Leaf surface resistance, xylem pressure potential, and some atmospheric factors were measured for three summers in a dominant white oak tree growing in an oak-hickory forest. Distinctive opening and closing patterns in leaf surface resistance were noted in both sun and shade leaves. Hydroactive stomatal closure began as xylem pressure potential decreased below -21 and -25 bars in shade and sun leaves respectively. Data from one summer were used to develop a series of regression equations to predict leaf surface resistance while data from two other summers were used to test the equations. Two approaches were used in analyzing data: leaf surface resistance was either assumed to be a function of several environmental and plant variables or a function of one environmental or plant variable. In the first approach, a function including solar radiation, xylem pressure potential, and the interaction between xylem pressure potential and vapor pressure deficit provided the least squares best fit to the data (R² $apE; 0.50) but such equations provided poor estimates of leaf surface resistance. In the second approach, the use of single variable equations was determined by a series of "if" statements. No significant differences between predicted and observed values were noted and the equations appeared to predict realistic values of leaf surface resistance under a range of environmental conditions. A three-dimensional response surface relating leaf surface resistance to vapor pressure deficit and predawn (base) xylem pressure potential is discussed. Forest Sci. 21:201-211.
Research Technician, Weyerhaeuser Research Center, Hot Springs, Arkansas
Publication date: June 1, 1975
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Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.