Effects of afforestation and vegetation dynamics on soil erosion in a semi-arid environment (SE Spain)

摘要

Management policies in Mediterranean areas have traditionally encouraged the establishment of tree cover, in order to increase the complexity of the vegetation structure. To evaluate the effectiveness of these management policies, we studied the role of six vegetation cover types over 4 hydrological years (1995/96-1998/99) in 22 hydrological plots (8x2 m~2). In the Ventos-Agost catchment (Alicante, Spain). Each of the six types represented different stages of successional pathways and afforestation actions that had been found in semi-arid Spain: bare land (B), dry grassland (Dg), shrubland (S), afforested dry grassland with Aleppo pine (Ag), afforested shrubland with Aleppo pine (As) and Alpha grass steppe (St). The results suggest that shrubby or herbaceous vegetation could control runoff and sediment yield as effectively as trees. Runoff rates of As, Ag, S and Dg plots were less than 1% of the precipitation volume. Runoff in Alpha grass steppes and denuded areas were 2% and 4%, respectively. Soil losses in vegetated plots averaged 0.04 t.ha~(-1)y~(-1) and increased 25-fold in bare areas. The results from the studied vegetation cover types along the successional pathways and possible management policies shows that the afforestation with a Pinus halepensis stratum do not reduces significantly the erosion in comparison to the natural succession stages. The restoration of the semi-arid ecosystems with autochthonous shrub species can be a useful method for the reduction of soil erosion effects.