- The ECN vegetation programme is nationally unique with respect to the high frequency of measurement (annual to tri-annual surveys). It thus provides a particularly sensitive record of recent long-term botanical change.
- Analyse of these data revealed a network-wide increase in both plant species richness (i.e. the number of species occurring within a defined area) and a metric summarising the soil pH preference of plant communities (Ellenberg R). The increase in this metric suggested that plant communities were gradually shifting in composition towards species characteristic of less acid soils.
- This was further supported by assessment of trends of individual species, which again showed that the majority of plant species increasing in frequency have a preference for soils with higher pH.
- Results therefore provide the first definitive evidence of widespread improvements in vegetation diversity as a consequence of partial environmental recovery from acidification, resulting in turn from reduced levels of acid deposition, although increased species richness in some lowland sites could also be linked to a series of wetter summers in recent years, and reduced occurrence of drought.
- The observation that UK vegetation species richness appears to be responding positively to declining acid deposition, provides a new perspective on the relationship between levels of air pollution and plant diversity.
- Negative spatial relationships between levels of nitrogen deposition and species richness have often been interpreted primarily in terms of evidence for the impacts of the nutrient enriching effects of nitrogen, and have been used to establish international guidelines for acceptable levels of N deposition under Critical Loads policy. However, levels of N deposition have tended to correlate strongly with levels of acid deposition (historically dominated by sulphur deposition).
- The study therefore highlights a clear policy need for a more thorough evaluation of the relative impacts of atmospheric eutrophication and acidification on botanical biodiversity, and demonstrates the value of ECN data as a particularly important element of the evidence-base in this field.
Reference: Rose, R., Monteith, DT., Henrys, P., Smart, S., Wood, C., Morecroft, M., Andrews, C., Beaumont, D., Benham, S., Bowmaker, V., Corbett, S., Dick, J., Dodd, B., Dodd, N., Flexen, M., McKenna, C., McMillan, S., Pallett, D., Rennie, S., Schafer, S., Scott, T., Sherrin, L., Turner, A. and Watson, H. (2016). Evidence for increases in vegetation species richness across the UK Environmental Change Network sites linked to changes in air pollution and weather patterns. Ecological Indicators, 68, 52-62. DOI: 10.1016/j.ecolind.2016.01.005.