Nitrogen deposition and Critical Load exceedance: effects on health, growth and diversity of forest vegetation in Italy. Abstracts & Programme of the International Conference “Biological Reactions of Forests to Climate Change and Air Pollution”, Kaunas, Lithuania.

Concern about the actual and potential effects of Nitrogen (N) deposition on forests embraces almost all the forest ecosystem’s compartments, including vegetation, soil biota, soil and soil solution, and run-off. Particular emphasis was put on the role of N as a: (i) factor stimulating growth, thus enhancing Carbon uptake; (ii) possible cause of nutritional imbalance, thus causing possible problems with tree health because of altered susceptibility to pests and disease; and (iii) factor altering the composition and richness of ground vegetation. In the frame of the Italian forest monitoring programme CONECOFOR, a study was undertaken to investigate the effect of actual N deposition and exceedance of N Critical Load (CL) on forest vegetation at selected forest ecosystems spread across a range of environmental condition and deposition loads. At these plots atmospheric deposition have been measured over the past 15 years together with a suite of other variables, including meteorology, ozone, soil- and foliar nutrients contents, species diversity, tree health and growth. The study was conducted as follows: firstly, the Simple Mass Balance (SMB) method was used to estimate CL and calculate exceedance with respect to the actual deposition load; secondly, a set of predictors and response variables was identified. Thirdly, sub-sets of predictors were used to investigate effects of N deposition on the nutritional status of the plots and to model the response variable of interest; finally, the model’s residuals (modeled-measured) were investigated with respect to N deposition values and CL exceedance. Results of this study will be presented in terms of N deposition, CL exceedances, and estimated effects on tree health, growth and species diversity.