Productions 2019

Publications dans Hal pour l'année 2019


HAL : Dernières publications

  • [hal-02629130] Identifying the tree species compositions that maximize ecosystem functioning in European forests

    1. Forest ecosystem functioning generally benefits from higher tree species richness, but variation within richness levels is typically large. This is mostly due to the contrasting performances of communities with different compositions. Evidencebased understanding of composition effects on forest productivity, as well as on multiple other functions will enable forest managers to focus on the selection of species that maximize functioning, rather than on diversity per se. 2. We used a dataset of 30 ecosystem functions measured in stands with different species richness and composition in six European forest types. First, we quantified whether the compositions that maximize annual above-ground wood production (productivity) generally also fulfil the multiple other ecosystem functions (multifunctionality). Then, we quantified the species identity effects and strength of interspecific interactions to identify the “best” and “worst” species composition for multifunctionality. Finally, we evaluated the real-world frequency of occurrence of best and worst mixtures, using harmonized data from multiple national forest inventories. 3. The most productive tree species combinations also tended to express relatively high multifunctionality, although we found a relatively wide range of compositions with high- or low-average multifunctionality for the same level of productivity. Monocultures were distributed among the highest as well as the lowest performing compositions. The variation in functioning between compositions was generally driven by differences in the performance of the component species and, to a lesser extent, by particular interspecific interactions. Finally, we found that the most frequent species compositions in inventory data were monospecific stands and that the most common compositions showed below-average multifunctionality and productivity. 4. Synthesis and applications. Species identity and composition effects are essential to the development of high-performing production systems, for instance in forestry and agriculture. They therefore deserve great attention in the analysis and design of functional biodiversity studies if the aim is to inform ecosystem management. A management focus on tree productivity does not necessarily trade-off against other ecosystem functions; high productivity and multifunctionality can be combined with an informed selection of tree species and species combinations.

    ano.nymous@ccsd.cnrs.fr.invalid (Lander Baeten) 27 May 2020

  • [hal-02624939] Using stable isotope approach to quantify pond dam impacts on isotopic niches and assimilation of resources by invertebrates in temporary streams: a case study

    Fishponds built across streams can greatly affect their functioning, especially through loss of ecological continuity but also changes in water availability and trophic resources. Yet, their consequences on communities and stream functioning remain largely understudied. We investigated effects of fishpond dams on the trophic ecology of macroinvertebrate communities in temporary low-order streams using C and N stable isotopes. Food resources and macroinvertebrates were sampled in one upstream and one downstream site of two temporary streams, one stream without (reference stream) versus one with a fishpond (impacted stream) and used for isotopic analyses. Results suggested moderate effects of fishponds on the upstream tributaries. In contrast, at the downstream impacted site, ten times higher macroinvertebrate biomass and modifications in the trophic niches were recorded, likely due to changes in resource availability/quality and dam-related hydrology. By modifying the food sources as well as water fluxes, fishpond dams tend to alter macroinvertebrate communities but also shift the trophic dynamics downstream. This assessment stresses the need for exploring their impacts on food webs and nutrient fluxes at larger downstream distances to better understand their effects before drawing conclusions in regard to their management.

    ano.nymous@ccsd.cnrs.fr.invalid (Brian Four) 16 Jun 2022

  • [hal-02011754] Explaining the larger seed bank of an invasive shrub in non-native versus native environments by differences in seed predation and plant size

    •Background and aims - Large, persistent seed banks contribute to the invasiveness of non-native plants, and maternal plant size is an important contributory factor. We explored the relationships between plant vegetative size (V) and soil seed bank size (S) for the invasive shrub (Ulex europaeus) in its native range and in non-native populations, and identified which other factors may contribute to seed bank variation between native and invaded regions. •Methods - We compared the native region (France) with two regions where Ulex is invasive, one with seed predators introduced for biological control (New Zealand) and another where seed predators are absent (La Réunion). We quantified seed bank size, plant dimensions, seed predation, and soil fertility for six stands in each of the three regions.•Key results - Seed banks were 9 to 14 times larger in the two invaded regions compared to native France. We found a positive relationship between current seed bank size and actual plant size, and that any deviation from this relationship was probably due to large differences in seed predation and/or soil fertility. We further identified three possible factors explaining larger seed banks in non-native environments: larger maternal plant size, lower activity of seed predators and higher soil fertility. •Conclusions - In highlighting a positive relationship between maternal plant size and seed bank size, and identifying additional factors that regulate soil seed bank dynamics in non-native ranges, our data offer a number of opportunities for invasive weed control. For non-native Ulex populations specifically, management focusing on 'S' (i.e. the reduction of the seed bank by stimulating germination, or the introduction of seed predators as biological control agents), and/or 'V' (i.e. by cutting mature stands to reduce maternal plant biomass) offers the most probable combination of effective control options.

    ano.nymous@ccsd.cnrs.fr.invalid (Mark Bakker) 13 Feb 2019

  • [hal-02625305] Chilling and forcing temperatures interact to predict the onset of wood formation in Northern Hemisphere conifers

    The phenology of wood formation is a critical process to consider for predicting how trees from the temperate and boreal zones may react to climate change. Compared to leaf phenology, however, the determinism of wood phenology is still poorly known. Here, we compared for the first time three alternative ecophysiological model classes (threshold models, heat-sum models and chilling-influenced heat-sum models) and an empirical model in their ability to predict the starting date of xylem cell enlargement in spring, for four major Northern Hemisphere conifers (Larix decidua, Pinus sylvestris, Picea abies and Picea mariana). We fitted models with Bayesian inference to wood phenological data collected for 220 site-years over Europe and Canada. The chilling-influenced heat-sum model received most support for all the four studied species, predicting validation data with a 7.7-day error, which is within one day of the observed data resolution. We conclude that both chilling and forcing temperatures determine the onset of wood formation in Northern Hemisphere conifers. Importantly, the chilling-influenced heat-sum model showed virtually no spatial bias whichever the species, despite the large environmental gradients considered. This suggests that the spring onset of wood formation is far less affected by local adaptation than by environmentally driven plasticity. In a context of climate change, we therefore expect rising winter-spring temperature to exert ambivalent effects on the spring onset of wood formation, tending to hasten it through the accumulation of forcing temperature, but imposing a higher forcing temperature requirement through the lower accumulation of chilling.

    ano.nymous@ccsd.cnrs.fr.invalid (Nicolas Delpierre) 04 Apr 2024

  • [hal-02320571] Quelle pertinence du modèle diversité-productivité-perturbations pour analyser l’influence des pratiques agricoles sur la diversité des prairies permanentes du Massif central ?

    Un modèle a été réalisé pour évaluer l’impact des pratiques agricoles sur la diversité des prairies. Pour tester les prédictions d’un modèle théorique d’écologie, le modèle d’équilibre dynamique, nous avons suivi 18 prairies permanentes du Massif central aux pédoclimats et modes de gestion variés. Nous avons mis en évidence une diminution de la richesse spécifique liée à l’augmentation de la quantité de biomasse exportée (pâturée ou fauchée) et une diminution de la richesse fonctionnelle liée à l’augmentation de la productivité. Ces effets n’expliquent toutefois qu’une faible part de la variabilité observée entre sites. La quantité de biomasse exportée dépend du nombre de fauches et du chargement animal annuel ; la productivité était avant tout dépendante des précipitations durant la période d’étude, et non de la fertilisation. Nous discutons de l’intérêt et des limites de l’utilisation du modèle pour la gestion de la diversité des prairies.

    ano.nymous@ccsd.cnrs.fr.invalid (Rémi Perronne) 18 Oct 2019

  • [hal-02111822] Soils Drowned in Water Impoundments: A New Frontier

    Water impoundments have major impacts on biogeochemical cycles at the local and global scales. However, although reservoirs flood soils, their biogeochemical evolution below water and its ecological consequences are very poorly documented. We took advantage of the complete emptying of the Guerlédan Reservoir (Brittany, France) to compare the composition of soils flooded for 84 years with that of adjacent non-flooded soils used as reference, in 3 situations contrasted by their soil type (Cambisol and Podzol) and initial land-use (forest or grassland). In the annual drawdown zone, upper horizons of submerged soils are eroded, especially near the upper shore and on slopes. In the permanently drowned area, silty sediments cover drowned soils. Compared to reference soils, forest soils drowned for 84 years maintain their original morphological differentiation, but colors are dull, and the humus (O horizons) have virtually disappeared. Spodic horizons are depleted in poorly crystallized iron minerals while the accumulation of amorphous aluminum compounds remains unchanged. Soil bulk density increases as well as pH while total phosphorus content is almost unchanged. On the other hand, the pH of drowned grassland soils is lower by almost one unit, and the total phosphorus content was halved compared to reference soils. In this context, in addition to the effects of flooding, differences are attributed to post-1950 changes in agricultural practices i.e., liming and fertilization. Organic matter stocks decrease by almost 40%. This rate is similar in Cambisols and Podzols. Assuming that carbon was lost as CO2 and CH4, the corresponding flux averaged over the reservoir’s life is close to global areal estimates of CO2 emissions in temperate reservoirs and offsets a significant proportion of the carbon burial in reservoir sediments. Hence, flooded soils contribute significantly to the GHG budget of reservoirs, provide original long-term experimental sites to measure the effects of anoxia on soils and contain archives of past soil properties.

    ano.nymous@ccsd.cnrs.fr.invalid (Jim Félix-Faure) 26 Apr 2019

  • [hal-02624918] LiDAR-derived topography and forest structure predict fine-scale variation in daily surface temperatures in oak savanna and conifer forest landscapes

    In mountain landscapes, surface temperatures vary over short distances due to interacting influences of topography and overstory vegetation on local energy and water balances. At two study landscapes in the Sierra Nevada of California, characterized by foothill oak savanna at 276–481 m elevation and montane conifer forest at 1977–2135 m, we deployed 288 near-surface (5 cm above the surface) temperature sensors to sample site-scale (30 m) temperature variation related to hillslope orientation and vegetation structure and microsite-scale (2–10 m) variation related to microtopography and tree overstory. Daily near-surface maximum and minimum temperatures for the 2013 calendar year were related to topographic factors and vegetation overstory characterized using small footprint LiDAR imagery acquired by the National Ecological Observatory Network (NEON) Airborne Observation Platform (AOP). At both landscapes we recorded large site and microsite spatial variation in daily maximum temperatures, and less absolute variation in daily minimum temperatures. Generalized boosted regression trees were estimated to measure the influence of tree canopy density, understory solar radiation, cold-air drainage and pooling, ground cover and microtopography on daily maximum and minimum temperatures at site and microsite scales. Site-scale models based on indices of understory solar radiation and landscape position explained an average of 61–65% of daily variation in maximum temperature; site-scale models based on tree canopy density and landscape position explained 65–83% of variation in minimum temperatures. Models explained <15% of variation in microsite-scale maximum temperatures but within-site heterogeneity was significantly correlated with within-site heterogeneity in modeled understory radiation at both landscapes. Tree canopy density and slope explained 33% of microsite-scale variation in minimum temperatures at savanna sites. Our results demonstrate that it is feasible to model site-scale variation in daily surface temperature extremes and within-site heterogeneity in surface temperatures using LiDAR-derived variables, supporting efforts to understand cross-scale relationships between surface microclimates and regional climate change. Improved understanding of topographic and vegetative buffering of thermal microclimates across mountain landscapes is key to projecting microclimate heterogeneity and potential species’ range dynamics under future climate change.

    ano.nymous@ccsd.cnrs.fr.invalid (Frank W. Davis) 26 May 2020

  • [hal-02411666] The commonness of rarity: Global and future distribution of rarity across land plants

    A key feature of life’s diversity is that some species are common but many more are rare. Nonetheless, at global scales, we do not know what fraction of biodiversity consists of rare species. Here, we present the largest compilation of global plant diversity to quantify the fraction of Earth’s plant biodiversity that are rare. A large fraction, ~36.5% of Earth’s ~435,000 plant species, are exceedingly rare. Sampling biases and prominent models, such as neutral theory and the k-niche model, cannot account for the observed prevalence of rarity. Our results indicate that (i) climatically more stable regions have harbored rare species and hence a large fraction of Earth’s plant species via reduced extinction risk but that (ii) climate change and human land use are now disproportionately impacting rare species. Estimates of global species abundance distributions have important implications for risk assessments and conservation planning in this era of rapid global change.

    ano.nymous@ccsd.cnrs.fr.invalid (Brian Enquist) 31 May 2021

  • [hal-02903210] Habitats forestiers et forêts habitées

    Les 26 et 27 mars 2019 se tenait, au sein du Domaine national de Chambord, un colloque international regroupant une centaine de participants originaires d’une dizaine de pays. Cet évènement scientifique venait conclure le projet de recherche interdisciplinaire COSTAUD « Contribution des ongulés sauvages au fonctionnement de l’écosystème et aux services rendus à Chambord », financé par la Région Centre-Val de Loire au titre de son Appel à Projets de Recherche d’Intérêt Régional (édition 2015). Intitulé Habitats forestiers et forêts habitées, il visait à questionner les interactions existant en forêt et ses habitats associés entre la faune et les usages, modes de gestion et pratiques sociales, en se structurant autour de quatre thèmes. Le thème 1 du colloque s’est intéressé aux facteurs environnementaux et humains à l’origine des populations animales actuelles Dans le thème 2, il s’agissait d’interroger l’influence de la faune, en l’occurrence des grands herbivores, sur le fonctionnement des écosystèmes. Le thème 3 a abordé les conséquences des modes de gestion des habitats forestiers, afin d’en identifier les impacts sur la faune, notamment sur sa distribution spatiale. Enfin le thème 4 s’est intéressé à la manière dont la faune pouvait être valorisée par la société, c’est-à-dire aux usages et pratiques sociales associés à la faune sauvage et aux milieux forestiers.

    ano.nymous@ccsd.cnrs.fr.invalid (Christophe Baltzinger) 24 Nov 2021

  • [hal-04492051] Analyse de l'évolution de la production de truffe noire du Périgord (Tuber Melanosporum Vitad.) de 1903-1904 à 1988-1989 dans le Vaucluse


    ano.nymous@ccsd.cnrs.fr.invalid (Meili Baragatti) 06 Mar 2024

  • [hal-02621961] Améliorer la qualité des plants et leur taux de reprise


    ano.nymous@ccsd.cnrs.fr.invalid (Nathalie Ollat) 26 May 2020

  • [hal-02384184] Les réponses observées des arbres aux variations du climat (croissance, phénologie foliaire et fructification)

    Comme vient de l’indiquer Myriam Legay, la démarche générale est d’abord d’observer, pour comprendre les mécanismes puis simuler les effets des évolutions climatiques. Je vais donc vous parler des réponses observées des arbres aux variations du climat. Cet exposé a été préparé avec Nicolas Delpierre et d’autres contributeurs dont vous voyez ici les noms. Évaluer et comparer les réponses au climat des différents aspects du fonctionnement des arbres Quand on travaille sur les écosystèmes forestiers et les arbres, on a différents marqueurs des effets de l’environnement. Le premier, c’est la croissance radiale, le cerne annuel : le fonctionnement saisonnier des arbres est tel qu’en étudiant la croissance on peut étudier l’effet des paramètres environnementaux. Le deuxième marqueur, c’est la phénologie foliaire, à travers des dates de débourrement et des dates de sénescence. Et le troisième marqueur dont on dispose c’est la fructication, exprimée en données de biomasse ou de quantité de fruits. On a la chance extraordinaire, dans le réseau RENECOFOR, d’avoir l’ensemble de ces données depuis de nombreuses années, grâce à quoi on peut étudier le déterminisme environnemental de l’ensemble de ces marqueurs. On peut les étudier isolément (ils dépendent du climat, du temps qui fait, de la température, des pluies, etc.) et on peut aussi essayer de mettre en évidence les relations qu’il peut y avoir entre eux. L’objectif de cette présentation, c’est de proposer une synthèse du déterminisme environnemental de ces différents marqueurs en essayant de dégager les facteurs-clés, les périodes-clés (la saisonnalité de ces variations) et de trouver des relations entre les différents facteurs. Je me limiterai, faute de temps, aux résultats qui concernent les peuplements feuillus du réseau, hêtraies et chênaies, soit 20 peuplements de hêtre et 28 peuplements de chênes, donc 48 peuplements.

    ano.nymous@ccsd.cnrs.fr.invalid (François F. Lebourgeois) 28 Nov 2019

  • [hal-02384205] Améliorer la capacité du chêne sessile à répondre à des sécheresses extrêmes : Réduction de la densité des peuplements. Étude dendro-écologique de réseaux d’expérimentations sylvicoles à long terme

    Dans un contexte de changement climatique, les gestionnaires ont besoin de bases scientifiques pour adapter leurs itinéraires sylvicoles. Cela passe notamment par l’étude de l’influence de la compétition sur la réponse au climat et à ses variations.

    ano.nymous@ccsd.cnrs.fr.invalid (Anna Schmitt) 28 Nov 2019

  • [hal-03328388] Un outil en ligne pour accompagner le choix des essences forestières dans un contexte de changement climatique.


    ano.nymous@ccsd.cnrs.fr.invalid (Sophie Bertin) 30 Aug 2021

  • [hal-02964786] Le processus d'innovation technologique en sylviculture - Exemple des outils mécaniques de préparation du sol avant plantation

    Un changement de pratiques sylvicoles s’impose pour assurer le renouvellement des forêts face aux changements globaux présents et à venir. C’est d’autant plus vrai avec la plantation qui doit subir des printemps au climat très contrasté. Assurer le transfert aux praticiens et propriétaires est essentiel pour garantir leur réussite.

    ano.nymous@ccsd.cnrs.fr.invalid (Catherine Collet) 14 Oct 2020

  • [hal-02622295] Massive postglacial gene flow between European white oaks uncovered genes underlying species barriers

    Oaks are dominant forest tree species widely distributed across the Northern Hemisphere, where they constitute natural resources of economic, ecological, social and historical value. Hybridisation and adaptive introgression have long been thought to be major drivers of their ecological success. Therefore, the maintenance of species barriers remains a key question, given the extent of interspecific gene flow. In this study, we made use of the tremendous genetic variation among four European white oak species (31 million single nucleotide polymorphisms (SNPs)) to infer the evolutionary history of these species, study patterns of genetic differentiation and identify reproductive barriers. We first analysed the ecological and historical relationships among these species and inferred a long-term strict isolation followed by a recent and extensive postglacial contact using approximate Bayesian computation. Assuming this demographic scenario, we then performed backward simulations to generate the expected distributions of differentiation under neutrality to scan their genomes for reproductive barriers. We finally identified important intrinsic and ecological functions driving the reproductive isolation. We discussed the importance of identifying the genetic basis for the ecological preferences between these oak species and its implications for the renewal of European forests under global warming.

    ano.nymous@ccsd.cnrs.fr.invalid (Thibault Leroy) 07 Dec 2023

  • [cea-02363571] Sustainable bioenergy for climate mitigation: developing drought-tolerant trees and grasses

    Background and Aims Bioenergy crops are central to climate mitigation strategies that utilize biogenic carbon, such as BECCS (bioenergy with carbon capture and storage), alongside the use of biomass for heat, power, liquid fuels and, in the future, biorefining to chemicals. Several promising lignocellulosic crops are emerging that have no food role-fast-growing trees and grasses-but are well suited as bioenergy feedstocks, including Populus, Salix, Arundo, Miscanthus, Panicum and Sorghum. • Scope These promising crops remain largely undomesticated and, until recently, have had limited germplasm resources. In order to avoid competition with food crops for land and nature conservation, it is likely that future bio-energy crops will be grown on marginal land that is not needed for food production and is of poor quality and subject to drought stress. Thus, here we define an ideotype for drought tolerance that will enable biomass production to be maintained in the face of moderate drought stress. This includes traits that can readily be measured in wide populations of several hundred unique genotypes for genome-wide association studies, alongside traits that are informative but can only easily be assessed in limited numbers or training populations that may be more suitable for genomic selection. Phenotyping, not genotyping, is now the major bottleneck for progress, since in all lignocellulosic crops studied extensive use has been made of next-generation sequencing such that several thousand markers are now available and populations are emerging that will enable rapid progress for drought-tolerance breeding. The emergence of novel technologies for targeted genotyping by sequencing are particularly welcome. Genome editing has already been demonstrated for Populus and offers significant potential for rapid deployment of drought-tolerant crops through manipulation of ABA receptors, as demonstrated in Arabidopsis, with other gene targets yet to be tested. • Conclusions Bioenergy is predicted to be the fastest-developing renewable energy over the coming decade and significant investment over the past decade has been made in developing genomic resources and in collecting wild germplasm from within the natural ranges of several tree and grass crops. Harnessing these resources for climate-resilient crops for the future remains a challenge but one that is likely to be successful.

    ano.nymous@ccsd.cnrs.fr.invalid (G. Taylor) 14 Nov 2019

  • [hal-02181076] Air temperature optima of vegetation productivity across global biomes.

    The global distribution of the optimum air temperature for ecosystem-level gross primary productivity ([Formula: see text]) is poorly understood, despite its importance for ecosystem carbon uptake under future warming. We provide empirical evidence for the existence of such an optimum, using measurements of in situ eddy covariance and satellite-derived proxies, and report its global distribution. [Formula: see text] is consistently lower than the physiological optimum temperature of leaf-level photosynthetic capacity, which typically exceeds 30 °C. The global average [Formula: see text] is estimated to be 23 ± 6 °C, with warmer regions having higher [Formula: see text] values than colder regions. In tropical forests in particular, [Formula: see text] is close to growing-season air temperature and is projected to fall below it under all scenarios of future climate, suggesting a limited safe operating space for these ecosystems under future warming.

    ano.nymous@ccsd.cnrs.fr.invalid (Mengtian Huang) 11 Jul 2019

  • [hal-02168619] Nondestructive and Fast Vibration Phenotyping of Plants

    The frequencies of free oscillations of plants, or plant parts, depend on their geometries, stiffnesses, and masses. Besides direct biomechanical interest, free frequencies also provide insights into plant properties that can usually only be measured destructively or with low-throughput techniques (e.g., change in mass, tissue density, or stiffness over development or with stresses). We propose here a new high-throughput method based on the noncontact measurements of the free frequencies of the standing plant. The plant is excited by short air pulses (typically 100 ms). The resulting motion is recorded by a high speed video camera (100 fps) and processed using fast space and time correlation algorithms. In less than a minute the mechanical behavior of the plant is tested over several directions. The performance and versatility of this method has been tested in three contrasted species: tobacco (Nicotiana benthamian), wheat (Triticum aestivum L.), and poplar (Populus sp.), for a total of more than 4000 data points. In tobacco we show that water stress decreased the free frequency by 15%. In wheat we could detect variations of less than 1 g in the mass of spikes. In poplar we could measure frequencies of both the whole stem and leaves. The work provides insight into new potential directions for development of phenotyping.

    ano.nymous@ccsd.cnrs.fr.invalid (Emmanuel de Langre) 28 Jun 2019

  • [hal-02095574] Background mortality drivers of European tree species : climate change matters

    Increases in tree mortality rates have been highlighted in different biomes over the past decades. However, disentangling the effects of climate change on the temporal increase in tree mortality from those of management and forest dynamics remains a challenge. Using a modelling approach taking tree and stand characteristics into account, we sought to evaluate the impact of climate change on background mortality for the most common European tree species. We focused on background mortality, which is the mortality observed in a stand in the absence of abrupt disturbances, to avoid confusion with mortality events unrelated to long-term changes in temperature and rainfall. We studied 372 974 trees including 7312 dead trees from forest inventory data surveyed across France between 2009 and 2015. Factors related to competition, stand characteristics, management intensity, and site conditions were the expected preponderant drivers of mortality. Taking these main drivers into account, we detected a climate change signal on 45% of the 43 studied species, explaining an average 6% of the total modelled mortality. For 18 out of the 19 species sensitive to climate change, we evidenced greater mortality with increasing temperature or decreasing rainfall. By quantifying the mortality excess linked to the current climate change for European temperate forest tree species, we provide new insights into forest vulnerability that will prove useful for adapting forest management to future conditions.

    ano.nymous@ccsd.cnrs.fr.invalid (Adrien Taccoen) 14 Dec 2020

  • [hal-02264373] Additive effects of high growth rate and low transpiration rate drive differences in whole plant transpiration efficiency among black poplar genotypes

    Poplar plantations, widely used for the production of woody biomass, might be at high risk from the climate change-induced increase in the frequency of drought periods. Therefore, selecting improved genotypes, which are highly productive but with a high water use efficiency (WUE), is becoming a major target. The use of automated weighing systems in controlled environments facilitates the estimation of cumulated water loss and whole plant transpiration efficiency (TE). Differences in TE and leaf level intrinsic WUE as well as the contribution of underlying ecophysiological traits were determined in three contrasting P. nigra genotypes. Strong differences in TE among the selected genotypes were congruent with differences in leaf level intrinsic WUE. Our data show that a high total leaf area was overcompensated by a low per leaf area transpiration rate, leading to higher TE in highly productive genotypes originating from cool locations. Nocturnal water loss was relatively low but contributed to variations in TE among genotypes. In response to drought, leaf level WUE increased but not TE, suggesting that carbon losses due to whole plant respiration could offset the drought-induced increase in intrinsic WUE.

    ano.nymous@ccsd.cnrs.fr.invalid (Marie-Béatrice Bogeat-Triboulot) 06 Aug 2019

  • [hal-02346487] Precipitation mediates sap flux sensitivity to evaporative demand in the neotropics

    Transpiration in humid tropical forests modulates the global water cycle and is a key driver of climate regulation. Yet, our understanding of how tropical trees regulate sap flux in response to climate variability remains elusive. With a progressively warming climate, atmospheric evaporative demand [i.e., vapor pressure deficit (VPD)] will be increasingly important for plant functioning, becoming the major control of plant water use in the twenty-first century. Using measurements in 34 tree species at seven sites across a precipitation gradient in the neotropics, we determined how the maximum sap flux velocity (vmax) and the VPD threshold at which vmax is reached (VPDmax) vary with precipitation regime [mean annual precipitation (MAP); seasonal drought intensity (PDRY)] and two functional traits related to foliar and wood economics spectra [leaf mass per area (LMA); wood specific gravity (WSG)]. We show that, even though vmax is highly variable within sites, it follows a negative trend in response to increasing MAP and PDRY across sites. LMA and WSG exerted little effect on vmax and VPDmax, suggesting that these widely used functional traits provide limited explanatory power of dynamic plant responses to environmental variation within hyper-diverse forests. This study demonstrates that long-term precipitation plays an important role in the sap flux response of humid tropical forests to VPD. Our findings suggest that under higher evaporative demand, trees growing in wetter environments in humid tropical regions may be subjected to reduced water exchange with the atmosphere relative to trees growing in drier climates.

    ano.nymous@ccsd.cnrs.fr.invalid (Charlotte Grossiord) 05 Nov 2019

  • [hal-02485053] Effet de la chalarose (Hymenoscyphus fraxineus) sur la croissance radiale du frêne et sur son déterminisme climatique dans le nord de la France

    La chalarose du frêne (Hymenoscyphus fraxineus) est apparue dans le nord de la France entre 2010 et 2012. Afin de juger de l’effet du champignon sur la croissance radiale et sur la sensibilité au climat des frênes, 181 arbres adultes (âge et diamètre moyens : 100 ans et 50 cm) issus de 9 peuplements ont été échantillonnés en 2017 selon cinq niveaux de défoliation. Les peuplements sont purs et correspondent à des conditions sylvicole et écologique optimales pour l’essence (sols chimiquement riches et réserve utile en eau élevée autour de 150 mm). Sur la période 1920-2017, la croissance radiale a été d’en moyenne 2,3 } 0,4 mm par an. Pour les arbres peu défoliés en 2017 (≤ 25 %), la croissance est restée stable entre 2 et 2,5 mm par an après 2010 alors que, pour les autres catégories (> 25 %), elle a chuté d’autant plus que le niveau de défoliation était élevé (autour de 1 mm par an pour les défoliations supérieures à 75 %). Il est également apparu que les arbres défoliés à plus de 25% en 2017 avaient déjà une croissance plus faible depuis la fin des années 1990 et systématiquement plus faible depuis 2003 (différence de 15 à 25 %). Ces périodes ayant été particulièrement sèches dans la région étudiée, on peut émettre l’hypothèse d’une sensibilité plus forte au pathogène des arbres déjà affaiblis par des stress hydriques forts. Les modèles climatiques expliquent entre 50 et 60 % de la variation de la croissance des frênaies sauf pour les arbres les plus défoliés en 2017 (> 75 %) qui sont apparus peu sensibles au climat depuis toujours (taux d’explication des modèles climatiques de 25 %). Ainsi, dans le nord de la France et sur des stations très favorables, une bonne croissance correspond à des automnes pluvieux et des hivers doux bien arrosés suivis par un mois de mai chaud et pluvieux (facteur central pour la croissance). Depuis l’arrivée de la chalarose, les arbres les plus défoliés (> 25 %) répondent néanmoins de moins au moins au climat sauf aux conditions de fin d’été (pluies du mois d’août) ; période qui n’apparaissait pas déterminante sur le plus long terme. Des modifications du fonctionnement physiologique des arbres sont évoquées pour expliquer ces comportements. Finalement, notre étude a montré que les frênes étaient très réactifs au climat et que la chalarose a affecté préférentiellement les arbres déjà affaiblis par une succession de crises climatiques passées (sécheresses). Même si les frênes adultes semblent pouvoir tolérer un certain niveau de défoliation sans compromettre leur croissance, l’augmentation de la variabilité du climat et la récurrence des sécheresses pourraient déstabiliser les frênaies rendant leur gestion future encore plus complexe.

    ano.nymous@ccsd.cnrs.fr.invalid (François F. Lebourgeois) 19 Feb 2020

  • [hal-02384139] Fructification du Hêtre et des Chênes en France : rôle des températures, du pollen et du bilan de carbone et relation avec la croissance des peuplements

    Dans cette étude, nous avons analysé les déterminants environnementaux de la variabilité spatiale et temporelle de la fructification des trois espèces feuillues européennes majeures : Quercus robur, Quercus petraea et Fagus sylvatica. Nous avons étudié les relations entre la production de fruits, l’émission de pollen, les ressources carbonées et hydriques et les conditions climatiques sur la période 1994-2007 (14 ans) à partir de 48 peuplements du réseau RENECOFOR. La production moyenne des fruits est de 251 kg/ha/an pour les Chênes et de 174 kg/ha/an pour le Hêtre. Pour le Hêtre, la production suit un rythme bisannuel très net et est synchrone entre les sites. Elle apparaît beaucoup plus variable pour les Chênes sans synchronisme net. Pour les Chênes, la fructification dépend très fortement des conditions thermiques durant la période d’émission du pollen (début avril) confirmant l’hypothèse du synchronisme pollinique pour ces espèces. Pour le Hêtre, la production dépend très fortement des écarts de température estivale entre les années. Pour les deux espèces, les relations entre la production de fruits et les différents déterminants suivent des lois non linéaires avec des forts effets seuil et des interactions complexes. Enfin, pour le Hêtre, la croissance radiale est réduite en cas de forte fructification alors que les années de bonne glandée sont aussi des années de forte croissance pour les Chênes. Les deux espèces présentent donc deux comportements opposés concernant les stratégies d’allocation entre la croissance radiale et la production de fruits.

    ano.nymous@ccsd.cnrs.fr.invalid (François F. Lebourgeois) 28 Nov 2019

  • [hal-02311392] The functional trait spectrum of European temperate grasslands

    Questions What is the functional trait variation of European temperate grasslands and how does this reflect global patterns of plant form and function? Do habitat specialists show trait differentiation across habitat types? Location Europe. Methods We compiled 18 regeneration and non-regeneration traits for a continental species pool consisting of 645 species frequent in five grassland types. These grassland types are widely distributed in Europe but differentiated by altitude, soil bedrock and traditional long-term management and disturbance regimes. We evaluated the multivariate trait space of this entire species pool and compared multi-trait variation and mean trait values of habitat specialists grouped by grassland type. Results The first dimension of the trait space accounted for 23% of variation and reflected a gradient between fast-growing and slow-growing plants. Plant height and SLA contributed to both the first and second ordination axes. Regeneration traits mainly contributed to the second and following dimensions to explain 56% of variation across the first five axes. Habitat specialists showed functional differences between grassland types mainly through non-regeneration traits. Conclusions The trait spectrum of plants dominating European temperate grasslands is primarily explained by growth strategies which are analogous to the trait variation observed at the global scale, and secondly by regeneration strategies. Functional differentiation of habitat specialists across grassland types is mainly related to environmental filtering linked with altitude and disturbance. This filtering pattern is mainly observed in non-regeneration traits, while most regeneration traits demonstrate multiple strategies within the same habitat type.

    ano.nymous@ccsd.cnrs.fr.invalid (Emma Ladouceur) 26 May 2020

  • [hal-02399726] The cost of deer to trees: changes in resource allocation from growth-related traits and phenolic content to structural defence

    Background and aims-Plants may use various defence mechanisms to protect their tissues against deer browsing and the allocation of resources to defence may trade-off with plants' growth. In a context of increasing deer populations in European forests, understanding the resource allocation strategies of trees is critical to better assess their ability to face an increasing browsing pressure. The aim of this study was to determine how deer removal affects the resource allocation to both defensive and growth-related traits in field conditions for three tree species (Abies alba, Picea abies and Fagus sylvatica). Methods-We compared eight pairs of fenced-unfenced plots to contrast plots with and without browsing pressure. The pairs were set up in 2005 and 2014 to compare different fencing duration. We measured leaf and shoot traits related to the defence against herbivores (phenolic content, structural resistance, C:N ratio) and to the investment in plants' growth and productivity (specific leaf area and nutrient content). Key results-For the three species, the structural resistance of leaves and shoots was negatively correlated with SLA, nutrient content and phenolic content. For Abies alba, exclusion of deer decreased shoot structural resistance in favour of higher nutrient content, SLA and phenolic content. The fencing duration had no effect on the different measured traits. Conclusions-Our results support the assumption of a trade-off between structural defence and growth-related traits at the intraspecific scale for the three studied species. We also confirmed the hypothesis that exposure to deer browsing is involved in the resource allocation of woody species. For Abies alba, fencing led to a change in resource allocation from structural defence to growth-related traits and chemical defence.

    ano.nymous@ccsd.cnrs.fr.invalid (Julien Barrere) 09 Dec 2019

  • [hal-02165403] Infiltration from the Pedon to Global Grid Scales: An Overview and Outlook for Land Surface Modeling

    Infiltration in soils is a key process that partitions precipitation at the land surface into surface runoff and water that enters the soil profile. We reviewed the basic principles of water infiltration in soils and we analyzed approaches commonly used in land surface models (LSMs) to quantify infiltration as well as its numerical implementation and sensitivity to model parameters. We reviewed methods to upscale infiltration from the point to the field, hillslope, and grid cell scales of LSMs. Despite the progress that has been made, upscaling of local-scale infiltration processes to the grid scale used in LSMs is still far from being treated rigorously. We still lack a consistent theoretical framework to predict effective fluxes and parameters that control infiltration in LSMs. Our analysis shows that there is a large variety of approaches used to estimate soil hydraulic properties. Novel, highly resolved soil information at higher resolutions than the grid scale of LSMs may help in better quantifying subgrid variability of key infiltration parameters. Currently, only a few LSMs consider the impact of soil structure on soil hydraulic properties. Finally, we identified several processes not yet considered in LSMs that are known to strongly influence infiltration. Especially, the impact of soil structure on infiltration requires further research. To tackle these challenges and integrate current knowledge on soil processes affecting infiltration processes into LSMs, we advocate a stronger exchange and scientific interaction between the soil and the land surface modeling communities.

    ano.nymous@ccsd.cnrs.fr.invalid (Harry Vereecken) 25 Jun 2019

  • [hal-01938609] Impact of vegetation on the methane budget of a temperate forest

    Upland forest soils are known to be the main biological sink for methane, but studies have shown that net methane uptake of a forest ecosystem can be reduced when methane emissions by vegetation are considered. We estimated the methane budget of a young oak plantation by considering tree stems but also the understorey vegetation. Automated chambers connected to a laser‐based gas analyser, on tree stems, bare soil and soil covered with understorey vegetation, recorded CH4 fluxes for 7 months at 3 h intervals. Tree stem emissions were low and equated to only 0.1% of the soil sink. Conversely, the presence of understorey vegetation increased soil methane uptake. This plant‐driven enhancement of CH4 uptake occurred when the soil was consuming methane. At the stand level, the methane budget shifted from −1.4 ± 0.4 kg C ha−1 when we upscaled data obtained only on bare soil, to −2.9 ± 0.6 kg C ha−1 when we considered soil area that was covered with understorey vegetation. These results indicate that aerenchymatous plant species, which are known to reduce the methane sink in wetlands, actually increase soil methane uptake two‐fold in an upland forest by enhancing methane and oxygen transport and/or by promoting growth of methanotrophic populations.

    ano.nymous@ccsd.cnrs.fr.invalid (Caroline C. Plain) 28 Nov 2018

  • [hal-02154447] First evidences that the ectomycorrhizal fungus Paxillus involutus mobilizes nitrogen and carbon from saprotrophic fungus necromass

    Fungal succession in rotting wood shows a surprising abundance of ectomycorrhizal (EM) fungi during the late decomposition stages. To better understand the links between EM fungi and saprotrophic fungi, we investigated the potential capacities of the EM fungus Paxillus involutus to mobilize nutrients from necromass of Postia placenta, a wood rot fungus, and to transfer these elements to its host tree. In this aim, we used pure cultures of P. involutus in the presence of labelled Postia necromass (15N/13C) as nutrient source, and a monoxenic mycorrhized pine experiment composed of labelled Postia necromass and P. involutus culture in interaction with pine seedlings. The isotopic labelling was measured in both experiments. In pure culture, P. involutus was able to mobilize N, but C as well, from the Postia necromass. In the symbiotic interaction experiment, we measured high 15N enrichments in all plant and fungal compartments. Interestingly, 13C remains mainly in the mycelium and mycorrhizas, demonstrating that the EM fungus transferred essentially N from the necromass to the tree. These observations reveal that fungal organic matter could represent a significant N source for EM fungi and trees, but also a C source for mycorrhizal fungi, including in symbiotic lifestyle.

    ano.nymous@ccsd.cnrs.fr.invalid (Emila Akroume) 12 Jun 2019

  • [hal-02178452] Drought impacts on tree phloem

    On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of phloem function under drought. In particular, we show how phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in phloem transport. Overall, existing knowledge is consistent with the hypotheses that phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.

    ano.nymous@ccsd.cnrs.fr.invalid (Yann Salmon) 09 Jul 2019

  • [hal-02263853] Annotation data about multi criteria assessment methods used in the agri-food research: The French national institute for agricultural research (INRA) experience

    This data article contains annotation data characterizing MultiCriteria Assessment (MCA) Methods proposed in the agri-food sector by researchers from INRA, Europe's largest agricultural research institute (INRA, http://institut.inra.fr/en). MCA can be used to assess and compare agricultural and food systems, and support multi-actor decision making and design of innovative systems for crop production, animal production and processing of agricultural products. These data are stored in a public repository managed by INRA (https://data.inra.fr/; https://doi.org/10.15454/WB51LL).

    ano.nymous@ccsd.cnrs.fr.invalid (Geneviève Gésan-Guiziou) 05 Aug 2019

  • [hal-02561718] On the need to consider wood formation processes in global vegetation models and a suggested approach

    Abstract• Key messageDynamic global vegetation models are key tools for interpreting and forecasting the responses of terrestrial ecosystems to climatic variation and other drivers. They estimate plant growth as the outcome of the supply of carbon through photosynthesis. However, growth is itself under direct control, and not simply controlled by the amount of available carbon. Therefore predictions by current photosynthesis-driven models of large increases in future vegetation biomass due to increasing concentrations of atmospheric CO2may be significant over-estimations. We describe how current understanding of wood formation can be used to reformulate global vegetation models, with potentially major implications for their behaviour.

    ano.nymous@ccsd.cnrs.fr.invalid (Andrew D. Friend) 04 May 2020

  • [hal-02622305] Diagnosis of forest soil sensitivity to harvesting residues removal – A transfer study of soil science knowledge to forestry practitioners

    Forest biomass is a source of renewable energy that can contribute to meeting international targets for reducing greenhouse gas emissions. However, removing forest harvesting residues may cause important nutrient losses. Because negative effects of increased nutrient removal are not systematic, forest managers need tools for soil sensitivity assessment, to decide whether they can or not increase biomass harvesting without impairing long term forest productivity and health. This study follows two goals: (i) define forest ecosystem sensitivity indicators derived from soil physico-chemical analyses and (ii) build and test a simplified tool that predicts such soil sensitivity. After screening international literature, nutrient concentration in the topsoil was chosen as the simplest and currently most accurate indicator of soil sensitivity. With a consolidated database on French forest soils, we built diagnostic keys that predict soil sensitivity using only five parameters: humus form, topsoil texture, depth of CaCO3 apparition, ecological region, and rooting depth. We performed a statistical evaluation of the simplified tool on independent data sets and evaluated it in the field with potential users. As compared with the existing French forest soils sensitivity indicator, our diagnosis tool displayed lower high and low sensitivities classification errors and allowed to differentiate sensitivity into five elemental ones (Ca, Mg, K, P and N). All participating end users agreed with the necessity of such indicator and appreciated the simplicity of diagnosis with our tool. This study shows a complete research and development process, from the translation of scientific knowledge into an indicator of sustainable forest management to the simplification for assimilation.

    ano.nymous@ccsd.cnrs.fr.invalid (Samuel Durante) 26 May 2020

  • [hal-02154562] CarDen: A software for fast measurement of wood density on increment cores by CT scanning

    Increment cores are often used in wood science for measuring wood density of trees non destructively and at large scale, for instance with the objective to assess the available biomass in a forest resource. This paper presents a software allowing to measure by X-ray computed tomography (CT) the wood density of thousands increment cores. The software is able to process 3000 cores per hour semi-automatically. Manual intervention may be required to control and eventually adjust the positioning of the cores. The software was tested on 30 trees from 13 temperate species. Two increment cores were taken from each tree: one 5 mm diameter core and one 4 mm diameter core. The obtained CT density of the cores was compared to reference data obtained by volume and mass measurement on the 5 mm cores. The reference data were used for tuning the software settings by leave-one-out cross validation method. The obtained root mean square error was below 10 kg/m3 (1.7%) for the 5 mm cores. For the 4 mm cores, the root mean square difference with the reference density of the 5 mm cores was 25 kg/m(3) (4.2%).

    ano.nymous@ccsd.cnrs.fr.invalid (Philippe Jacquin) 12 Jun 2019

  • [hal-02624191] Short-term nitrogen dynamics are impacted by defoliation and drought in Fagus sylvatica L. branches

    The predicted recurrence of adverse climatic events such as droughts, which disrupt nutrient accessibility for trees, could jeopardize the nitrogen (N) metabolism in forest trees. Internal tree N cycling capacities are crucial to ensuring tree survival but how the N metabolism of forest trees responds to intense, repeated environmental stress is not well known. For 2 years, we submitted 9-year-old beech (Fagus sylvatica L.) trees to either a moderate or a severe prolonged drought or a yearly removal of 75% of the foliage to induce internal N cycling changes. During the second year of stress, in spring and summer, we sprayed N-15-urea on the leaves (one branch per tree). Then, for 14 days, we traced the N-15 dynamics through the leaves, into foliar proteins and into the branch compartments (leaves and stems segments), as well as its long-distance transfer from the labeled branches to the tree apical twigs. Defoliation caused a short- and mid-term N increase in the leaves, which remained the main sink for N. Whatever the treatment and the date, most of the leaf N-15 stayed in the leaves and was invested in soluble proteins (60-68% of total leaf N). N-15 stayed more in the proximal part of the branch in response to drought compared with other treatments. The long-distance transport of N was maintained even under harsh drought, highlighting efficient internal N recycling in beech trees. Under extreme constraints creating an N and water imbalance, compensation mechanisms operated at the branch level in beech trees and allowed them (i) to maintain leaf N metabolism and protein synthesis and (ii) to ensure the seasonal short- and long-distance transfer of recycled leaf N even under drastic water shortage conditions.

    ano.nymous@ccsd.cnrs.fr.invalid (Pierre-Antoine Chuste) 26 May 2020

  • [hal-02356964] Alpha diversity of vascular plants in European forests

    Aim. The former continental‐scale studies modelled coarse‐grained plant species‐richness patterns (gamma diversity). Here we aim to refine this information for European forests by (a) modelling the number of vascular plant species that co‐occur in local communities (alpha diversity) within spatial units of 400 m2; and (b) assessing the factors likely determining the observed spatial patterns in alpha diversity. Location. Europe roughly within 12°W–30°E and 35–60°N. Taxon. Vascular plants. Methods. The numbers of co‐occurring vascular plant species were counted in 73,134 georeferenced vegetation plots. Each plot was classified by an expert system into deciduous broadleaf, coniferous or sclerophyllous forest. Random Forest models were used to map and explain spatial patterns in alpha diversity for each forest type separately using 19 environmental, land‐use and historical variables. Results. Our models explained from 51.0% to 70.9% of the variation in forest alpha diversity. The modelled alpha‐diversity pattern was dominated by a marked gradient from species‐poor north‐western to species‐rich south‐eastern Europe. The most prominent richness hotspots were identified in the Calcareous Alps and adjacent north‐western Dinarides, the Carpathian foothills in Romania and the Western Carpathians in Slovakia. Energy‐related factors, bedrock types and terrain ruggedness were identified as the main variables underlying the observed richness patterns. Alpha diversity increases especially with temperature seasonality in deciduous broadleaf forests, on limestone bedrock in coniferous forests and in areas with low annual actual evapotranspiration in sclerophyllous forests. Main conclusions. We provide the first predictive maps and analyses of environmental factors driving the alpha diversity of vascular plants across European forests. Such information is important for the general understanding of European biodiversity. This study also demonstrates a high potential of vegetation‐plot databases as sources for robust estimation of the number of vascular plant species that co‐occur at fine spatial grains across large areas.

    ano.nymous@ccsd.cnrs.fr.invalid (Martin Večeřa) 18 Nov 2019

  • [hal-01972724] Influence of annual climatic variations, climate changes, and sociological factors on the production of the Périgord black truffle (Tuber melanosporum Vittad.) from 1903–1904 to 1988–1989 in the Vaucluse (France)

    From 1903–1904 to 1988–1989, the two World Wars and sociological factors as rural desertification and changes in land uses mainly explained the decline of black truffle production in the Vaucluse department, which well reflects that of the whole of France. These can be correlated with the annual climatic variations as well as, from 1924–1925 to 1948–1949, the raw production rates of the managed truffle orchard of Pernes-les-Fontaines located in Vaucluse. The two methods used (correlation coefficients and Bayesian functional linear regression with Sparse Step functions) gave consistent results: the main factor explaining the annual variations of truffle production was the summer climatic water deficit of the year n. A general model including the rural exodus and the cumulated climatic water deficit of summer months both allowed to well explain the evolution of truffle production from 1903–1904 to 1988–1989 in the Vaucluse and its huge decrease. During that period, global warming had little effect. However, in the twenty-first century, all the scenarios predict increased summer water stress for the Mediterranean region, which could greatly affect black truffle production.

    ano.nymous@ccsd.cnrs.fr.invalid (Meïli Baragatti) 07 Jan 2019

  • [hal-02052715] Compositional response of Amazon forests to climate change

    Most of the planet's diversity is concentrated in the tropics, which includes many regions undergoing rapid climate change. Yet, while climate-induced biodiversity changes are widely documented elsewhere, few studies have addressed this issue for lowland tropical ecosystems. Here we investigate whether the floristic and functional composition of intact lowland Amazonian forests have been changing by evaluating records from 106 long-term inventory plots spanning 30 years. We analyse three traits that have been hypothesized to respond to different environmental drivers (increase in moisture stress and atmospheric CO2 concentrations): maximum tree size, biogeographic water-deficit affiliation and wood density. Tree communities have become increasingly dominated by large-statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season. However, among newly recruited trees, dry-affiliated genera have become more abundant, while the mortality of wet-affiliated genera has increased in those plots where the dry season has intensified most. Thus, a slow shift to a more dry-affiliated Amazonia is underway, with changes in compositional dynamics (recruits and mortality) consistent with climate-change drivers, but yet to significantly impact whole-community composition. The Amazon observational record suggests that the increase in atmospheric CO2 is driving a shift within tree communities to large-statured species and that climate changes to date will impact forest composition, but long generation times of tropical trees mean that biodiversity change is lagging behind climate change.

    ano.nymous@ccsd.cnrs.fr.invalid (Adriane Esquivel-Muelbert) 28 Feb 2019

  • [hal-02628795] Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale.

    The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses. We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO2 response curves, including data from 141 C3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common‐garden datasets, respectively. The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin. We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.

    ano.nymous@ccsd.cnrs.fr.invalid (Dushan P Kumarathunge) 27 May 2020

  • [hal-02436352] Single-image photogrammetry for deriving tree architectural traits in mature forest stands: a comparison with terrestrial laser scanning

    We compared two methods for detailed individual tree measurements: single image photogrammetry (SIP), a simplified, low-cost method, and the state-of-the-art terrestrial laser scanning (TLS). Our results provide evidence that SIP can be successfully applied to obtain accurate tree architectural traits in mature forests.ContextTree crown variables are necessary in forest modelling; however, they are time consuming to measure directly, and they are measured in many different ways. We compare two methods to obtain crown variables: laser-based and image-based. TLS is an advanced technology for three-dimensional data acquisition; SIP is a simplified, low-cost method.AimsTo elucidate differences between the methods, and validate SIP accuracy and usefulness for forest research, we investigated if (1) SIP and TLS measurements are in agreement in terms of the most widely used tree characteristics; (2) differences between the SIP traits and their TLS counterparts are constant throughout tree density and species composition; (3) tree architectural traits obtained with SIP explain differences in laser-based crown projection area (CPA), under different forest densities and stand compositions; and (4) CPA modelled with SIP variables is more accurate than CPA obtained with stem diameter-based allometric models. We also examined the correspondence between local tree densities extracted from images and from field measurements.MethodsWe compared TLS and SIP in a temperate pure sessile oak and mixed with Scots pine stands, in the Orléans Forest, France. Standard major axis regression was used to establish relations between laser-based and image-based tree height and diameter at breast height. Four SIP-derived traits were compared between the levels of stand density and species composition with a t test, in terms of deviations and biases to their TLS counterparts. We created a set of linear and linear mixed models (LMMs) of CPATLS, with SIP variables. Both laser-based and image-based stem diameters were used to estimate CPA with the published allometric equations; the results were then compared with the best predictive LMM, in terms of similarity with CPATLS measurement. Local tree density extracted from images was compared with field measurements in terms of basic statistics and correlation. ResultsTree height and diameter at breast height were reliably represented by SIP (Pearson correlation coefficients r = 0.92 and 0.97, respectively). SIP measurements were affected by the stand composition factor; tree height attained higher mean absolute deviation (1.09 m) in mixed stands, compared to TLS, than in pure stands (0.66 m); crown width was more negatively biased in mixed stands (− 0.79 m), than in pure stands (− 0.05 m); and diameter at breast height and crown asymmetry were found unaffected. Crown width and mean branch angle were key SIP explanatory variables to predict CPATLS. The model was approximately 2-fold more accurate than the CPA allometric estimations with both laser-based and image-based stem diameters. SIP-derived local tree density was similar to the field-measured density in terms of mean and standard deviation (9.6 (3.5) and 9.4 (3.6) trees per plot, respectively); the correlation between both density measures was significantly positive (r = 0.76).ConclusionSIP-derived variables, such as crown width, mean branch angle, branch thickness, and crown asymmetry, were useful to explain tree architectural differences under different densities and stand compositions and may be implemented in many forest research applications. SIP may also provide a coarse measure of local competition, in terms of number of neighbouring trees. Our study provides the first test in mature forest stands, for SIP compared with TLS.

    ano.nymous@ccsd.cnrs.fr.invalid (Kamil Kędra) 13 Jan 2020

  • [hal-02154543] Climatic Suitability Derived from Species Distribution Models Captures Community Responses to an Extreme Drought Episode

    The differential responses of co-occurring species in rich communities to climate changeparticularly to drought episodeshave been fairly unexplored. Species distribution models (SDMs) are used to assess changes in species suitability under environmental shifts, but whether they can portray population and community responses is largely undetermined, especially in relation to extreme events. Here we studied a shrubland community in SE Spain because this region constitutes an ecotone between the Mediterranean biome and subtropical arid areas, and it has recently suffered its driest hydrological year on record. We used four different modeling algorithms (Mahalanobis distance, GAM, BRT, and MAXENT) to estimate species' climatic suitability before (1950-2000) and during the extreme drought. For each SDM, we related species' climatic suitability with their remaining green canopy as a proxy for species resistance to drought. We consistently found a positive correlation between remaining green canopy and species' climatic suitability before the event. This relationship supports the hypothesis of a higher vulnerability of populations living closer to their species' limits of aridity tolerance. Contrastingly, climatic suitability during the drought did not correlate with remaining green canopy, likely because the exceptional episode led to almost zero suitability values. Overall, our approach highlights climatic niche modeling as a robust approach to standardizing and comparing the behavior of different co-occurring species facing strong climatic fluctuations. Although many processes contribute to resistance to climatic extremes, the results confirm the relevance of populations' position in the species' climatic niche for explaining sensitivity to climate change.

    ano.nymous@ccsd.cnrs.fr.invalid (Gerard Sapes) 12 Jun 2019

  • [hal-02623508] Impact of bias correction and downscaling through quantile mapping on simulated climate change signal: a case study over Central Italy

    Quantile mapping (QM) represents a common post-processing technique used to connect climate simulations to impact studies at different spatial scales. Depending on the simulation-observation spatial scale mismatch, QM can be used for two different applications. The first application uses only the bias correction component, establishing transfer functions between observations and simulations at similar spatial scales. The second application includes a statistical downscaling component when point-scale observations are considered. However, knowledge of alterations to climate change signal (CCS) resulting from these two applications is limited. This study investigates QM impacts on the original temperature and precipitation CCSs when applied according to a bias correction only (BC-only) and a bias correction plus downscaling (BC + DS) application over reference stations in Central Italy. BC-only application is used to adjust regional climate model (RCM) simulations having the same resolution as the observation grid. QM BC + DS application adjusts the same simulations to point-wise observations. QM applications alter CCS mainly for temperature. BC-only application produces a CCS of the median ~ 1 °C lower than the original (~ 4.5 °C). BC + DS application produces CCS closer to the original, except over the summer 95th percentile, where substantial amplification of the original CCS resulted. The impacts of the two applications are connected to the ratio between the observed and the simulated standard deviation (STD) of the calibration period. For the precipitation, original CCS is essentially preserved in both applications. Yet, calibration period STD ratio cannot predict QM impact on the precipitation CCS when simulated STD and mean are similarly misrepresented.

    ano.nymous@ccsd.cnrs.fr.invalid (Lorenzo Sangelantoni) 26 May 2020

  • [hal-02627690] From xylogenesis to tree rings: wood traits to investigate tree response to environmental changes

    It is noteworthy that the largest part of global vegetation biomass depends on a thin layer of cells: the vascular cambium. Understanding the wood formation processes and relationships with environmental factors is a crucial and timely research question requiring interdisciplinary efforts, also to upscale the information gained and to evaluate implications for tree growth and forest productivity. We provide an overview of wood formation processes up to tree-ring development, bearing in mind that the combined action of intrinsic factors and environmental drivers determines the anatomical traits of a tree ring formed at a specific time and position within the tree’s architecture. After briefly reviewing intrinsic factors, we focus attention on environmental drivers highlighting how a correct interpretation of environmental signals in tree rings must be grounded in a deep knowledge of xylogenesis and consequent wood anatomical traits. We provide guidelines on novel methods and approaches recently developed to study xylem formation. We refer to existing literature on established techniques for retrospective analyses in tree-ring series of anatomical and isotopic traits, to assess long-term ecophysiological responses to environmental variations, also giving advice on possible bias because of interand within-tree variability. Finally, we highlight that, once the temporal axis of intra-annual tree-ring variability of xylem traits is established by xylogenesis analysis, a multidisciplinary approach linking classical dendro-ecology, wood functional traits (dendro-anatomy) and eco-physiology (here focusing on dendro-isotopes) allows a better interpretation of past environmental events hidden in tree rings, and more reliable forecasts of wood growth in response to climate change.

    ano.nymous@ccsd.cnrs.fr.invalid (Veronica de Micco) 26 May 2020

  • [hal-02942682] Robust Response of Terrestrial Plants to Rising CO2

    Human-caused CO 2 emissions over the past century have caused the climate of the Earth to warm and have directly impacted on the functioning of terrestrial plants. We examine the global response of terrestrial gross primary production (GPP) to the historic change in atmospheric CO 2. The GPP of the terrestrial biosphere has increased steadily, keeping pace remarkably in proportion to the rise in atmospheric CO 2. Water-use efficiency, namely the ratio of CO 2 uptake by photosynthesis to water loss by transpiration, has increased as a direct leaf-level effect of rising CO 2. This has allowed an increase in global leaf area, which has conspired with stimulation of photosynthesis per unit leaf area to produce a maximal response of the terrestrial biosphere to rising atmospheric CO 2 and contemporary climate change. Rising Atmospheric CO 2 and Global Climate Change Emissions of CO 2 associated with human industrial activity and land-use change over the past century have significantly impacted on global climate, causing global warming of about 1.0°C [1]. The anthropogenic CO 2 emission rate is continuing to increase, and the future rise in atmospheric CO 2 will undoubtedly lead to more climate change, including increases in the frequency of extreme climate events such as heatwaves, droughts, and storms [2]. Global climate change has the potential to significantly stress terrestrial vegetation [3], for example with hot, dry air, soil moisture deficits, or flooding. This could lead to a carbon-climate feedback in which widespread tree mortality and forest decline contribute to accelerating accumulation of CO 2 in the atmosphere [4-6]. On the other hand, plants interact directly with atmospheric CO 2 , and they can potentially respond to rising atmospheric CO 2 concentrations by increasing photosynthetic rates and water-use efficiency (see Glossary) [7-10]. Water-use efficiency in this context is defined as the amount of CO 2 taken up by photosynthesis for a given amount of water lost to the atmosphere by transpiration (Box 1). Understanding emergent responses of the production of terrestrial vegetation to the potentially opposing impacts of global climate change and CO 2 fertilization is crucial for formulating effective mitigation and adaptation strategies [11]. At a global scale, there is currently an imbalance between the amount of CO 2 absorbed by the terrestrial biosphere through photosynthesis and the amount released back to the atmosphere through plant respiration, decomposition, fire, and emissions from land-use change [12]. This is commonly referred to as the land carbon sink. It is slowing the rate of increase in atmospheric CO 2 that would otherwise result from anthropogenic CO 2 emissions. Predicting the future behaviour of the land carbon sink is one of the most important challenges in carbon cycle science, given the potential that feedbacks could accelerate the rate of future climate change [13]. This requires a thorough understanding of the process through which the terrestrial biosphere captures CO 2-photosynthesis. Highlights Global climate change caused by CO 2 emissions can stress terrestrial vegetation , potentially decreasing production. On the other hand, CO 2 interacts directly with plants, stimulating leaf-level photo-synthesis and water-use efficiency. The rise in atmospheric CO 2 concentration over the past century presents an opportunity for gauging the strength of the terrestrial biosphere response to these potential impacts. Atmospheric proxy and model analysis both suggest that global terrestrial photosynthesis has increased in nearly constant proportion to the rise in atmospheric CO 2 concentration, a maximal response by the terrestrial biosphere. An accurate understanding of the impacts of climate change on terrestrial vegetation is essential for managing risks associated with human-caused climate change: gauging the historic response of terrestrial photosynthesis is an important step in this direction.

    ano.nymous@ccsd.cnrs.fr.invalid (Lucas A Cernusak) 18 Sep 2020

  • [hal-02184245] Time shifts in height and diameter growth allocation in understory European beech (Fagus sylvatica L.) following canopy release

    Understory trees experience a succession of canopy opening and closure events during their lifetime. Preferential allocation of their biomass to height or diameter growth is part of the acclimation process to their immediate environment. In this study, we investigated annual height and diameter increments in Fagus sylvatica understory trees submitted to canopy release. Annual height and diameter increments were obtained from retrospective stem analysis from the top of the tree to the stump on 39 understory trees. The relationship between height and diameter increments was investigated and temporal correlations among successive annual height and diameter increments were analyzed. An asymptotic relationship between annual height and diameter increment indicates that stem height growth was limited in understory trees. The intercept significantly differed from zero suggesting that height growth never stopped even when diameter growth was null. Following canopy release events, immediate diameter growth increase was observed while the height growth response was delayed, resulting in a time shift in the growth allocation strategy. Strong and asymmetric temporal correlations between annual height and diameter increments were observed: past annual diameter growth was positively correlated to present height growth. In understory trees, tree height is the main factor determining their potential growth since it determines their access to above-canopy light. However, the precedence of diameter growth over height growth suggests that tree growth is driven by diameter instead of height. This apparent discrepancy may be explained by the fact that, under closed canopy conditions, stem allometry reaches a functional threshold that forces tree to grow in diameter before growing in height.

    ano.nymous@ccsd.cnrs.fr.invalid (Estelle Noyer) 15 Jul 2019

  • [hal-02178455] Estimation of phloem carbon translocation belowground at stand level in a hinoki cypress stand

    At stand level, carbon translocation in tree stems has to match canopy photosynthesis and carbohydrate requirements to sustain growth and the physiological activities of belowground sinks. This study applied the Hagen-Poiseuille equation to the pressure-flow hypothesis to estimate phloem carbon translocation and evaluate what percentage of canopy photosynthate can be transported belowground in a hinoki cypress (Chamaecyparis obtusa Sieb. et Zucc.) stand. An anatomical study revealed that, in contrast to sieve cell density, conductive phloem thickness and sieve cell hydraulic diameter at 1.3 m in height increased with increasing tree diameter, as did the concentration of soluble sugars in the phloem sap. At tree level, hydraulic conductivity increased by two orders of magnitude from the smallest to the largest trees in the stand, resulting in a stand-level hydraulic conductance of 1.7 × 10-15 m Pa-1 s-1. The osmotic potential of the sap extracted from the inner bark was -0.75 MPa. Assuming that phloem water potential equalled foliage water potential at predawn, the turgor pressure in the phloem at 1.3 m in height was estimated at 0.22 MPa, 0.59 MPa lower than values estimated in the foliage. With this maximal turgor pressure gradient, which would be lower during day-time when foliage water potential drops, the estimated stand-level rate of carbon translocation was 2.0 gC m-2 day-1 (30% of daily gross canopy photosynthesis), at a time of the year when aboveground growth and related respiration is thought to consume a large fraction of photosynthate, at the expense of belowground activity. Despite relying on some assumptions and approximations, this approach, when coupled with measurements of canopy photosynthesis, may further be used to provide qualitative insight into the seasonal dynamics of belowground carbon allocation.

    ano.nymous@ccsd.cnrs.fr.invalid (Daniel Epron) 09 Jul 2019

  • [hal-02629182] Phenology of wood formation in larch (Larix decidua Mill.) trees growing along a 1000-m elevation gradient in the French Southern Alps

    center dot Key message Spring temperature increase is the main driver of larch tree wood formation onset along a 1000-m elevation gradient in the Southern Alps, while its cessation is more probably controlled by water stress at the lowest elevation and photoperiod at higher ones. center dot Context The survival of perennial plants depends on their adaptation to changing environment and specially temperature, which in trees is notably implemented through wood formation process. center dot Aims Our main objective is to understand how the phenology of wood formation is related to environmental factors and to temperature in particular. center dot Methods We monitored the xylogenesis of 60 larch trees, distributed in four stands along an elevation gradient of 1000 m in the French Southern Alps. center dot Results Cambial activity started around mid-May at the lowest site (1350 m) and around mid-June at the highest one (2300 m), showing a delay of 5.4 days per degrees C. The onset of wall-thickening and mature phenophases followed the same linear trend with a delay of 5.2 and 3 days per degrees C, respectively. Phenophase cessations followed a parabolic trend with trees from the lowest site finishing their growth the first, while those from 1700 m finished the last. Our results show that the onset of xylem formation is mainly driven by spring temperature increase, while its cessation is more related to photoperiod, with water shortage being able to hasten it. center dot Conclusion Future climatic changes will most probably increase growing season length (but not necessarily wood production) and shift upwards the optimal elevation for larch growth in the Southern Alps.

    ano.nymous@ccsd.cnrs.fr.invalid (Seyedeh Masoumeh Saderi) 27 May 2020

  • [hal-02179547] Introduction to the invited issue on phloem function and dysfunction

    Introduction to the invited issue on phloem function and dysfunction

    ano.nymous@ccsd.cnrs.fr.invalid (Daniel Epron) 10 Jul 2019

  • [hal-02154444] Biomechanical control of beech pole verticality (Fagus sylvatica) before and after thinning: theoretical modelling and ground-truth data using terrestrial LiDAR

    Premise of the Study Thinning is a frequent disturbance in managed forests, especially to increase radial growth. Due to buckling and bending risk associated with height and mass growth, tree verticality is strongly constrained in slender trees growing in dense forests and poor light conditions. Tree verticality is controlled by uprighting movements implemented from local curvatures induced by wood maturation stresses and/or eccentric radial growth. This study presents the first attempt to compare the real uprighting movements in mature trees using a theoretical model of posture control. Methods Stem lean and curvature were measured by Terrestrial LiDAR Scanner (TLS) technology before and 6 years after thinning and compared to unthinned control poles. Measures for several tree and wood traits were pooled together to implement a widely used biomechanical model of tree posture control. Changes in observed stem lean were then compared with the model predictions, and discrepancies were reviewed. Key Results Even under a highly constrained environment, most control poles were able to counterbalance gravitational curvature and avoid sagging. Thinning stimulated uprighting movements. The theoretical uprighting curvature rate increased just after thinning, then slowed after 2 years, likely due to the stem diameter increase. The biomechanical model overestimated the magnitude of uprighting. Conclusions Most suppressed beech poles maintain a constant lean angle, and uprighting movements occur after thinning, indicating that stem lean is plastic in response to light conditions. Acclimation of posture control to other changes in growth condition should be investigated, and lean angles should be measured in forest inventories as an indicator of future wood quality.

    ano.nymous@ccsd.cnrs.fr.invalid (Estelle Noyer) 12 Jun 2019

  • [hal-02625058] Quantifying intra-annual dynamics of carbon sequestration in the forming wood: a novel histologic approach

    Key message This study presents a novel histologic approach to quantify the intra-annual dynamics of carbon sequestration in forming wood. This innovative approach, based on repeated measurements of xylem apparent density, is more direct, and more accurate than the previously published cellular-based approach. Moreover, this new approach, which was tested here on softwoods, is also applicable to hardwoods without any modification. Context Forest ecosystems are key players of the terrestrial carbon cycle. Indeed, wood represents the principal carbon pool of terrestrial biomass, accumulated in trees through cambial activity. Aims Here, we present a novel, simple, and fast approach to accurately estimate the intra-annual dynamics of aboveground woody biomass production based on image analysis of forming xylem sections. Methods During the 2015 growing season, we weekly collected wood samples (microcores) containing the forming xylem on seven Norway spruces (Picea abies (L.) Karst), grown in Hesse forest (North-East France). The microcores were prepared to allow the observation of the forming tissues with an optical microscope. Xylem apparent density and radial increment were then measured directly on images of the histological sections. In order to compare our “histologic approach” with the previously published “cellular approach,” we also counted the number of tracheids in each differentiation zones, and measured the tracheid dimensions all along the last-formed tree ring. Results The two approaches yielded comparable meaningful results, describing xylem size increase and aboveground woody biomass production as bell-shaped curves culminating in May and June respectively. However, the histologic approach provided a shorter time lag between xylem size increase and biomass production than the cellular one. Conclusion Better quantification of the shift between stem growth in size and in biomass will require addressing the knowledge gap regarding lignin deposition kinetics. Nevertheless, our novel histologic approach is simpler and more direct than the cellular one, and may open the way to a first quantification of intra-annual dynamics of woody biomass production in angiosperms, where the cellular approach is hardly applicable.

    ano.nymous@ccsd.cnrs.fr.invalid (Anjy Nandrianina Andrianantenaina) 26 May 2020


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