Showing papers by "Valérie Daux published in 2015"
University of Bern1, Centre national de la recherche scientifique2, Paul Scherrer Institute3, University of Mainz4, Natural Environment Research Council5, Swiss Federal Institute for Forest, Snow and Landscape Research6, Forschungszentrum Jülich7, Stanford University8, National Center for Atmospheric Research9, University of Exeter10, Columbia University11, University of Basilicata12, University of Vienna13, University of Barcelona14, Finnish Environment Institute15, American Museum of Natural History16, AGH University of Science and Technology17, Swansea University18, Silesian University of Technology19, Vytautas Magnus University20, University of Naples Federico II21, Anglia Ruskin University22
TL;DR: In this article, the authors used long-term δ13C tree-ring measurements across a European forest network to reconstruct the physiologically driven response of intercellular CO2 caused by atmospheric CO2 (Ca) trends.
Abstract: Considering the combined effects of CO2 fertilization and climate change drivers on plant physiology leads to a modest increase in simulated European forest transpiration in spite of the effects of CO2-induced stomatal closure. The Earth’s carbon and hydrologic cycles are intimately coupled by gas exchange through plant stomata1,2,3. However, uncertainties in the magnitude4,5,6 and consequences7,8 of the physiological responses9,10 of plants to elevated CO2 in natural environments hinders modelling of terrestrial water cycling and carbon storage11. Here we use annually resolved long-term δ13C tree-ring measurements across a European forest network to reconstruct the physiologically driven response of intercellular CO2 (Ci) caused by atmospheric CO2 (Ca) trends. When removing meteorological signals from the δ13C measurements, we find that trees across Europe regulated gas exchange so that for one ppmv atmospheric CO2 increase, Ci increased by ∼0.76 ppmv, most consistent with moderate control towards a constant Ci/Ca ratio. This response corresponds to twentieth-century intrinsic water-use efficiency (iWUE) increases of 14 ± 10 and 22 ± 6% at broadleaf and coniferous sites, respectively. An ensemble of process-based global vegetation models shows similar CO2 effects on iWUE trends. Yet, when operating these models with climate drivers reintroduced, despite decreased stomatal opening, 5% increases in European forest transpiration are calculated over the twentieth century. This counterintuitive result arises from lengthened growing seasons, enhanced evaporative demand in a warming climate, and increased leaf area, which together oppose effects of CO2-induced stomatal closure. Our study questions changes to the hydrological cycle, such as reductions in transpiration and air humidity, hypothesized to result from plant responses to anthropogenic emissions.
349 citations
TL;DR: In this article, the authors used tree-ring width chronologies of Abies squamata and Sabina squamat to detect a long-term persistent warming trend, starting in the 1820s, at a rate of 0.45 ± 0.09°C/century (1820−2009).
Abstract: Despite instrumental records showing recent large temperature rises on the Tibetan Plateau (TP), only a few tree-ring temperature reconstructions do capture this warming trend. Here, we sampled 260 trees from seven Alpine treeline locations across the southeast TP. Standardized tree-ring width chronologies of Abies squamata and Sabina squamat were produced following Regional Curve Standardization detrending. The leading principal component of these records is well correlated with the regional summer (JJA) minimum temperature (MinT) (R2 = 0.47, P < 0.001, 1953–2009). Hence we produce a regional summer MinT reconstruction spanning the last 212 years. This reconstruction reveals a long-term persistent warming trend, starting in the 1820s, at a rate of 0.45 ± 0.09 °C/century (1820–2009). This trend is also detected since the 1820s in the Asian summer MinT reconstruction produced by the PAGES 2K project, with a very close warming rate (0.43 ± 0.08 °C/century, 1820–1989). Our record also displays an enhanced multi-decadal variability since the mid-twentieth century. The 1990s–2000s are the warmest of our whole record, due to the superposition of the gradual warming trend and decadal variability during this interval. The strongest decadal cooling occurs during the 1950s and the largest warming trend during the 1970s. The magnitude of warming from 1973 to 2003 was larger than the total warming trend from 1820s to 2009. Extreme events are also more frequent since 1950. The pattern of multi-decadal variability has similarities with the Atlantic multi-decadal oscillation, suggesting common causality. CMIP5 historical simulations fail to capture both the magnitude and timing of this multi-decadal variability. The ensemble CMIP5 average produces a steady warming trend starting in the 1970s, which only accounts for about 60 % of the observed warming trend during this period. We conclude that TP summer temperature could reflect a climate response to increased greenhouse gas concentrations, however modulated by multi-decadal variations common with the Atlantic sector.
41 citations
TL;DR: In this paper, the authors used correlation analysis and a forward process-based model to investigate changes in climate limitation of the interannual tree-ring growth of Nothofagus pumilio at the upper treeline along a precipitation gradient in northern Patagonia.
37 citations