Climate Change and the Expansion of Ghost Forests

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Climate change is impacting much of what we consider ‘normal’ on Earth. In addition to changing weather patterns, ocean currents, and the geographic range of terrestrial and marine species, climate changes are causing an expansion of ‘ghost forests’ along the East Coast of the United States.

Climate changes are causing different species of trees to die around the world. Forest mortality rates can be caused by a variety of factors, including changing air temperatures and precipitation levels, habitat shifts, insect infestations, increased wildfire intensity, and rising sea levels.

Along the geography of the East Coast of the United States, large swathes of forest are declining at increasing rates. These ‘ghost forests’ are experiencing mortalities due to climate changes that are altering their environment rapidly. 

What is a ghost forest?

Ghost forests are forests made up of dead or dying trees, named for the gray and skeleton-like appearance of the trees that are dead but left standing. These forests are located in areas closer to the ocean where flooding, sea level rise, and storm surges have pushed saltwater inland. Many trees located in forest habitats are sensitive to salt, and exposure to saltwater can cause damage to the trees that can lead to mortality.

A ghost forest on Capers Island, South Carolina. Photo: NOAA.
A ghost forest on Capers Island, South Carolina. Photo: NOAA.

The East Coast is feeling the impacts of climate change through an increase in storms, flooding events, and sea level rise. Wetland areas are particularly vulnerable to environmental changes and have long been undervalued; wetlands are home to a hugely diverse range of wildlife, insulate surrounding areas from flooding events, and are able to store large amounts of carbon.

Unfortunately, wetlands have long been targeted as areas to be ‘tamed.’ Wetlands are drained, paved over, and otherwise altered to meet the needs of the urban areas around them. Without the protective buffer of wetlands, storm surges, sea level rise, and coastal flooding encroach upon people’s homes, businesses and other infrastructure. Other environmental habitats, like forests, are also left vulnerable.

The Expansion of Ghost Forests

Ghost forests are expanding along the East Coast due to a combination of drought conditions and tropical storms. Trees in wetland areas are dying at increasing rates because they are exposed to saltwater more often; a flood or storm surge that may have occurred once in 100 years in the past may now occur once every 20 years or more. This consistent exposure to saltwater can damage the roots of trees, keeping them from absorbing the freshwater and nutrients they need to grow and thrive.

Ghost Forest in North Carolina’s marshy Albemarle-Pamlico Peninsula.  Image: Landsat 8, NASA, November 25, 2019.
Ghost Forest in North Carolina’s marshy Albemarle-Pamlico Peninsula. Parts of this refuge have lost up to 70% of trees since the 1980s, leaving behind ghost forests. Image: Landsat 8, NASA, November 25, 2019.

Researchers from North Carolina State University and Duke University are studying the effects of saltwater intrusion on forests in North Carolina to determine when a forest that has been exposed to saltwater becomes a ghost forest. The researchers are utilizing soil samples, sediment samples, monitoring regional hydrology, and vegetation plots alongside spatial maps to track the expansion of ghost forests in the state. The data gathered by this project is essential for understanding the factors that play into the creation of ghost forests as well as the environmental point at which a forest that is struggling becomes a ghost forest.

Map showing the expansion of ghost forests in South Carolina.
Vegetation has changed on the eastern portion of the Albemarle-Pamlico Peninsula from 2001 (a) to 2014 (b). The right illustration overlays the change (c), with increased areas of tan, yellow, and orange indicating the spread of “transition-ghost forests.” Map: Smart et al., Environ. Res. Lett. 15 (2020) 104028, https://doi.org/10.1088/1748-9326/aba136, CC BY 4.0.

The study found that climate change is certainly a factor in the creation and expansion of ghost forests, although it isn’t the only one. Runoff from agriculture and wastewater ditches can also create pathways for saltwater to intrude upon wetlands and forests, contributing to their decline. This information is key for changing how agricultural workers, environmental managers, regional climate mitigation planners and others interact with one another and the environment that supports us all.

What is the Difference Between Ghost Forests and Gray Ghost Forests?

Gray ghost forests, like ghost forests, are areas of forest that are experiencing mass mortalities due to environmental factors. A ghost forest can be caused by saltwater intrusion, while a gray ghost forest is caused by a particular insect infestation. 

The southern regions of the Appalachian Mountains are home to eastern and Carolina hemlock trees which provide essential habitat for a variety of wildlife. These trees are vulnerable to an infestation of the invasive hemlock woolly adelgid, an insect that is native to Asia. The insect is able to suck sap from hemlock and spruce trees and forms a white mass at the base of the trees’ needles. Ultimately, the hemlock woolly adelgid infestation can decimate forests. 

Gray ghost forest in the southern Appalachians. A hemlock woolly adegid infestation has killed many hemlock trees in the Linville Gorge area of Pisgah National Forest in North Carolina. Photo: U.S. Forest Service/Steve Norman.
Gray ghost forest in the southern Appalachians. A hemlock woolly adegid infestation has killed many hemlock trees in the Linville Gorge area of Pisgah National Forest in North Carolina. Photo: U..S. Forest Service/Steve Norman.

The hemlock woolly adelgid can be transported by people, animals, and the wind. The infestation of this insect has resulted in tree mortality across the southern Appalachians and has begun to impact trees in the northern range of the forest as well. Infestations of this insect are influenced by warming temperatures. 

Effects of Expansion of Ghost Forests on Wildlife

The expansion of both gray ghost forests and ghost forests have an impact on wildlife that rely on these habitats for food and shelter. Many migratory animals rely on wetland environments for food during and after their lengthy journeys and can build nests, burrows, or dens in these areas to rest and reproduce. When these trees die, this essential habitat is altered.

When ghost forests appear, new vegetation thrives in their place. Standing trees give way to plants that are more tolerant of salty soils and water, like shrubs and grasses. This creates a shift from species that thrive in high, forested environments to those that are able to find food and shelter closer to the ground. 

Research into the impacts of ghost forests on wildlife is ongoing. In one focus area, 56 different bird species were identified. Each of these utilizes ghost forests habitat differently, and may be able to adapt to a future that looks very different than the present. However, many species are left vulnerable as their habitat disappears and as other species move into their territory. 

Future Implications of Ghost Forests

Future climate projections indicate that, without dramatic changes to how we live our lives, air and water temperatures will continue to rise while storms and coastal flooding become more regular. Sea level rise threatens to inundate habitat that is relied upon by an incredible number of diverse species. All of these factors influence the expansion of ghost and gray ghost forests on the East Coast and elsewhere around the world. The loss of this habitat leaves many questions not only for humanity, but for the plants and animals that once thrived in these environments as well. 

References

Ford, D’Lyn. How Sea Level Rise Affects Birds in Coastal Forests. 9 May 2019. Retrieved from https://news.ncsu.edu/2019/05/how-sea-level-rise-affects-birds-in-coastal-forests/

Rutgers. “Ghost Forests” Expanding Along Northeast US Coast. 16 March 2021. Retrieved from https://www.rutgers.edu/news/ghost-forests-expanding-along-northeast-us-coast

Sacatelli, Rachel, Lathrop, Richard G., Kaplan, Marjorie. Impacts of Climate Change on Coastal Forests in the Northeast US. December 2020. Retrieved from https://docs.google.com/viewer?url=https%3A%2F%2Fwww.sas.rutgers.edu%2Fcms%2Fclimate%2Fimages%2FImpacts_of_Climate_Change_on_Coastal_Forests_in_the_Northeast_US__Sacatelli_R._Lathrop_R.G._and_Kaplan_M_2020_December_FINAL.pdf

Science Friday. Embracing the Salt and Adapting to Sea Level Rise. 17 May 2019. Retrieved from https://www.sciencefriday.com/segments/embracing-the-salt-and-adapting-to-sea-level-rise/

US Geological Survey. Southeast CASC Helps Produce New Study on How Sea Level Rise Affects Birds in Coastal Forests. 9 May 2019. Retrieved from https://www.usgs.gov/center-news/southeast-casc-helps-produce-new-study-how-sea-level-rise-affects-birds-coastal-forests

Worley Firley, Stephanie. US Department of Agriculture. Researchers track ‘gray ghosts’ across southern Appalachians. 21 February 2017. Retrieved from https://www.usda.gov/media/blog/2014/04/30/researchers-track-gray-ghosts-across-southern-appalachians

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