Long-term changes of salt marsh communities by cattle grazing

Abstract

Over a period of 9 years a grazing experiment was carried out in the mainland salt marsh of the Leybucht (Niedersachsen) with three stocking rates, namely, 0.5 ha 1, 1 h a -~, and 2 cattle ha ~. These were also compared with an abandoned area. The results are based on sampling of the invertebrates in 1980, 1981, 1982, and 1988, and of the vegetation in 1980 and 1988. The rate of sedimentation is highest in the Puccinellia maritima-zone and decreases with the increase of stocking rates. The Elymus pycnanthus vegetation type becomes dominant in the higher salt marsh in the abandoned site. The canopy height decreases with increasing stocking rate, whereas a gradient in the structure of the vegetation develops with the lowest stocking rate. The population densities, the species-richness and the community diversity of invertebrates increases after the cessation of grazing. The high rate of sedimentation in the abandoned site promotes the immigration of species from higher salt marsh levels and adjacent grasslands, and eventually halotopophilous species and communities may disappear. On the other hand grazing reduces numerous species living both in or on upper parts of the vegetation or being sensitive to trampling by cattle. The community structure shows that the salt marsh ecosystem changed from a food web dominated by plant feeding animals to a food web dominated by animals foraging on detritus. The salt marsh management has to be differentiated into both ungrazed and lightly grazed areas (each 50 ~/o) or an overall grazing in large areas with less than 0.5 cattle h a -

Structure of the invertebrate fauna in salt marshes of the Wadden Sea coast of Schleswig-Holstein influenced by sheep-grazing

“…Increasing food resources support population development for Symplecta stictica (Limoniidae) and also Nernotelus notatus (Stratiomyidae). Andresen et al (1990) demonstrated in their cattle-grazing study report that grazing changes community structure from dominance of herbivores to dominance of detritivores. The same is true here, except for collembolans, which do not react the same way under cattle grazing as they do under sheep grazing.…”

“…In that study, a suction sampler with high efficiency only for epigaeic species was used, while a Kempsonextraction was used in this study with high efficiency for endofauna. Nevertheless, cattleand sheep-grazing appear to affect the fauna in the same way (Andresen et al, 1990;Grell, 1992), although they influence the abiotic environment differently.…”

“…The same is true here, except for collembolans, which do not react the same way under cattle grazing as they do under sheep grazing. In this study they increased in biomass towards the intensively grazed Festuca-sites, whereas they were extremely diminished in number through grazing according to Andresen et al (1990). In that study, a suction sampler with high efficiency only for epigaeic species was used, while a Kempsonextraction was used in this study with high efficiency for endofauna.…”

“…The effects of grazing and trampling by cattle, horses and sheep have already been under critical discussion (Bakker, 1990;Prokosch, 1990). The effects of different intensities of cattle grazing have been studied by Irmler & Heydemann (1986), Andresen et al (1990) and Grell (1992). However, sheep grazing is different from cattle grazing.…”

“…The supralittoral area of the Wadden Sea is formed by the salt marshes, a transient zone between the intertidal reaches and the marsh polders, In an undisturbed supralittoral ecosystem, flooding frequency and sedimentation/erosion processes rule the salt marsh succession from the low-lying Spartina-and Salicornia-stages to the high-lying Juncetum gerardii-stage with Festuca rubra litoralis (Andresen et al, 1990: Heydemann, 1981. Human interference superimposes on the landscape's evolution through land reclamation with intensive drainage, recreational activities, and grazing by sheep, geese, "Publication No 38 of the project Ecosystem Research Wadden Sea ~ 9 Bioloqische Anstalt Hetqoland, Hamburq cattle or horses.…”