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[hal-05550584] Continental Contrasts in Climate Extremes That Control Tree Fecundity
In 2023, more than half of olive harvests ( Olea europaea ) across Spain, Greece, and Türkiye were lost to drought. The same year late freeze destroyed 90% of the peach crop ( Prunus persica ) on the Georgia Piedmont and the apple crop ( Malus domestica ) in central New York, Vermont, and southern Quebec. Climate extremes now rank with the costliest threats to agriculture, but their role in forest recovery from diebacks that are happening globally is unknown for lack of tree fecundity estimates in forests. Tolerance of climate extremes could depend on past exposure but constrained by phylogenetic conservatism. We report a continental scale analysis of climate extremes and forest fecundity across North America and Europe showing that responses to late freeze and drought are happening now. Species differences are not explained by the traits typically included in ecological studies and they are weakly associated with phylogeny. Late freeze, that is, freezing temperatures that follow the onset of flower development in spring, is shown to be “normal” in North America, but not Europe, potentially explaining failed seed production due to delayed onset and the resultant shorter growing period by North American transplants dating back at least to the 18th century. Drought has thus far had the greatest impacts in dry forested regions, but here too, species differences are not explained by traditional trait values. If responses have been buffered from drought and late freeze by past exposure, acclimation and local adaptation prove inadequate as extremes intensify.
ano.nymous@ccsd.cnrs.fr.invalid (James S Clark) 13 Mar 2026
https://hal.science/hal-05550584v1
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[hal-05620731] Bridging the Energy Balance Gap in Eddy‐Covariance Measurements: Insights From Standardized Network Data
The lack of energy balance closure in Eddy‐Covariance (EC) measurements is a well‐known, still unresolved challenge in micrometeorology, with energy balance closure (EBC) rates typically ranging between 60% and 80%. While numerous hypotheses have been proposed to explain this imbalance, the relative contributions of neglected energy storage terms, data quality and flux processing options remain insufficiently disentangled. Using standardized ICOS and NEON datasets, we show that a significant portion of the observed energy imbalance can be attributed to overlooked or inconsistently handled energy components and turbulent flux quality control. Using data drawn from 84 sites, we show that comprehensive energy accounting—including soil heat flux, storage terms (soil, air, biomass), photosynthetic energy demand, and strict quality filtering of turbulent fluxes—improved EBC by 16% on average, with site‐specific gains up to 40%. However, we also identify a persistent residual imbalance that is unlikely to be resolved through methodological refinements or additional measurements alone, pointing to fundamental physical processes that are not accounted for in the standard measurement and processing. We argue that this unresolved imbalance should be explicitly acknowledged and bounded, rather than implicitly absorbed into correction schemes, and we outline practical guidance for diagnosing and interpreting EBC in standardized flux networks. This perspective evaluates methodological advances and residual uncertainties, providing an actionable framework for the appropriate use of EC energy fluxes in carbon, water, and climate research.
ano.nymous@ccsd.cnrs.fr.invalid (Giacomo Nicolini) 12 May 2026
https://hal.inrae.fr/hal-05620731v1
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[hal-05422406] Understory plant indicator values poorly perform at monitoring temporal changes in French forest soil chemical properties
Understory plant communities are widely used to infer soil conditions through species indicator values (IVs), scores reflecting species’ ecological preferences for factors such as soil acidity, moisture, or nutrient levels. While their reliability to describe soil conditions along spatial gradients is well established, their ability to capture temporal changes in soil chemistry remains largely untested at both temporal and geographical scales. We combined 26 years of vegetation monitoring with two French national soil surveys (1993–1997; 2007–2012) across 102 permanent forest plots to assess the reliability of community soil indices (CSIs) as bioindicators of soil pH, carbon-to-nitrogen ratio (C/N), and extractable phosphorus. CSIs were computed by averaging species IVs for each plot and survey. Temporal dynamics of measured soil properties and CSIs were analyzed using mixed-effects models at the national scale, while local trends were estimated separately for each plot to directly compare measured and vegetation-inferred changes. CSIs showed strong spatial correlations with measured pH and C/N, but weaker relationships for phosphorus. In contrast, no significant coupling was found between temporal changes in CSIs and measured soil parameters, with frequent mismatches in both direction and magnitude at the plot level. Measured soil dynamics were mainly driven by initial edaphic conditions and stand age, whereas CSI dynamics responded primarily to canopy openness and anthropogenic disturbances such tree harvesting. These findings confirm the value of IVs for spatial bioindication but highlight their limited sensitivity for detecting long-term soil changes, especially where soil changes remain modest.
ano.nymous@ccsd.cnrs.fr.invalid (Robinson Ribémont) 07 Jan 2026
https://hal.science/hal-05422406v1
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[hal-05448009] Trait-dependent declines of threatened endemic trees following plant invasion on a tropical oceanic island
Biological invasions are a leading cause of the ongoing biodiversity crisis, and particularly so on islands. However, the role of invasive alien plants (IAPs) as a driver of native plant declines and extinctions remains unclear. The inherently slow and gradual nature of plant extinctions, especially that of long-lived woody species, could be a reason. Here, we examined temporal trends in subpopulations of 28 threatened endemic tree (TET) taxa. We questioned the frequency with which they decline in association with IAPs on Reunion Island (South-West Indian Ocean), and asked whether the most susceptible TET taxa exhibit characteristics that could reveal the underlying ecological mechanisms. We resurveyed 182 historically described subpopulations and tested whether observed trends of juvenile and adult TETs correlate with the abundance in IAPs using path analyses, while distinguishing TET taxa with respect to their leaf–height–seed characteristics and extinction risk. The trend of adult TETs was not affected by IAPs but that of juvenile TETs was negatively correlated with the abundance of IAPs in the understory layer. This was particularly the case for TET taxa with conservative resource-use strategies (low specific leaf area or low maximum height), whose juveniles might be particularly susceptible to competition with IAPs, but not for TET taxa with large seeds, whose metabolic reserves make seedlings more likely to attain a critical size. These findings suggest that IAPs can significantly contribute to the extinction dynamics of trees, primarily by limiting regeneration through competitive exclusion, and that their impacts vary depending on the traits of the affected taxa.
ano.nymous@ccsd.cnrs.fr.invalid (Robin Pouteau) 08 Jan 2026
https://hal.science/hal-05448009v1
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[hal-05574299] Amazon rainforests are rejuvenating their canopies by producing more photosynthetically efficient young leaves under climate change
Leaf age structure strongly regulates canopy photosynthesis in Amazon rainforests yet its large-scale patterns and dynamics remain poorly understood. Here we map the fraction of leaf area of photosynthetically efficient young leaves (fyoung) using remote sensing data and assess its spatiotemporal variability from 2001 to 2023. We find that fyoung varies markedly with elevation and canopy height: tall or mountain forests (canopy ≥32 m or elevation ≥300 m) exhibit higher fyoung than short or lowland forests, reflecting higher leaf turnover driven by stronger radiation, greater atmospheric dryness and longer dry seasons. Across the basin, fyoung increased significantly in 85.2% of forests during 2001–2023, linked to decreasing precipitation, rising sunlight, intensifying atmospheric dryness and lengthening dry seasons. This widespread trend towards more juvenile leaves is projected to persist under future climate change. Our findings reveal a fundamental shift in Amazon leaf age structure and highlight its importance for predicting future photosynthetic responses in a warmer, drier climate.
ano.nymous@ccsd.cnrs.fr.invalid (Xueqin Yang) 31 Mar 2026
https://hal.science/hal-05574299v1
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[hal-05578664] Lower prevalence of Lyme disease pathogens in mixed deciduous – coniferous forests
A growing number of studies demonstrate the consequences of biodiversity loss on the increased prevalence of vector-borne diseases such as Lyme borreliosis. Given that vertebrate host species differ in their competence for pathogen transmission, it has been hypothesized that greater host diversity, which is more likely to occur in mixed forests, would reduce pathogen prevalence in ticks through a dilution effect. However, empirical evidence remains mixed, particularly in Europe, and recent studies suggest that habitat characteristics and vegetation structure may also play a key role in the risk of tick-borne disease. We sampled ticks along gradients of forest compositional diversity in a network of seven sites in Europe to assess the combined effect of tree and understorey plant diversity on ticks and associated pathogens. We found that several forest habitat characteristics were associated with variations in Ixodes ricinus densities and infection rates. The proportion of I. ricinus nymphs infected by Borrelia was lower in mixed than in pure forests. The prevalence of Borrelia and Rickettsia respectively increased and decreased with the richness of understorey plants. Ixodes ricinus larvae density increased with the proportion of plants palatable to roe deer (Capreolus capreolus). Our results suggest that forest diversity, at both tree and understorey levels, influences ticks and associated pathogens through several direct and potential indirect mechanisms such as effects on vertebrate hosts, particularly herbivores. Habitat and resource diversification of vertebrate hosts provides a useful theoretical framework to guide forest management toward reducing human health risks.
ano.nymous@ccsd.cnrs.fr.invalid (Audrey Bourdin) 03 Apr 2026
https://hal.inrae.fr/hal-05578664v1
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[hal-05614542] Etude des carbonates de calcium amorphes (CCA) dans les microalgues Tetraselmis cordiformis par CRYO MEB
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ano.nymous@ccsd.cnrs.fr.invalid (C Blavignac) 06 May 2026
https://hal.science/hal-05614542v1
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[hal-05594648] Quercus robur and Q. petraea responses to hydroclimatic changes and extremes in the Loire River valley, central France
With more frequent and severe droughts under ongoing global warming impacting European forests, major components of French forest ecosystems, such as oak woodlands, are at increasing risk of decline. Tree-ring width (TRW) records provide valuable insights into both short-and long-term drought impacts on tree growth and have been widely used to improve our understanding of the spatial and temporal patterns of drought effects on forest ecosystems. However, such data are still lacking for oaks in central France over the past decade, and no highresolution studies have yet explored oak responses to drought in French floodplain environments. Here, we investigated the climatic sensitivity, long-term growth response, and drought impact on TRW over the last century in two oak species from the Loire River basin in central France: riparian Quercus robur and non-riparian Q. petraea. Tree growth in both species was positively correlated with growing season SPEI and precipitation, and negatively with summer maximum temperature. Growth of riparian oaks was additionally influenced by summer river discharge and exhibited higher and more stable sensitivity to hydroclimatic variability than Q. petraea, reflecting species-specific traits and local site conditions. Despite these differences, both species showed consistent growth reductions during drought years, with full recovery to pre-drought growth levels not always achieved in the following year. Nevertheless, similar long-term growth patterns, with no overall decline over the last century, suggest a certain capacity of oaks to buffer drought impacts. These findings highlight the importance of continued monitoring of drought effects across contrasting ecological contexts and have direct management implications, particularly for Loire River riparian forests protected under the Natura 2000 network and encompassing national nature reserves.
ano.nymous@ccsd.cnrs.fr.invalid (Charlie Hureau) 17 Apr 2026
https://hal.science/hal-05594648v1
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[hal-05508569] Decreasing frequency and extent of frost damage in European oaks over 1961-2021
<div><p>Late spring frosts (LSF) have substantial ecological and economic impacts in the temperate and boreal zones. Yet, the effects of climate warming on the frequency (i.e., probability of LSF in a given year, in %) and extent (i.e., percentage of trees in a population damaged by a given LSF event) of LSF damage remain underexplored. Here, extending a budburst model that accounts for within-population variability, we developed and evaluated a new model of LSF damage occurrence and extent using 1,220 observations of LSF damage to newly emerged leaves from 304 oak populations in France (1997-2021). Our model simulations reveal that overall, French oak populations are, over time, less exposed to LSF amid ongoing climate change. We observed an overall decline in the frequency (-0.22 % per year) and extent (-0.34 % per year) of LSF damage in French oak populations over the past six decades (1961-2021). These trends are largely driven by the temporal advance of both the last spring frost day and budburst dates, with the last spring frost day advancing at a slightly faster rate (-0.28 days per year) than budburst (-0.21 days per year). This temporal mismatch explains why, contrary to the common assumption that earlier budburst increases frost risk, earlier budburst was in fact associated with a lower frequency of LSF damage. Nevertheless, considerable geographical variability emerged, with declines in damage frequency being more pronounced in continental regions, whereas declines in damage extent were more pronounced in coastal regions. Our findings underscore the importance of considering both LSF frequency and extent when assessing frost risks in a warming climate, offering a comprehensive framework for future ecological and economic evaluations of LSF impacts.</p></div>
ano.nymous@ccsd.cnrs.fr.invalid (Jianhong Lin) 13 Feb 2026
https://hal.inrae.fr/hal-05508569v1
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[hal-05549218] A database of cross-sectional images for testing the biometric traceability of oak (Quercus petraea (Matt.) Liebl. and Quercus robur L.) logs under realistic acquisition conditions
Key message The Biomtrace_extension database contains 8341 RGB images of the butt end of 695 French oak logs. This database was created with the aim of developing biometric traceability methods based on realistic photo acquisitions in the field for tracking logs from the forest to primary processing. No such database was previously available. Photos of the same logs were taken on two dates several months apart, up to more than 100 days apart for some sites. Images were acquired in three specific cases in order to test the sensitivity and limitations of recognition algorithms under conditions that may occur in practice: (1) traceability based on photos taken before and after log extraction; (2) sensitivity of traceability to the quality of photos (angle of the shot and distance to the log); (3) robustness of traceability to partial or complete trimming of the log end. The database also includes manual reference measurements performed on the images, as well as outputs from image preprocessing algorithms. Tables containing site and image characteristics are also provided. The Biomtrace_extension database is available at https://doi.org/10.57745/RKDTKY and metadata are provided at: https://metadata-afs.nancy.inra.fr/geonetwork/srv/fre/catalog.search#/metadata/5f2842a0-15ec-48be-8f1c-e44334654cc5 .
ano.nymous@ccsd.cnrs.fr.invalid (Fleur Longuetaud) 12 Mar 2026
https://hal.science/hal-05549218v1
