Climate and man as sctructural stability factors of soils. A study along climatological and altitudinal gradients

Abstract

Climate determines the vegetation cover, the hydrological and erosional processes and the soil characteristics, especially his structure. The former, and concretely the aggregate stability has been used as indicator of the degree of ecosystem degradation and the soil erodibility. In the present study the influence of climate on the geomorphologic processes is studied by means of the aggregate stability measurements. Soils developed under different climatic conditions have been selected along climatological-altitudinal gradients in the south-east of the Iberian Peninsula (NW of the Betic Range, Alacant) and the south of Bolivia (Andean Range, Tarija). On both sites, the study was carried out on natural (climax vegetation) and anthropic transects, where cultivated soils in Bolivia and soils degraded by forest fire, clear-cutting and afforestation in Alacant were selected. The results demonstrate that in the natural transect the climate determine the quality of the soil aggregates: the soils developed under wet climates are more stables than the soils developed under arid climates. However, the soils degraded by the human use shows a similar relationship (cultivated fields in Bolivia), or a very complex behaviour due to the different land uses along the transect (anthropic transect, Alacant). As a general conclusion, the human use determines a strong reduction of the aggregates stability in semiarid environments. On the NW of the Betic range and the eastern part of the Andean Range, in the south of Bolivia, the human use results in the degradation of the natural ecosistems due to the reduction of the aggregate stability. Aggregates are more stable under wet than dry conditions.