Winter Season Tree Sap Flow and Stand Transpiration in an Intensively-Managed Loblolly and Slash Pine Plantation

Abstract

On the lower gulf coastal plain of the southeastern United States, meteorological conditions during the winter months of November to February remain conducive to aboveground physiological activity, with frequent periods of high radiation, and temperatures seldom falling below freezing. While a number of studies have investigated southern pine physiology during the winter months (Drew and Ledig, 1981; 156 Boltz et al., 1986; Day et al., 1991; Teskey et al., 1994; Murthy et al., 1997), most of these studies have focused on organ-level responses. Few, if any, have examined physiological processes at the whole-tree or stand level. The primary objective of this study was to quantify winter season transpiration rates of trees and stands of loblolly (Pinus taeda L.) and slash (Pinus elliottii Engelm.) pine. Transpiration is an important process, both in terms of hydrology (Whitehead and Kelliher, 1991; McNulty et al., 1996) as well as tree and stand physiology (e.g., Monteith 1995), and is closely linked to productivity at various scales (Leuning, 1995; Le Maitre and Versfeld, 1997). As such, measurements of winter transpiration rates will be useful for understanding the environmental limits to southern pine productivity. In addition, by conducting measurements in plantations that have undergone intensive cultural treatments, we will gain insight into the water balance of stands under management scenarios that are becoming increasingly common (Sedjo and Botkin, 1997).