Reference: Kirwan, M. L., & Gedan, K. B. (2019). Sea-level driven land conversion and the formation of ghost forests. Nature Climate Change, 9(6), 450-457. DOI: 10.1038/s41558-019-0488-7
Sea level rise, which has been accelerating for the last century, poses numerous ecological and economic threats. Will you be impacted? Even if you don’t live directly on the coast, the answer is most likely yes. With sea level predicted to rise by 0.4 to 1.2 meters by 2100, more than 600 million people living in low-lying coastal areas around the globe are expected to be directly impacted.
Flooding from sea level rise has been most extensive along a “hotspot” on the Atlantic coast from Massachusetts to North Carolina, particularly along the mid-Atlantic, which is also where many ghost forests are located. Forests aren’t the only type of land being impacted by rising seas. Observations of abandoned agricultural land because of increased salinity have been made globally. This represents a threat to the global food supply, which may eventually impact you.
Ecosystems in proximity to the coast will also be affected, mainly through flooding and increased salt levels in water and soil. Forests and agricultural land will convert to marshes and mangroves, resulting in the loss of productive agricultural land and the formation of ghost forests, which form where trees have died because of flooding and salinization. Wetlands are highly valuable ecosystems and provide many ecosystem services, which are benefits we receive from the natural environment. The conversion of upland ecosystems to wetlands may make up for the loss of wetlands as they are submerged with sea level rise and ensure that we continue to receive the many benefits that wetlands provide, such as flood protection and water filtration.
Most sea level rise studies focus on impacts to coastal ecosystems, such as wetlands. Therefore, Matthew Kirwan and Keryn Gedan explored how upland ecosystems like forests may change as sea level rises enough to reach them in order to fill the gap in knowledge.
How do ghost forests form?
The formation of ghost forests can be a gradual process or can be triggered by a specific event, such as a hurricane. Young trees often die first, leaving a forest of old trees. Then, salt-tolerant species establish in the understory as the older trees die, leaving behind dead tree trunks and new wetlands. This conversion of uplands to wetlands is essential for wetlands to survive sea level rise. The formation of new wetlands as sea levels rise may compensate for the loss of existing wetlands as they are inundated.
What role do we play?
Flood control measures like seawalls and dykes, as well as coastal development, may prevent the conversion of upland ecosystems to wetlands. For example, in western Europe and China, flood control structures prevent ecosystems from converting into other ecosystem types, while the southeastern and mid-Atlantic United States lack these structures and experience land conversion. We can also facilitate the migration of wetlands in our own backyards by removing barriers, such as roads and other impervious surfaces. Much of the land predicted to be submerged is rural and privately owned, giving landowners an opportunity to participate in land conversion.
What do we still need to learn?
Since wetlands are ecologically beneficial, the researchers suggest three areas for future exploration to ensure successful wetland migration. Since most land to be submerged is rural and privately owned, it is important to better understand the dynamics of land conversion specifically on this kind of land. It is also important to figure out incentives to prioritize wetland migration or upland protection. Since submergence of low-lying areas by the sea will continue into the future and spread upland, undertaking this research will help to ensure that we continue to receive benefits.