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Light and water availability are likely to vary over the lifespan of closed-canopy forest trees, with understory trees experiencing greater limitations to growth by light and canopy trees greater limitation due to drought. As drought and shade have opposing effects on isotope discrimination (Δ13C), paired measurement of ring width and Δ13C can potentially be used to differentiate between water and light limitations on tree growth. We tested this approach for Cedrela trees from three tropical forests in Bolivia and Mexico that differ in rainfall and canopy structure. Using lifetime ring width and Δ13C data for trees of up to and over 200 years old, we assessed how controls on tree growth changed from understory to the canopy. Growth and Δ13C are mostly anti-correlated in the understory, but this anti-correlation disappeared or weakened when trees reached the canopy, especially at the wettest site. This indicates that understory growth variation is controlled by photosynthetic carbon assimilation due to variation in light levels. Once trees reached the canopy, inter-annual variation in growth and Δ13C at one of the dry sites showed positive correlations, indicating that inter-annual variation in growth is driven by variation in water stress affecting stomatal conductance. Paired analysis of ring widths and carbon isotopes provides significant insight in what environmental factors control growth over a tree's life; strong light limitations for understory trees in closed-canopy moist forests switched to drought stress for (sub)canopy trees in dry forests. We show that combined isotope and ring width measurements can significantly improve our insights in tree functioning and be used to disentangle limitations due to shade from those due to drought. [ABSTRACT FROM AUTHOR]

Author(s): Kerstin S. Treydte (corresponding author) [1]; Gerhard H. Schleser [2]; Gerhard Helle [2]; David C. Frank [1]; Matthias Winiger [3]; Gerald H. Haug [4]; Jan Esper [1] Twentieth-century warming [...]

The response of evapotranspiration to anthropogenic warming is of critical importance to the water and carbon cycle. Conflicting observations about changes of evapotranspiration stem mostly from the brevity of observations in time and space as well as a high degree of internal variability. Here we present the first gridded reconstruction of the European summer vapour pressure deficit (VPD) for the past four centuries. The gridded reconstruction is based on 26 European tree-ring oxygen isotope records and is performed using a Random Forest approach. Based on our reconstruction, we show that from the mid- 1700s a trend towards higher VPD occurred in Central Europe and the Mediterranean region which is based on the simultaneous increase in temperature and decrease in precipitation. This increasing VPD trend continues throughout the observational period and recent times. Climate model projections show this increase in VPD for the Mediterranean region continuing until the end of the 21st century, whereby the extent depends on the amount of greenhouse gas emissions. In contrast, projected VPD in North and Central Europe shows a tendency towards higher VPD only in the highest emission scenario. The reconstructed, observed and modelled VPD for past present and future is available here: https://doi.org/10.5281/zenodo.5958837 (Balting, D. F. et al., 2022). [ABSTRACT FROM AUTHOR]

Advances in accelerator mass spectrometry have resulted in an unprecedented amount of new high-precision radiocarbon (14C) -dates, some of which will redefine the international 14C calibration curves (IntCal and SHCal). Often these datasets are unaccompanied by detailed quality insurances in place at the laboratory, questioning whether the 14C structure is real, a result of a laboratory variation or measurement-scatter. A handful of intercomparison studies attempt to elucidate laboratory offsets but may fail to identify measurement-scatter and are often financially constrained. Here we introduce a protocol, called Quality Dating, implemented at ETH-Zürich to ensure reproducible and accurate high-precision 14C-dates. The protocol highlights the importance of the continuous measurements and evaluation of blanks, standards, references and replicates. This protocol is tested on an absolutely dated German Late Glacial tree-ring chronology, part of which is intercompared with the Curt Engelhorn-Center for Archaeometry, Mannheim, Germany (CEZA). The combined dataset contains 170 highly resolved, highly precise 14C-dates that supplement three decadal dates spanning 280 cal. years in IntCal, and provides detailed 14C structure for this interval. [ABSTRACT FROM AUTHOR]

We investigate the annual variability of δ18O tree ring records from sites distributed all over Europe covering the last 400 years. An Empirical Orthogonal Function (EOF) analysis reveals two distinct modes of variability on the basis of the existing δ18O tree ring records. The first mode of δ18O variability is associated with anomaly patterns of the El Niño-Southern Oscillation (ENSO) and reflects a multi-seasonal climatic signal. The ENSO signal is visible for the last 130 years, but is found weak during the period 1600 to 1850 suggesting that the relationship between ENSO and the European climate may not stable over time. The second mode of δ18O variability, which captures an out-of-phase variability between northwestern and southeastern European δ18O tree ring records, is related to a regional summer atmospheric circulation pattern revealing a pronounced centre over the North Sea. Locally, the δ18O anomalies associated with this mode show the same (opposite) sign with temperature (precipitation). We infer that the investigation of large-scale atmospheric circulation patterns and related teleconnections far beyond instrumental records can be done with oxygen isotopic signature derived from tree rings. However, the European δ18Ocel tree network needs to be consolidated and updated, as well as additional research on the stationarity of reconstructed climate signals and the stationarity of teleconnections is advisable. [ABSTRACT FROM AUTHOR]

The African baobab, Adansonia digitata, has great paleoclimatological potential because of its wide distributional range and millennial lifespan. However, dendroclimatological approaches are hampered by dating uncertainties due to its parenchyma-dominated wood anatomy. Here, securely-dated time series of annual wood increment growth and intra-ring stable isotopes of carbon and oxygen of cellulose for a baobab tree from Oman covering 1941 to 2005 were established. Precise dating with the bomb peak by highly resolved 14C measurements proved the annual character of the baobab's growth rings. But, F14C values of tree-ring cellulose were found up to 8.8 % lower than in the corresponding atmospheric CO2 for the period around the bomb peak. In conjunction with a considerable autocorrelation of the δ13C series this points to the incorporation of previous years' carbon significantly affecting the average age of derived wood. Terminal parenchyma bands, marking the tree-ring boundaries, were found to be significantly younger than their corresponding tree ring indicating that parenchyma tissue is alive for many years undergoing cell division, reorganization and potential growth. No autocorrelation was found in the δ18O series of tree-ring cellulose despite the huge water-storage potential of this stem-succulent tree species. Tree-ring width and stable isotope ratios have revealed significant climate sensitivity. δ18O was found to be a good climate proxy followed by tree-ring width and δ13C. Tree-ring width and intra-ring δ18Omin correlated well with each other and with precipitation amount for the period from pre-monsoon May to the end of the monsoon season in September/October. Intra-annual stable isotope courses were found rather similar for both δ13C and δ18O. Years with particularly low monsoon rain were reflected by increased stable isotope values in the mid-section of intra-annual courses. Distinct patterns with low subseasonal isotope values seem indicative for years with heavy rainfall events from pre-monsoonal cyclones. Rain events from post-monsoonal cyclones may also be recorded, however, only two years of observation prevent from a conclusive evaluation. [ABSTRACT FROM AUTHOR]