Agroforestry: hydrological impacts

In addition to their social and economic value, forests and agroforestry (AF) have been widely promoted as a viable solution to overcome the loss of ecosystem functions associated with the conversion of natural landscapes for human use (Jose,2009). AF systems vary in the density and configuration of trees in farming landscapes from a few scattered trees or line plantings to dense and complex agro forests. However, the relationship between tree cover and water supply is not straightforward and forest/agriculture policies are often at odds with scientific understanding. In the tropics, forest/farming and water policies were often based on the assumption that tree-covered landscapes are the most appropriate way to maximize water yield, regulate seasonal flows, and ensure high water quality under all hydrological and ecological situations (Calder et al., 2007). According to this assumption, conserving or extending tree cover in upstream watersheds is the most effective way to enhance water availability for agricultural, industrial, and domestic use and prevent floods in downstream areas. Various national agencies, often with international confounding, are spending vast sums of money on tree planting and soil conservation efforts based on the belief that ‘more trees mean more water’.

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