干旱区生态环境知识资源中心

The fragile soils at the transition between semiarid and arid areas are continuously threatened by human activity, which frequently involves the elimination of plant cover. We studied the impact of vegetation removal on soil characteristics in semiarid Mediterranean Spain using two plots (15 m x 5 m), installed on a north facing slope of 23%. Vegetation was removed from one of the plots (disturbed plot), and changes in the soil characteristics were compared with an undisturbed control plot. Fifty-five months after vegetation removal the organic carbon content decreased by 35%, the percentage of stable aggregates by 31% and soil bulk density increased by 8%. The models that best represented the changes of these parameters with time were linear equations. There were no significant differences between the water retention capacity or saturated hydraulic conductivity of the treatments. The rapid loss of soil organic matter and the consequences in terms of physical soil properties were considered to be the main factors in soil degradation. No symptoms of natural recovery were observed in the disturbed plot and the tendency was for a steady deterioration in soil behaviour. This means that human activity or climatic change leading to less vegetation could result in irreversible soil degradation in semiarid areas.