International Geographical Congress edition:32 location:Köln, Germany date:26-30 August 2012
In human-modified landscapes, land use/-cover change may have a profound effect on riverine water and sediment fluxes. The effect of forest cover on water yields has been demonstrated for small catchments where natural vegetation was removed and/or replaced by plantation forests. Little is known about disturbed ecosystems where forest plantations have been established on highly degraded land. In this paper, we analyse the hydrological response to complex forest cover change for a highly degraded Andean catchment. The land cover analysis (1963-2007) indicates different pathways of change : deforestation, reforestation, and spontaneous recovery. Forest cover changes occur in spatially distinct regions, with deforestation taking place in remote uplands and recovery and reforestation were particularly important in the lower parts where agricultural and bare lands are prevalent. There was a net average loss of native forests of ca. 45.5 ha y-1, and 74% of the total deforestation results from conversion from native forests to agricultural land. The total area of 'bare land' decreased with 28 ha y-1. Time series analyses of streamflow and rainfall data (1979-2007) indicate that the removal of native forest (by -22%) has contributed to the increase in total annual water yield, through an increase in annual baseflow by 25mm. The observed changes in extreme events are important as the maximum daily runoff decreased by ca. 5 mm despite somewhat higher daily rainfall amounts. The observed decrease in peakflows cannot be explained by clearcut of native forest, as the effect of deforestation on surface runoff generation is limited. This reduction is, on the contrary, related to reforestation of degraded lands to exotic forest plantations as well as spontaneous recovery of vegetation on remaining grazing lands.