Organic carbon and nitrogen losses influenced by vegetation removal in a semiarid mediterranean soil

A reduction in plant cover can lead to an increase in the erosion processes that diminish soil quality. Any rise in temperature resulting from predicted climate changes may aggravate this effect, particularly in semiarid Mediterranean areas. Bearing this in mind, the capacity of a soil to preserve organic matter becomes very important if the soil is to maintain its physical and chemical properties. Soil organic carbon and nitrogen changes were evaluated in a non-disturbed (with natural vegetation) and a disturbed (all vegetation manually clipped to ground level) pine system. Nine years after vegetation removal significant differences (p < 0.01) were found in the soil organic carbon content between plots (top 20 cm), but not in total nitrogen. In the disturbed plot 0.0232 Mg ha(-1) y(-1) of soil organic carbon were lost through erosion and 4.30 Mg ha(-1) y(-1) through mineralization. In the first 48 months after vegetation removal the soil organic carbon content fell from 40.3 to 28.0 g kg(-1). In the last 60 months of the experiment the amount of organic carbon in the soil fell from 28.0 to 27.7 g kg(-1). This result was mainly attributable to the intense oxidization, which took place during the first 60 months, of organic matter linked to the coarse soil mineral fraction. Up to the 72(nd) month the losses by erosion were a total of 532.7 g, which rose to 1284.4 g by the end of the experiment (108 months). The effect of vegetation removal in a Mediterranean semiarid area leads to a rapid decline in the amount of organic carbon stored in the soil. Such perturbation is irreversible if left to nature.