The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Publisher Copyright: © 2022, The Author(s).Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.Peer reviewe

New tools for timber provenancing

Trees are affected by a set of spatially and/or temporarily varying biotic and abiotic factors. The effect of these factors is reflected in the width and structure of tree rings, which are widely used to study species ecology and their responses to climate. Moreover, tree-ring width time series are also used for dating and identification of the geographical origin of archaeological or historical timber – dendroprovenancing. The latter is usually done by statistical matching of tree-ring width sequence of a given timber to a network of regional and local chronologies from the same species or genera. However, despite multiple successful applications, this method also has clear pitfalls, such as lack of long reference tree-ring width chronologies from areas with intensive logging history; or possible strong teleconnections between reference chronologies over large distances leading to coarse-scale results. Therefore, to overcome these limitations and to improve dendroprovenancing results, other wood-anatomical features or chemical characteristics have to be used. The potential of additional variables retrieved from the wood has been recently tested and showed promising results for timber tracking, e.g. its chemical composition or DNA. However, until now time series of xylem-anatomical features have been largely ignored in timber-provenancing studies. This is most likely due to the time-consuming and labour-intensive data acquisition and challenging preparation of archaeological timber for precise wood-anatomical measurements. But with recent improvements in wood- preparation techniques and image-analysis software, it became possible to acquire a sufficient amount of data derived from various xylem-anatomical features in an efficient way. This thesis aims to evaluate the value of xylem-anatomical features as well as of archaeological DNA (aDNA) in addition to TRW for timber-provenancing studies. In the context of the ForSEAdiscovery project, the potential of vessel size of ring-porous oak, blue intensity variables derived from pine trees, and aDNA extracted from historical oak timber to enhance dendroprovenancing precision was assessed. Moreover, a conceptually new method, i.e. based on individual time-series rather than on average chronologies, was applied. This was done by means of Principal Component Gradient Analyses (PCGA). A description is provided for each of the chapters on their research and findings below. To assess the potential of oak earlywood vessels for timber provenancing, samples from nine oak stands in Northern Spain (Cantabria and the Basque country) were collected (Chapter 2). From this set of samples, vessel size and latewood-width time series were created. Based on variation in latewood-width time series, it was possible to differentiate between Cantabrian and Basque forest stands, i.e. in East-West direction. The difference in response to the summer temperature was found to be the main factor leading to such a differentiation. At the same time, variation in vessels size enabled the grouping of trees from the Basque country according to the continentality gradient, i.e. North-South direction, based on a difference in response of vessel size to winter and spring temperatures. These results suggest that the approach of combining latewood width with vessel size leads to a higher precision dendroprovenancing and pinpointing the origin of oak timber on a finer scale. Leave-one-out analyses confirmed this conclusion. In Chapter 3, the potential of wood-density related Blue Intensity (BI) variables in addition to TRW for dendroprovenancing pine timber in drought limited areas was evaluated. The network of the BI and TRW time series was created from six pine forests from Central Spain and Southern Spain. PCGA of the derived time series revealed a grouping of trees according to their elevation category based on the BI time series. However, it failed to group trees according to their geographical provenance both for the TRW and BI series. Trees were correctly assigned to their origin based on TRW, but only within the predefined by the BI elevation groups. Based on these results, it is possible to conclude that a multi-variable approach comprising of BI and TRW assists in enhancing pine-timber dendroprovenancing in dry areas. In Chapter 4, the potential of extracting and using aDNA for oak-timber provenancing on different scales was evaluated. Thirty samples from historical buildings from Spain, Latvia and Denmark were analysed. Two different extraction protocols in two genetic laboratories were tested. Furthermore, two different haplotype identification methods were applied. From 60% of the samples, at least one marker showed the presence of the aDNA with a varying percentage per extraction protocol. An existing haplotype distribution map was used to identify the potential source area of material from two study cases. The results suggest that genetic analyses have a strong potential for pinpointing timber origin, though until now only in combination with the TRW based method. Improvements in DNA extraction from degraded wood and amplification protocols are essential for future applications in dendroprovenancing studies. In Chapter 5, the main outcomes of each of the core chapters are discussed and contextualized in a broader perspective of dendroprovenancing. The potential of oak earlywood vessels in solving actual timber provenancing challenges in other regions in Europe is discussed. The added value of using the individual tree approach was tested and its strong potential in improving timber provenancing is confirmed. Based on the results derived from the core chapters, and from other studies conducted in the framework of the ForSEAdiscovery project on the same samples, a decision tree was created in order to facilitate oak and pine timber provenancing in the region. In conclusion, the multivariable approach has demonstrated a strong potential to enhance the precision of timber provenancing. However, for a successful application, specific climatic gradients were required for both genera (Chapters 2 & 3). Therefore, the decision on a suitable approach should be based on the specific provenancing conditions and should be comprised of multiple variables.</p

Data from: Multi-variable approach pinpoints origin of oak wood with higher precision

Aim: Spatial variations of environmental conditions translate into biogeographic growth patterns of tree growth. This fact is used to identify the origin of timber by means of dendroprovenancing. Yet, dendroprovenancing attempts are based on ring-widths measurements, and neglect additional tree-ring parameters. To explore the effect of including additional variables in dendroprovenancing, we investigate whether and, if so, why the incorporation of wood-anatomical parameters can increase the precision of identifying the origin of oak wood. Since such features reflect environmental conditions of different periods – which vary between source regions – we hypothesize that their inclusion allows more precise dendroprovenancing. Location: Europe, Spain. Taxon: Quercus robur L., Quercus petraea (Matt.) Liebl., Quercus faginea Lam., Quercus pyrenaica Willd. Methods: We sampled four oak species resembling a longitudinal and an elevational/continental gradients. We measured multiple tree-ring variables to (1) extract meaningful variables, (2) represent statistical relations among variables, (3) analyse regional-specific growth patterns in individual time series and (4) determine underlying climate-growth relationships. Leave-one-out analyses were used to test whether a combination of selected variables allows dendroprovenancing of a randomly selected tree within the area. Results: A combination of latewood width and earlywood vessels size can be used to pin-point the origin of oak wood with higher precision than latewood width only. Variation in latewood widths appointed the wood to areas across the longitudinal gradient, whereas variation in vessels assigned wood to locations along a latitudinal/topographic gradient. The climatic factors behind these gradients are respectively an East-West gradient in June-July temperature, and a North-South gradient in winter/ spring temperatures. The leave-one-out analyses supported the robustness of the results. Main conclusions: Integration of multiple tree-ring variables in combination with multivariate techniques leads to higher precision in the dendroprovenancing of ring-porous oak species

Tree-ring chronologies, stable strontium isotopes and biochemicalcompounds: Towards reference datasets to provenance Iberianshipwreck timbers

International audienceStudies on the provenance of wood for shipbuilding contribute widely to the fields of archaeology, anthropology,environmental history, cultural geography, and palaeoclimatology. The development of reference datasets todetermine the date and provenance of shipwreck timbers is therefore a paramount undertaking. Here we compileand present recent advances in the development of tree-ring chronologies, stable strontium isotope ratios andchemical biomarkers aimed to determine the date and provenance of Iberian shipwreck timbers. A set of oak andpine tree-ring chronologies have been developed from living trees covering the past 500 and 800 years,respectively, and have served to confirm the provenance of the wood used in an 18th-century Spanish ship of theRoyal Navy. Stable strontium isotopic signatures have been obtained from soil and living trees at 26 sitesthroughout the Iberian Peninsula, providing a climate-independent geochemical network to source the origin ofhistoric timbers. However, retrieving the original isotopic signature from waterlogged samples remains unsuccessful,stressing the need to develop effective protocols to separate the seawater signal from the originalstrontium isotope ratios in the wood. Analyses of organic compounds in wood of living trees have proven suitableto discriminate species and provenances, but results on shipwreck timbers are inconclusive and should be furtherexplored. Our regional approach has the potential to be expanded to other areas and archaeological timbers fromdifferent periods throughout the Anthropocene. We highlight the strengths and weaknesses of the techniquespresented when applied to waterlogged wood, propose GIS tools to interpret and visualize combined results, andstress the need to expand these type of reference datasets to allow for multiproxy dendroprovenancingapproaches

Towards a new approach for dendroprovenancing pines in the Mediterranean Iberian Peninsula

Dendroprovenancing studies frequently use site chronologies to identify the origin of archaeological and historical timber. However, radial growth (tree-ring width, TRW) of tree species is influenced by both local and regional climate scales. Here we investigate how the use of annually-resolved Blue Intensity (BI) measurements can enhance dendroprovenancing precision of black pine (Pinus nigra Arn.) and Scots pine (P. sylvestris L.) on the Iberian Peninsula. Principal Component Gradient Analyses (PCGA) was used to assess geographical patterns of annual variation in different TRW and BI proxies of pine trees from two mountain ranges in the Central System and Andalusia in Spain. Local climate-growth relationships were quantified to identify underlying causes of identified groups with diverse growth patterns. Two distinct elevational groups were observed when performing PCGA on latewood BI time series with the response to summer drought as the main factor causing the differences. Both P. nigra and P. sylvestris BI time series were found to be more related to summer drought at low-elevation sites showing an increase in sensitivity at lower latitudes. PCGA of TRW time series allowed to discriminate between trees from Andalusia and Central System within the elevation groups. February and October temperatures were found to be the main climatic factors causing the differences in TRW time series among the high- elevation sites, whereas for low-elevation trees it was the average winter temperature influencing TRW. A subsequent leave-one-out analyses confirmed that including latewood BI time series improves the precision of dendroprovenancing of pine wood in the Iberian Peninsula.</p

An intensive tree-ring experience: Connecting education and research during the 25th European Dendroecological Fieldweek (Asturias, Spain).

The European Dendroecologial Fieldweek (EDF) provides an intensive learning experience in tree-ring research that challenges any participant to explore new multidisciplinary dendro-sciences approaches within the context of field and laboratory settings. Here we present the 25th EDF, held in Asturias, NW Spain, in summer 2014. The course, with 33 participants and 10 instructors from 18 countries included advanced training in dendrochronology skills, an overview of tree-ring broad fields and methodological basics to deal with specific research questions as well as applied advanced micro-projects in dendroarchaeology (DAR), dendroclimatology (DCL), dendrogeomorphology (DGM), forest dynamic (FD) and plant anatomy (PA). The results demonstrated the potential of tree-ring research in the Asturias region. The DAR group researched archaeological samples from different contexts (Oviedo cathedral choir stalls, Segovia cathedral roof timbers, Ribadeo shipwreck ship timbers and Bronze Age site charcoal) and explored the supply of wood in different periods. The DCL group established that the Quercus robur and Castanea sativa ring-width measurements show weak climate-growth correlations, where for many trees this is likely caused by management. The strength of the climatic signal could be enhanced using undisturbed settings. The DGM group found that Corylus avellana and Salix spp. are challenging species for dendrogeomorphological studies. Debris-flow events were detected by the presence of tension wood, growth reduction and scars, and their incidences were also supported by local meteorological data. The FD group found that tree growth decreases with increasing competition, a pattern more pronounced in C. sativa than in Pinus sylvestris forest plantations. The results indicate that wood production could be increased by applying thinning treatments on C. sativa. The PA group showed that xylem conduits and phloem area are organized according to the common needs for water supply to leaves and obtain photosynthetic products, regardless site growing conditions for P. sylvestris and Tusilago farfara. In conclusion, this EDF has been a model for interdisciplinary research and international collaboration that has demonstrated that high-quality research and education can be conducted within one week. The EDFs provide an important service to the dendrochronological community and demonstrate the usefulness of this educational-scientific and multi-cultural experience