Watershed functions in productive agricultural landscapes with trees

Watershed functions are often discussed in terms of deforestation and reforestation, but require a more careful diagnosis of problems and solutions. Criteria and indicators that are based on the quantity, tim-ing and quality of river flows are influenced by a combination of effects, including the green and brown cover provided by plant canopies and surface litter layers, the soil surface properties and soil structure, and the landscape-level drainage network. Opportunities for agroforestry and other forms of conserva-tion farming to maintain and restore watershed functions are dependent on the relatively rapid options for restoring green and brown cover, the asymmetric (rapid degradation, slow recovery) dynamics of soil structure and on modification of landscape-level drainage. Data for the watersheds of Mae Chaem in northern Thailand and Way Besai in Lampung, Indonesia, indicate that land-cover change has a relatively small effect on low river flow. We focus here on the changes in soil structure as the ‘slow vari-able’ that tends to dominate the long-term opportunities for keeping watersheds productive as well as suppliers of quality water at the desired time

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