Heather Moorland Vegetation and Air Pollution: A Comparison and Synthesis of Three National Gradient Studies
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Large-scale spatial gradient studies are increasingly used to understand the impacts of air pollution and devise appropriate conservation and policy responses, but how consistent are the conclusions we draw from these surveys? Here, we address this question by comparing three independent gradient studies from the same habitat, UK heather moorlands. We harmonise and re-analyse vegetation data from these surveys in relation to cumulative nitrogen deposition, sulphur deposition and other potential drivers and use these results to assess the possible impacts of air pollution in this habitat. Air pollution variables explain more variance in species richness and composition than other variables in the vast majority of analyses. Untangling the relative contribution of nitrogen and (legacy) sulphur deposition is difficult due to strong correlation, but it is likely that nitrogen deposition is currently the dominant driver of change. There is consistency in the negative correlation between species richness and nitrogen deposition, but some variability in the form of this relationship due to small sample sizes. Across surveys there is a high degree of consistency in species identified as either positively or negatively correlated to nitrogen deposition, and no evidence for systematic differences. We conclude that relatively small surveys across wide gradients can provide useful information on potential drivers of diversity, as well as identify sensitive and tolerant species. Our results strongly suggest that nitrogen deposition has a severe and widespread impact on the biodiversity of British heather moorlands and is causing changes in plant communities, including promoting the spread of at least one invasive species.
KeywordsPollution Heathland Bryophytes Ordination Nitrogen deposition
RJP, NBD and SJMC were supported by the UK Natural Environment Research Council through the European Union FP6 BiodivERsA (ERA-NET) project PEATBOG. Data collection was supported by DEFRA through the UKREATE and Terrestrial Umbrella programmes.
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