, vegetation cover, and productivity. The maps reflect this process, with steppes replacing local areas of savanna in agro-pastoral regions (a 760 sq km gain between 1975 and 2013). Similarly, in more extreme cases of drought-induced loss of vegetation cover, overgrazing, and soil erosion, savannas or steppes become bare and unproductive, even in the rainy season. These areas are mapped as bare soils. The area of bare soil increased significantly, by 42 percent between 1975 and 2013, especially in the Pastoral Ferruginous Zone. This trend was confirmed by field studies, which also documented the expansion of the badlands along fossil valleys where severe erosion has removed the topsoil. On a positive note, the decrease of sandy surfaces (-144 sq km between 1975 and 2013) can be explained by the success of coastal dune reforestation and stabilization efforts.
Finally, the large expansion of settlements — villages, towns and cities — illustrates the rapid population increase in Senegal, particularly in the big cities of Dakar and Touba. While the population tripled between 1975 and 2013, the area occupied by towns and cities grew from 530 sq km in 1975 to 850 sq km in 2000 and to 1,450 sq km in 2013, or a 172 percent increase over 38 years.