Ecosystem Vulnerability to Climate Change in the Southeastern United States

Rising temperatures and shifting rainfall are already affecting many plants and animals, and the effects are expected to grow — from changes in the timing of seasonal events to shifts in where species live and how wildfires behave. To aim conservation well, managers need timely, thorough information about how climate change affects natural communities, especially in regions as rich in species as the southeastern United States.

Assessing climate-change vulnerability species by species is common and useful, but assessing whole ecosystems gives a fuller picture: it can take in changes to disturbances such as fire and flood, to water and to landforms, and interactions between species — food webs, competition, pests and diseases, and invasions.

A montane grass and heath bald. Alan Cressler, USGS.

Two studies, two approaches

Two 2016 U.S. Geological Survey reports together assessed 19 terrestrial, aquatic, riparian and coastal ecosystems, from Appalachian mountaintops to Texas canyons to Caribbean mangroves. They combined what is known about each ecosystem's distribution, processes and habitats, plant communities, physical stresses such as water, soil chemistry, terrain and temperature, disturbances such as wildfire and flood scouring, species of conservation concern, human threats such as resource extraction and land-use change, conservation options, and gaps in knowledge.

• Geospatial analysis for broad ecosystems (Costanza and others). For widespread ecosystems such as wet pine savannas and hardwood forests, the team mapped exposure, sensitivity and adaptive capacity using climate projections, current and future land use, elevation, fragmentation, protection status, sea-level rise and coastal flooding, and vegetation models, filling gaps from the literature.
• Literature synthesis for ecological islands (Cartwright and Wolfe). "Insular" ecosystems — small, isolated like islands among different surroundings, sharply bounded and tied to particular rocks, landforms and soils — include rock outcrops, isolated prairies and barrens, isolated wetlands and flood-scoured riverbanks. Mapping data are too coarse for them, and decades of local botanical studies had rarely considered climate change, so the team drew that literature together as a foundation for future work.

Together the studies span ecosystems from dozens of square metres to thousands of square kilometres.

A granite outcrop. Alan Cressler, USGS.

A longleaf pine savanna. Alan Cressler, USGS.

A flood-scoured riparian area. Alan Cressler, USGS.

What both studies found

• Many processes interact. Beyond warming and changing rainfall, effects will come from local changes in disturbance, urban growth, pollution, water and interactions between species.
• Rare species are at risk, especially range-restricted plants found only in insular ecosystems.
• Fragmentation weakens resilience. Whether natural, as in ecological islands, or caused by land-use change, it lengthens the distance species must travel to reach newly suitable habitat and exposes them to edge effects — encroaching competitors and loss of core habitat.
• Uncertainty is high. Downscaled climate forecasts disagree about future rainfall, and too little is known about evapotranspiration and the exchange between groundwater and surface water to predict how ecosystems' water will change. For many ecosystems, how climate drives pollination, food webs and competition is also unknown.
• Geodiversity matters. Because biodiversity is tied to landforms such as rock outcrops and depression wetlands, conserving a variety of landforms, soils and bedrock helps conserve species.

Pyne's ground plum, of limestone cedar glades. Alan Cressler, USGS.

Spreading avens, of high-elevation outcrops in the southern Appalachians. Alan Cressler, USGS.

Cumberland false rosemary, of riverscour ecosystems on the Cumberland Plateau. Nora Murdock, NPS.

Research priorities

Managers need predictions for whole ecosystems, not just species. The studies call for hypothesis-driven research on:

1. how changes in water affect how ecosystems work;
2. how different changes combine — for example, warmer soil together with more frequent drought;
3. how climate shapes interactions between species, including phenological mismatch, when the timing of, say, flowering and pollinators drifts apart;
4. how climate change affects management options — for example, fewer days with weather suitable for prescribed burns;
5. how scale and resolution affect modelled forecasts.

Wildfires and controlled burns are vital to many southeastern ecosystems, and how climate change will alter them is an important frontier of research. Alan Cressler, USGS.

Sources

• Jennifer M. Cartwright and Jennifer Costanza, Ecosystem Vulnerability to Climate Change in the Southeastern United States, USGS Fact Sheet 2016–3052, August 2016. https://doi.org/10.3133/fs20163052
• J. M. Cartwright and W. J. Wolfe, Insular Ecosystems of the Southeastern United States, USGS Professional Paper 1828, 2016. http://dx.doi.org/10.3133/pp1828
• Jennifer Costanza and others, Assessing Climate-Sensitive Ecosystems in the Southeastern United States, USGS Open-File Report 2016–1073. http://dx.doi.org/10.3133/ofr20161073
• A photograph of Millboro leatherflower, by the Virginia Department of Conservation and Recreation, is not reproduced here.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.