During 2010 to 2013, much of the Western Gulf Region (LA, TX, OK, and AR) experienced an exceptionally extreme drought that caused billions of dollars in agricultural losses. Climate change projections predict that this region will experience lower water availability and more severe summer droughts over the coming decades. Loblolly pine (Pinus taeda) is the dominate timber species of the southeast and brings in billions of dollars to the southern economy. Understanding tree characteristics and silvicultural techniques that contribute to drought tolerance is critical in maintaining productive plantations and healthy forests across the southeast. Pines and other plants depend on carbon storage to maintain homeostasis during droughts. Photosynthesis rates can be used to detect drought stress and carbon assimilation rates. In this study we measured the photosynthesis rates of three different loblolly pines: 1) a commonly used open pollinated North Carolina genotype; 2) a clonal variety propagated from a North Carolina tree with superior form; and 3) a native Louisiana stock type. A drought treatment was initiated to simulate extreme drought for each treatment. A year before the drought treatment, we reduced the density of half of the experimental units to create a thinned treatment for each of the three tree types.
Results/Conclusions
Prior to drought initiation, there was no variation in photosynthetic rates. Previous basal area increment research found that the open pollinated trees maintained normal growth rates better than the clonal variety during the southern drought in 2011 (unpublished research). Blazier et al. 2018 found that the photosynthesis rate of the clonal variety was most sensitive to summer drought compared to all other varieties tested. We expect our results to confirm that the open pollinated North Carolina variety is more drought resistant than the clonal variety. Thinning is also expected to increase water availability and reduce drought stress compared to non-thinned treatments. The implications of this research will inform plantation landowners with ways to maintain their pine plantations during drought. This research will also inform conservationists to ways they can maintain healthy forests in the face of climate change. Thinning will reduce resource competition between trees and contribute to greater longevity in natural forests. This research will inform both landowners and conservationists for methods to use to adapt forests to a changing climate.