Sudden Vegetation Dieback
What is it?
Sudden vegetation dieback (SVD) is when large areas of salt marsh vegetation rapidly turn brown and die, leaving bare peat. Without the vegetation, erosion of sediment occurs rapidly leaving the marsh peat full of holes – the areas where SVD has occurred are often described as looking like Swiss cheese or a honeycomb. SVD primarily affects saltmarsh cordgrass (Spartina alterniflora), but may also impact saltmeadow hay (Spartina patens), rush (Juncus) species, and other saltmarsh species. The dieback often begins along creek banks with further dieback occurring in what appears to be a random pattern.
While marshes are dynamic systems and patches of Spartina grasses often die in one area and regenerate in another, the rapidity and vastness of the SVD in Atlantic and Gulf coast marshes has many scientists and wetland professionals extremely concerned. SVD involves thousands of acres of eastern and Gulf coast marsh and, in many cases, the marshes are not regenerating. In Louisiana, SVD and marsh browning (the rapid browning, but not necessarily death, of saltmarsh plants) affected over 100,000 acres during the summer of 2000.
When and where is SVD occurring?
First noted (dates are approximate):
- 1990 in Florida panhandle
- 1999 in Connecticut
- 1999 in Rhode Island
- 2000 in Louisiana (approx. 200,000 acres of marsh turned brown)
- 2002 in Georgia
- 2002 in Massachusetts
- 2003 in Long Island, New York
- 2006 in Delaware Inland Bays
What causes SVD? A case for Forensic Ecology…
Scientists are researching several different avenues of thought on the cause(s) of sudden wetland dieback, and there does not appear to be any single answer. Rather it appears that there are multiple interacting factors causing the dieback, and different locations appear to have different factors at work. So far, there are no definitive answers.
Hypotheses on the cause of SVD include climate change, hydrologic changes, nutrient pollution, fungi (the African dust hypothesis), and predation.
In Louisiana, there was a severe drought in 1999. This drought may have stressed the Spartina alterniflora leaving it susceptible to a strain of the fungus Fusarium. In addition, the lack of water may have caused high soil acidity and changes in soil chemistry, leading to toxic conditions for the salt marsh plants. Once the drought ended, researchers noted recovery in some of the marshes. In 2005 another dieback occurred, concurrent with a drought event. However, according to a 2006 US Geological Survey report, drought could not be determined to be the causal agent, and the cause of the dieback is still unknown. The cause or causes remain unresolved in New England as well.
What are scientists doing?
Research and monitoring efforts are underway at numerous sites including Louisiana, Delaware’s Inland Bays and Cape Cod National Seashore. Scientists in Connecticut and Louisiana are researching the effects of Fusarium strains on Spartina alterniflora. The New England Estuarine Research Society (NEERS) has set up a website and List Server on the subject. In New England, scientists and wetland professionals have begun annual meetings to discuss SVD and research/monitoring results.