Sea level rise linked to climate change is creating ‘ghost forests’ in coastal areas of the United States and reducing the landscape’s ability to store carbon, according to a study led by researchers from North Carolina and Florida.
It says saltwater intrusion is killing coastal trees, which are being replaced by low-growing, salt-tolerant shrubs and grasses. A survey of around 4,000 sq kilometres of the Albemarle-Pamlico Peninsula region of North Carolina found that 15 per cent of this area (167 sq km) had changed to dead trees or ‘ghost forests’ in just over a decade.
The study is published online in the October edition of the international journal Environmental Research Letters.
The research team was led by geospatial analyst Lindsey Smart from North Carolina State University and Paul Taillie, a wildlife ecologist at the University of Florida. They used satellite images and light detection ranging (LiDAR) surveys to map the ecosystem changes and to estimate their impact on landscape carbon storage.
“Although recent research has investigated the drivers and rates of coastal forest decline, the associated changes in carbon storage across large extents have not been quantified,” the study says.
“Ours is the first study to examine landscape-scale aboveground carbon dynamics related to ghost forest proliferation, a phenomenon unique to temperate regions. Our objectives were to map the 13-year spread of ghost forests in a large low-lying coastal region, quantify the associated loss in aboveground carbon, and compare forest loss from ghost forest spread to other sources of disturbance e.g. wildfires and forestry activities.”
The study builds on earlier research by Paul Taillie on the impact of ghost forests on North Carolina bird species which was published in Plos One in May 2019. It found that the birds most affected by the loss of coastal forest habitat were “canopy-dwelling species, such as black-throated green warbler, eastern wood-pewee, and pine warbler”.
In the most recent study, mapping surveys showed coastal forest ecosystems were “shrinking precipitously” due to the impacts of climate change and human pressures such as land clearing for urban development.
“In response to increased salinization and inundation, freshwater-dependent coastal forests are retreating upslope, leaving behind dead trees surrounded by salt-tolerant shrubs and herbaceous plant species,” it says.
“These ‘ghost forests’ are common along the North Atlantic Coast and Gulf of Mexico, varying geographically in extent and conversion rates due to spatial variation in plant community composition.”
The study says these ‘multi-layered and structurally complex” coastal forest ecosystems are being replaced by marshes with low-growing shrubs and grasses.
“Losses in structural complexity have important implications for carbon storage. Because aboveground carbon is closely linked with plant height, we expect that conversion from forest to marsh will decrease aboveground carbon storage.
“As evidenced in other biomes, the transition from forest to herbaceous plant communities (e.g. grasslands) decreases aboveground carbon storage and increases albedo, which exacerbates the effects of greenhouse gases. In coastal systems, the impacts of ghost forest proliferation on ecosystem services, particularly carbon storage, are understudied.”
But what about Australia? Hasn’t there been research into saltwater intrusion in Kakadu National Park wetlands and other coastal areas in the Top End? Well, you could weep with frustration and anger when the top item produced by a Google search is an October 2004 (that’s the climate change denying Howard government) leaflet published by the federal Department of Environment that’s headed “Saltwater Intrusion – A Natural Process”.
“Saltwater intrusion appears to be linked to climatic and oceanographic processes such
as wet season floods, stronger than average monsoonal activity, storm surges, higher
than average sea level conditions and very high tides,” it says.
According to this leaflet, “more than half the paperbark forest” at Point Farewell in Kakadu has been killed by saltwater intrusion but this loss is dismissed as part of “a natural process”.
The US study led by Smart and Taillie argues that saltwater intrusion caused by rising sea levels ” is often considered an ‘invisible’ threat because shifts in soil chemistry are difficult to measure at large spatial scales and are not generally perceived by the public.”
“Because coastal forests serve as buffers against storm surges, provide habitat for wildlife species, and preserve productivity of lands in coastal communities, the ability to identify landscape-scale transitions from forest to marsh is ecologically and economically important,” it says.
“This study highlights potential opportunities for targeted human interventions to preserve the region’s carbon sink.
“Studies in highly dynamic coastal systems at fine scales across broad spatial extents are rare, posing challenges for monitoring and forecasting coastal ecosystem change. However, with increasing availability of data from aerial- and satellite-based LiDAR platforms, our methods can be applied in other low-lying coastal plains to develop landscape-scale measurements of historical impacts from sea level rise and identify areas most vulnerable to future impacts.”
the hound 