SEDIMENT YIELD UNDER DIFFERENT LAND USES IN THE SPANISH PYRENEES

The effects of different land uses on soil conservation and sediment yield were studied by means of experimental plots and other direct and indirect evidence in the Central Spanish Pyrenees. The purpose was to compare the traditional land uses with the present ones, in order to explain some of the landscape characteristics and, especially, the state of soil conservation. The work attempts to identify the land uses that contribute more to the sustainability of a mountain area affected by significant and generalized land-use changes in recent decades. The results obtained suggest that the traditional cereal agriculture greatly contributes to soil erosion and responds rapidly to precipitation. This probably accounts for the state of damage of many soils used for cereal cultivation over many centuries. Meadows yield much water and few sediments, and dense shrub cover yields very little water and very few sediments. The burning of the dense shrub cover produces a sudden increase in runoff and erosion, although a few months later sediment yield reverts back to rates similar to those prevailing before the fire. Now, the reduction of the area of cultivated land, the abandonment of shifting agriculture, the replacement of cereals by meadows, and the expansion of bushes in the former cultivated fields will cause a decrease in sediment yield.