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A Guide to Understanding How Natural Ecosystems will be Transformed in the Southeast

November 19, 2019

A Guide to Understanding 
How Natural Ecosystems will be Transformed
in the Southeast
NCA4 Webinar Series –  Key Message 3

Fourth National Climate Assessment (NCA4) Webinar Series

The Southeast CASC is hosting a six-part webinar series designed to help our partners and stakeholders in the Southeast more readily access the large amount of information synthesized in the Fourth National Climate Assessment Volume II (NCA4). We will highlight the key messages contained in the Southeast, Tribes & Indigenous Peoples, and U.S. Caribbean chapters of the NCA4, connect you directly to related elements of the volume, and make connections to relevant research, publications, and data from the Southeast CASC and others.

Below is a brief overview of this week’s webinar topic – Key Message 3: Natural Ecosystems will be Transformed.
Wednesday, November 20, 2019, 12 pm ET

The SE CASC has created a Guide to Understanding the Southeast Chapter of the NCA4, which provides background information and a comprehensive overview of the entire chapter. Stay tuned for the release of the Guide to Understanding the Tribes and Indigenous Peoples Chapter and Guide to Understanding the U.S. Caribbean Chapter of the NCA4.

Key Message 3: Natural Ecosystems will be Transformed

“The Southeast’s diverse natural systems, which provide many benefits to society, will be transformed by climate change (very likely, high confidence). Changing winter temperature extremes, wildfire patterns, sea levels, hurricanes, floods, droughts, and warming ocean temperatures are expected to redistribute species and greatly modify ecosystems (very likely, high confidence). As a result, the ecological resources that people depend on for livelihood, protection, and well-being are increasingly at risk, and future generations can expect to experience and interact with natural systems that are much different than those that we see today (very likely, high confidence).”

Southeastern ecosystems are uniquely located in a transition zone between tropical and temperate climates. The temperate ecosystems include hardwood forests, pine-dominated forests, and salt marshes, while the more tropical regions support mangrove forests, coral reefs, and tropical freshwater wetlands. The diverse ecosystems represented here provide a wealth of ecological resources and services, such as recreational opportunities, providing habitats for fish and wildlife species, the minimization of flooding impacts, and carbon sequestration. However, these services, which people depend on for livelihoods, protection, and well being, are increasingly at risk from the impacts of climate change.
For more detail related to this Key Message, also see:
NCA4, Chapter 7: Ecosystems, Ecosystem Services, and Biodiversity

Drivers of Ecosystem Impacts in the Southeast:
– Warming Winter Temperature Extremes
– Changing Patterns of Fire
– Rising Sea Levels and Hurricanes
– Drought and Extreme Rainfall
– Warming Ocean Temperatures

Figure Downloads from Key Message 3:
Note that each figure on the NCA4 website has an eyeball icon associated with it that gives users access to detailed metadata. This can be used to recreate the figures and accurately portray the findings. Some figures have a gear icon that directs the reader to the Climate Resilience Toolkit, a powerful resource with hundreds of case studies and a Climate Explorer tool that allows users to explore dozens of climate parameters at the zip code level. In addition, we have created pdf versions of each figure for ease of saving the image with associated legend. These pdf files are linked below.

Figure 19.15 Projected Changes in Plant Hardiness Zones

Increasing winter temperatures are expected to result in a northward shift of the zones conducive to growing various types of plants, known as plant hardiness zones. These maps show the mean projected changes in the plant hardiness zones, as defined by the U.S. Department of Agriculture, by the late 21st century (2070–2099) under a higher scenario (RCP8.5). The USDA plant hardiness zones are based on the average lowest minimum temperature for the year, divided into increments of 5°F. Based on these projected changes, freeze-sensitive plants, like oranges, papayas, and mangoes, would be able to survive in new areas. Sources: NOAA NCEI and CICS-NC.
(Link to Figure 19.15 | Downloadable PDF)

Figure 19.16: Salt Marsh Conversion to Mangrove Forest

Where tropical and temperate ecosystems meet, warmer winter temperatures can lead to large ecological changes such as mangrove forest replacement of salt marshes along the Gulf and Atlantic Coasts. Mangrove forests are sensitive to freezing temperatures and are expected to expand northward at the expense of salt marshes. The figure shows the relationship between temperature and the percentage area dominated by mangrove forests. Mangrove expansion would entail a grassland-to-forest conversion, which would affect fish and wildlife habitat and many societal benefits. Source: adapted from Osland et al. 2013.
(Link to Figure 19.16 | Downloadable PDF)

19.17 Transitioning Coastal Ecosystems

In Louisiana and parts of northern Florida, future coastal wetlands are are expected to look and function more like the mangrove-dominated systems currently present in South Florida and the Caribbean. Like salt marshes (left), mangrove forests (right) provide coastal protection against wind and waves (Ch. 20: U.S. Caribbean, KM 2). Photo credit: Michael Osland.
(Downloadable PDF)

CASE STUDY: Prescribed Fire

With wildfire projected to increase in the Southeast, prescribed fire (the purposeful ignition of low-intensity fires in a controlled setting), remains the most effective tool for reducing wildfire risk. Department of Defense (DoD) lands represent the largest reservoirs of biodiversity and native ecosystems in the region. Military activities are a frequent source of wildfires, but increases in prescribed fire acres show a corresponding decrease in wildfire ignitions for DoD. Climate resilience by DoD is further achieved through restoration of native longleaf pine forests that occupy a wide range of site types, including wetland and well-drained soils—the latter leading many to characterize this forest as being drought resistant. In addition to proactive adaptation through prescribed fire, DoD has been a leader in climate strategies that include regional conservation planning, ecosystem management, endangered species recovery, and research funding.

Figure 19.19: (top) A helicopter drops water on a 1,500-hectare wildfire on Hurlburt Field (Eglin Air Force Base) in Florida in June of 2012. (bottom) The increased use of prescribed fire at Ft. Benning, Georgia, led to a decrease in wildfire occurrence from 1982 to 2012. Photo credit: Kevin Hiers, Tall Timbers. Figure source: adapted from Addington et al. 2015. Reprinted by permission of CSIRO Australia, ©CSIRO.
(Link to Figure 19.19 | Downloadable PDF)

Additional Case Studies from the U.S. Climate Resilience Toolkit:
– Case Study: Setting Conservation Priorities for Preserving Wildlife Habitat
– Case Study: Incorporating Climate Change Into a New Forest Management Plan

Evidence, Likelihood, and Confidence for Key Message 3

Evidence of impacts to the Southeast are supported by the geography of the region, which contains a large number of cities located at or below sea level at an increased risk of flooding. Additionally, the natural climate of the Southeast provides a conducive atmosphere for health issues including the spread of disease. Uncertainties include population projections, shifts in immigration or migration rates, and shifting demographics. See more.

SE CASC publications relevant to this Key Message include:

SE CASC funding and researchers have implemented projects relevant to this Key Message:

  • Ecological Implications of Mangrove Forest Migration in the Southeastern United States.
    Project details.
  • Enhancing the Adaptive Capacity of Coastal Wetlands in the Face of Sea-Level Rise and Coastal Development. Project details.
  • Identifying the Ecological and Management Implications of Mangrove Migration in the Northern Gulf of Mexico. Project details.
  • Assessing Climate-Sensitive Ecosystems in the Southeastern United States. Project details.

View a Guide to Understanding the Southeast Chapter of the NCA4