Impacts of nitrogen deposition on vascular plants in Britain: an analysis of two national observation networks
- 1Centre for Ecology and Hydrology, Lancaster Environment Centre, Bailrigg, Lancaster, LA1 4AP, UK
- 2Department of Environment, Earth and Ecosystems, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
- 3Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
- 4Botanical Society of the British Isles (BSBI), c/o 97 Dragon Parade, Harrogate, North Yorkshire, HG1 5DG, UK
- 5Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BB, UK
- 6Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd, LL57 2UW, UK
Abstract. Large areas of Great Britain currently have nitrogen (N) deposition at rates which exceed the thresholds above which there is risk of damage to sensitive components of the ecosystem (critical loads). Previous studies have focussed primarily on the relationship of species richness to nitrogen, whereas here we look at individual species. We used data from two national observation networks over Great Britain to examine the response of individual vascular plant species to N in acid grasslands, calcareous grasslands and heathlands. Presence absence records of individual species, along with mean Ellenberg N scores, within 10 km hectads were modelled against N deposition whilst at the same time controlling for the effects of climate, land use and sulphur deposition using generalised additive models. Ellenberg N showed a significant increase with increasing N deposition in almost all habitats across both surveys indicating increased fertility. Many individual species showed strong relationships with N deposition and clear negative trends in species prevalence to increasing nitrogen were found in all habitats. A number of these species were either habitat dominants or possessed traits known to be influential in controlling ecosystem function. Many community dominants showing significant negative relationships with N deposition highlight a potentially significant loss of function. Some species that showed negative relationships to N showed signs of decline at low levels, far below the current critical load levels. Some species also showed continuous changes as N deposition levels rose above the current critical load values. This work contributes to the growing evidence base suggesting species level impacts at low N deposition values.