Transpiration on the rebound in lowland Sumatra

Following large-scale conversion of rainforest, rubber and oil palm plantations dominate lowland Sumatra
(Indonesia) and other parts of South East Asia today, with potentially far-reaching ecohydrological consequences.
We assessed how such land-use change affects plant transpiration by sap flux measurements at 42
sites in selectively logged rainforests, agroforests and rubber and oil palm monoculture plantations in the
lowlands of Sumatra. Site-to-site variability in stand-scale transpiration and tree-level water use were explained
by stand structure, productivity, soil properties and plantation age. Along a land-use change trajectory forestrubber-
oil palm, time-averaged transpiration decreases by 43 ± 11% from forest to rubber monoculture
plantations, but rebounds with conversion to smallholder oil palm plantations. We uncovered that particularly
commercial, intensive oil palm cultivation leads to high transpiration (827 ± 77mm yr−1), substantially surpassing
rates at our forest sites (589 ± 52mm yr−1). Compared to smallholder oil palm, land-use intensification
leads to 1.7-times higher transpiration in commercial plantations. Combined with severe soil degradation, the
high transpiration may cause periodical water scarcity for humans in oil palm-dominated landscapes. As oil palm
is projected to further expand, severe shifts in water cycling after land-cover change and water scarcity due to
land-use intensification may become more widespread.