Increasing status of non-native vascular plants in the Sefton Coast sand-dune system, north Merseyside, UK

Over 460 non-native (alien) taxa were recorded in a Sefton Coast sand-dune vascular plant inventory, their proportion in the flora increasing after 1999. Between 2005/06 and 2018, twice as many non-native as native plants were found. An analysis of occurrences of native and non-native taxa in six major habitat types found that a higher proportion of aliens was present in scrub/woodland and disturbed ground, while native plants had more occurrences in fixed dunes/dune grasslands, dune heath and wetlands. No differences between the two groups were detected for strandline/shingle and embryo/mobile dune habitats. Twenty-four non-native and 14 native taxa showed invasive characteristics in the duneland. The former included especially Hippophae rhamnoides and Rosa rugosa, both constituting major threats to sand-dune biodiversity. Particularly invasive native plants were Arrhenatherum elatius, Betula spp., Salix cinerea, and Ulex europaea. The main findings accord with studies elsewhere in Britain and Europe showing recent increases of neophytes in semi-natural habitats and that both non-native and native species can have invasive traits. The open habitats of coastal dunes seem to be particularly susceptible to plant invasions.

The grazing of British sand dune vegetation

SynopsisThe herbaceous vegetation of sand dunes is quite strongly influenced by a number of different grazing animals, principally vertebrates. Between 1985 and 1987 forty-eight dune sites were visited and studied, information being recorded on the vegetation and grazing status of 777 quadrats.The results of the survey confirm that the dominant grazing animal in British sand dunes is the rabbit. Over 70% of the quadrats are regarded as being rabbit-grazed directly and over 98% of the dune sites sampled appeared to be affected by rabbit grazing to some extent. Just over a third of the sites were grazed by cattle and a similar proportion by sheep; generally it was either cattle or sheep although five sites were grazed by both. There was only one site significantly grazed by ponies although a number of other sites were grazed occasionally by passing ponies.The intensity of grazing was very variable. Out of the forty-eight sites, three were regarded as being ungrazed and a further ten only lightly grazed, while nine sites were considered to be heavily grazed. However the remaining twenty-six sites were recognised as being intermediate only to the extent of not being obviously overgrazed or undergrazed. It was further recognised that the present state of the vegetation tended to reflect the grazing management in the recent past rather than current practice. A change in the grazing management often took many years to effect a permanent change in the vegetation.The grazing requirements to promote species diversity are very different for the different habitat types. In the yellow dunes the plant community is open with bare ground for colonisation and plant competition is not intense. There is thus little need for the control of plant growth by grazing.Dune grassland, in the narrow sense, needs to be grazed to maintain plant species diversity. The purpose of grazing is to remove prolific growth from the most vigorously growing plants to reduce competition. Lower grazing intensities are needed for all the year round grazing than when grazing is first applied to an area or is a permanent measure for limited periods of the year only.Dune slacks are generally best grazed by cattle and, with the higher soil moisture, grazing intensities can be higher than those applied to dune grassland. Excessive grazing is likely to cause serious damage to both the soil and the vegetation, especially in the wetter areas.Dune heath vegetation has a low productivity and its own special management problems. It needs to be grazed (or cut or burnt) to maintain the internal mosaic by the successful regeneration of the main species, but too much grazing will lead to conversion to a species-poor acid grassland.