title: Exploring continental-scale stand health - N : P ratio relationships for European forests.
abstract: Understanding the relationship between nitrogen (N) availability and stand health in forest ecosystems is crucial, because a large proportion of European forests is subjected to N-deposition levels beyond their retention capacity. We used data from a long-term forest monitoring programme (ICP Forests) to test the relationship between an index of N availability, foliar nitrogen : phosphorus (N : P) ratios, tree defoliation and discoloration. We hypothesized a segmented response of stand health to N : P ratios and an improved model-fit after correcting for climatic covariates. In accordance with the hypothesis, we found a segmented response with a breakpoint for conifer defoliation at N : P ratios as low as 7.3. Inclusion of climatic variables improved the fit of the models, but there was significant collinearity with N : P. Increases in N availability appear, at least for conifers, to have a negative effect on tree health even under N-limiting conditions. Regulation of N-deposition levels is consequently as timely as ever. We propose that increases in tree defoliation, other than resulting in serious plant fitness issues, may represent early diagnostic symptoms of N-addition related imbalances.
authors.affiliation: Institut für Biologie, Freie Universität Berlin, Altensteinstr. 6, D-14195, Berlin, Germany.|Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), D-14195, Berlin, Germany.
authors.forename: Stavros D
authors.initials: SD
authors.lastname: Veresoglou
authors.affiliation: CSIC, Cerdanyola del Valles, 08193, Barcelona, Catalonia, Spain.|CREAF, Cerdanyola del Valles, 08193, Barcelona, Catalonia, Spain.
authors.forename: Josep
authors.initials: J
authors.lastname: Peñuelas
authors.affiliation: Thünen Institute for World Forestry, Hamburg, Germany.
authors.forename: Richard
authors.initials: R
authors.lastname: Fischer
authors.affiliation: Finnish Forest Research Institute (Metla), Northern Unit, PO Box 16, FI-96301, Rovaniemi, Finland.
authors.forename: Pasi
authors.initials: P
authors.lastname: Rautio
authors.affiliation: CSIC, Cerdanyola del Valles, 08193, Barcelona, Catalonia, Spain.|CREAF, Cerdanyola del Valles, 08193, Barcelona, Catalonia, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Sardans
authors.affiliation: Finnish Forest Research Institute, PO Box 413, 90014, Oulun yliopisto, Oulu, Finland.
authors.forename: Päivi
authors.initials: P
authors.lastname: Merilä
authors.affiliation: Institute of Forestry, Kneza Viseslava 3, 11000, Belgrade, Serbia.
authors.forename: Mara
authors.initials: M
authors.lastname: Tabakovic-Tosic
authors.affiliation: Institut für Biologie, Freie Universität Berlin, Altensteinstr. 6, D-14195, Berlin, Germany.|Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), D-14195, Berlin, Germany.
authors.forename: Matthias C
authors.initials: MC
authors.lastname: Rillig
mesh_terms: D002980:Climate; D003116:Color; D005060:Europe; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D013312:Stress, Physiological; D064028:Tracheophyta / Q000378:metabolism*; D014197:Trees / Q000378:metabolism*
chemical_list: D010758:Phosphorus; D009584:Nitrogen
keywords: Bayesian inference; N : P ratios; defoliation; forest health; nitrogen (N) deposition; plant stoichiometry; visual crown assessment