Agroforestry and watershed functions of tropical land use mosaics

An ‘ecohydrology’ approach involves more than a focus on the degree of forest cover in the upper watersheds, as the quantity, timing and quality of water flows is determined by the land cover and land use in the whole landscape. We discuss the different perceptions that still exist on the special relations between ‘forest’ and ‘watershed functions’ and consider which specific function is relevant for whom. Land use change can modify the evapotranspiration and hence the total water yield of a catchment, but also the pathways that water will take and hence the amount of soil particles, nutrients, agrochemicals and (in arid regions) salt that it will carry downstream. Evenness of river flow is influenced by the infiltration rates in the landscape if small areas are considered. Partial spatial independence of rainfall becomes a dominant explanation of ‘evenness of flow’ when larger areas are considered, reducing the relative importance of land use. Agroforestry options for the riparian zone can have a major impact on the water quality and evenness of flow perceived downstream, probably exceeding the importance of forest cover in upper watersheds.

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