Nitrogen deposition and the reduction of butterfly biodiversity quality in the Netherlands

Butterfly decline in Northern Europe is a cause of concern and it has been hypothesised that this is due to nitrogen deposition inducing excess early growth of plants. It has also been changing the quality of the food available to larvae. We tested these hypotheses by linking butterfly biodiversity quality indices (species richness, population, biomass, conservation value, evenness (Simpsonʹs Index) and modelled species richness (Chao 1 and 2)) with nitrogen Critical Load Exceedence (nCLE) data. An index of butterfly sensitivity to nitrogen was also created (Species Nitrogen Value Index (SNVI)). Using PCA, datasets were tested for associations and relationships. sults included multiple biodiversity quality indices based on 17 years of data (aggregated into three periods of six, six and five years to give 287 datasets) in four habitat types (grassland, heathland, woodland and farmland). With the exception of heathland the analysis showed that nitrogen deposition and all other indices (except SNVI) were in decline. athland the last 11 years did not show any significant decline. Heathland also showed an anomalous biodiversity quality profile for these last 11 years, suggesting that the sensitivity of heathland to nitrogen deposition will require further considerable efforts to achieve a nitrogen deposition that is not in exceedence of the critical load. t restoration will take time due to the multiple hindrances to colonisation, which in the case of heathland might prevent successful butterfly colonisation for the foreseeable future. These results indicate the efficacy of butterfly biodiversity quality and nCLE as indicators for the SEBI 2020 process (Streamlining European Biodiversity Indicators) by showing the relationship between them.