Abiotic and biotic forest disturbances can have many impacts to forest ecosystem services, including to forest water use. Studies on impacts to forest evapotranspiration have been conducted on the mountain pine beetle (Dendroctonus ponderosae) in western North America, but not on the southern pine beetle (Dendroctonus frontalis), which is a native pest of loblolly pine (Pinus taeda) and shortleaf pine (Pinus echinata), in the southeastern United States. Stressed pine trees produce pheromones that attract southern pine beetles and, with enough stressed trees, beetle populations can quickly grow to epidemic levels and attack healthy trees, which results in widespread tree mortality. This study aimed to examine the impact of southern pine beetle spots on canopy density and evapotranspiration in loblolly pine stands in the Homochitto National Forest from 2012-2021. Locations of documented beetle spots from the USDA Forest Service were used to extract normalized difference vegetation index (NDVI) values using Landsat satellite observations on Google Earth Engine, and evapotranspiration data at stand level from the OpenET platform for two years pre- and post-southern pine beetle detection for comparative analysis. Results demonstrate that southern pine beetle outbreaks reduce NDVI and evapotranspiration, but also highlight that other factors (e.g., understory vegetation) can result in stand-by-stand variation in hydrologic cycle impacts. Further, this study demonstrates that satellite observations can provide critical environmental data on impacts of forest pests. By understanding the relationships between biotic disturbance agents and forest water use capability in forest ecosystems, we can improve our understanding of the impacts of forest disturbance agents on ecosystem services and possibly help direct management of forest stands impacted by these disturbances.
Goodnow et al. (Wed,) studied this question.