Abstract: Grazed coastal grassland in eastern Denmark -

Managing plant communities to preserve rare plant species

This study analyzes vegetation of coastal grassland in an embanked nature reserve (c. 2000 ha) south

of Copenhagen on the island Amager. The focus is on grazing effects on abundance of Iris spuria,

Selinum dubium and Cerastium subtetrandrum. The main objectives are to identify plant communities

and site factors related to the target species. Considering the ecological requirements of the species it is

possible to estimate their potential distribution in the study area. Based on these results, management on

the rare plants is discussed. Vegetation data, consisting of 73 relevés collected in summer 2008, are classified

using TWINSPAN analysis and ordination by DCA. Thus, the main vegetation units and underlying

environmental gradients are identified and assigned to plant communities known from the literature.

Recent vegetation changes are analysed by DCA using published data from 2004 and 2006. The main

factors defining the grassland vegetation of Vestamager are salinity, moisture and grazing. Nutrientpoor,

salt-affected and grazed communities of the Lolio-Cynosuretum are the most common vegetation

type in the study area. This association can be divided into a subtype of moist grassland, including

species of wetland meadows (Molinion), and drier grassland, with floristic affinities to Mesobromion. In

the southwest of the study area, with slightly higher salinity, the Lolio-Cynosuretum is replaced by

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Juncetum gerardii salt marshes. Within the salt marshes pioneer vegetation is developed on ant hills. The

transition between geo- and hydrolitoral is colonized by brackish reeds. On intensely grazed, moist to

wet sites the Lolio-Cynosuretum is replaced by the Ranunculo repentis-Alopecuretum geniculati. Tall

grassland dominated by Calamagrostis epigejos develops under reduced grazing pressure.

Iris spuria and Selinum dubium occur with one stand each in the north of the study area. The populations

are associated with drier parts of the Lolio-Cynosuretum juncetosum gerardii. Smaller populations

of Selinum dubium are found in Plantago major communities. Cerastium subtetrandrum is represented

with several small populations on ant hills in salt-pioneer marsh. Iris spuria is sensitive to grazing, and

thus the intensification of grazing on Vestamager has resulted in a decreasing population of this species

in the past years. Selinum dubium is more tolerant, and vegetative individuals are able to persist in

grazed areas. Cerastium subtetrandrum depends indirectly on grazing. Potential habitats of this species

are maintained by grazing. Intensification of grazing and shrub clearance have reduced cover of woody

species and tall grasses promoting less competitive species. Recently, a development towards open saltinfluenced

grassland can be observed, albeit without increasing floristic diversity. Optimal conservation

of the target species seems only feasible if a more diverse management is applied. For conservation of

Iris spuria and Selinum dubium a local reduction of grazing is recommended including exclosures.

Preservation of Cerastium subtetrandrum, however, depends on low vegetation, which calls for relatively

intense grazing. In the long term, higher diversity will only be achieved by spatio-temporal variation

of grazing intensity which would also accommodate the different demands of the target species.

Keywords: Cerastium subtetrandrum, conservation management, grazing variation, Iris spuria, salt

marsh, Selinum dubium, target species.