Scholars@Duke publication: Increasing pathlength resistance and within-canopy shading similarly attenuate transpiration in accruing collocated stands of five pine species

Increasing pathlength resistance and within-canopy shading similarly attenuate transpiration in accruing collocated stands of five pine species

Publication , Journal Article

Boroski, CA; Maier, CA; Palmroth, S; Domec, JC; Wang, Y; Oren, R

Published in: Agricultural and Forest Meteorology

February 15, 2026

In forested regions dominated by management for timber production, quantifying biosphere-atmosphere exchange of mass and energy over accruing forests is essential for accurate estimates of water yield and carbon sequestration. Environmental conditions drive transpiration rates, a dominant portion of evapotranspiration in forests. However, differences among species and stand characteristics set limits to canopy-scale transpiration. Both canopy leaf area and height increase rapidly as stands develop, increasing within-canopy shading and pathlength resistance of water flow to leaves, respectively. Understanding these dynamics is important to accurately quantifying water use and informing forest and watershed management strategies. We measured sap-flux in five co-occurring Southeastern U.S. pine species for nearly five years at a common garden site on a sandy loam soil in the Duke Forest, Durham, NC. Despite significant differences among these species in crown architecture, sapwood area per unit of ground area, and canopy leaf area, their leaf-scale transpiration rate displayed similar sensitivity to vapor pressure deficit. Sensitivity to soil moisture decline varied among species. Under standard conditions, leaf and canopy transpiration declined with increased pathlength resistance (greater height), ostensibly dominating over the impact of within-canopy shading (higher leaf area). The results suggest that transpiration of these pine species on sandy soil can be approximated assuming a similar physiology, but that accurately estimating it during the rapid phase of stand development requires not only accounting for the effect of increasing canopy leaf area, but also for increasing hydraulic resistance with tree height, especially in open or thinned stands.