A02 - Tree and palm water use characteristics in rainforest transformation systems

Following large-scale conversion of rainforest, rubber and oil palm plantations are becoming dominant land-use types in lowland Sumatra and other tropical regions, with potentially far-reaching ecohydrological consequences. We assessed how the land-use change trajectory from forest to rubber and then to oil palm affects plant transpiration using sap flux measurements. From forest to rubber monoculture, transpiration decreases by 43%, but rebounds after conversion to oil palm plantations. Our data suggest that particularly intensive oil palm cultivation leads to high transpiration, substantially surpassing rates at our forest sites. For prediction and rapid assessment of plant water use and evapotranspiration, we tested two drone-based methods. Photogrammetry derived crown volumes explained the observed spatial variability in tree and palm water use very well. Thermal imagery based modelling of evapotranspiration yielded high temporal agreement with eddy covariance measurements for an oil palm plantation. We think that such airborne methods offer promising opportunities for analyses of evapotranspiration at a higher number of study sites and at a high spatial resolution. Our objectives for phase 3 are to assess landscape-scale variability and to identify spatial controls of evapotranspiration. We will test hypotheses regarding the importance of vegetation structure, soil characteristics, landscape position and management intensity. Our methods spectrum will include drone-based thermography and photogrammetry, and leaf area index assessments from the ground. Anticipated study sites are the Landscape Assessment, the B11 Oil Palm Biodiversity Enrichment Experiment and the Oil Palm Management Experiment. This study shall contribute to an improved understanding of controls of evapotranspiration, and an overall synthesis by addressing trade-offs between land use and ecosystem services.