Radial growth is a fitness related trait that is expected to vary among forest tree populations when habitat conditions change. Yet, the genetic variability of ring-width and radial growth–climate relationships among geographic origins within species is rarely investigated. This is what we analyzed in the European black pine, Pinus nigra J.F. Arnold (1785), a forest tree species widely but patchily distributed. Using four partially replicated common gardens in France, we show that late spring minimum temperatures affect radial growth negatively and early summer precipitations positively across all provenances. In contrast, there was a strong provenance effect on mean ring-widths, as well as high phenotypic plasticity and significant genotype by environment interactions in most provenances and all subspecies. Provenances of the subspecies P.n. subsp. salzmannii often displayed the smallest mean ring widths except in the least fertile common garden. A few provenances of P.n. subsp. pallasiana, P.n. subsp. laricio and P.n. subsp. nigra performed equally well in all common gardens. Climate smart forestry should consider provenance and not just subspecies recommendations for plantations where black pine is not native, either for ecological restoration or timber production. Pinus nigra J.F. Arnold (1785), the European black pine, is a forest tree species widely but patchily distributed throughout southern Europe, from isolated locations in North Africa to the Black Sea and Western Asia. While it has been widely used as a plantation species since the mid-nineteenth century because of its rapid growth even on rather poor soils, the effect of geographic origin within genetic lineage on radial growth and climate sensitivity has not yet been assessed. We analyze the effects of geographic origin on radial growth variability and radial growth–climate relationships within four subspecies of the European black pine. Using a tree-ring to climate relationship approach and a 40-year-long chronology, we first estimated how variable the effect of monthly climate was on radial growth, among 16 provenances within four subspecies, in four bioclimatically contrasted common gardens in France. We then used the tree-ring data to estimate genetic and plasticity effects and to test for the existence of genotype by environment interactions. Lastly, we ranked the growth performance of the different subspecies and provenances measured in each common garden. There were few differences in climate effects among provenances and subspecies. Late spring minimum temperatures affect radial growth negatively and early summer precipitations positively. The provenance effect on ring-widths was stronger than the subspecies effect. Radial growth phenotypic plasticity was high across the four common gardens and so were genotype by environment interactions in most subspecies. Provenances of the subspecies P.n. subsp. salzmannii often displayed the smallest mean ring widths except in the least fertile test site. Provenance, in addition to subspecies variability should be considered in climate-smart forestry practice, whether for ecological restoration and timber production.
In Mediterranean environments, droughts are identified as a major factor of vulnerability, in particular in forestry ecosystems which are exposed to increasingly frequent and intense droughts induced by climatic changes. Moreover, these ecosystems are mainly located in karstic environments, with a crucial importance of groundwater for anthropic and vegetation uses, but also with complex and heterogeneous surface and hydrogeological processes. For instance, recent ecophysiological and isotopic studies have shown that tree roots are able to extract water deep enough in the epikarst to sustain transpiration during water stress periods (Carrière et al. 2020). However, the quantification of water stocks, aquifer recharge and their dynamics are not yet fully established in such a context. This calls for using models suited to the complexity of the environment, able to improve knowledge of both groundwater recharge and forests hydric processes. The modelling challenges are to adapt models to karstic environment constraints, in order to: jointly simulate diffuse infiltration into the superficial part of the root zone and fast preferential infiltration into the network of karstic fractures, and simulate the transpiratory and water extraction processes throughout the root zone. jointly simulate diffuse infiltration into the superficial part of the root zone and fast preferential infiltration into the network of karstic fractures, and simulate the transpiratory and water extraction processes throughout the root zone. Toward this objective, we improved a detailed SVAT model (SiSPAT,Braud et al. 1995) devoted to simulate energy and water exchanges into the epikarst, by including a new groundwater module able to allocate surface runoff into the network of fractures. This new version was implemented, and then evaluated for the first time on two mediterranean forest sites included in the ICOS network, namely the forest sites of Font-Blanche (Bouches-du-Rhône), managed by URFM INRAE and URFM 2025) and Puéchabon (Hérault), managed by CEFE (CNRS and CEFE 2025). Performances obtained between observed and modeled soil water content, soil temperature and energy fluxes were particularly good. These results highlighted the necessity of representing both diffuse and preferential flows in SVAT modelling for karstic areas, to correctly reproduce surface flux dynamics. Moreover, it was also shown that preferential infiltration builds up deep water storage throughout the year, and considerably improves transpiration processes during water stress periods. This newly integrated process also significantly affected the simulation of the other hydrological balance components, largely reducing runoff and water storage into the soil, through introducing a groundwater recharge flow as observed in this area. Finally, results allowed us to reduce uncertainties in quantitative estimates of groundwater recharge, through a better control of evapotranspiration at the surface. Our modelling approach shows new promising results, both in terms of performances obtained on two karstic forest sites and of the knowledge of processes at the surface-groundwater interface. This study opens further perspectives on the integrated functioning of the critical zone in karstic environments from mechanistic models. Next steps will concern the coupling between water and carbon cycles, through the development of a new module devoted to photosynthesis and improved stomatal conductance. This step is under progress, and will allow us to study the impacts of future droughts in a context of climatic changes.
While the Late Glacial evolution of Pyrenean glaciers is rather well-known, Holocene glacier behavior is much less constrained, except for the Little Ice Age period. In this study, we attempt to bridge this knowledge gap by dating four moraines in the Western-Central Pyrenees using in situ chlorine-36 cosmic-ray exposure dating of moraine boulders. Ages of 11.2 ± 1.5 ka, 7.8 ± 1.1 ka, 3.0 ± 0.6 ka and 972 ± 208 yr were obtained, constituting the most robust directly dated Holocene glacier chronology in the Pyrenees. The moraine age of 7.8 ± 1.1 ka (n = 5) is a novel finding as no evidence for significant contemporary glacial advance exists at any other site in the Pyrenees or in the Alps/elsewhere in Europe. We tentatively link this moraine to the 8.2 ka cold event. We propose a paleoclimatic interpretation of this Holocene glacial evolution, in conjunction with the radiocarbon ages from nearby peat bog cores. Further, we hypothesize on the role of Mid-Holocene warm periods on the melting of permafrost within rock glacier complexes and how they translate into peat bog deposits in the vicinity of the moraines. Finally, based on archeological evidence (construction and ceramic remains) collected in the center of Troumouse Cirque, the possible influence of its glacier variability on first human settlements in the region is discussed.
Global warming increases ecosystem respiration (ER), creating a positive carbon-climate feedback. Thermal acclimation, the direct responses of biological communities to reduce the effects of temperature changes on respiration rates, is a critical mechanism that compensates for warming-induced ER increases and dampens this positive feedback. However, the extent and effects of this mechanism across diverse ecosystems remain unclear. By analyzing CO2 flux data from 93 eddy covariance sites worldwide, we observed thermal acclimation at 84 % of the sites. If sustained, thermal acclimation could reduce projected warming-induced nighttime ER increases by at least 25 % across most climate zones by 2041-2060. Strong thermal acclimation is particularly evident in ecosystems at high elevation, with low-carbon-content soils, and within tundra, semi-arid, and warm-summer Mediterranean climates, supporting the hypothesis that extreme environments favor the evolution of greater acclimation potential. Moreover, ecosystems with dense vegetation and high productivity such as humid tropical and subtropical forests generally exhibit strong thermal acclimation, suggesting that regions with substantial CO2 uptake may continue to serve as strong carbon sinks. Conversely, some ecosystems in cold continental climates show signs of enhancing thermal responses, the opposite of thermal acclimation, which could exacerbate carbon losses as climate warms. Our study underscores the widespread yet climate-specific patterns of thermal acclimation in global terrestrial ER, emphasizing the need to incorporate these patterns into Earth System Models for more accurate carbon-climate feedback projections.
