Assessing the Community Land Model (CLM5) for Quantifying Energy, Water, and Carbon Balances in Loblolly and Longleaf Pine Ecosystems in Southeastern United States

Abstract Southeastern U.S. longleaf pine savannas have been reduced to less than 5% of their original extent, giving space to fast‐growing, high‐density loblolly pine plantations. Restoring longleaf pine savannas is an alternative that has been discussed to reduce evapotranspiration and increase water yield, which is of great relevance in resource management and ecosystem restoration. Understanding the benefits of forest management and restoration requires advanced tools to better quantify the fundamental processes of energy, water, and carbon interactions at stand, landscape, and regional scales. We implement and assess the Community Land Model Version 5 (CLM5) at two long‐term research sites, one representing a typical loblolly pine ( Pinus taeda ) plantation with a high tree density and another a typical longleaf pine ( Pinus palustris ) savanna with a low tree density. We also carry out numerical experiments exploring potential differences in energy, water, and carbon balances under alternate land cover scenarios at each site. Using tailored parameterizations for loblolly and longleaf pine and an adjusted C4 grass parameterization, we found that CLM5 reasonably captured the overall observed stand structure and functions at both sites, performing substantially better than with the default parameterizations. Our numerical experiments indicated 8%–17% lower evapotranspiration and 30%–125% higher water yield for longleaf pine savanna compared to loblolly pine plantation. However, net ecosystem production (NEP) and NEP‐based water use efficiency were 60% lower for longleaf pine savanna than loblolly pine plantation. Our modeling framework could be implemented regionally in future studies to support forest management decisions and longleaf pine restoration initiatives.