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Nitrogen impacts on vascular plants in Britain: an analysis of two national observation networks

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Author(s): P. A. Henrys | C. J. Stevens | S. M. Smart | L. C. Maskell | K. J. Walker | C. D. Preston | A. Crowe | E. Rowe | D. J. Gowing | B. A. Emmett

Journal: Biogeosciences Discussions
ISSN 1810-6277

Volume: 8;
Issue: 4;
Start page: 7441;
Date: 2011;
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ABSTRACT
Large areas of the United Kingdom 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), and are predicted to continue to do so. Previous studies have shown that this excess N can be very damaging to semi-natural ecosystems. However, such studies have focussed primarily on the relationship of species richness to nitrogen, possibly missing the risk that increased deposition can have on individual plant species. To address this gap in knowledge, we used data from two national observation networks over Great Britain: the vascular plant database and the Botanical Society of the British Isles local change network to examine the response of individual vascular plant species to nitrogen in acid grasslands, calcareous grasslands and heathlands. Presence absence records of individual species, along with mean Ellenberg 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. Many individual species showed strong relationships with N deposition and clear negative trends in species prevalence to increasing nitrogen were found in all habitats. Species that showed negative relationships to N showed signs of decline at low levels, far below the current critical load levels.
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