The impact of changing agroforestry mosaics on catchment water yield and quality in Southeast Asia

• Bogor Agricultural University, Indonesia
• CSIRO Land and Water, Australia
• Chiang Mai University, Thailand
• Lampung University, Indonesia
• Forest and Nature Conservation Research and Development Centre, Indonesia
• Australian National University, Australia
• Center for Soil and Agroclimate Research, Indonesia
• Brawijaya University, Indonesia
• National University of Singapore, Singapore

Forest conversion in much of the uplands of Southeast Asia has resulted in a gradual loss of forest functions as the landscapes evolve into mosaics of agriculture, agroforestry and forest remnants. Inappropriate policies have frequently fuelled disputes about use of land for forest or agriculture, leading to unnecessary conflict between upland and lowland farmers. Thousands of poor communities inhabiting upland watersheds are blamed for the destruction of forests and associated hydrological functions that affect communities downstream. This has led to restrictions on land use, and there is little chance of secure land tenure for such communities.

Research is needed to gain greater understanding of the watershed hydrology in these agroforestry landscape mosaics and to use the knowledge to develop more equitable policies and practices for upland farmers. This project will test the hypothesis that some farmer-developed agroforestry mosaics are as effective as the original forest cover in protecting water yield and water quality.

This project will study selected watersheds to characterise current land use and ongoing trends in land-use change, and determine their effects on filter functions and overall impacts on water quantity, seasonal effects and sediment loads. Studies will also test soil and water movement in landscape mosaics at catchment scale; quantify the trade-off between watershed functions and profitability of land use for current and possible future land-use mosaics, and explore alternative practices through farmer participation.

A number of models (some well tested, others under development) will serve as research tools, as internal communication tools (clarifying assumptions, gaps in data and knowledge, (dis)agreement between expectations and observations), as a source of visualisations and summary results for external communication, and as project output. It is anticipated that the 'catchment modelling toolkit' developed within the CRC for Catchment Hydrology will provide the basis for much of the modelling carried out in this project. This toolkit comprises a number of modules that can be linked together in different ways to develop a catchment-scale model of appropriate complexity. The degree of complexity considered appropriate is determined by the input data availability, purpose, and who will be end-users of the model.

It is anticipated that fairly simple models will suffice in this study. This is because the input data availability is low, the purpose of the model is to evaluate the impact of alternative scenarios (rather than providing quantitative fits to observational data), and the end-users of the model (catchment managers in Indonesia and Thailand) will have limited knowledge of catchment processes. As some of the models are intended for future use by catchment managers special attention will be given to tailoring the user interface for user-friendliness and training the end-users. All models must be adaptable for incorporating the negotiation support system that will be the main implementation pathway for this project.