Lateral extent • Elevation change • Changes in creek and marsh • Changes in floristic composition • Changes in vegetation vigour

Changes in vegetation vigour

Changes in the 'vigour' of marsh vegetation, which may be defined as a decrease in the density, height or leaf area, can have a significant effect on tidal current and wave energy dissipation and, thereby, both on marsh surface sedimentation/erosion and the risk of overtopping of sea defences landward of the marsh. In extreme cases, total 'dieback' of vegetation may occur, leaving a largely bare surface or one on which algae becomes established, forming extensive mats. Change in vegetation vigour may be brought about by natural biological and soil successional mechanisms, by pollution or introduced pathogens. Potentially, changes in rainfall and temperature patterns could be significant in promoting or reducing rates of growth. As stated above, extensive dieback is a phenomenon which has been reported to affect Spartina marshes in the UK, especially on the south coast. The reasons have been extensively investigated and several possible causal mechanisms have been identified (Pye, 2000; Raybould, 2000).

Grazing can have a major effect on the vigour and general physiology of saltmarsh plants, and hence on physical processes. Many of the more sandy marshes in western Britain are heavily grazed and recharacterised by a relatively short sward (Adam, 2000). Marshes in Eastern England have also been extensively grazed historically but the practice is now much more restricted in most areas.