Carbon 1213 dating
However, logistic constraints meant we could either sample multiple years for a small subset of species and/or sites, or we could sample across the entire species pool, but only for two contrasting years at each site.As the main goal of our analysis is to understand whether or not carbon isotope ratios and stem growth show a clear and coordinated response to drought across Europe’s forests, we chose to focus on the later of these two options.For each stem, we recorded the diameter at breast height (D; to the nearest 0.1 cm using diameter tape) and used the crown illumination index (CII) to characterize crown dominance by scoring stems from 1 (suppressed crown receiving no direct light) to 5 (fully exposed dominant crown; Clark and Clark ) to characterize annual soil water availability at each site between 19.Using the output of the model we then identified drought and non-drought years for each Fun Div EUROPE site, as is described in detail in Grossiord et al. Briefly, the BILJOU model uses daily meteorological data (precipitation, global radiation, air temperature and humidity, wind speed), alongside information on soil water holding capacity and leaf area index to predict temporal variation in soil water content.While for isotopes we only sampled large dominant trees, for growth we wanted to explicitly account for the dependency of growth on tree size and therefore used a size-stratified random sampling approach to select trees for coring that would ensure all size classes would be represented by the sample [see Jucker et al. Once collected, wood cores were stored in polycarbonate sheeting and allowed to air dry before being mounted on wooden boards and sanded with progressively finer grit sizes.A high resolution flatbed scanner (2400 dpi optical resolution) was then used to image the cores.When REW for further details on the selection of drought and non-drought years).We note that ideally we would have liked to select multiple drought and non-drought years from each site, in order to better tease apart the abiotic and biotic drivers of isotopic signatures and growth trends.
Trees were selected for coring at random, but only dominant and co-dominant trees (defined on the basis of D and CII) were target for isotope analysis to avoid the confounding effect of shading on δ).Because the amount of In addition to using tree cores for isotope analyses, we also used them to assess growth responses to drought.Tree cores collected to measure growth were collected at the same time as those for isotope analysis, but the number of trees samples was larger (2950 in total, for an average of 113 cores per species at each site, of which those cored for isotopes were mostly a subset).Samples were oven-dried for 72 h at 60 °C to reach constant weight before being filed with a scalpel for tree-ring dating.Because photosynthates from one growing season can be remobilized and allocated to earlywood formation in the following year (Offermann et al. Wood sampled were then ground, yielding between 0.4 and 1.5 mg of wood powder, weighed using a high-precision scale (MX5, Mettler Toldedo, Viroflay, France), placed in tin capsules, and analysed at the Stable Isotope Facility of UC Davis, California, USA with a PDZ Europa 20–20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK).
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To do this we first reconstructed each tree’s past diameters by progressively subtracting annual diameter increment (assumed to be twice the radial growth) from its current day diameter which was measured in the field in 2012.