Fertilization can compensate for decreased water availability by increasing the efficiency of stem volume production per unit of leaf area for loblolly pine (Pinus taeda) stands

Abstract

Over half of the standing pine timber volume in the southeastern USA is composed of loblolly pine (Pinus taeda L.), making it the most important tree species in the region. Future climate variability may impact productivity of these forests due to reduced water availability. To determine the effects of nutrient availability and decreased water availability on stand-level water use efficiency and growth efficiency, we examined the interactive effects of fertilization and reduced throughfall on whole-tree water use, stand-level canopy transpiration, leaf area index (LAI), and stand-level stem volume growth. This study was conducted over the 6th and 7th growing seasons (2013–2014) of a loblolly pine plantation in southeastern Oklahoma. Across all plots, throughfall reduction reduced volumetric soil water content (VWC) from 13.6% to 10.9% for soil depths of 0–12 cm and from 22.3% to 19.9% for soil depths of 12–45 cm and reduced stand volume growth from 20.9 to 17.9 m3·ha−1. Across all plots, fertilization increased LAI by 12%, increased stand volume growth from 18.3 to 20.5 m3·ha−1, and increased water use efficiency of stem volume production by 18%. These results indicate that fertilization can benefit stand growth of loblolly pine plantations even when soil moisture is limiting, in part, by increasing the efficiency of water use.