The ability to provide fresh drinking water is a critical ecosystem service of forests, and for many households in the southeastern United States, forests are the only source of municipal water supply. About 32 percent of the Southeast’s total annual water supply originates on state and private forest lands and another 3.4 percent on National Forest System land.
But water resources in southeastern forests are stressed from urban sprawl, increased water usage, climate variability, and, increasingly, wildland fire. Last year, 2015, was a record year for wildland fire with more than 10 million acres burned in the U.S.
Many research projects currently focus on sustaining forest ecological functions and forests’ ability to supply water for future generations, including a Joint Fire Science Program-funded study on the effects of wildland and prescribed fires on water quantity across the landscape.
U.S. Forest Service Eastern Forest Environmental Threat Assessment Center research hydrologists Ge Sun and Dennis Hallema, who have been conducting this study since 2014, recently presented an invited seminar on their results to fellow researchers at the Joseph W. Jones Ecological Research Center in southwestern Georgia, where the Flint River has experienced profound effects of water stress due to increasing drought and irrigation demands for agriculture. Since the 1970s, water yields have declined rapidly in the region, resulting in lower streamflow in the Lower Flint River Basin.
For over two decades, Jones Center scientists have studied the effects of low-intensity prescribed burns across 30,000 acres at their research site Ichauway, much of which is open canopy longleaf pine-savanna managed with prescribed burns approximately every two years to simulate the natural frequent wildfire regime. Their long-term field experiments focus on vegetation responses to fire suppression and fire reintroduction, including responses to chronic stress (competition for light, water, and soil nutrients between pines and oaks when there is no fire) and episodic stress (effects of fire reintroduction). Understanding the local effects of fire on ecosystem dynamics can also help researchers understand how fires affect water supply — the goal of Sun and Hallema’s project.
Sun and Hallema have observed the effects of drought on water supply in southwestern Georgia — and in other parts of the Southeast as well. During their Jones Center seminar, they presented results showing a 40 percent decline in water yield in the Carolina Sandhills in South Carolina over a period of only 10 years. This change was mostly caused by declining precipitation, with no apparent link to prescribed burning in the Carolina Sandhills National Wildlife Refuge that occupies a quarter of the watershed.
In this case, the impact of prescribed burning is vastly different from wildland fire effects in the western United States where large wildfires have been responsible for catastrophic floods and severe erosion. Regardless, water security will continue to present important challenges in water planning for both the West and the Southeast, where many forests have transformed into dense, fire-suppressed mixed pine-oak forests whose greater biomass results in generally higher water use compared to pre-colonial times.
The careful planning of a sustainable future for ecosystems with a natural or simulated frequent fire regime, such as those studied by Jones Center scientists, calls for a flexible and adaptable approach based on the natural resilience of these ecosystems and must account for a broad spectrum of possible responses to projected social-economic, forest composition, and climate conditions. Water resources planning is an essential part of this process.
For more information, email Dennis Hallema at email@example.com.