Productions 2022

Publications dans HAL pour l'année 2022


HAL : Dernières publications

  • [hal-03647971] Effect of tree demography and flexible root water uptake for modeling the carbon and water cycles of Amazonia

    Amazonian forest plays a crucial role in regulating the carbon and water cycles in the global climate system. However, the representation of biogeochemical fluxes and forest structure in dynamic global vegetation models (DGVMs) remains challenging. This situation has considerable implications to simulate the state and dynamics of Amazonian forest. This study aims at simulating the dynamic of the evapotranspiration (ET), productivity (GPP), biomass (AGB) and forest structure of wet tropical forests in the Amazon basin using the updated ORCHIDEE land surface model. The latter is improved for two processes: stand structure and demography, and plant water uptake by roots. Stand structure is simulated by adapting the CAN version of ORCHIDEE, originally developed for temperate forests. Here, we account for the permanent recruitment of young individual trees, the distribution of stand level growth into 20 different cohorts of variable diameter classes, and mortality due to asymmetric competition for light. Plant water uptake is simulated by including soil-to-root hydraulic resistance (RS). To evaluate the effect of the soil resistance alone, we performed factorial simulations with demography only (CAN) and both demography and resistance (CAN-RS). AGB, ET and GPP outputs of CAN-RS are also compared with the standard version of ORCHIDEE (TRUNK) for which eco-hydrological parameters were tuned globally to fit GPP and evapotranspiration at flux tower sites. All the model versions are benchmarked against in situ and regional datasets. We show that CAN-RS correctly reproduce stand level structural variables (as CAN) like diameter classes and tree densities when validated using in-situ data. Besides offering the key advantage to simulate forest's structure, it also correctly simulates ET and GPP and improves fluxes spatial patterns when compared to TRUNK. With the new formulation of soil water uptake, which is driven by soil water availability rather than root-biomass, the simulated trees preferentially use water in the deepest soil layers during the dry seasons. This improves the seasonality of ET and GPP compared to CAN, especially on clay soils for which the soil moisture potential drops rapidly in the dry season. Nevertheless, since demography parameters in CAN-RS are constant for all evergreen tropical forests, spatial variability of AGB and basal area across the Amazon remains too uniform compared to observations, and are very comparable to the TRUNK. Additional processes such as climate driven mortality and phosphorus limitation on growth leading to the prevalence of species with different functional traits across the Amazon need to be included in the future development of this model.

    ano.nymous@ccsd.cnrs.fr.invalid (Emilie Joetzjer) 22 Jul 2024

  • [hal-04066774] Linking ecological niche models and common garden experiments to predict phenotypic differentiation in stressful environments: Assessing the adaptive value of marginal populations in an alpine plant

    Environmental variation within a species' range can create contrasting selective pressures, leading to divergent selection and novel adaptations. The conservation value of populations inhabiting environmentally marginal areas remains in debate and is closely related to the adaptive potential in changing environments. Strong selection caused by stressful conditions may generate novel adaptations, conferring these populations distinct evolutionary potential and high conservation value under climate change. On the other hand, environmentally marginal populations may be genetically depauperate, with little potential for new adaptations to emerge. Here, we explored the use of ecological niche models (ENMs) linked with common garden experiments to predict and test for genetically determined phenotypic differentiation related to contrasting environmental conditions. To do so, we built an ENM for the alpine plant Silene ciliata in central Spain and conducted common garden experiments, assessing flowering phenology changes and differences in leaf cell resistance to extreme temperatures. The suitability patterns and response curves of the ENM led to the predictions that: (1) the environmentally marginal populations experiencing less snowpack and higher minimum temperatures would have delayed flowering to avoid risks of late-spring frosts and (2) those with higher minimum temperatures and greater potential evapotranspiration would show enhanced cell resistance to high temperatures to deal with physiological stress related to desiccation and heat. The common garden experiments revealed the expected genetically based phenotypic differentiation in flowering phenology. In contrast, they did not show the expected differentiation for cell resistance, but these latter experiments had high variance and hence lower statistical power. The results highlight ENMs as useful tools to identify contrasting putative selective pressures across species ranges. Linking ENMs with common garden experiments provides a theoretically justified and practical way to study adaptive processes, including insights regarding the conservation value of populations inhabiting environmentally marginal areas under ongoing climate change.

    ano.nymous@ccsd.cnrs.fr.invalid (Javier Morente-López) 12 Apr 2023

  • [hal-03873631] High exposure of global tree diversity to human pressure

    Safeguarding Earth’s tree diversity is a conservation priority due to the importance of trees for biodiversity and ecosystem functions and services such as carbon sequestration. Here, we improve the foundation for effective conservation of global tree diversity by analyzing a recently developed database of tree species covering 46,752 species. We quantify range protection and anthropogenic pressures for each species and develop conservation priorities across taxonomic, phylogenetic, and functional diversity dimensions. We also assess the effectiveness of several influential proposed conservation prioritization frameworks to protect the top 17% and top 50% of tree priority areas. We find that an average of 50.2% of a tree species’ range occurs in 110-km grid cells without any protected areas (PAs), with 6,377 small-range tree species fully unprotected, and that 83% of tree species experience nonnegligible human pressure across their range on average. Protecting high-priority areas for the top 17% and 50% priority thresholds would increase the average protected proportion of each tree species’ range to 65.5% and 82.6%, respectively, leaving many fewer species (2,151 and 2,010) completely unprotected. The priority areas identified for trees match well to the Global 200 Ecoregions framework, revealing that priority areas for trees would in large part also optimize protection for terrestrial biodiversity overall. Based on range estimates for >46,000 tree species, our findings show that a large proportion of tree species receive limited protection by current PAs and are under substantial human pressure. Improved protection of biodiversity overall would also strongly benefit global tree diversity.

    ano.nymous@ccsd.cnrs.fr.invalid (Wen-Yong Guo) 28 Nov 2022

  • [hal-03714709] A standardized morpho-functional classification of the planet's humipedons

    It was time to take stock. We modified the humipedon classification key published in 2018 to make it easier and more practical. This morpho-functional taxonomy of the topsoil (humipedon) was only available in English; we also translated it into French and Italian. A standardized morpho-functional classification of humipedons (roughly the top 30–40 cm of soil: organic and organomineral surface horizons) would allow for a better understanding of the functioning of the soil ecosystem. This paper provides the founding principles of the classification of humipedon into humus systems and forms. With the recognition of a few diagnostic horizons, all humus systems can be determined. The humus forms that make up these humus systems are revealed by measuring the thicknesses of the diagnostic horizons. In the final part of the article, several figures represent the screenshots of a mobile phone or tablet application that allows for a fast recall of the diagnostic elements of the classification in the field. The article attempts to promote a standardized classification of humipedons for a global and shared management of soil at planet level.

    ano.nymous@ccsd.cnrs.fr.invalid (Augusto Zanella) 11 Jul 2022

  • [hal-03926053] The distribution of carbon stocks between tree woody biomass and soil differs between Scots pine and broadleaved species (beech, oak) in European forests

    While the impacts of forest management options on carbon (C) storage are well documented, the way they affect C distribution among ecosystem components remains poorly investigated. Yet, partitioning of total forest C stocks, particularly between aboveground woody biomass and the soil, greatly impacts the stability of C stocks against disturbances in forest ecosystems. This study assessed the impact of species composition and stand density on C storage in aboveground woody biomass (stem + branches), coarse roots, and soil, and their partitioning in pure and mixed forests in Europe. We used 21 triplets (5 beech-oak, 8 pine-beech, 8 pine-oak mixed stands, and their respective monocultures at the same sites) in seven European countries. We computed biomass C stocks from total stand inventories and species-specific allometric equations, and soil organic C data down to 40 cm depth. On average, the broadleaved species stored more C in aboveground woody biomass than soil, while C storage in pine was equally distributed between both components. Stand density had a strong effect on C storage in tree woody biomass but not in the soil. After controlling for stand basal area, the mixed stands had, on average, similar total C stocks (in aboveground woody biomass + coarse roots + soil) to the most performing monocultures. Although species composition and stand density affect total C stocks and its partitioning between aboveground woody biomass and soil, a large part of variability in soil C storage was unrelated to stand characteristics.

    ano.nymous@ccsd.cnrs.fr.invalid (Richard Osei) 25 Oct 2023

  • [hal-04201573] Fonctionnement des arbres et des semis soumis à ennoyage : ajustements écophysiologiques, désordres métaboliques et adaptations

    Noyées par une nappe temporaire, les racines manquent rapidement d’oxygène et les arbres ou semis doivent adapter leur fonctionnement. Sont détaillés ici les mécanismes écophysiologiques et les adaptations contribuant à la tolérance de la contrainte d’hypoxie chez certaines espèces, en l’état actuel des connaissances.

    ano.nymous@ccsd.cnrs.fr.invalid (Nathalie Bréda) 09 Jul 2024

  • [hal-04201602] Les sols forestiers à nappe temporaire : fonctionnement, particularités et enjeux actuels

    Pour fixer les idées, cet article propose quelques rappels et détaille les particularités des sols forestiers à nappe perchée temporaire : conditions de formation d’une nappe perchée, formation des traces d’hydromorphie, sensibilité au tassement et principales contraintes pour les essences forestières. Il aborde enfin les principaux enjeux auxquels la recherche devra répondre pour l’avenir.

    ano.nymous@ccsd.cnrs.fr.invalid (Caroline Petitjean) 10 Jul 2024

  • [hal-04456551] Comportement des chênes pédonculé et sessile sur deux sols à engorgement temporaire en Lorraine

    Dans les années 1970-1980, l'INRA (aujourd'hui INRAE) a installé des plantations expérimentales de chênes sur deux types de sol à nappe temporaire de la Plaine lorraine, en forêts communales de Charmes et Damas-aux-bois (88). Le but initial était de tester différents types d’« assainissement » destinés à améliorer la reprise et la croissance des chênes. Après 4 à 5 décennies, ce dispositif continue de livrer des informations précieuses.

    ano.nymous@ccsd.cnrs.fr.invalid (François Lebourgeois) 09 Jul 2024

  • [hal-03829175] PSDR4 ASTRAL - Acteurs et Services écosystémiques des Territoires RurAux Lorrains

    Des enjeux forts de valorisation des ressources territoriales sont posés en Lorraine qui place en interaction cultures, élevages, forêts, zones de friches et zones urbanisées. ASTRAL s’est interrogé sur les complémentarités à rechercher entre usages des sols pour produire une diversité de services écosystémiques, sur les représentations associées à ces services ainsi que sur les dispositifs d’action collective et les réseaux d’acteurs qui impulsent, accompagnent ou freinent les dynamiques territoriales. La démarche méthodologique a combiné analyses quantitatives et cartographiques de bases de données géographiques, observations de terrain et expérimentations, mesures de services en parcelles, enquêtes qualitatives et situations d’observation participante. Outre des travaux conduits à l’échelle régionale, cette démarche a été déployée dans trois études de cas territoriales, lieux de différentes formes d’interactions avec les acteurs locaux et les habitants. ASTRAL a produit de nouvelles connaissances sur les organisations et dynamiques territoriales des usages des sols aux échelles régionale et territoriale, sur les mécanismes à l’origine de la fourniture de services écosystémiques ainsi que sur les organisations sociales qu’ils suscitent, qui dépendent étroitement des contextes politiques et économiques locaux. Le projet a notamment montré que les friches, qu’elles soient naturelles ou industrielles, peuvent être des lieux d’expérimentations scientifiques, sociales, culturelles afin d’encourager la réappropriation de leurs territoires par les riverains. Il a aussi mis en évidence le rôle déterminant des associations qui, proches des populations, construisent des problématiques sociales qui touchent l’environnement, l’alimentation et la ruralité, et permettent la structuration de mobilisations inédites en milieu rural pour favoriser une transition agroécologique de l’agriculture incluant une reconnexion avec l’alimentation.

    ano.nymous@ccsd.cnrs.fr.invalid (Catherine Mignolet) 25 Oct 2022

  • [hal-03638143] Historical landscape matters for threatened species in French mountain forests

    Ancient forests are known to host a biodiversity of high ecological distinctiveness and are likely to provide habitat for red-listed species. Yet, few studies have investigated the role of forest continuity for the conservation of threatened species. We used species-presence data on red-listed species from 12 taxonomic groups (Spermatophyta, Pteridophyta, Bryophyta, Lichens, Chiroptera, Aves, Squamata, Amphibia, Coleoptera, Lepidoptera, Odonata and Orthoptera) to ascertain if ancient forests are an important habitat for threatened species in five mountain and subalpine protected areas in France. We compared the effect of the amount of historical forest (1853–1860) with the effect of the amount of current forest on the distribution of red-listed species in six circular landscape buffers ranging in radius from 100 to 1500 m. We showed that the amount of historical forest in the landscape had a positive effect on forest Spermatophyta, Bryophyta, Coleoptera and edge forest Pteridophyta with a better predictive power than current forest area, highlighting a colonization credit in recent forests. Conversely, edge-forest lepidopterans were more negatively affected by historical than by current forest area, highlighting an extinction debt in recent forests. Our findings underline that implementing protective measures of ancient forests would be a better strategy than afforestation to preserve threatened forest species in mountain and subalpine forest landscapes.

    ano.nymous@ccsd.cnrs.fr.invalid (Sylvain Mollier) 23 Nov 2023

  • [hal-03926054] Identification and spatial extent of understory plant species requiring vegetation control to ensure tree regeneration in French forests

    Abstract Key message Fifteen species are most susceptible to require vegetation control during tree regeneration in the range of our study. Among these 15 species, Rubus fruticosus , Pteridium aquilinum , and Molinia caerulea cover each more than 300,000 ha of open-canopy forests. Context Vegetation control, i.e., the reduction of competitive species cover, is often required to promote tree seedling establishment during the forest regeneration stage. The necessity to control understory vegetation largely depends on the species to be controlled. In order to plan forest renewal operations, it is critical to identify which species require vegetation control during the regeneration stage and to quantify the forest area affected by these species. Aims We aimed at identifying the main species requiring vegetation control and at estimating the forest area they cover at the national level. Methods Using National Forest Inventory data, we created four indicators based on two levels of plant cover, cross-referenced with two levels of canopy opening, and compared them to the outcome of a survey of forest manager practices. Results The best indicator was the one that represented the proportion of forests with open canopy where the species was present with a large cover in the understory. In non-Mediterranean France, according to the indicator, a total of 15 species were found to frequently require vegetation control during the tree regeneration stage. Pteridium aquilinum , Molinia caerulea , and Rubus fruticosus were the main species, and each covered more than 300,000 ha of forest with open canopies, representing about 13% of the total forest area with open canopies outside of the Mediterranean area. Conclusions Forests covered by species requiring vegetation control according to forest managers represent a large share of the forest area undergoing regeneration. This study provides the first list of species that require vegetation control based on a methodological protocol that makes it possible to calculate the area associated with each species.

    ano.nymous@ccsd.cnrs.fr.invalid (Noé Dumas) 02 Feb 2023

  • [hal-03863446] Genotypic and tissue-specific variation of Populus nigra transcriptome profiles in response to drought

    Climate change is one of the most important challenges for mankind in the far and near future. In this regard, sustainable production of woody crops on marginal land with low water availability is a major challenge to tackle. This dataset is part of an experiment, in which we exposed three genetically differentiated genotypes of Populus nigra originating from contrasting natural habitats to gradually increasing moderate drought. RNA sequencing was performed on fine roots, developing xylem and leaves of those three genotypes under control and moderate drought conditions in order to get a comprehensive dataset on the transcriptional changes at the whole plant level under water limiting conditions. This dataset has already provided insight in the transcriptional control of saccharification potential of the three Populus genotypes under drought conditions and we suggest that our data will be valuable for further in-depth analysis regarding candidate gene identification or, on a bigger scale, for meta-transcriptome analysis.

    ano.nymous@ccsd.cnrs.fr.invalid (Christian Eckert) 30 Jun 2024

  • [hal-03518443] Global maps of soil temperature

    Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.

    ano.nymous@ccsd.cnrs.fr.invalid (Jonas Lembrechts) 03 Mar 2022

  • [hal-03846703] Stronger legacy effects of cropland than of meadows or pastures on soil conditions and plant communities in French mountain forests

    Question Differences in understory vegetation between ancient and recent forests have been thoroughly explored; however, few studies have investigated the legacies of different former land uses in recent forests. Indeed, due to more intense agricultural practices (tillage and fertilisation), legacy effects are expected to be stronger in former cropland or meadows than in former pastures. Our objectives were to compare soil conditions, taxonomic composition and functional composition of understory plant communities in recent forests located on former pastures, meadows or cropland, with ancient forests as a reference.LocationTarentaise Valley, Savoy, France Methods Based on land-use maps surveyed between 1862 and 1864, we selected 82 forest sites with different former land uses in mountain forests in the French Alps and carried out soil sampling and botanical surveys. To account for potential confounding factors (altitude, canopy cover, tree species composition), we applied multiple linear regressions to analyse soil properties, canonical correspondence analysis to analyse plant taxonomic composition and multi-species generalized linear mixed-effects models to analyse relationships between plant functional composition and former land uses. Results The soils of former cropland were richer in nutrients and more alkaline compared to other past land uses, while soils on former pastures and meadows differed only slightly from ancient forests. Ancient forests were characterised by acidophilic, shade-tolerant, low-stature, forest-dependent species, whereas former cropland was characterised by calcicolous non-forest species. Former pasture and meadow communities displayed a distinct taxonomic composition compared to other past land uses, but a functional composition closer to ancient forest than to former cropland. Conclusion Former cropland has a stronger legacy effect than former pastures or meadows. This could explain small differences between ancient and recent forests observed in previous studies conducted in mountain landscapes where former cropland was rare.

    ano.nymous@ccsd.cnrs.fr.invalid (Sylvain Mollier) 23 Nov 2023

  • [hal-03926055] With increasing site quality asymmetric competition and mortality reduces Scots pine (Pinus sylvestris L.) stand structuring across Europe

    Heterogeneity of structure can increase mechanical stability, stress resistance and resilience, biodiversity and many other functions and services of forest stands. That is why many silvicultural measures aim at enhancing structural diversity. However, the effectiveness and potential of structuring may depend on the site conditions. Here, we revealed how the stand structure is determined by site quality and results from site-dependent partitioning of growth and mortality among the trees. We based our study on 90 mature, even-aged, fully stocked monocultures of Scots pine (Pinus sylvestris L.) sampled in 21 countries along a productivity gradient across Europe. A mini-simulation study further analyzed the site-dependency of the interplay between growth and mortality and the resulting stand structure. The overarching hypothesis was that the stand structure changes with site quality and results from the site-dependent asymmetry of competition and mortality. First, we show that Scots pine stands structure across Europe become more homogeneous with increasing site quality. The coefficient of variation and Gini coefficient of stem diameter and tree height continuously decreased, whereas Stand Density Index and stand basal area increased with site index. Second, we reveal a site-dependency of the growth distribution among the trees and the mortality. With increasing site index, the asymmetry of both competition and growth distribution increased and suggested, at first glance, an increase in stand heterogeneity. However, with increasing site index, mortality eliminates mainly small instead of all-sized trees, cancels the size variation and reduces the structural heterogeneity. Third, we modelled the site-dependent interplay between growth partitioning and mortality. By scenario runs for different site conditions, we can show how the site-dependent structure at the stand level emerges from the asymmetric competition and mortality at the tree level and how the interplay changes with increasing site quality across Europe. Our most interesting finding was that the growth partitioning became more asymmetric and structuring with increasing site quality, but that the mortality eliminated predominantly small trees, reduced their size variation and thus reversed the impact of site quality on the structure. Finally, the reverse effects of mode of growth partitioning and mortality on the stand structure resulted in the highest size variation on poor sites and decreased structural heterogeneity with increasing site quality. Since our results indicate where heterogeneous structures need silviculture interventions and where they emerge naturally, we conclude that these findings may improve system understanding and modelling and guide forest management aiming at structurally rich forests.

    ano.nymous@ccsd.cnrs.fr.invalid (Hans Pretzsch) 06 Jan 2023

  • [hal-03926051] Beech and hornbeam dominate oak 20 years after the creation of storm-induced gaps

    Oak (Quercus petraea (Matt.) Liebl. and Quercus robur L. grouped), European beech (Fagus sylvatica L.) and hornbeam (Carpinus betulus L.) are three major species of western and central European forests. When conditions are suitable for the three species, silvicultural management often favours oak because of its greater economic interest. Forest managers know that beech and hornbeam are strong competitors for oak during the regeneration phase, but the conditions that influence the relative success of the regeneration of the three species growing in mixture are still poorly characterised. The natural regeneration of the three species 20 years after canopy openings was studied based on 108 study sites established in 2001 in French forests impacted by the windstorms Lothar and Martin in 1999. In spring and summer 2018 and 2019, all saplings over 0.1 m in height were counted, species were identified and diameter at breast height (DBH) was measured for all saplings over 1.30 m. The height of the saplings with the highest and median DBH in each plot was recorded for each species. Mixed models were used to analyse the combined effects of former stand type, distance from the edge of the gap and soil conditions on species presence, sapling abundance, DBH and height. The modelling approach highlighted the preponderant role of the initial seed rain on the presence and sapling density of the three species compared to interspecific competition or distance from the edge. The two latter factors had a secondary effect on sapling DBH and height. Beech and hornbeam saplings were more abundant than oak saplings regardless of soil conditions (on average, 3097, 3063 and 344 saplings ha(-1), respectively), suggesting a strong competitive ability of these two species. Oak was present on 22% (43% for hornbeam and 68% for beech) of the studied plots, at a low density but with a height and DBH similar to that of beech or hornbeam. This result highlights the high dissemination capacity of beech and hornbeam, which prevents the establishment of a stand dominated by oak. When seeking to obtain oak-dominated stands in the lowlands of Europe, the abundance of beech and hornbeam can be a limiting factor that could lead to the disappearance of oak from large areas if no silvicultural operations are performed to promote it.

    ano.nymous@ccsd.cnrs.fr.invalid (Lucie Dietz) 02 Feb 2023

  • [hal-03880260] Regional climate moderately influences species-mixing effect on tree growth-climate relationships and drought resistance for beech and pine across Europe

    Increasing species diversity is considered a promising strategy to mitigate the negative impacts of global change on forests. However, the interactions between regional climate conditions and species-mixing effects on climate-growth relationships and drought resistance remain poorly documented. In this study, we investigated the patterns of species-mixing effects over a large gradient of environmental conditions throughout Europe for European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), two species with contrasted ecological traits. We hypothesized that across large geographical scales, the difference of climate-growth relationships and drought resistance between pure and mixed stands would be dependent on regional climate. We used tree ring chronologies derived from 1143 beech and 1164 pine trees sampled in 30 study sites, each composed of one mixed stand of beech and pine and of the two corresponding pure stands located in similar site conditions. For each site and stand, we used Bootstrapped Correlation Coefficients (BCCs) on standardized chronologies and growth reduction during drought years on raw chronologies to analyze the difference in climate-tree growth relationships and resistance to drought between pure and mixed stands. We found consistent large-scale spatial patterns of climate-growth relationships. Those patterns were similar for both species. With the exception of the driest climates where pure and mixed beech stands tended to display differences in growth correlation with the main climatic drivers, the mixing effects on the BCCs were highly variable, resulting in the lack of a coherent response to mixing. No consistent species-mixing effect on drought resistance was found within and across climate zones. On average, mixing had no significant effect on drought resistance for neither species, yet it increased pine resistance in sites with higher climatic water balance in autumn. Also, beech and pine most often differed in the timing of their drought response within similar sites, irrespective of the regional climate, which might increase the temporal stability of growth in mixed compared to pure stands. Our results showed that the impact of species mixing on tree response to climate did not strongly differ between groups of sites with distinct climate characteristics and climate-growth relationships, indicating the interacting influences of species identity, stand characteristics, drought events characteristics as well as local site conditions.

    ano.nymous@ccsd.cnrs.fr.invalid (Géraud de Streel) 14 Dec 2022

  • [hal-03678147] Do <sup>2</sup> H and <sup>18</sup> O in leaf water reflect environmental drivers differently?

    We compiled hydrogen and oxygen stable isotope compositions (delta H-2 and delta O-18) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water delta H-2 was more closely correlated with delta H-2 of xylem water or atmospheric vapour, whereas leaf water delta O-18 was more closely correlated with air relative humidity. This resulted from the larger proportional range for delta H-2 of meteoric waters relative to the extent of leaf water evaporative enrichment compared with delta O-18. We next expressed leaf water as isotopic enrichment above xylem water (Delta H-2 and Delta O-18) to remove the impact of xylem water isotopic variation. For Delta H-2, leaf water still correlated with atmospheric vapour, whereas Delta O-18 showed no such correlation. This was explained by covariance between air relative humidity and the Delta O-18 of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that H-2 and O-18 in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.

    ano.nymous@ccsd.cnrs.fr.invalid (Lucas Cernusak) 25 May 2022

  • [hal-04224602] Contrasting anatomical and biochemical controls on mesophyll conductance across plant functional types

    Summary Mesophyll conductance (gm) limits photosynthesis by restricting CO2 diffusion between the substomatal cavities and chloroplasts. Although it is known that gm is determined by both leaf anatomical and biochemical traits, their relative contribution across plant functional types (PFTs) is still unclear. We compiled a dataset of gm measurements and concomitant leaf traits in unstressed plants comprising 563 studies and 617 species from all major PFTs. We investigated to what extent g limits photosynthesis across PFTs, how gm relates to structural, anatomical, biochemical, and physiological leaf properties, and whether these relationships differ among PFTs. We found that gm imposes a significant limitation to photosynthesis in all C3 PFTs, ranging from 10–30% in most herbaceous annuals to 25–50% in woody evergreens. Anatomical leaf traits explained a significant proportion of the variation in g m ( R 2 &gt; 0.3) in all PFTs except annual herbs, in which gm is more strongly related to biochemical factors associated with leaf nitrogen and potassium content. Our results underline the need to elucidate mechanisms underlying the global variability of gm. We emphasise the underestimated potential of gm for improving photosynthesis in crops and identify modifications in leaf biochemistry as the most promising pathway for increasing gm in these species.

    ano.nymous@ccsd.cnrs.fr.invalid (Jürgen Knauer) 02 Oct 2023

  • [hal-03772046] Seasonal variation of leaf thickness: An overlooked component of functional trait variability

    • The dry and wet seasons in the Neotropics have strong effects on soil water and nutrient availability, as well as on forest dynamics. Despite these major effects on forest ecology, little is known on how leaf traits vary throughout the seasons in tropical rainforest trees. • Here, we investigated the influence of seasonal variations in climate and soil characteristics on leaf trait variation in two tropical tree species. We measured two leaf traits, thickness and water mass per area, in 401 individuals of two species of Symphonia (Clusiaceae) in the Paracou research station in French Guiana tropical lowland rainforest. • We found a significant effect of seasonal variation on these two leaf traits. Soil relative extractable water was a strong environmental predictor of leaf trait variation in response to seasonal variation. Reduced soil water availability during the dry season was associated with increased leaf thickness and water mass per area, possibly as a result of stomatal closure. • Our findings advocate the need to account for environmental seasonality when studying leaf traits in seasonal ecosystems such as tropical forests.

    ano.nymous@ccsd.cnrs.fr.invalid (S. Schmitt) 07 Sep 2022

  • [hal-03518448] Tropical and subtropical Asia's valued tree species under threat

    Tree diversity in Asia’s tropical and subtropical forests is central to nature-based solutions. Species vulnerability to multiple threats, which affectstheprovision of ecosystem services,is poorly understood. We conducteda region-wide, spatially explicit vulnerability assessment(including overexploitation, fire, overgrazing, habitat conversion, andclimate change) of63socio-economically important tree speciesselected from national priority lists and validated by anexpert network representing20 countries. Overall, 74% of the most important areas for conservation of these trees fall outside of protected areas, with species severelythreatened across 47% of their native ranges. The most imminent threats areoverexploitation and habitat conversion, with populations being severely threatened in an average of 24% and 16% of their distribution areas. Optimistically, our results predict relativelylimited overall climate change impacts, however, some of thestudy species arelikelyto lose more than 15% of their habitat by 2050 because of climate change. We pinpoint specific natural forest areas in Malaysia and Indonesia(Borneo) as hotspots for on-site conservationof forest genetic resources, more than 82% of which do not currently fall within designated protected areas. We also identify degraded lands in Indonesia (Sumatra) as priorities for restoration where planting or assisted natural regeneration will help maintain these species into the future, while croplands in Southern India are highlighted as potentially important agroforestry options.Our study highlights the need for regionally coordinated action for effective conservation and restoration.

    ano.nymous@ccsd.cnrs.fr.invalid (Hannes Gaisberger) 09 Jan 2022

  • [hal-04054146] Characterizing the calibration domain of remote sensing models using convex hulls

    The ever-increasing availability of remote sensing data allows production of forest attributes maps, which are usually made using model-based approaches. These map products are sensitive to various bias sources, including model extrapolation. To identify, over a case study forest, the proportion of extrapolated predictions, we used a convex hull method applied to the auxiliary data space of an airborne laser scanning (ALS) flight. The impact of different sampling efforts was also evaluated. This was done by iteratively thinning a set of 487 systematic plots using nested sub-grids allowing to divide the sample by two at each level. The analysis were conducted for all alternative samples and evaluated against 56 independent validation plots. Residuals of the extrapolated vali-dation plots were computed and examined as a function of their distance to the model calibration domain. Extrapolation was also characterized for the pixels of the area of interest (AOI) to upscale at population level. Results showed that the proportion of extrapolated pixels greatly reduced with an increasing sampling effort. It reached a plateau (ca. 20% extrapolation) with a sampling intensity of ca. 250-calibration plots. This contrasts with results on model's root mean squared error (RMSE), which reached a plateau at a much lower sampling intensity. This result emphasizes the fact that with a low sampling effort, extrapolation risk remains high, even at a relatively low RMSE. For all attributes examined (i.e., stand density, basal area, and quadratic mean diameter) estimations were generally found to be biased for validation plots that were extrapolated. The method allows an easy identification of map pixels that are out of the calibration domain, making it an interesting tool to evaluate model transferability over an area of interest (AOI). It could also serve to compare &quot;competing &quot; models at a variable selection phase. From a model calibration perspective, it could serve a posteriori, to evaluate areas (in the auxiliary space) that merit further sampling efforts to improve model reliability.

    ano.nymous@ccsd.cnrs.fr.invalid (J.P. Renaud) 31 Mar 2023

  • [hal-03903795] Modeling and propagating inventory‐based sampling uncertainty in the large‐scale forest demographic model “MARGOT”

    Models based on national forest inventory (NFI) data intend to project forests under management and policy scenarios. This study aimed at quantifying the influence of NFI sampling uncertainty on parameters and simulations of the demographic model MARGOT. Parameter variance–covariance structure was estimated from bootstrap sampling of NFI field plots. Parameter variances and distributions were further modeled to serve as a plug‐in option to any inventory‐ based initial condition. Forty‐year time series of observed forest growing stock were compared with model simulations to balance model uncertainty and bias. Variance models showed high accuracies. The Gamma distribution best fitted the distributions of transition, mortality and felling rates, while the Gaussian distribution best fitted tree recruitment fluxes. Simulation uncertainty amounted to 12% of the model bias at the country scale. Parameter covariance structure increased simulation uncertainty by 5.5% in this 12%. This uncertainty appraisal allows targeting model bias as a modeling priority.

    ano.nymous@ccsd.cnrs.fr.invalid (Timothée Audinot) 16 Dec 2022

  • [hal-03768111] Multisource forest inventories: A model-based approach using k-NN to reconcile forest attributes statistics and map products

    Forest map products are widely used and have taken benefit from progresses in the multisource forest inventory approaches, which are meant to improve the precision of forest inventory estimates at high spatial resolution. However, estimating errors of pixel-wise predictions remains difficult, and reconciling statistical outcomes with map products is still an open and important question. We address this problem using an original approach relying on a model-based inference framework and k-nearest neighbours (k-NN) models to produce pixel-wise estimations and related quality assessment. Our approach takes advantage of the resampling properties of a model-based estimator and combines it with geometrical convex-hull models to measure respectively the precision and accuracy of pixel predictions. A measure of pixel reliability was obtained by combining precision and accuracy. The study was carried out over a 7,694 km2 area dominated by structurally complex broadleaved forests in centre of France. The targeted forest attributes were growing stock volume, basal area and growing stock volume increment. A total of 819 national forest inventory plots were combined with auxiliary data extracted from a forest map, Landsat 8 images, and 3D point clouds from both airborne laser scanning and digital aerial photogrammetry. k-NN models were built independently for both 3D data sources. Both selected models included 5 auxiliary variables, and were generated using 5 neighbours, and most similar neighbours distance measure. The models showed relative root mean square error ranging from 35.7% (basal area, digital aerial photogrammetry) in calibration to 63.4% (growing stock volume increment, airborne laser scanning) in the validation set. At pixel level, we found that a minimum of 86.4% of the predictions were of high precision as their bootstrapped coefficient of variation fall below calibration’s relative root mean square error. The amount of extrapolation varied from 4.3% (digital aerial photogrammetry) to 6.3% (airborne laser scanning). A relationship was found between extrapolation and k-NN distance, opening new opportunities to correct extrapolation errors. At the population level, airborne laser scanning and digital aerial photogrammetry performed similarly, offering the possibility to use digital aerial photogrammetry for monitoring purposes. The proposed method provided consistent estimates of forest attributes and maps, and also provided spatially explicit information about pixel predictions in terms of precision, accuracy and reliability. The method therefore produced high resolution outputs, significant for either decision making or forest management purposes.

    ano.nymous@ccsd.cnrs.fr.invalid (Ankit Sagar) 30 Aug 2023

  • [hal-03619993] Embedding non-industrial private forest owners in forest policy and bioeconomy issues using a Living Lab concept

    International policies have set sustainable development goals that put emphasis on bioeconomy strategies based on renewable resources. The forestry sector, by providing bio-based products, is expected to take part in this bioeconomy with, among other things, the reduction of society's dependence on fossil fuels. Nevertheless, in Europe, the forestry sector is facing an increase in the number of small private forest ownerships, called non-industrial private forests (NIPF), where wood mobilization is difficult due to both ownership fragmentation and the lack of interest of non-industrial forest owners in existing forest-wood chains. Although many policy instruments have been put in place to address this situation, the problem persists for two main reasons. First, a lack of use of policy instruments by forest owners and second, a lack of collaboration between stakeholders. To provide solutions, we propose a methodology to design territorial projects with non-industrial forest owners in the framework of a Living Lab innovation process. This paper presents both the general method developed and analyzed through open and user-centered innovation concepts and its practical implementation in the Vosges department in France. Our results show how the Living Lab approach can improve the acceptance, adoption and use of policy instruments by NIPF owners and how it promotes multi-stakeholder collaborations to design and deploy innovative solutions. The main interest of our study is to provide a methodology to pilot a forestry Living Lab for policy makers and practitioners, based on rigorous concepts of innovation management. Finally, future developments and limitations of our study are discussed in a global research perspective.

    ano.nymous@ccsd.cnrs.fr.invalid (Maxence Arnould) 04 Jan 2024

  • [hal-03757303] Comparative Copper Resistance Strategies of Rhodonia placenta and Phanerochaete chrysosporium in a Copper/Azole-Treated Wood Microcosm

    Copper-based formulations of wood preservatives are widely used in industry to protect wood materials from degradation caused by fungi. Wood treated with preservatives generate toxic waste that currently cannot be properly recycled. Despite copper being very efficient as an antifungal agent against most fungi, some species are able to cope with these high metal concentrations. This is the case for the brown-rot fungus Rhodonia placenta and the white-rot fungus Phanerochaete chrysospo- rium, which are able to grow efficiently in pine wood treated with Tanalith E3474. Here, we aimed to test the abilities of the two fungi to cope with copper in this toxic environment and to decontaminate Tanalith E-treated wood. A microcosm allowing the growth of the fungi on industrially treated pine wood was designed, and the distribution of copper between mycelium and wood was analysed within the embedded hyphae and wood particles using coupled X-ray fluorescence spectroscopy and Scanning Electron Microscopy (SEM)/Electron Dispersive Spectroscopy (EDS). The results demon- strate the copper biosorption capacities of P. chrysosporium and the production of copper-oxalate crystals by R. placenta. These data coupled to genomic analysis suggest the involvement of additional mechanisms for copper tolerance in these rot fungi that are likely related to copper transport (import, export, or vacuolar sequestration).

    ano.nymous@ccsd.cnrs.fr.invalid (Gaurav Pandharikar) 22 Aug 2022

  • [hal-04007808] Assessment of soil compaction and rutting in managed forests through an airborne LiDAR technique

    To ensure sustainable forest management, the assessment and monitoring of soil compaction and rutting are essential. Here, we used airborne light detection and rangingderived digital terrain model (LiDAR-derived DTM), available for the forest of Compiègne in northern France, to compute a spatial index of soil rutting. Following an environmental systematic sampling design, we selected 45 plots representative of the forest stand conditions where we subsequently extracted information from the DTM to compute the cumulative length of ruts (CLR). To assess the quality of this LiDAR-derived index, we related the CLR index to in-situ soil and vegetation parameters such as soil texture, soil pH, and understory plant species composition. Floristic surveys were carried out across all 45 plots to generate plant species response curves along the CLR gradient. We found soil texture, soil type, and soil pH to be important determinants of CLR. For instance, CLR was the highest in soils with the highest clay content. A total of 22 out of the 94 understory plant species we analyzed showed a significant response curve along the CLR gradient. Most important, the occurrence probability of species associated with wet soils and stagnant waters (e.g., Juncus effusus), like those found in ruts, increased with CLR. Other species associated with dry soils (e.g., Hedera helix) showed a negative response curve along the CLR gradient. In conclusion, the proposed index (CLR) has proven useful to remotely assess soil compaction and rutting after logging operations.

    ano.nymous@ccsd.cnrs.fr.invalid (Hamza Mohieddinne) 12 Jun 2023

  • [hal-03639012] Climate and ungulate browsing impair regeneration dynamics in spruce-fir-beech forests in the French Alps

    Abstract Key message Different components of water balance and temperature reduce density and height growth of saplings of Picea abies (L.) H. Karst (Norway spruce), Abies alba Mill. (silver fir) and Fagus sylvatica L. (European beech) in mixed uneven-aged forests in the French Alps and Jura mountains. Ungulate browsing is an additional pressure on fir and beech that could jeopardise the renewal of these species in the future. Context The uncertainty in tree recruitment rates raises questions about the factors affecting regeneration processes in forests. Factors such as climate, light, competition and ungulate browsing pressure may play an important role in determining regeneration, forest structures and thus future forest composition. Aims The objective of this study was to quantify sapling densities and height increments of spruce, fir and beech and to identify dominant environmental variables influencing them in mixed uneven-aged forests in the French Alps and Jura mountains. Methods Sapling height increment and density were recorded in 152 plots, and non-linear mixed models were obtained to establish relations between them and environmental factors known to affect regeneration, namely altitude, slope, aspect, canopy openness, soil characteristics, temperature, precipitation and ungulate browsing. Results Regeneration density, varying from 0 to 7 saplings per m 2 , decreased with sapling height and was also negatively affected for spruce by PET, but positively for fir by precipitation and for beech by mean annual soil water content. Height increment reached up to 50 cm annually, increasing with sapling height and canopy openness and decreasing under high maximum summer temperatures for spruce and beech. The statistical effect of different environmental variables varied slightly among species but trends were quite similar. Additionally, ungulate browsing was high, with fir being the most intensely browsed, followed closely by beech, while spruce was rarely browsed. Conclusions All these results suggest that more temperature warming and a decrease in water availability could negatively impact sapling growth and density in the three species, with possible reduction of forest renewal fluxes. The observed increase of ungulate populations leading to increased browsing could be particularly detrimental to fir saplings.

    ano.nymous@ccsd.cnrs.fr.invalid (Mithila Unkule) 12 Apr 2022

  • [hal-03554126] The number of tree species on Earth

    One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global ground-sourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are ∼73,000 tree species globally, among which ∼9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness.

    ano.nymous@ccsd.cnrs.fr.invalid (Roberto Cazzolla Gatti) 31 May 2022

  • [hal-03502713] Uncovering the critical soil moisture thresholds of plant water stress for European ecosystems

    Understanding the critical soil moisture (SM) threshold (θcrit) of plant water stress and land surface energy partitioning is a basis to evaluate drought impacts and improve models for predicting future ecosystem condition and climate. Quantifying the θcrit across biomes and climates is challenging because observations of surface energy fluxes and SM remain sparse. Here, we used the latest database of eddy covariance measurements to estimate θcrit across Europe by evaluating evaporative fraction (EF)-SM relationships and investigating the covariance between vapor pressure deficit (VPD) and gross primary production (GPP) during SM dry-down periods. We found that the θcrit and soil matric potential threshold in Europe are 16.5% and −0.7 MPa, respectively. Surface energy partitioning characteristics varied among different vegetation types; EF in savannas had the highest sensitivities to SM in water-limited stage, and the lowest in forests. The sign of the covariance between daily VPD and GPP consistently changed from positive to negative during dry-down across all sites when EF shifted from relatively high to low values. This sign of the covariance changed after longer period of SM decline in forests than in grasslands and savannas. Estimated θcrit from the VPD–GPP covariance method match well with the EF–SM method, showing this covariance method can be used to detect the θcrit. We further found that soil texture dominates the spatial variability of θcrit while shortwave radiation and VPD are the major drivers in determining the spatial pattern of EF sensitivities. Our results highlight for the first time that the sign change of the covariance between daily VPD and GPP can be used as an indicator of how ecosystems transition from energy to SM limitation. We also characterized the corresponding θcrit and its drivers across diverse ecosystems in Europe, an essential variable to improve the representation of water stress in land surface models.

    ano.nymous@ccsd.cnrs.fr.invalid (Zheng Fu) 25 Oct 2023

  • [hal-03543468] Sphagnum physiological responses to elevated temperature, nitrogen, CO2 and low moisture in laboratory and in situ microhabitats: a review

    Sphagnum mosses are considered peatland engineers because of their ability to create conditions inducing carbon accumulation. Here, we report on a review of the effects of four environmental variables (elevated temperature, N and CO2 and reduced moisture) on the capitulum biomass, length increment, respiration, photosynthetic capability, N and P exchange and content of the 3 most studied Sphagnum subgenera (Acutifolia, Cuspidata, Sphagnum). Overall, we observe that, when compared to in situ experiments, laboratory experiments tend to exacerbate length increments and underestimate maximum photosynthesis in most of the studies inventoried. This review underscores some differences among results that can be associated with the used of different protocols (e.g. exposure time, instrumental analysis). Studies that investigated the impact of elevated temperature (2-5 degrees C) on Sphagnum reveal an increase in length, respiration and photosynthesis regardless of the experimental conditions and subgenus. Elevated N (3-23 g Nm(-2)y(-1)) on the other hand appears to reduce the length increment but had contrasting effects on photosynthesis. Some divergent responses are found with Cuspidata species because of their tolerance to high doses of N. Low moisture reduces the length increment and photosynthesis of species of the Cuspidata and Sphagnum subgenera but has different effects on species of the Acutifolia subgenus, which are relatively tolerant to water fluctuations. Responses to elevated CO2 have no clear trends reported. Allelochemical interactions between Sphagnum, their microbiome or surrounding mosses or other plants were found to be determinant to Sphagnum responses under those variables and reinforce the interest of such investigations.

    ano.nymous@ccsd.cnrs.fr.invalid (Geneviève Chiapusio) 26 Jan 2022

  • [hal-03519397] Do trait responses to simulated browsing in Quercus robur saplings affect their attractiveness to Capreolus capreolus the following year?

    With the rise of large herbivore populations in most northern hemisphere forests, browsing is becoming an increasingly important driver of forest regeneration dynamics. Among other processes affecting the regeneration, the concept of plant-herbivore feedback loops holds that browsed saplings are more subject to subsequent herbivory. This phenomenon is interpreted as a consequence of compensatory growth following browsing since fast growth is generally associated with higher digestibility and lower defense against herbivores. However, studies linking browsing-induced trait variations to subsequent attractiveness to herbivores are still lacking, especially in the forest context. In this study, we experimentally examine the existence of a feedback loop between oak (Quercus robur L.) and roe deer (Capreolus capreolus) and investigate its underlying morphological and chemical traits. We simulated single and repeated roe deer browsing on nursery-grown oak saplings and measured the changes in sapling height growth, lateral branching, leaf traits and winter shoot traits over two years. We conducted winter feeding trials with tame roe deer one year after the first treatment to test the effect of simulated browsing on sapling attractiveness. Simulated browsing reduced sapling height growth but had no effect on branching. Simulated browsing had no effect on leaf traits after half a year, but decreased the phenolic content and increased the fiber content of winter shoots the following winter. Contrary to our predictions, roe deer preferentially browsed control saplings over saplings previously browsed. After two years, repeated browsing promoted fast carbon acquisition leaf traits (high chlorophyll, high specific leaf area and low fiber content), reduced leaf phenolic content and increased leaf digestibility. We showed that a reduction in 1-year-old oak sapling height growth following browsing, combined with increased structural defense at the expense of chemical defense in winter shoots the following winter, was correlated with reduced browsing pressure, thereby challenging the feedback loop hypothesis. However, we also demonstrated that repeated browsing promoted fast carbon acquisition leaf traits in 2.5-year-old saplings, which tend to support the existence of a feedback loop on older and more intensively browsed saplings. As such, our study provides empirical evidence that morphological and physiological trait responses to browsing influence oak sapling attractiveness, but that the direction and magnitude of this effect depend on the ontogenic stage of the sapling and on the number of browsing events.

    ano.nymous@ccsd.cnrs.fr.invalid (Julien Barrere) 05 Jan 2024

  • [hal-03694879] Climate change-induced background tree mortality is exacerbated towards the warm limits of the species ranges

    Key message : An influence of the recent changes in temperature or rainfall was demonstrated, increasing background tree mortality rates for 2/3 of the 12 studied tree species. Climate change-induced tree mortality was exacerbated towards the warm or dry limits of the species ranges, suggesting in these areas a progressive replacement by more xeric species. Context : Despite the identification of climate change effects on tree mortality in various biomes, the characterization of species-specific areas of vulnerability remains poorly understood. Aims : We sought to assess if the effects of temperature and rainfall changes on background tree mortality rates, which did not result from abrupt disturbances, were linked to climate change intensity only, or if they also depended on the tree’s location along climatic gradients. Methods : We modelled background mortality for 12 of the most common European tree species using 265,056 trees including 4384 dead trees from the French national forest inventory. To explain mortality, we considered variables linked to tree characteristics, stand attributes, logging intensity and site environmental characteristics, and climate change effects. Results : We found an influence of temperature and rainfall changes on 9 species out of 12. For 8 of them, climate change-induced tree mortality was exacerbated towards the warm or dry limits of the species ranges. Conclusion ; These results highlight that tree mortality varies according to the climate change intensity and the tree location along temperature and rainfall gradients. They strengthen the poleward and upward shifts of trees forecasted from climate envelope models for a large number of European tree species.

    ano.nymous@ccsd.cnrs.fr.invalid (Adrien Taccoen) 30 Aug 2023

  • [hal-04225282] The early arrival of spring doesn’t boost annual tree growth

    Analysis of when and how fast temperate deciduous trees in North America grow suggests that the earlier onset of the growing season induced by climate change does not result in extra carbon sequestration from wood production.

    ano.nymous@ccsd.cnrs.fr.invalid (Cyrille B K Rathgeber) 02 Oct 2023

  • [hal-03654545] Estimating natural background concentrations for dissolved constituents in groundwater: A methodological review and case studies for geogenic fluoride

    Knowledge of the natural background concentrations of groundwater constituents is important for the management of groundwater resources, particularly for the assessment of groundwater contamination and the establishment of clean-up goals and regulatory target levels. In recent years, an increasing number of studies have assessed the natural background concentrations of dissolved constituents in groundwater using a variety of different methods, each with its own assumptions, advantages and limitations. The objective of this paper is to provide a methodological basis for improving the estimation of natural background concentrations of groundwater constituents. To this end, this paper critically reviews the different approaches used to determine natural background concentrations of dissolved constituents in groundwater. In addition, two regional case studies of fluoride in Canadian groundwater are presented to illustrate the estimation of background concentrations for natural groundwater constituents. The review of existing methods shows that the use of pristine groundwater samples is not possible in many cases, due to the widespread influence of human activities. The widely used pre-selection method can provide misleading results because of inadequate selection criteria and poor statistical significance associated with the reduction of the dataset. A variety of model-based methods have been developed, but these methods are all based on assumptions that cannot be verified. Relying on the user's experience and previous knowledge of the groundwater system, exploratory data analysis has many advantages and can be applied for both anthropogenic and natural constituents. The case studies show that the exploratory data analysis approach provides critical information to determine the sources of groundwater constituents and to properly delineate groundwater bodies for which background values will be established. Natural background concentrations should always be considered as theoretical values due to their spatio-temporal variability and scale dependence, and thresholds as concentration values above which further investigation is required.

    ano.nymous@ccsd.cnrs.fr.invalid (Raphaël Bondu) 05 Jan 2024

  • [hal-04201604] Les sols forestiers à nappe temporaire : fonctionnement, particularités et enjeux actuels

    Pour fixer les idées, cet article propose quelques rappels et détaille les particularités des sols forestiers à nappe perchée temporaire : conditions de formation d’une nappe perchée, formation des traces d’hydromorphie, sensibilité au tassement et principales contraintes pour les essences forestières. Il aborde enfin les principaux enjeux auxquels la recherche devra répondre pour l’avenir.

    ano.nymous@ccsd.cnrs.fr.invalid (Caroline Petitjean) 11 Sep 2023

  • [hal-03778748] Comment déterminer l'exposition aux changements climatiques des zones de production forestière française ? Méthodologie utilisée dans le projet ESPERENSE pour cibler les zones d’intérêt pour l’installation d’essais de comparaison d’essences et de provenances

    Les dernières observations de dépérissements et l’analyse de leurs causes tendent à confirmer la vulnérabilité de certaines des principales essences forestières françaises vis-à-vis des changements climatiques. Conscients de ces enjeux, les gestionnaires s’interrogent sur la conduite et le renouvellement de leurs peuplements. Le réseau multi organismes ESPERENSE se met en place pour rechercher des réponses à ces interrogations via l’organisation d’un réseau d’essais de comparaison d’essences et de provenances. Afin de rationaliser l'effort expérimental, une méthodologie a été établie pour prioriser les zones du territoire métropolitain dans lesquelles une recherche des alternatives aux essences en place doit être menée. Elle consiste à sélectionner les zones à fort enjeu de production de bois, et qui sont en même temps déjà en situation préoccupante ou qui le seront à l’avenir du fait des évolutions du climat en s’appuyant sur 3 différentes approches de modélisation. Le principe consiste donc à évaluer le risque par la combinaison des enjeux et de leur exposition. La démarche de construction de ce zonage est détaillée. Les cartes résultant de ce travail sont mises à disposition pour les principales essences françaises.

    ano.nymous@ccsd.cnrs.fr.invalid (Hedi Kebli) 16 Sep 2022

  • [hal-03684741] Engorgement en eau puis sécheresse affectent différemment la croissance de jeunes chênes pédonculés et sessiles

    Dans la littérature, le chêne pédonculé (Quercus robur) est réputé plus tolérant à l’engorgement en eau du sol que le chêne sessile (Quercus petraea) qui, à l’opposé, serait plus tolérant à la sécheresse. En forêt, ces deux espèces sont souvent confrontées à la succession dans le temps de ces deux contraintes, engorgement puis sécheresse, dans la même année. Il nous a semblé important de mieux comprendre et caractériser l’effet de cette succession sur la dynamique de croissance des deux chênes. Pour cela, nous avons essayé de reproduire, en conditions semi-contrôlées, une contrainte édaphique de sécheresse estivale précédée ou non par un épisode d’engorgement printanier sur de jeunes plants en pot.

    ano.nymous@ccsd.cnrs.fr.invalid (Thierry Ameglio) 14 Mar 2023

  • [hal-03643415] A limited number of species is sufficient to assign a vegetation plot to a forest vegetation unit

    Aims: Inventorying the habitats composing Natura 2000 sites is mandatory in the European Union and is necessary to implement relevant conservation measures. Vegetation plots, recording the presence or abundance of all plant species co-occurring within a plot, are currently used to identify terrestrial Natura 2000 habitat types, whose descriptions are mainly based on phytosociological units. However, vegetation plots are time-consuming and frequently restricted to the growing season. Moreover, no vegetation plots can be regarded as exhaustive, and significant inter-observer variation has been highlighted. We studied whether reducing the number of recorded species and the time spent carrying out a vegetation plot had an impact on vegetation unit assignment using species presence. We also studied if vegetation plots recorded in winter could be used for vegetation unit assignment. Location: Mainland France. Methods: We used 273 vegetation plots covering French temperate and mountainous forests. The time at which species were sighted was recorded. We also estimated whether a species was recognisable in winter. We used a classification program to compare assignments based on complete and incomplete vegetation plots. Results: Ten species and five minutes were sufficient to assign a plot to an association, and to an alliance, seven species and four minutes. Vegetation unit assignment proved feasible in winter, especially at the alliance level. Conclusions: We confirmed that a limited number of species is sufficient to assign vegetation plots to vegetation units. However, mapping habitats requires habitat identification and delimitation. This study confirms current field habits, particularly when creating a habitat map, usually based on a limited number of recorded species. Lastly, it confirms that the use of vegetation plots coming from a great variety of sources is relevant to create habitat time series, crucial tools for monitoring habitats at a national scale.

    ano.nymous@ccsd.cnrs.fr.invalid (Lise Maciejewski) 15 Apr 2022

  • [hal-03860136] Plant root growth against a mechanical obstacle: the early growth response of a maize root facing an axial resistance is consistent with the Lockhart model

    Plant root growth is dramatically reduced in compacted soils, affecting the growth of the whole plant. Through a model experiment coupling force and kinematics measurements, we probed the force–growth relationship of a primary root contacting a stiff resisting obstacle, which mimics the strongest soil impedance variation encountered by a growing root. The growth of maize roots just emerging from a corseting agarose gel and contacting a force sensor (acting as an obstacle) was monitored by time-lapse imaging simultaneously to the force. The evolution of the velocity field along the root was obtained from kinematics analysis of the root texture with a particle image velocimetry derived technique. A triangular fit was introduced to retrieve the elemental elongation rate or strain rate. A parameter-free model based on the Lockhart law quantitatively predicts how the force at the obstacle modifies several features of the growth distribution (length of the growth zone, maximal elemental elongation rate and velocity) during the first 10 min. These results suggest a strong similarity of the early growth responses elicited either by a directional stress (contact) or by an isotropic perturbation (hyperosmotic bath).

    ano.nymous@ccsd.cnrs.fr.invalid (Manon Quiros) 18 Nov 2022

  • [hal-03518445] Anthropogenic climate change increases vulnerability of Magnolia species more in Asia than in the Americas

    Quantifying anthropogenic climate change vulnerability is essential for estimating the risk of species extinction and developing conservation strategies. The Magnolia genus is widespread in the Americas and Asia, with nearly half of species currently threatened. Here, we used climate-niche factor analysis to study the vulnerability of Magnolia species to future climate change. We found that the vulnerability of Magnolia species to future climate change is negatively related to range size. We further identified that narrow-ranged Magnolia species distributed in Asia are more vulnerable than those distributed in the Americas, with protected area coverage also lower in Asia than the Americas. Moreover, the conservation status ranking of Magnolia species classified by the IUCN Red List will likely be changed under climate change, as some Near Threatened and Least Concern species were estimated to be more vulnerable to climate change than species currently classified as Endangered. Our results highlight that conservation assessments, policies and actions need to consider spatial vulnerabilities of species to climate change.

    ano.nymous@ccsd.cnrs.fr.invalid (Wen-Ting Wang) 09 Jan 2022

  • [hal-03880254] The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

    Abstract 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.

    ano.nymous@ccsd.cnrs.fr.invalid (Roberto Salomón) 01 Dec 2022

  • [hal-04321804] A critical thermal transition driving spring phenology of Northern Hemisphere conifers

    Despite growing interest in predicting plant phenological shifts, advanced spring phenology by global climate change remains debated. Evidence documenting either small or large advancement of spring phenology to rising temperature over the spatio‐temporal scales implies a potential existence of a thermal threshold in the responses of forests to global warming. We collected a unique data set of xylem cell‐wall‐thickening onset dates in 20 coniferous species covering a broad mean annual temperature (MAT) gradient (−3.05 to 22.9°C) across the Northern Hemisphere (latitudes 23°–66° N). Along the MAT gradient, we identified a threshold temperature (using segmented regression) of 4.9 ± 1.1°C, above which the response of xylem phenology to rising temperatures significantly decline. This threshold separates the Northern Hemisphere conifers into cold and warm thermal niches, with MAT and spring forcing being the primary drivers for the onset dates (estimated by linear and Bayesian mixed‐effect models), respectively. The identified thermal threshold should be integrated into the Earth‐System‐Models for a better understanding of spring phenology in response to global warming and an improved prediction of global climate‐carbon feedbacks.

    ano.nymous@ccsd.cnrs.fr.invalid (Jian‐guo Huang) 04 Dec 2023

  • [hal-03654399] Examination of aboveground attributes to predict belowground biomass of young trees

    Just as the aboveground tree organs represent the interface between trees and the atmosphere, roots act as the interface between trees and the soil. In this function, roots take-up water and nutrients, facilitate interactions with soil microflora, anchor trees, and also contribute to the gross primary production of forests. However, in comparison to aboveground plant organs, the biomass of roots is much more difficult to study. In this study, we analyzed 19 European datasets on above- and belowground biomass of juvenile trees of 14 species to identify generalizable estimators of root biomass based on tree sapling dimensions (e.g. height, diameter, aboveground biomass). Such estimations are essential growth and sequestration modelling. In addition, the intention was to study the effect of sapling dimension and light availability on biomass allocation to roots. All aboveground variables were significant predictors for root biomass. But, among aboveground predictors of root biomass plant height performed poorest. When comparing conifer and broadleaf species, the latter tended to have a higher root biomass at a given dimension. Also, with increasing size, the share of belowground biomass tended to increase for the sapling dimensions considered. In most species, there was a trend of increasing relative belowground biomass with increasing light availability. Finally, the height to diameter ratio (H/D) was negatively correlated to relative belowground biomass. This indicates that trees with a high H/D are not only more unstable owing to the unfavorable bending stress resistance, but also because they are comparatively less well anchored in the ground. Thus, single tree stability may be improved through increasing light availability to increase the share of belowground biomass.

    ano.nymous@ccsd.cnrs.fr.invalid (Peter Annighöfer) 28 Apr 2022

  • [hal-04126514] AquaDesign: A tool to assist aquaculture production design based on abiotic requirements of animal species

    Farming new species and promoting polyculture can enhance aquaculture sustainability. This implies to define the rearing conditions that meet the ecological requirements of a target species and/or to assess if different species can live in the same farming environment. However, there is a large number of rearing conditions and/or taxon combinations that can be considered. In order to minimise cumbersome and expensive empirical trials to explore all possibilities, we introduce a tool, AquaDesign. It is based on a R-script and package which help to determine farming conditions that are most likely suitable for species through in silico assessment. We estimate farming conditions potentially suitable for an aquatic organism by considering the species niche. We define the species n-dimensional niche hypervolume using a correlative approach in which the species niche is estimated by relating distribution data to environmental conditions. Required input datasets are mined from several public databases. The assistant tool allows users to highlight (i) abiotic conditions that are most likely suitable for species and (ii) combinations of species potentially able to live in the same abiotic environment. Moreover, it offers the possibility to assess if a particular set of abiotic conditions or a given farming location is potentially suitable for the monoculture or the polyculture of species of interest. Our tool provides useful pieces of information to develop freshwater aquacultures. Using the large amount of biogeographic and abiotic information available in public databases allows us to propose a pragmatic and operational tool even for species for which abiotic requirements are poorly or not available in literature such as currently non-produced species. Overall, we argue that the assistant tool can act as a stepping stone to promote new aquatic productions which are required to enhance aquaculture sustainability.

    ano.nymous@ccsd.cnrs.fr.invalid (Grégoire Butruille) 13 Jun 2023

  • [hal-03613329] Parenchyma fractions drive the storage capacity of non‐structural carbohydrates across a broad range of tree species

    Premise: Nonstructural carbohydrates (NSC) play a key role in tree performance and functioning. NSC are stored in radial and axial parenchyma (RAP) cells, but it is not known if this relationship is altered among species and climates, or is linked to functional traits describing xylem structure (wood density) and tree stature.Methods: In a systematic review, we collated data for NSC content and RAP fractions in stems for 68 tree species. To examine their relationships with climate factors and other functional traits, we also recovered climate data at each tree's location, as well as wood density and maximum height. A phylogenetic tree was established to examine the role of species’ evolutionary relationships on the associations between NSC, RAP and functional traits.Key Results: Across all 68 tree species, NSC was positively correlated with RAP and mean annual temperature. but relationships were only weakly significant in temperate species and angiosperms. When separating RAP into radial parenchyma (RP) and axial parenchyma (AP), both NSC and wood density were positively correlated with RP but not with AP. Taller trees had less dense wood and lower RAP, but no relationship with NSC.Conclusions: NSC is stored mostly in radial parenchyma that increases in warmer climates, but this relationship was only weakly linked to wood density and tree height. Our analysis of evolutionary relationships demonstrated that RAP fractions and NSC content were always closely related, suggesting that RAP can act as a reliable proxy for potential NSC storage capacity in tree stems.

    ano.nymous@ccsd.cnrs.fr.invalid (Guangqi Zhang) 18 Mar 2022

  • [hal-03736228] Non-structural carbohydrates and morphological traits of leaves, stems and roots from tree species in different climates

    Objectives: Carbon fixed during photosynthesis is exported from leaves towards sink organs as non-structural carbohydrates (NSC), that are a key energy source for metabolic processes in trees. In xylem, NSC are mostly stored as soluble sugars and starch in radial and axial parenchyma. The multi-functional nature of xylem means that cells possess several functions, including water transport, storage and mechanical support. Little is known about how NSC impacts xylem multi-functionality, nor how NSC vary among species and climates. We collected leaves, stem and root xylem from tree species growing in three climates and estimated NSC in each organ. We also measured xylem traits linked to hydraulic and mechanical functioning. Data description: The paper describes functional traits in leaves, stems and roots, including NSC, carbon, nitrogen, specific leaf area, stem and root wood density and xylem traits. Data are provided for up to 90 angiosperm species from temperate, Mediterranean and tropical climates. These data are useful for understanding the trade-offs in resource allocation from a whole-plant perspective, and to better quantify xylem structure and function related to water transportation, mechanical support and storage. Data will also give researchers keys to understanding the ability of trees to adjust to a changing climate.

    ano.nymous@ccsd.cnrs.fr.invalid (Guangqi Zhang) 22 Jul 2022

  • [hal-04019710] Provenance Differences in Water-Use Efficiency Among Sessile Oak Populations Grown in a Mesic Common Garden

    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 (δ 13 C). 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 (WUE i ), estimated from tree ring δ 13 C, was compared among and within populations for three climatically contrasted years. The adaptive character of WUE i was evaluated by relating population mean WUE i , as well as its plasticity to drought, to the pedoclimatic conditions of their provenance sites. The contribution of WUE i to tree and population fitness was finally assessed from the relationship between WUE i and tree radial growth (GI). Results Significant differences in WUE i were found among populations but a much larger variability was observed within than among populations. The population WUE i 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 WUE i 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 WUE i 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 WUE i also had a higher GI. Conclusion The correlations observed at the common garden site between (i) population means of WUE i 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.

    ano.nymous@ccsd.cnrs.fr.invalid (Arivoara Rabarijaona) 13 Mar 2023

  • [hal-04453135] Drought affects the fate of non-structural carbohydrates in hinoki cypress

    Tree species that close stomata early in response to drought are likely to suffer from an imbalance between limited carbohydrate supply due to reduced photosynthesis and metabolic demand. Our objective was to clarify the dynamic responses of non-structural carbohydrates to drought in a water-saving species, the hinoki cypress (Chamaecyparis obtusa Sieb. et Zucc.). To this end, we pulse-labeled young trees with 13CO2 10 days after the beginning of the drought treatment. Trees were harvested 7 days later, early during drought progression, and 86 days later when they had suffered from a long and severe drought. The labeled carbon (C) was traced in phloem extract, in the organic matter and starch of all the organs, and in the soluble sugars (sucrose, glucose and fructose) of the most metabolically active organs (foliage, green branches and fine roots). No drought-related changes in labeled C partitioning between belowground and aboveground organs were observed. The C allocation between non-structural carbohydrates was altered early during drought progression: starch concentration was lower by half in the photosynthetic organs, while the concentration of almost all soluble sugars tended to increase. The preferential allocation of labeled C to glucose and fructose reflected an increased demand for soluble sugars for osmotic adjustment. After 3 months of a lethal drought, the concentrations of soluble sugars and starch were admittedly lower in drought-stressed trees than in the controls, but the pool of non-structural carbohydrates was far from completely depleted. However, the allocation to storage had been impaired by drought; photosynthesis and the sugar translocation rate had also been reduced by drought. Failure to maintain cell turgor through osmoregulation and to refill embolized xylem due to the depletion in soluble sugars in the roots could have resulted in tree mortality in hinoki cypress, though the total pool of carbohydrate was not completely depleted.

    ano.nymous@ccsd.cnrs.fr.invalid (Chiaki Tsuji) 12 Feb 2024

  • [hal-03517053] Identifying the main drivers of the seasonal decline of near-infrared reflectance of a temperate deciduous forest

    The physical mechanisms behind correlations of earth observations and remote sensing products are of vital importance. The so-called 'near-infrared reflectance of vegetation' (NIR V) and gross primary production (GPP) show high correlations among different ecosystems and temporal scales but the underlying relationship is still poorly understood. NIR V is defined as the product of normalized difference vegetation index (NDVI) and nearinfrared (NIR) canopy reflectance (R NIR). We examined this relationship in the case of a temperate deciduous forest in Germany. GPP, R NIR and NIR V all exhibited a strong rise during leaf development in spring and a continual decline after the maximum in early summer. The decline of NIR V in late summer was mainly driven by the decline of R NIR , since NDVI remained saturated. Here we tested the R NIR decline attributions to changes in leaf area index, leaf optical properties, canopy structure, sun-sensor geometry, or understory vegetation by measuring seasonal variations of those factors of the temperate deciduous forest. Leaf area was nearly constant between May and mid September, leaf albedo decreased slightly, leaf angles increased over time towards more vertical leaves, and understory reflectance decreased considerably. We simulated the seasonal R NIR decline of the forest using the radiative transfer model FRT and quantified the sensitivity of the decline to variations in the measured parameters. FRT captured well the observed seasonal R NIR decline by Sentinel 2 using the measured optical and structural properties. Decreasing understory reflectance alone explained 43% of the simulated R NIR decrease, while leaf angle variations explained 31%, the solar zenith angle (SZA) 21%, leaf albedo 7%, and LAI 0%. The effect size of the SZA depended on the viewing angle and would hence be different for different satellites and for local instruments. The results may help to better understand and help to track seasonal changes in forest structure and leaf optical properties using remote sensing techniques. They also suggest that the proposed link between the seasonal evolution of GPP and NIR V may be weaker than expected.

    ano.nymous@ccsd.cnrs.fr.invalid (Niklas Hase) 07 Jan 2022


Date de modification : 29 août 2023 | Date de création : 25 avril 2023 | Rédaction : Corinne Martin