Individual study: Long-term changes of salt marsh vegetation communities in response to different cattle grazing regimes at Leybucht, Niedersachsen, northern Germany
Andresen H., Bakker J.P., Brongers M., Heydemann B. & Irmler U. (1990) Long-term changes of salt marsh communities by cattle grazing. Vegetatio (now Plant Ecology). Plant Ecology, 137-148
Many European salt marshes have been traditionally grazed and cut for hay. Whilst hay-making has virtually ceased, grazing is still commonly practiced in northwest Europe Intensive grazing for agricultural purposes results in a short turf of fairly uniform vegetation structure. Abandoning grazing on salt marshes, conversely eventually results in tall forb communities with accumulated litter and a decrease in plant species diversity. This present study compared the longterm effects (over nine years) of areas grazed under different cattle stocking rates, and an area where there was no grazing, on sedimentation rates, and the structure and species composition of plant and invertebrate communities on a salt marsh in northern Germany. The effects these grazing regimes on saltmarsh plants are summarized here.
Study site: The study was undertaken on coastal saltmarsh located at Leybucht, Niedersachsen (53º 31'N, 7º08'E) northern Germany. The study site prior to the experiment had been heavily grazed (2 cattle/ha).The marsh includes a narrow strip of a pioneer community (glasswort Salicornia stricta zone), a broad lower salt marsh community (common saltmarsh-grass Puccinellia maritima zone) and a narrow higher salt marsh community (red fescue Festuca rubra zone).
Grazing regimes: In 1980, three exclosures of 10 ha each were established with 0.5 cattle/ha, 1 cattle/ha and zero grazing, and these were compared with the heavily grazed area. These grazing regimes were continued for 8 years.
Vegetation sampling: In 1980 and 1988, species abundance within the differently grazed and non-grazed areas was quantified by point quadrat sampling along a gradient from the higher salt marsh down to the tidal flats. The vegetation was subdivided into high canopy i.e. flowering (as opposed to non-flowering) sea aster Aster tripolium, and an understorey of other shorter vegetation, comprising mainly grasses. The height of both layers was measured (n = 20) at 50 m intervals along the gradient.
Changes in species abundance: A 'sea couch Elymus pycnanthus salt-marsh community' vegetation type became dominant in the higher salt marsh in the exclosure subject to no grazing. Puccinellia maritima became dominant in the lower salt marsh in all sites but was very rare in the higher salt marsh in the exclosure with no grazing. A.tripolium occurred more frequently in the higher salt marsh with increasing stocking rates. F.rubra and creeping bent Agrostis stolonifera occurred most frequently in the higher, grazed salt marsh.
Bare soil was virtually absent in the non-grazed exclosure, but increased with increasing stocking rates, particularly in the lower salt marsh. The occurrence of lower salt marsh and annual species, i.e. Salicornia stricta, shrubby sea-blite Suaeda maritima, common cord-grass Spartina anglica, lesser sea-spurrey Spergularia salina (Syn.S.marina) and Danish scurvy-grass Cochlearia danica in the grazed sites appeared to be related to the occurrence of bare soil.
Vegetation structure: The canopy height, unsurprisingly, decreased with increasing stocking rate. The canopy height of the flowering Aster increased from the highest zone down towards the tidal flats in the grazed sites regardless of grazing intensity, indicating a decrease of grazing impact towards the tidal flat; this was not evident in the exclosure with no grazing.
However, non-flowering Aster only occurred in the higher salt marsh with the highest stocking rate and its canopy height over the whole gradient decreased significantly with increasing stocking rates. The height of the understorey was higher in the ungrazed exclosure than in the grazed sites along most of the gradient; the effects of differences in the stocking rates were small, especially in the higher salt marsh. The canopy height of the understorey vegetation in the lightly grazed site was significantly higher than in the more heavily grazed sites in the lower salt marsh, indicating a stronger impact in the lower salt marsh with increased grazing intensity.
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