Potential for Augmenting Water Yield by Restoring Longleaf Pine (Pinus palustris) Forests in the Southeastern United States

Abstract

Over 95% of original longleaf pine (Pinus palustris) (LLP) forests have been converted to other land uses, including loblolly pine (Pinus taeda L) (LOP), croplands, urban uses during the past two centuries in the southeastern United States (U.S.) for socioeconomic developments. Restoring the LLP forests represents a contemporary forest management objective to improve wildlife habitat, water yield, and overall ecosystem services and resilience to a changing climate. Given the importance of understanding ecohydrological processes for guiding restoration efforts, this study compared evapotranspiration (ET) measurements at eight eddy covariance flux sites dominated by LLP or LOP forests in the southeastern U.S. In addition, we developed a “paired stands” approach to compare remote sensing based ET estimates and associated site biophysical properties for approximately 1,600 LLP-LOP pairs. We found significant differences in ET, ET/Precipitation ratio, and water yield/precipitation ratio between the two types of pine forests, and these differences are explained by surface properties and management histories. Compared to LOP, the LLP forests generally had lower ET due to their significantly (p < 0.05) lower leaf area index but higher land surface temperature and albedo. Regionally, forest ET differences increased with the increase in atmospheric dryness index (reference ET/precipitation ratio). Therefore, we conclude that large-scale restoration of LLP forests has the potential to reduce ET and augment water yield in the long run, especially in relatively drier watersheds. Maintaining low stand tree density and understory leaf area characteristic of natural LLP ecosystems through active forest management is critical for enhancing forest water supply. Our study provides the scientific basis for large scale restoration of a diminishing ecosystem for benefiting water resources in the southeastern U.S.