Nitrogen deposition effects on plant species diversity; threshold loads from field data

• Published in: Environmental pollution (1987) 2013-08, Vol.179, p.218-223
• Main Authors: Tipping, E., Henrys, P.A., Maskell, L.C., Smart, S.M.
• Format: Article
• Language: English
• Subjects: Air Pollutants - analysis; Air Pollutants - toxicity; Animal and plant ecology; Animal, plant and microbial ecology; Biodiversity; Biological and medical sciences; Biological diversity; bogs; Countryside Survey; critical load; Demecology; Deposition; Diversity; Ecosystem; Environmental Monitoring; Estimates; Fundamental and applied biological sciences. Psychology; Grasslands; Great Britain; Hydrogen-Ion Concentration; nitrogen; Nitrogen - analysis; Nitrogen - toxicity; Nitrogen deposition; nitrogen fixation; Plants; Plants - classification; Plants and fungi; Pollution abatement; Regression; Soil - chemistry; species diversity; Species richness; Thresholds; United Kingdom; Woodlands
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2013.04.008

National-scale plant species richness data for Great Britain in 1998 were related to modelled contemporary N deposition (Ndep) using a broken stick median regression, to estimate thresholds above which Ndep definitely has had an effect. The thresholds (kg N ha−1 a−1) are 7.9 for acid grassland 14.9 for bogs, 23.6 for calcareous grassland, 7.8 for deciduous woodland and 8.8 for heath. The woodland and heath thresholds are not significantly greater than the lowest Ndep, which implies that species loss may occur over the whole range of contemporary Ndep. This also applies to acid grassland if it is assumed that Ndep has substituted for previous N fixation. The thresholds for bog and calcareous grassland are both significantly above the lowest Ndep. The thresholds are lower than the mid-range empirical Critical Loads for acid grassland, deciduous woodland and heath, higher for bogs, and approximately equal for calcareous grassland. •We assembled species richness and N deposition data for five UK semi-natural habitats.•We determined threshold deposition rates above which species richness declines.•Woodland, heath and acid grassland show species loss at all deposition rates.•Bog and calcareous grassland thresholds exceed the lowest deposition rates.•The thresholds differ from empirical critical loads for four of the five habitats. Analysis of extensive field data provides estimates of nitrogen deposition rates above which plant species richness is reduced.