A new method for measuring stand sapwood area in forests

Abstract

Abstract We introduce a novel methodology for measuring stand sapwood area (SA), which provides a useful indicator of evapotranspiration from forest stands. The method is demonstrated in a 73‐year‐old Eucalyptus regnans forest comprising 784 stems over a 5 ha area. We used photos of stump cross‐sections to differentiate sapwood from heartwood and found 90% of stump segments to have a visible transition boundary. The digital images were corrected for lens distortion and scaled to an actual cross‐sectional area, with resulting stump perimeters corresponding well with field‐measured perimeters traced using string (root‐mean‐square error = 4 cm, R 2 = 0.99). Calculated SA and basal area (BA) at stump height were coupled with tree and sapwood taper data to predict the SA:BA ratio at 1.3 m height ( ). Tree taper data were coupled with stump dimensions data in a mixed‐effects model to predict each stump's BA at 1.3 m, and sapwood taper data from buttress logs were used to improve each stems . Using this procedure, we found our study site to have an of 0.21 and total stand SA at 1.3 m height of 9.3 m 2 ha −1 . We quantified the bias in traditional estimates that use cores to measure sapwood thickness and diameter tape to calculate SA. We show traditional methods underestimate that increases with tree diameter and decreases with stem circularity, whereas our methodology gave more accurate measures of SA in large buttressing trees. Our methodology also provides a more efficient way of generating maps of SA variation across large forested catchments. Copyright © 2014 John Wiley & Sons, Ltd.