Does fire promote landward migration of coastal marsh assemblages vulnerable to sea level rise?

Dr. Loretta Battaglia, Dr. Julia Cherry, Dr. Mark Woodrey

Coastal plant communities along the Northern Gulf of Mexico coast are subject to chronic sea level rise (SLR) and increasingly intense tropical storms.  Some species are resilient and cope with rising seas by trapping inorganic sediment and accreting organic material. When rates of SLR exceed their capacity for vertical resilience, landward migration is necessary for long-term persistence in the landscape.  Upslope vegetation, often dominated by long-lived woody species, creates dispersal and establishment barriers to migration of herbaceous marsh species, leaving the latter highly vulnerable when they are squeezed at the seaward end of their distributions.  We hypothesized that disturbance to upslope vegetation opens establishment opportunities and promotes landward establishment of marsh.  In April 2015, we identified four pine island-marsh complexes at Grand Bay National Estuarine Research Reserve, Mississippi, USA; two were burned and two were left unburned to serve as controls.  In July 2015, we initiated a reciprocal community transplant experiment using the four dominant vegetation types on these islands:  salt marsh, brackish marsh, fresh marsh and pine savanna.  Preliminary results indicate successful upslope establishment and poor survival of downslope transplants in all assemblage types.  Species richness is highest where assemblages were migrated upslope several zones.

Longer term survival and expansion are expected to be greater where barriers have been removed with prescribed fire.  We posit that loss of resilience at local scales is a necessary prerequisite to invasion by species better suited to future climates.  This coupling is an essential mechanism by which landscapes maintain fluidity and resilience to climate change at larger scales.

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