Sap flow measurements have long been used to measure transpiration in individual trees and there exist some well established methods for upscaling individual tree volumetric transpiration to areal transpiration in plantation and forest plots. However, where edge effects are significant, such as in tree belts, the area the volumetric transpiration is to be projected upon is unknown. This paper provides a methodology for estimaing the area that a tree belt hydrologically occupies by using either measurements of tree root density or soil moisture distribution. An application of the proposed methodology shows that simply assuming that the area of the tree belt is the crown projected area could lead to an overestimation of the areal transpiration of 100%.
Crosbie, R. S., Wilson, B., Hughes, J., & McCulloch, C. (2007). The upscaling of transpiration from individual trees to areal transpiration in tree belts. Plant and Soil, 305(1-2), 25-34. https://doi.org/10.1007/s11104-007-9420-4