Individual study: Low intensity cattle grazing maintains plant communities in wet dune valleys after near-eradication of European rabbit Oryctolagus cuniculus on the island of Vlieland, Friesland, the Netherlands
Aptroot A., van Dobben H.F., Slim P.A. & Olff H. (2007) The role of cattle in maintaining plant species diversity in wet dune valleys. Biodiversity and Conservation, 16, 1541-1550
The internationally important coastal dune region of the West Frisian islands and part of the chain of barrier islands separating the Wadden Sea from the North Sea, constitute the most extensive natural habitat in the Netherlands. Most are designated as national park or nature reserve, and are managed to maintain the dune flora and fauna; there is special concern regarding conservation of its specialized plant communities, heavily influenced by successional processes. The most important factor that used to check succession was rabbit Oryctolagus cuniculus grazing. However, after myxomatosis in the late 1950s and then rabbit viral haemorrhagic disease (RVHD) in the late 80s, rabbits were almost eradicated and vegetation succession increased. In an attempt to replace the rabbit grazing (and disturbance via digging), low density cattle grazing was initiated in a dune area on the island of Vlieland in 1993, and the effects on the vegetation was monitored.
Study area: The vegetation of the central part of Vlieland (53˚17'N, 5˚00'E) has been monitored by means of permanent plots over 33 years (1972–2005), primarily to follow succession in the various vegetation types present. Several plots were surrounded by wire mesh from 1974 to 1978, to exclude rabbits. Cattle grazing was allowed in part of the area from 1993 onward, thus affording an opportunity to evaluate and compare the effectiveness of rabbits and cattle in influencing succession.
Monitoring: Within the permanent plots (usually 3 x 3 m in size), the succession of species-rich wetland vegetation in dune valleys into species-poor dwarf shrub vegetation was followed: abundance and cover, and phenology (vegetative/in buds/flowers/fruits) was noted for all vascular plant species, and the cover of moss and lichen species was recorded. Observations paid special attention to, the often highly specialized, cryptogamic species. The plots were surveyed in the last weeks of June, over the 33 years.
Low density cattle grazing and associated disturbance was found to be an effective substitute for rabbits in countering succession, thus preserving the plant species diversity and dune communities. The differences between areas excluded from, and those open to rabbit grazing, were significant, but were not long-lasting after the exclosures were opened again to the rabbits. The Cladina lichen-rich Empetrum-heathland in the dunes appeared to be a vegetation stage in a probably cyclic succession that might be triggered by grazing.
In conclusion, the total vascular plant, moss and lichen diversity of this dune ecosystem can be maintained by a combination of extensive (low intensity) cattle grazing through a regular but limited re-creation of pioneer (early succession) situations.
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