Species-specific tree water use characteristics in reforestation stands in the Philippines

Reforestation in the tropics offers opportunities for restoration of ecosystem services, biodiversity conservation, wood production and carbon sequestration. The potentially high water use rates associated with reforestations will however require that a balance is found between wood production or carbon fixation and the use of water resources. Species selection has been put forward as a measure to control tree water use of reforested stands but species-specific information is at present very limited. We studied ten broad-leaved tree species in 12-year-old reforestations on Leyte island, the Philippines. Objectives were (1) to identify environmental and tree structural controls on water use and (2) to test for differences in water use characteristics across species. The studied species included eight native species, four of which were dipterocarps, and two species not native to the region but widely planted in the tropics. Per species five well-exposed individuals were equipped with thermal dissipation probes to measure sap flux density. A Jarvis-type model, with global radiation and vapour pressure deficit as explanatory variables, was applied at the tree level and successfully predicted measured sap flux densities. The model parameters suggested significant species differences in maximum sap flux density, differing twofold across species, as well as in sap flux response to environmental variables. Maximum transpiration rates per unit crown area varied up to a factor of four across species. Maximum water use rates were strongly related to tree diameter (Radj2=0.65) and weaker, though significant, to estimated aboveground biomass (Radj2=0.34). Despite its size dependence, tree water use rates differed about twofold for a given diameter or biomass depending on species, which leads us to conclude that species selection indeed offers opportunities to control tree water use in reforested stands.