Spartina Salt Marshes in Southern England: I. The Effects of Sheep Grazing at the Upper Limits of Spartina Marsh in Bridgwater Bay

Abstract

Controlled sheep grazing experiments using replicated plots showed that a tall marsh vegetation with Phragmites communis and Scirpus maritimus tenas to replace ungrazed Spartina marsh where its upper limits are on soft mud with salinity reduced by fresh water seepage. Grazing favored the spread of Puccinellia maritima, the tillering of Spartina and a reduction in Atriplex hastata. Results suggested that in the plot areas, Spartina was likely to be replaced by Phragmites marsh in about 8 years in ungrazed conditions and by Puccinellia marsh in about 10 years under grazing. Measurements of the standing crop weights of Spartina and Atriplex give mean values between 7000-8000 kg/ha for both. The presence of large quantities of Spartina drift at the top of the marsh is important in opening up the dense Spartina swards for the rapia invasion of Phragmites, Scirpus and Puccinellia into the gaps so formed.