Impacts of Drought and 40% Throughfall Reduction on Water Relations of a Longleaf Pine Stand

Abstract

Projections of increased frequency and severity of climatic- induced drought have raised concerns about the health, productivity and composition of forests in the southeastern United States. Longleaf pine (Pinus palustris Mill.) is a native species that thrives on sites that are frequently disturbed by fire and is thought to be more tolerant of drought stress than other southern pines, making it a suitable species to withstand future climate conditions. However, the limits and mechanisms of that presumed drought tolerance are not known. In-situ manipulation of water availability was used in this study to examine the effects of drought on water relations in a longleaf pine plantation. Specifically, the effects of a 40% reduction in throughfall precipitation on leaf water potential, sap flux density, whole-tree hydraulic conductance, and productivity were investigated. Following the installation of the throughfall reduction treatment in May 2016, a prolonged natural drought occurred wherein little to no precipitation fell on the site from September 2016 until the end of November 2016. Throughfall reduction did not influence leaf water potential or productivity during the 2016 natural drought but did reduce sap flux density and whole-tree hydraulic conductance. As natural drought conditions alleviated in 2017, the 40% throughfall reduction treatment did reduce sap flux density, but did not significantly affect leaf water potential, whole-tree hydraulic conductance, or productivity. Longleaf pine survived severe water deficit and throughfall reduction by reducing transpiration but not growth, and thus may be a suitable species for drought prone sites.