Up-scaling to stand transpiration of an Asian temperate mixed-deciduous forest from single tree sapflow measurements

Abstract

Species diversity in mixed forest stands is one of the factors that complicate up-scaling of transpiration from individual trees to stand level, since tree species are architecturally and functionally different. In this study, thermal dissipation probes were used to measure sap flow in five different tree species in a mixed-deciduous mountain forest in South Korea. Easily measurable tree characteristics that could serve to define individual tree water use among the different species were employed to scale up transpiration from single trees to stand level. Tree water use (TWU) was derived from sap flux density (SFD) and sapwood area (SA). Canopy transpiration E was scaled from TWU while canopy conductance (gc) was computed from E and VPD. SFD, TWU and gc were correlated with tree diameter at breast height (DBH) for all the five measured species (SFD: R 2 = 0.21, P = 0.036; TWU: R 2 = 0.83, P \ 0.001; gc: R 2 = 0.63, P \ 0.001). Maximum stand transpiration (E) during June, before the onset of the Asian monsoon rains, was estimated at 0.97 ± 0.12 mm per day. There was a good (R 2 = 0.94, P \ 0.0001) agreement between measured and estimated E using the relationship between TWU and DBH. Our study shows that using functional models that employ converging traits among species could help in estimating water use in mixed forest stands. Com- pared to SA, DBH is a better scalar for water use of mixed forest stands since it is non-destructive and easily obtainable.