Conversion of matorral land to Pinus forest : some hydrological and erosional impacts / Reboisement de matorral en Pinus : quelques impacts hydrologiques et érosifs

Abstract

Bench terracing and Pinus afforestation of land under matorral vegetation carried out as part of a soil conservation scheme in central Spain, was found to have major impacts on overland flow generation and soil erosion. Minimal overland flow and soil losses occurred under dense undisturbed «Cistus matorral», although localized disturbance of the vegetation gave rise to high erosional losses. Within the bench terraced area overland flow volumes were very high with annual runoff coefficients ranging from 4,5% where trees were well established to 21% on a poorly vegetated plot. Annual erosional losses on bench terraced areas with poor tree growth were the equivalent of 100 to 3,500 years of erosion under undisturbed matorral, and provide a good measure of erosion in the early years following land use conversion. Soil factors, in particular soil moisture, porosity, permeability and aggregate stability are of major importance in understanding the hydrological and erosional response of the matorral and the Pinus afforested land. It is proposed that the management of mature matorral vegetation communities may provide a more effective soil conservation strategy than bench terraced conifer afforestation.