Spatio‐temporal patterns of tree growth as related to carbon isotope fractionation in European forests under changing climate

Aim To decipher Europe-wide spatiotemporal patterns of forest growth dynamics and their associations with carbon isotope fractionation processes inferred from tree rings as modulated by climate warming. Location Europe and North Africa (30‒70°N, 10°W‒35°E). Time period 1901‒2003. Major taxa studied Temperate and Euro-Siberian trees. Methods We characterize changes in the relationship between tree growth and carbon isotope fractionation over the 20th century using a European network consisting of 20 site chronologies. Using indexed tree-ring widths (TRWi), we assess shifts in the temporal coherence of radial growth across sites (synchrony) for five forest ecosystems (Atlantic, Boreal, cold continental, Mediterranean and temperate). We also examine whether TRWi shows variable coupling with leaf-level gas exchange, inferred from indexed carbon isotope discrimination of tree-ring cellulose (Δ13Ci). Results We find spatial autocorrelation for TRWi and Δ13Ci extending over up to 1,000 km among forest stands. However, growth synchrony is not uniform across Europe, but increases along a latitudinal gradient concurrent with decreasing temperature and evapotranspiration. Latitudinal relationships between TRWi and Δ13Ci (changing from negative to positive southwards) point to drought impairing carbon uptake via stomatal regulation for water saving occurring at forests below 60°N in continental Europe. A rise in forest growth synchrony over the 20th century together with increasingly positive relationships between TRWi and Δ13Ci indicate intensifying drought impacts on tree performance. These effects are noticeable in drought-prone biomes (Mediterranean, temperate and cold continental). Main conclusions At the turn of this century, convergence in growth synchrony across European forest ecosystems is coupled with coordinated warming-induced drought effects on leaf physiology and tree growth spreading northwards. Such a tendency towards exacerbated moisture-sensitive growth and physiology could override positive effects of enhanced leaf intercellular CO2 concentrations, possibly resulting in Europe-wide declines of forest carbon gain in the coming decades

Klimato signalai Europos izotopų tnkle ISONET

Over the last three years, 16 European isotope labs collaborated in the EU project ISONET (co-ordinator: G. Schleser, http//www.isonet-online.de) on developing the first large-scale network of 13C, 18O and 2H in from oak, pine and cedar tree-rings, covering sites from Fennoscandia to the Mediterranean region. The sampling design considered not only ecologically “extreme” sites, with a single climate factor predominantly determining tree growth, as required for ring width and wood density analyses (Bräuning & Mantwill 2005, Briffa et al. 2001, 2002, Frank & Esper 2005a, b), but also temperate regions with diffuse climate signals recorded in the ‘traditional’ tree ring parameters. This strategy, however, may enable expanding climatic reconstructions into regions not yet well covered. As reported earlier (Treydte et al. 2005), the aim is to estimate temperature, humidity and precipitation variations with annual resolution, to reconstruct local to European scale climate variability over the last 400 years. Climate variability is addressed on intra-annual to century timescales. This strategy should allow understanding both, high frequency variations including the exploration of seasonality signals and extreme events, and longer-term trends including source water/air mass changes and baseline variability across Europe. Here we present first climate calibration results for the 20th century, using 13C and 18O data from up to 25 sites currently available in the networkVytauto Didžiojo universiteta

Europos izotopų tinklas ISONET: pirmieji rezultatai

Within the EU-Project ISONET (co-ordinator: G. Schleser, http//www.isonet-online.de), 13 partner institutions collaborate to develop the first large-scale network of stable isotopes (C, O and H), integrating 25 European tree sites reaching from the Iberian Peninsula to Fennoscandia. Key species are oak and pine. The sampling design considers not only ecologically “extreme” sites, with mostly a single climate factor dominating tree growth, as supportive for ring width and wood density analyses (Bräuning & Mantwill 2005; Briffa et al. 2001, 2002; Frank & Esper 2005a, b), but also temperate regions with diffuse climate signals recorded in the ‘traditional’ tree ring parameters. Within the project we aim to estimate temperature, humidity and precipitation variations with annual resolution, to reconstruct local to European scale climate variability over the last 400 years. Climate variability is addressed on three timescales, namely decade-century, interannual and intra-annual. This strategy allows understanding of both, high frequency (high resolution exploration of seasonality signals, and extreme events) and longer-term trends (source water/air mass dominance, baseline variability) in site specific and synoptic climate across Europe. Here we present results from initial network analyses considering first data of carbon (δ13C) and oxygen (δ18O) isotopes, to evaluate (a) common patterns in these networks and (b) their potential for detailed climate reconstruction beyond the information commonly achieved from ring width and density analysesVytauto Didžiojo universiteta