Effects of long-term grazing management on sand dune vegetation of high conservation interest Katharina Plassmann, M. Laurence M. Jones & Gareth Edwards-Jones Abstract Question: Can long-term grazing management maintain and restore species-rich sand dune plant communities within a sand dune site of high con- servation interest? Location: Newborough Warren, North Wales, UK. Methods: Vegetation changes that occurred between 1987 and 2003, subsequent to grazing by domestic livestock being introduced to the site after decades with little or no stock grazing, were analysed using data collected from permanent monitoring quadrats over a 16-year period. Results: At the plant community level, grazing brought about a shift from a tall-grass dominated, species-poor community to a more species-rich com- munity in the dry dunes, but did not change community type in dune slacks. However, at the species level, grazing enhanced the abundance of some desired perennial, annual and biennial species, graminoids and bryophytes in both habitat types. The increased frequency of positive indicator species for habitat condition suggests that grazing was beneficial for species of conservation interest. Ellenberg nitro- gen (N) values decreased after grazing in dry habitats but showed no long-term change independent of grazing, suggesting no increase in site fertility over the study period. Surprisingly, light (L) values also decreased in the dry dunes after grazing. Conclusions: Long-term grazing management can play an important role for the conservation of dune communities and associated species. Because of its positive effects on species diversity, plant commu- nities and habitat condition in sand dunes, livestock grazing is recommended for conservation manage- ment. Keywords: Atmospheric nitrogen deposition; Con- servation grazing; Ellenberg; Newborough Warren; Permanent quadrats. Nomenclature: Stace (1997), Coppins (2002), Smith (1990, 2004). Introduction Coastal dunes are vulnerable and threatened ecosystems (van der Meulen et al. 2004). Within Europe, their area has declined by about 40% since 1900 and by about one-third since the late 1970s (O’Briain 2005). They have been damaged by a variety of human activities, including agriculture, tourism, coastal defence, housing and industry de- velopment (van der Meulen & van der Maarel 1989; Doody et al. 1993; van der Maarel & Usher 1997). Climate change and rising sea levels could further threaten these low-lying coastal habitats (Pye 2001; Brown & McLachlan 2002). Another threat to many dune systems is that they are more vegetated than they have been for centuries. This leads to increased stability and de- velopment towards scrub and woodland vegetation with an associated loss of species diversity (Westhoff 1989; Houston 1997). Several factors have con- tributed to this situation, including active measures taken to stabilize dunes, such as the afforestation of parts of dune systems and planting of Ammophila arenaria (Jungerius & van der Meulen 1988; Westh- off 1989). Eutrophication caused by increased atmospheric deposition of nutrients also leads to increased physical stabilization of dunes, accelerates succession and promotes tall, dense vegetation, all of which result in the loss of species diversity, especially those species associated with early suc- cessional communities (ten Harkel & van der Meulen 1996; Jones et al. 2004; Plassmann et al. 2009b; Remke et al. 2009). Another important fac- tor is the general reduction of grazing pressure on dunes (van der Maarel & van der Maarel-Versluys 1996). The diversity of many dune areas has devel- oped because of a long history of grazing by rabbits (Oryctolagus cuniculus) and domestic stock (Ran- Plassmann, K. (corresponding author, katrinplass- mann@web.de) & Edwards-Jones, G. (g.e.jones@ bangor.ac.uk): School of the Environment and Natural Resources, Bangor University, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK. Jones, M.L.M. (lj@ceh.ac.uk): Centre for Ecology and Hydrology Bangor, Environment Centre Wales, Dei- niol Road, Bangor, Gwynedd LL57 2UW, UK. Applied Vegetation Science 13: 100–112, 2010 DOI: 10.1111/j.1654-109X.2009.01052.x & 2009 International Association for Vegetation Science