Prediction of species response to atmospheric nitrogen deposition by means of ecological measures and life history traits

1 The main objective of this study was to predict the responses of vascular plant species to atmospheric nitrogen deposition and enhanced soil nitrogen levels. The study was carried out in deciduous forests located in three regions of southern Sweden. The abundance of vascular plants, as well as soil pH and nitrogen mineralization rates, were studied in a total of 661 sample plots. 2 We calculated an ecological measure (N-dev value) for all species based on their observed vs. expected nitrification ratios at a given soil pH, and compared its accuracy in predicting abundance changes with results using life history traits. Data from long-term field studies and fertilization experiments were used for validation. 3 N-dev values were positively correlated between neighbouring regions. Values for the southernmost region (Skane) were also positively related to the changes in species frequency observed in large-scale flora surveys and permanent plot studies in that area and with species changes reported from Central Europe. Values from one of two other regions were also consistent. N-dev values from Skane (but no other region) predicted species responses in short-term fertilization experiments. 4 No life history trait was as good a predictor as N-dev, although plant height, leaf anatomy, leaf nitrogen concentration and phenology showed significant correlations. Attributes related to taxonomy, life form, relative growth rate and habitat type showed no agreement with the changes in species abundance. 5 We predict that species with the following attribute syndrome will increase in abundance in response to enhanced nitrogen levels: those favoured by a high soil nitrification ratio relative to other species at a given soil pH, tall stature, hydro- to helomorph anatomy, high leaf nitrogen concentration and a late phenological development.