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Exploring continental‐scale stand health – N : P ratio relationships for E uropean forests
Author(s) -
Veresoglou Stavros D.,
Peñuelas Josep,
Fischer Richard,
Rautio Pasi,
Sardans Jordi,
Merilä Päivi,
TabakovicTosic Mara,
Rillig Matthias C.
Publication year - 2014
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.12665
Subject(s) - collinearity , ecosystem , scale (ratio) , tree (set theory) , limiting , phosphorus , nitrogen , ecology , environmental science , biology , zoology , mathematics , statistics , chemistry , geography , combinatorics , organic chemistry , mechanical engineering , cartography , engineering
Summary 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.