Coastal Forests Are Dying—And It’s Not Agriculture to Blame Anymore
The Disappearing Wetlands
Wetlands are disappearing and it is more than only the drying of water. It is the silent collapse of natural defences, carbon reservoirs, and biodiversity. Wetlands filter pollutants and surfeit nutrients from wastewater, and remove suspended solids and pathogens through the processes of sedimentation and plant uptake, which enhances the quality of the water. Wetlands also play a prominent role in climate change mitigation owing to their high carbon capturing capacity.
Wetlands are distinctive ecosystems, many of which for ages were drained for human land use. They are already under enormous pressure from urbanisation and pollution, however, now they are facing an even graver threat: rising seas and saltwater intrusion that disrupt freshwater ecosystems and alter their delicate balance. As sea level rises, saltwater gradually creeps into inlands in hydrologically altered landscapes, transforming the freshwater wetlands into saline wastelands by threatening the survival of myriad species that depend on them. Significant traces of wetland deforestation and fragmentation of wetland habitats even in the midst of protected areas have been found. Between 1780 and 1980, the majority of North America’s freshwater forested wetlands were deforested and drained.
Monitoring Forested Wetland Loss
In a new study on forested wetlands of North America, the authors analysed landcover features using remote sensing data collected by the National Oceanic and Atmospheric Administration (NOAA) Coastal Change Analysis Program. Forested swamps and bogs found along the south-eastern Atlantic and Gulf coasts of the United States are widespread iconic landscape features supporting a diverse array of species that provide significant ecosystem services. The North American Coastal Plain is a large geologic region of 1.13 million sq.km that stretches from Massachusetts to Northern Mexico and is recognised as a global biodiversity hotspot that is under substantial anthropogenic pressure.
Drivers of Coastal Wetland Change
The authors assessed the total extent of coastal forested wetland and their rate of loss across the entire Coastal Plain from 1996 to 2016. During this time period, over 2,000 patches of wetland were lost totalling 13,682 sq.km, an area equivalent in size to the US state of Connecticut and constituting 8% of forested coastal wetlands across the North American Coastal Plain.The rate of coastal forest loss within the North American Coastal Plain is 684 sq.km/year which is more than threefold the global estimate of coastal mangrove loss of 210 sq.km/year.
The authors also examined the predictive power of the hypothesised climate drivers and basin topography while explaining variation in the rates of coastal forested wetland area loss using a generalised linear model. The greater part of the forests of this region have transitioned to scrub-shrub and marsh habitats. Agricultural conversion, in contrast to previous drivers of coastal forested wetland loss, accounted for only about 3% of total coastal forested wetland losses observed since 1996. Direct losses attributable to sea level rise and intensified inland flooding make up only about 2% of coastal forested wetlands transforming to open water.
78% of the variation in coastal wetland deforestation along the South Atlantic and Gulf Coasts can be attributed to a combination of various factors, including variation in the rate of rising of the sea level, landings of tropical storms, and the average elevation of coastal watersheds. It suggests that short-term fluctuations and extreme climatic events are more dangerous to coastal wetlands than progressive sea-level rise alone. At the same time the reclamation from agricultural development of 0.6% was a negligible component of total forested wetlands regrowth. This indicates that the escalating volatility caused by climate change may pose a bigger threat to wetlands than constant sea-level rise. Unlike preceding centuries, when agriculture was considered as the primary driver, at present times coastal wetland degradation is directly linked to climatic stresses such as unpredictable floods, saltwater intrusion, and increasing sea levels. In this regard, diminishing wetlands are both a symptom and a warning sign of climatic instability.
A Climate Crisis for Coastal Wetlands
The findings of this study indicate that accelerating climate change is reducing the spatial extent of a threatened and unique coastal habitat with rich biodiversity across the North American Coastal Plain. It is reasonable to expect that these coastal forested wetlands will be similarly threatened not only by agricultural conversion, but climate change-driven sea-level rise and freshwater salinization as well. If wetlands vanish under these associated pressures of both sea-level rise and salinization, we will not only lose the wetlands but also the frontline defence of nature against severe storms, storm floods, and climate instability. The crawling tide of this saltwater intrusion is a warning bell and protecting wetlands is the only chance we have of keeping them from turning into barren, lifeless swamps. This can be done by implementing strict land use regulations to limit urban encroachments and effective use of remote sensing-based monitoring systems for timely detection of degradation risk of wetland loss.
Source Article: White Jr, E. E., Ury, E. A., Bernhardt, E. S., & Yang, X. (2022). Climate change driving widespread loss of coastal forested wetlands throughout the North American coastal plain. Ecosystems, 25(4), 812-827. https://doi.org/10.1007/s10021-021-00686-w
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