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The current distribution area of the two sympatric oaks Quercus petraea and Q. robur covers most of temperate Western Europe. Depending on their geographic location, populations of these trees are exposed to different climate constraints, to which they are adapted. Comparing the performances of trees from contrasting populations provides the insight into their expected resilience to future climate change required for forest management. In this study, the descendants of 24 Q. petraea and two Q. robur provenances selected from sites throughout Europe were grown for 20 years in three common gardens with contrasting climates. The 2420 sampled trees allowed the assessments of the relationship between radial growth and climate. An analysis of 15-year chronologies of ring widths, with different combinations of climate variables, revealed different response patterns between provenances and between common gardens. As expected, provenances originating from sites with wet summers displayed the strongest responses to summer drought, particularly in the driest common garden. All provenances displayed positive significant relationships between the temperature of the previous winter and radial growth when grown in the common garden experiencing the mildest winter temperatures. Only eastern provenances from continental cold climates also clearly expressed this limitation of growth by cold winter temperatures in the other two common gardens. However, ecological distance, calculated on the basis of differences in climate between the site of origin and the common garden, was not clearly related to the radial growth responses of the provenances. This suggests that the gradient of genetic variability among the selected provenances was not strictly structured according to climate gradients. Based on these results, we provide guidelines for forest managers for the assisted migration of Quercus petraea and Q. robur provenances.

Quercus robur and Q. petraea are major European forest tree species. They have been affected by powdery mildew caused by Erysiphe alphitoides for more than a century. This fungus is a biotrophic foliar pathogen that diverts photosynthetate from the plant for its own nutrition. We used a dendrochronological approach to investigate the effects of different levels of infection severity on the radial growth of young oak trees. Oak infection was monitored at individual tree level, at two sites in southwestern France, over a five-year period (2001-2005). Mean infection severity was almost 75% (infected leaf area) at the end of the 2001 growing season, at both sites, but only about 40% in 2002, and 8%, 5% and 2% in 2003, 2004 and 2005, respectively. Infection levels varied considerably between trees and were positively related between 2001 and 2002. Increment cores were taken from each tree to assess annual ring widths and increases in basal area. Annual radial growth was standardised to take the effect of tree size into account. Annual standardised radial growth was significantly and negatively correlated with infection severity in the same year, for both 2001 and 2002, and at both sites. The decrease in growth reached 70-90% for highly infected trees. The earlywood width was poorly correlated with infection severity, but the proportion of latewood in tree rings was lower in highly infected trees (60%) than in less heavily infected trees (85%). Infection in 2001 and 2002 was found to have a cumulative effect on radial growth in these years, together with a delayed effect detectable in 2003. Thus, even non-lethal pathogens like powdery mildew can have a significant impact on tree functioning. This impact should be taken into account in growth and yield models, to improve predictions of forest net primary production.

Drought‐related tree mortality had become a widespread phenomenon in forests around the globe. This process leading to these events and its complexity is not fully understood. Trees in the dry timberline are exposed to ongoing drought, and the available water for transpiration in the soil can determine their survival chances. Recent drought years led to 5%–10% mortality in the semi‐arid pine forest of Yatir (Israel). The distribution of dead trees was, however, highly heterogeneous with parts of the forest showing >80% dead trees (D plots) and others with mostly live trees (L plots). At the tree level, visible stress was associated with low pre‐dawn leaf water potential at the dry season (−2.8 MPa vs. −2.3 MPa in non‐stressed trees), shorter needles (5.5 vs. 7.7 mm) and lower chlorophyll content (0.6 vs. 1 mg/g dw). Trends in tree‐ring widths reflected differences in stress intensity (30% narrower rings in stressed compared with unstressed trees), which could be identified 15–20 years prior to mortality. At the plot scale, no differences in topography, soil type, tree age or stand density could explain the mortality difference between the D and L plots. It could only be explained by the higher surface rock cover and in stoniness across the soil profile in the L plots. Simple bucket model simulations using the site’s long‐term hydrological data supported the idea that these differences could result in higher soil water concentration (m3/m3) in the L plots and extend the time above wilting point by several months across the long dry season. Accounting for subsurface heterogeneity may therefore critical to assessing stand‐level response to drought and projecting tree survival, and can be used in management strategies in regions undergoing drying climate trends. A plain language summary is available for this article. Plain Language Summary

The Digne-les-Bains ammonite slab is one of the most impressive geosites of the UNESCO Global Geopark of Haute-Provence and Réserve Naturelle Nationale Géologique de Haute-Provence. Its importance rests on the number of fossils as well as their size and the high quality of the outcrop and its huge potential. It is an important subject for research in paleontology and sedimentology, as well as geoconservation. Open to the public since the 1980s it now benefits from new equipment and is ready for new adventures.

The pace of tree microevolution during Anthropocene warming is largely unknown. We used a retrospective approach to monitor genomic changes in oak trees since the Little Ice Age (LIA). Allelic frequency changes were assessed from whole‐genome pooled sequences for four age‐structured cohorts of sessile oak (Quercus petraea) dating back to 1680, in each of three different oak forests in France. The genetic covariances of allelic frequency changes increased between successive time periods, highlighting genome‐wide effects of linked selection. We found imprints of parallel linked selection in the three forests during the late LIA, and a shift of selection during more recent time periods of the Anthropocene. The changes in allelic covariances within and between forests mirrored the documented changes in the occurrence of extreme events (droughts and frosts) over the last 300 years. The genomic regions with the highest covariances were enriched in genes involved in plant responses to pathogens and abiotic stresses (temperature and drought). These responses are consistent with the reported sequence of frost (or drought) and disease damage ultimately leading to the oak dieback after extreme events. They provide support for adaptive evolution of long‐lived species during recent climatic changes. Although we acknowledge that other sources (e.g., gene flow, generation overlap) may have contributed to temporal covariances of allelic frequency changes, the consistent and correlated response across the three forests lends support to the existence of a systematic driving force such as natural selection.

• This study aims to link three-dimensional coarse root architecture to tree stability in mature timber trees with an average of 1-m rooting depth. • Undamaged and uprooted trees were sampled in a stand damaged by a storm. Root architecture was measured by three-dimensional (3-D) digitizing. The distribution of root volume by root type and in wind-oriented sectors was analysed. • Mature Pinus pinaster root systems were organized in a rigid 'cage' composed of a taproot, the zone of rapid taper of horizontal surface roots and numerous sinkers and deep roots, imprisoning a large mass of soil and guyed by long horizontal surface roots. Key compartments for stability exhibited strong selective leeward or windward reinforcement. Uprooted trees showed a lower cage volume, a larger proportion of oblique and intermediate depth horizontal roots and less wind-oriented root reinforcement. • Pinus pinaster stability on moderately deep soils is optimized through a typical rooting pattern and a considerable structural adaptation to the prevailing wind and soil profile.

In the context of climate change, the water‐use efficiency (WUE) of highly productive tree varieties, such as eucalypts, has become a major issue for breeding programmes. This study set out to dissect the genetic architecture of carbon isotope composition (δ¹³C), a proxy of WUE, across several environments. A family of Eucalyptus urophylla × E. grandis was planted in three trials and phenotyped for δ¹³C and growth traits. High‐resolution genetic maps enabled us to target genomic regions underlying δ¹³C quantitative trait loci (QTLs) on the E. grandis genome. Of the 15 QTLs identified for δ¹³C, nine were stable across the environments and three displayed significant QTL‐by‐environment interaction, suggesting medium to high genetic determinism for this trait. Only one colocalization was found between growth and δ¹³C. Gene ontology (GO) term enrichment analysis suggested candidate genes related to foliar δ¹³C, including two involved in the regulation of stomatal movements. This study provides the first report of the genetic architecture of δ¹³C and its relation to growth in Eucalyptus. The low correlations found between the two traits at phenotypic and genetic levels suggest the possibility of improving the WUE of Eucalyptus varieties without having an impact on breeding for growth.

Context: As a widespread species, sessile oak (Quercus petraea) populations occupy a wide range of ecological conditions, with large gradients of soil water availability. Drought acclimation involves a plastic increase in water-use efficiency (WUE), a trait that is easily measured using the carbon isotope composition (δ13C). However, the question remains whether WUE is an adaptive trait that impacts the fitness of trees in natural environments.Objectives and Methods: To investigate whether WUE was a drought-adaptive trait, we studied a sample of 600 trees originating from 16 provenances, grown for 21 years in a common garden. Intrinsic WUE (WUEi), estimated from tree ring δ13C, was compared among and within populations for three climatically contrasted years. The adaptive character of WUEi was evaluated by relating population mean WUEi, as well as its plasticity to drought, to the pedoclimatic conditions of their provenance sites. The contribution of WUEi to tree and population fitness was finally assessed from the relationship between WUEi and tree radial growth (GI).Results: Significant differences in WUEi were found among populations but a much larger variability was observed within than among populations. The population WUEi of the juvenile oak trees growing in the relatively mesic conditions of the common garden showed no relationship with a modeled water deficit index for the provenance sites. However, a higher population WUEi plasticity to severe drought was related to a higher proportion of silt and carbon and a lower proportion of sand in the soil of the provenance sites. In response to severe drought, populations with a higher increase in WUEi showed a lower decrease in GI. Populations with lower GI reduction were from sites with higher vapor pressure deficit in May–July (VPD). For the wet year only, populations with a higher WUEi also had a higher GI.Conclusion: The correlations observed at the common garden site between (i) population means of WUEi plasticity to drought and soil texture of the provenance sites, and (ii) GI plasticity to drought and VPD, suggested a local adaptation of sessile oak.

To develop sources of renewable energy and to reduce greenhouse gas emissions, increasing attention has been given to the extraction of forest biomass, especially in the form of harvest residues. However, increasing the removal of biomass, and hence nutrients, has raised concerns about the sustainability of site fertility and forest productivity. The environmental cost of harvesting belowground biomass is still not fully understood. The objectives of this study were to (i) estimate the stocks of belowground biomass that potentially can be collected; (ii) measure the nutrient (N, P, K, Ca, Mg) concentrations of the different root compartments (stumps, coarse and thin roots); and to (iii) quantify the biomass and nutrient exports under different scenarios, including harvests of above and belowground compartments. The study was carried out on Pinus pinaster stands located in south‐western France. Results showed that roots could be a significant fuelwood resource, particularly at forest clear cutting. Negative relationships between root diameter and root nutrient concentration were observed, independently of root function or tree age. Such relationships can be used to accurately simulate nutrient concentrations in roots as well as nutrient exports. Combining our original results on roots with previously published data on the aboveground compartments showed that nutrient losses were higher in canopy harvest scenarios than in root harvest scenarios. This was mainly due to high nutrient concentrations of needles. We concluded that stump and root harvest could be sustainable in our study context, conversely to foliage harvest. Because thin roots have higher nutrient concentrations than coarse roots and the proportion of thin roots increased with an increase in the distance from the tree, collecting roots only in the close vicinity of the stumps should limit nutrient exports (particularly N) without unnecessarily reducing fuelwood biomass.

Dendroecology is based on the estimation of target population climate sensitivity from a finite number of trees (N). Recent studies showed a sample size-related bias in the estimations of climate-tree growth relationships, decreasing sample size leading to a weakening of the bootstrapped correlation coefficients. The present analysis points out that the bias equals the squared root of the expressed population signal of the growth chronology built from N trees and then proposes a correction factor to accurately estimate the population sensitivity to climate. The interests, limits, and implications of this correction are illustrated from 504 individual growth chronologies of silver fir (Abies alba [Mill.]) sampled in the Jura Mountains (France) along an altitudinal gradient of increasing climate forcing. This data set was split into three groups of 168 trees (low, medium, and high elevation). Our results show that the signal common to all trees strengthened with increasing climate forcing and that the accuracy of the correction slightly decreased with both decreasing sample size and climate forcing. Corrected bootstrapped correlation coefficients still underestimated the strength of the population climate-tree growth relationships when less than 10 trees were used at low elevation against 4 at high altitude.