Patterns in time and space on Solent saltmarshes : a combined palaeoecological and experimental approach

Abstract

The effects of three biotic factors (a new species, grazing, and plant-plant interactions) were considered on the spatial patterns and temporal changes observed on coastal methods and manipulative field experiments were conducted at several locations in the Solent region. The Solent has a rich resource of saltmarsh habitats, which are of high scientific value and are of national conservation importance. Palaeoecological saltmarshes. Palaeoecological investigations were carried out on three sites (Beaulieu, Hythe and Marchwood) to investigate the long term effects of the appearance of the hybrid grass Spartina anglica C.E. Hubbard (common cord grass). Historical records were researched to complement the data obtained from the analysis of sediment cores, to characterise the saltmarsh environments before the appearance of the new species. The evidence suggests that before S. anglica appeared in the region (in the second half of the nineteenth century), mudflat and pioneer marsh were much more significant features of the Solent coast than they are at present. Manipulative experiments were carried out at two locations on the Beaulieu Estuary. The effects of excluding large wild grazing animals (principally geese, rabbits and deer) on the plant communities were investigated by constructing experimental exclosures. These were monitored for three years, after which above ground biomass was harvested from randomly selected parts. Excluding grazing animals produced rapid structural changes in the plant canopy. Palatable species, which had previously been suppressed by grazing (e.g. Plantaeo maritima L.), proliferated rapidly. Some low-growing species, which had previously been conspicuous in the community (e.g. Armeria maritima (Mill.)), declined significantly, possibly due to shading by the increased growth of other species. The importance of competition and facilitation in setting the positions of two plant species within the zonation of a saltmarsh was investigated by transplanting them to different vertical zones. When the lower marsh grass S. anglica was transplanted to the upper marsh it was outcompeted by more competitive plant species. When the surrounding above ground vegetation was removed, it grew successfully. The upper marsh rush Juncus gerardii Loisel was transplanted to the lower marsh. This species could not tolerate the harsher physical conditions at a lower level, but that the presence of neighbouring plant growth increased its success.

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