Inferring Nitrogen Deposition from Plant Community Composition 2

15 Chronically elevated reactive nitrogen deposition has a severe impact on many ecosystems, and there is 16 widespread interest in the possibility of using plant community composition to estimate the level of 17 nitrogen deposition and consequent impacts. Existing approaches use a variety of simple measures 18 including functional type ratios, Ellenberg numbers, and diversity indices. We propose an alternative 19 approach in which species-environment models are constructed using national datasets designed to 20 capture broad-scale deposition patterns. We construct models using partial least squares, weighted 21 average, and maximum likelihood Gaussian logit regression for two British semi-natural habitats, and 22 test how well they predict N deposition by cross-validation. We find that performance is good with R 23 values up to 0.7, and suggest that such models may be a useful addition to the bioindication toolbox. 24