The direct and indirect effects of plantation forestry expansion on usable water in the southeastern US

The southern United States, particularly its Southeastern region, includes some of the most intensively managed forests. Currently, planted pines are at some 40 million acres and occupy about 20 percent of entire forested area in the southern United States. Economic models predict accelerated areal expansion in pine plantations within the Southeastern US by industry and private owners, in part, due to federal policies to reduce timber harvesting from western forests. Over the last 50 years, this expansion primarily replaced natural and thus older pine forests with younger and faster growing Loblolly pines. Given the regional scale of this land-cover change, future water resources planning for the Southeastern US must account for the rapid areal expansion in pine plantation area. This project evaluates the direct effects of this rapid land-use conversion on evapotranspiration (loss of water to the atmosphere directly from the soil and through plants) and groundwater recharge, as well as its indirect effects on summertime rainfall initiation within the Southeast region. Given that forests are “first-users” of precipitated water, this direct effect can significantly alter “usable” water in the Southeastern. With regards to the indirect effects, the link between root-zone soil water and the initiation of rainfall is now attracting significant attention as potentially having a key role on the alterations brought about by the replacement of natural forests with other uses. Previous studies focused either on aboveground pathways of water movement or on below ground processes. Here, a complete soil-plant-atmosphere mathematical model is proposed to address the impacts of pine plantation expansion. The model and its various components will be evaluated individually and collectively against a number of long-term field experiments.

Given the rapid growth of the human population in the southeastern US, the consequences of increased drought frequency and duration can be severe on usable water resources as trees are “first users” of precipitated water. Hence, the broader significance of this project lies in the development of mechanistic mathematical models that can identify future vulnerabilities of water resources resulting from pine plantation expansion. This project supports a graduate student and a post-doctoral fellow, which enables integration of research and inter-disciplinary training in hydrology, ecology, and atmospheric sciences and prepares the next generation of scientists to tackle complex societal problems such as large scale land cover changes and water resources vulnerability. As a general public outreach, the project leverages recent initiatives at the North Carolina Museum of Natural Sciences that seeks to showcase museums as illuminating the intersection between scientific discovery and advancements in addressing societal problems to the public.