Self-organization and vegetation collapse in salt marsh ecosystems

It is a premise in ecology that undisturbed ecosystems are relatively stable, and hence that sudden changes in ecosystem are likely to result from external, mostly human influences. Johan van de Koppel, Daphne van der Wal, Jan P. Bakker, and Peter M. J. Herman present a combined theoretical and empirical study indicating that natural processes within salt-marsh ecosystems can lead to ecosystem destruction. They model salt-marsh development based on the mutually enforcing interaction between plant growth and accumulation of sediment.

Observations from Dutch salt marshes confirm the model predictions that at first, plant-sediment feedback buffers the salt marsh from the strong physical gradient that characterizes the marine-terrestrial boundary, and improves plant growth along the gradient. However, as a consequence of this process, the edge of the salt marsh and the adjacent intertidal flat becomes increasingly steep and vulnerable to wave attack. Disturbance due to for instance a storm, may induce a cascade of vegetation collapse and severe erosion on the cliff edge, leading to salt-marsh destruction. Seawards of this cliff new pioneer vegetation can develop, leading to rejuvenation of the salt marsh.

The study shows that on short timescales, natural processes improve the functioning of salt-marsh ecosystems. On longer timescales, however, the same processes increase ecosystem vulnerability and may lead to collapse of salt-marsh vegetation.