Individual study: The effect of cessation of cattle and sheep grazing on common saltmarsh-grass Puccinellia maritima-dominated salt-marsh vegetation at Skallingen, Jutland, Denmark
Jensen A. (1985) The effect of cattle and sheep grazing on salt-marsh vegetation at Skallingen, Denmark. Vegetatio (now Plant Ecology), 37-48
Domestic animals (mostly cattle and sheep) have been widely grazed on salt marshes in Denmark for hundreds of years, and only a few salt marshes and seashore meadows have been left unaffected by this practice. Consequently, the morphology and the vegetation of nearly all Danish salt marshes have been affected. The first six years of exclosure experiments where traditional sheep and cattle grazing was ceased within Puccinellion maritimae vegetation, are described.
Study area: The salt marsh is located on the peninsula of Skallingen situated on the west coast of southern Jutland, Denmark. The marsh has a well-developed creek system which drains into a tidal channel. The marsh is divided into a grazed (1,100 ha) and an ungrazed area (300 ha). Around 500 sheep and 500 cattle graze from May to October; the grazing fulfils both agricultural and conservation objectives (the salt marsh was declared a nature reserve in 1938).
Exclosures: During early spring 1972, eight 40 m x 60 m exclosures were established in different parts of the grazed salt marsh to study the effects of a sudden change to no grazing on the vegetation and sediments. Two of the exclosures (A and B, about 500 m apart) on homogenous stands of common saltmarsh-grass Puccinellia maritima-dominated marsh were analysed in this study. This plant community is quite attractive to sheep and cattle, so that the grazing intensity was comparatively high and above the average of the overall stocking level of 0.5 sheep and 0.5 cattle/ha.
Vegetation monitoring: Plant species present in each exclosure were recorded from August 1971 (before the exclosures were erected) to August 1978. For each exclosure, two permanent plots (1 m x 5 m) were established, one placed within, and the other outside it. Vegetation cover and bare ground was measured by the point quadrat method and all species present in the plot were listed.
The results of these experiments are discussed in relation to the natural development of the vegetation that occurred in a permanent plot in the ungrazed part of the salt marsh.
Exclosure A: Total vegetation cover increased dramatically during six years without grazing (average of both plots with grazing 85%; and ungrazed 138%. Note: value above 100% due to point quadrat sampling method). No change in species composition took place during the six years, but all species increased in cover. The perennials sea purslane Halimione portulacoides and common sea-lavender Limonium vulgare showed the largest increases (both from about 5 to 10% cover), and more surprisingly, the cover of the annuals glasswort Salicornia europaea and annual sea-blight Suaeda maritima also increased, despite the amount of bare ground, available for seedlings decreasing. P.maritima maintained its dominance increasing in cover from just <80% to just>80%). These changes, plus accumulation of plant litter, greatly altered the appearance of the ungrazed plots, and there was an obvious increase in number of flowering tillers and seed production, although this was not measured.
Exclosure B: Total vegetation cover was very similar after six years without grazing, however there were changes in species abundances and composition. Sea wormwood Artemisia maritima colonized whereas S. europaea disappeared. Cover of red fescue Festuca rubra (c.55% to72%) and H.portulacoides (c.22% to 60% - values read of graphs) showed marked increases, whilst cover of P.maritima fell dramatically from 40% to 5%, and sea arrow-grass Triglochin maritima from c.7% to <1%. The covers of L.vulgare, sea plantain Plantago maritima and sea aster Aster tripolium were also reduced but to a much lesser extent.
Conclusions: From these results, it can be seen that when grazing is terminated, a burst of post-grazing changes in the vegetation rapidly takes place after which more natural, competitive interactions occur, but such changes may be difficult to predict and are presumably dependent on quite localised environmental and biotic factors.
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