Variability of Sapflow in a Pinus Radiata Plantation and the Robust Estimation of Transpiration

Abstract

The spatial and temporal variability in heat pulse estimates of sapflow within and among 8-year-old plantation radiata pine trees in southeastern Australia is examined with an aim to establish sampling requirements and strategies associated with estimating transpiration from a population (stand) of trees. Sampling variability in sapwood velocity profiles within a tree did not contribute to a large sampling error in flux. Sapflow velocities at varying depths within the sapwood were highly correlated over several days. Following a short period necessary to characterize the nature of the velocity profile, velocity at any one depth was adequate for flux estimation. Fluxes varied widely among trees, necessitating large sample sizes for estimating stand transpiration at a reasonable level of precision and confidence. Variation in flux among trees was not explainable in terms of differences in tree size or spacing. The temporal patterns in the fluxes among trees were in close synchrony, indicating that a meaningful mean stand flux can be estimated from a single tree once this pattern of variation is determined. These findings suggest that following a short period of characterization of the patterns of sapflow movements within and among individual trees, scarce sampling resources may be reallocated to provide a more robust measure of stand transpiration.