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Spatial variability and temporal trends in water-use efficiency of European forests

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Saurer Matthias, Spahni Renato, Joos Fortunat, Leuenberger Markus, Loader Neil, McCarrol Danny, Gagen Mary, Puolter B, Siegwolf Rolf, Andreu-Hayles Laia, Boettger Tatjana, Dorado Linan I, Fairchild I, Gutierrez Emilie, Haupt M, Hilasvuori Emmi, Heinrich I, Helle Gerd, Grudd H, Jalkanen R, Levanic T, Linderholm H, Robertson Ian, Sonninen E, Treydte Kerstin,
Project iTREE-Long-term variability of tree growth in a changing environment - identifying physiological mechanisms using stable C and O isotopes in tree rings.
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Original article (peer-reviewed)

Journal Global Change Biology
Volume (Issue) 20(12)
Page(s) 3700 - 3712
Title of proceedings Global Change Biology
DOI 10.1111/gcb.12717


The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located across Europe are investigated to determine the intrinsic water-use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 1901–2000. The results were compared with simulations of a dynamic vegetation model (LPX-Bern 1.0) that integrates numerous ecosystem and land–atmosphere exchange processes in a theoretical framework. The spatial pattern of tree-ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south-to-north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil-water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase of iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation–climate feedbacks are currently still poorly constrained by observational data.