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

Rainforest transformation alters ecosystem water cycles with respect to the magnitude of fluxes, their spatial heterogeneity and their temporal variability. In the first study period, the focus was on mean stand transpiration rates in forests, jungle rubber and rubber and oil palm monocultures on upland sites. We used a sap flux method with an adjustment for the assessment of oil palms. The estimated transpiration by oil palm plantations was almost as high as by forests; it was lower in rubber plantations. The day-today fluctuation of transpiration was much lower in oil palms than in forest trees. In the next study period, we want to address in more detail the variability in plant water use across sites as well as mechanisms controlling tree and palm water use. The sites will comprise the core plots including the riparian sites, the biodiversity enrichment experiment and the oil palm management experiment. Regarding the mechanisms controlling plant water use, we plan to study the importance of stem water storage dynamics for plant water use. The methods include different sap flux techniques, which are foreseen for a high number of replicates (Granier-type thermal dissipation probes) and particular organs such as the roots in the study of the stem water storage (heat ratio method). Further, we plan to screen canopy leaf temperatures from an unmanned aerial vehicle to provide a tool for the rapid assessment of tree and palm water use characteristics. The study may thus lead to a better evaluation and understanding of changes in tree and palm water use characteristics as a consequence of rainforest transformation.