Temporal stability of climate‐isotope relationships in tree rings of oak and pine (Ticino, Switzerland)

Abstract

[1] Climate reconstructions based on stable isotopes in tree rings commonly rely on the assumption that climate-isotope relations are stable over time. However, studies of tree ring growth have revealed trends thought to result from either physiological changes or changes in the climate-growth relationship. We investigated whether or not similar trends exist for tree ring stable isotopic ratios using a statistical approach. Correlations between climate (temperature and precipitation amount) and tree ring cellulose d 13 C and d 18 O of oak and pine from Ticino, Switzerland, were calculated for the period AD 1660-2000. Climate calibration of tree rings was enabled by long-term monthly resolved temperature and precipitation data sets on the basis of instrumental and documentary proxy data. Overall, five findings have been identified: (1) Isotopic ratios in tree rings most strongly reflect conditions of the current growing season, (2) temporally stable climate signals are found in pine d 13 C only, (3) all other correlations between tree ring isotopes and climate are temporally unstable and characterized by shifts in correlation sign and strength, (4) climate signals in oak are strongest in the 20th century, and (5) tree ring d 13 C reflects local climatic conditions while d 18 O is influenced by large-scale synoptic circulation. The nonstationary relationships observed could reflect changes in the relationship between the climate variables or a physiological adaptation to warmer conditions. Our results provide a cautionary note for the calibration of long tree ring series with 20th century relationships, at least for trees located at ecologically nonextreme sites.

French summer droughts since 1326 CE: a reconstruction based on tree ring cellulose <i>δ</i><sup>18</sup>O

“…Szczepanek et al, 2006;Reynolds-Henne et al, 2007;Treydte et al, 2007;Loader et al, 2008;Saurer et al, 2008;Hilasvuori and Berninger, 2010;Haupt et al, 2011). The validity of the local drought reconstructions from Fontainebleau and Angoulême is supported by the high correlations between the drought index and δ 18 O c , as well as by the verification of the models with independent data.…”

“…However, the climate in France might have been more heterogeneous in the past. Changes in seasonal aspects of climate or in the relationship between temperature and humidity can alter the way these variables act on δ 18 O c (Barbour et al, 2002;MassonDelmotte et al, 2005;Reynolds-Henne et al, 2007). While temperature variations are likely to be coherent between the sites at a timescale which is relevant for the proxy, precipitation patterns are generally more variable in space.…”

“…The climate sensitivity of trees is known to change with time (e.g. Reynolds-Henne et al, 2007;Friedrichs et al, 2009;Dorado Liñán et al, 2011;Mérian et al, 2011;Voelker, 2011;Linares et al, 2012;Rozas and Olano, 2013;Candela-Galván et al, 2015), due to tree age, changes in the timing and length of the growing season or in the atmospheric CO 2 concentration. In addition, the response of trees to climate changes may depend on their local environment, e.g.…”

Stability of climate signal in carbon and oxygen isotope records and ring width from Scots pine (Pinus sylvestris L.) in Finland

“…This phenomenon leads to an underestimation of recent warming and to uncertainties in calibration of tree ring proxies to temperature records. Instability of correlations between climate and tree ring isotope ratios was also observed in a recent study from the Alps (Reynolds-Henne et al, 2007).…”

Summer temperature dependency of larch budmoth outbreaks revealed by Alpine tree-ring isotope chronologies

“…Correlation analysis was conducted on a monthly basis from March of the previous year to December of the current year as well as on seasonal averages, using bootstrapped correlation analysis for significance testing (P \ 0.05; Guiot 1991). To quantify temporal changes in the relationship between climate and tree-ring isotopes, we additionally calculated moving correlations over 40-year time windows, thus producing a time series of bootstrapped correlation coefficients on a monthly basis from January to October of the current year (Biondi and Waikul 2004;Reynolds-Henne et al 2007). …”