Detecting Stress in Southern Live Oak (Quercus Virginia) and Sand Live Oak (Q.Virginiana Var. Geminata)

Abstract

Walt Disney World (Florida, U.S.) arborists evaluated three affordable and easy-to-use measures of tree stressleaf chlorophyll concentration, leaf temperature, and water potentialfor use in detecting water and physical injury stress in live oak. The evaluation included observations of trees being relocated, and experiments of girdled trees and trees subjected to various watering regimes. Leaf chlorophyll concentration was largely unresponsive to stress and unlikely to be useful as a stress indicator in sand live oak and southern live oak. Both water potential and leaf temperature were responsive to imparted stressors and have potential as indicators of stress in sand live oak and southern live oak. Water potential exhibited a predictable and consistent response to both water stress and physical injury. Inadequately watered live oaks, and oaks subject to relocation, had lower water potentials than oaks with an adequate water regime or in situ. By contrast, live oaks injured by girdling had higher water potential than nongirdled trees. Leaf temperature was less sensitive and less robust at detecting stress than water potential, but still potentially useful. Leaf temperature was greater for a nonirrigated relocated tree than an irrigated relocated tree, and for relocated trees when rootballed and immediately after relocation. Leaf temperature was largely unresponsive to girdling or mild water stress.