Forêts de montagne et changement climatique : impacts et adaptation

Les impacts du changement climatique sur les forêts de montagne sont déjà perceptibles et les prévisions nous montrent, par leurs contradictions, la complexité des phénomènes en jeu. L’objectif de cette étude bibliographique est d’abord de caractériser les principaux effets du changement climatique, principalement dans les forêts alpines, puis de présenter différentes options d’adaptation devant permettre de conserver les services actuellement fournis par la forêt. L’épicéa, le sapin et le hêtre, dominants dans les Alpes françaises, y sont privilégiés

Managing tree species diversity and ecosystem functions through coexistence mechanisms

International audienceAbstractKey messageA better transfer to managers of studies examining the functional role of tree species diversity would be achieved by explicitly addressing two missing links: the effect of management interventions on coexistence mechanisms and the relationships between coexistence mechanisms and ecosystem functions.ContextPlant species diversity has been shown to promote a wide array of ecosystem functions and ecosystem services. However, scientific results concerning relationships between species diversity or species mixing and ecosystem functions have not been well transferred to management practices so far. Part of the problem lies in the difficulty of assessing whether interesting species mixtures can persist over the long term and how management influences ecosystem functions.AimsWe argue that a better transfer of knowledge to managers would be achieved by addressing two missing links: (i) the effect of management interventions on coexistence mechanisms and (ii) the relationships between coexistence mechanisms and ecosystem functions.MethodsTo do so, we first provide a brief overview of the recent scientific results on relations between tree diversity (or two-species mixing) and ecosystem functions, focusing on studies dealing with productivity and stability in forests. We further introduce the key question of whether mixed stands are transient or permanent. We then briefly present key elements of modern coexistence theory and illustrate them with three examples in forest ecosystems. We finish by discussing how management interventions in forests can affect coexistence mechanisms and by addressing some methodological perspectives.ResultsWe provide examples of management actions (e.g. gap-based silviculture, preferentialselection of the most frequent species, preferential selection of the most competitive species, plantingweakly competitive species) that may increase the strength of coexistence mechanisms.ConclusionAnalysing long-term management impacts on species coexistence and ecosystem functions with a combination of long-term monitoring of large permanent plots and mechanistic dynamic model simulations will be useful to develop relevant practices favouring mixed forests in the long term

Divergent occurrences of juvenile and adult trees are explained by both environmental change and ontogenetic effects

Recent climate warming has fueled interest into climate-driven range shifts of tree species. A common approach to detect range shifts is to compare the divergent occurrences between juvenile and adult trees along environmental gradients using static data. Divergent occurrences between life stages can, however, also be caused by ontogenetic effects. These include shifts of the viable environmental conditions throughout development (?ontogenetic niche shift') as well as demographic dependencies that constrain the possible occurrence of subsequent life stages. Whether ontogenetic effects are an important driver of divergent occurrences between juvenile and adult trees along large-scale climatic gradients is largely unknown. It is, however, critical in evaluating whether impacts of environmental change can be inferred from static data on life stage occurrences. Here, we first show theoretically, using a two-life stage simulation model, how both temporal range shift and ontogenetic effects can lead to similar divergent occurrences between adults and juveniles (juvenile divergence). We further demonstrate that juvenile divergence can unambiguously be attributed to ontogenetic effects, when juveniles diverge from adults in opposite direction to their temporal shift along the environmental gradient. Second, to empirically test whether ontogenetic effects are an important driver of divergent occurrences across Europe, we use repeated national forest inventories from Sweden, Germany and Spain to assess juvenile divergence and temporal shift for 40 tree species along large-scale climatic gradients. About half of the species-country combinations had significant juvenile divergences along heat sum and water availability gradients. Only a quarter of the tree species had significant detectable temporal shifts within the observation period. Furthermore, significant juvenile divergences were frequently associated with opposite temporal shifts, indicating that ontogenetic effects are a relevant cause of divergent occurrences between life stages. Our study furthers the understanding of ontogenetic effects and challenges the practice of inferring climate change impacts from static data.Universidad de AlcaláMinisterio de Ciencia e InnovaciónAgencia Estatal de Investigació

Plant functional traits have globally consistent effects on competition.

Phenotypic traits and their associated trade-offs have been shown to have globally consistent effects on individual plant physiological functions, but how these effects scale up to influence competition, a key driver of community assembly in terrestrial vegetation, has remained unclear. Here we use growth data from more than 3 million trees in over 140,000 plots across the world to show how three key functional traits--wood density, specific leaf area and maximum height--consistently influence competitive interactions. Fast maximum growth of a species was correlated negatively with its wood density in all biomes, and positively with its specific leaf area in most biomes. Low wood density was also correlated with a low ability to tolerate competition and a low competitive effect on neighbours, while high specific leaf area was correlated with a low competitive effect. Thus, traits generate trade-offs between performance with competition versus performance without competition, a fundamental ingredient in the classical hypothesis that the coexistence of plant species is enabled via differentiation in their successional strategies. Competition within species was stronger than between species, but an increase in trait dissimilarity between species had little influence in weakening competition. No benefit of dissimilarity was detected for specific leaf area or wood density, and only a weak benefit for maximum height. Our trait-based approach to modelling competition makes generalization possible across the forest ecosystems of the world and their highly diverse species composition.We are especially grateful to the researchers whose long-term commitment to establish and maintain forest plots and their associated databases made this study possible, and to those who granted us data access: forest inventories and permanent plots of New Zealand, Spain (MAGRAMA), France, Switzerland, Sweden, US and Canada (for the provinces of Quebec provided by the Ministère des Ressources Naturelles du Québec, Ontario provided by OnTAP’s Growth and Yield Program of the Ontario Ministry of Natural Resources, Saskatchewan, Manitoba, New Brunswick, Newfoundland and Labrador), CTFS (BCI and LTER-Luquillo), Taiwan (Fushan), Cirad (Paracou with funding by CEBA, ANR-10-LABX-25-01), Cirad, MEFCP and ICRA (M’Baïki) and Japan. We thank MPI-BGC Jena, who host TRY, and the international funding networks supporting TRY (IGBP, DIVERSITAS, GLP, NERC, QUEST, FRB and GIS Climate). G.K. was supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Program (Demo-Traits project, no. 299340). The working group that initiated this synthesis was supported by Macquarie University and by Australian Research Council through a fellowship to M.W.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature1647

Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery

International audienceThe relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential

Defoliation induces a trade-off between reproduction and growth in a southern population of Beech

International audienceA recommendation – based on reviews by Three anonymous reviewers – of the article: Oddou-Muratorio, S., Petit, C., Journe, V., Lingrand, M., Magdalou, J. A., Hurson, C., Garrigue, J., Davi, H. and Magnanou, E. (2019). Crown defoliation decreases reproduction and wood growth in a marginal European beech population. bioRxiv, 474874, ver. 4 peer-reviewed and recommended by PCI Ecology. doi: 10.1101/47487

Dynamique du paysage et démographie des espèces arborées dominantes : la régénération du hêtre et du chêne sur les grands Causses

In the mountains of the Mediterranean Basin, the modifications of the land use drive a strong dynamics of the landscape. The woody species colonize the open area, but the maintenance of grazing and its variability in time and space prevent the existence of any equilibrium. The dynamics of the tree species accounts for a large part of this transformation. In this thesis, we studied the demographic dynamics of Fagus sylvatica and Que cus pubescens in representative habitats of the landscapes of the Causse du Larzac. Light-growth and light-mortality models show that the differences of shade tolerance explain the higher regeneration of the beech in pine understory, in comparison to the oak. We show then that the dynamics of establishment of these species in open habitat is limited by herbaceous competition especially for beech. The shrubs can indirectly facilitate the establishment of trees by reducing the biomass of highly competitive herbs. The advantage of the oak compared to the beech in open environment doesn't result therefore from a better growth in full light but of a better tolerance to herbs competition. The strategies of regeneration of the trees in open habitat with large herbivores, hardly covered in the literature, constitute yet an important part of their regeneration niche. We analyzed the dispersal by animals. The oak is dispersed to longer distance than the beech in open habitat, and the jay, an important dispersal agent, drives to a directed dispersal of the two species toward pine woods in a heterogeneous landscape. This dispersal can thus drive to an important dynamics of beech in the pine groves, whereas for oak the dynamics is limited by its low survival.: Dans les montagnes du pourtour Méditerranéen, les modifications de l`utilisation des terres ont conduit à une forte dynamique du paysage. Les ligneux colonisent les milieux ouverts, mais le maintien du pâturage, sa variabilité dans le temps et dans l`espace empêchent de définir tout point d`équilibre. La dynamique des espèces arborées constitue le processus le plus important de cette transformation. Dans cette thèse, nous étudié la dynamique démographique de Fagus sylvatica et Que cus pubescens dans des milieux représentatifs des paysages du Causse du Larzac. Des modèles reliant la croissance et la mortalité à l`éclairement montrent que, en sous étage de pin, les différences de tolérance à l`ombre expliquent que le hêtre ait une meilleure capacité de régénération que le chêne. Nous avons ensuite montré que la dynamique d`installation de ces espèces en milieu ouvert et tout particulièrement celle du hêtre, est limitée par la compétition des herbacées. Les buissons peuvent faciliter indirectement l`installation en réduisant la biomasse et la capacité de compétition des herbacées. L`avantage du chêne par rapport au hêtre en milieu ouvert ne résulte donc pas d`une meilleure croissance en pleine lumière mais d`une meilleure survie en compétition avec les herbacées. Les stratégies de régénération des arbres en milieux ouverts pâturés, largement ignorées dans la littérature, constituent pourtant une part importante de leur niche de régénération. Nous avons enfin analysé la dispersion par les animaux. Le chêne est dispersé à plus longue distance que le hêtre en milieu ouvert, et le geai, agent de dispersion important, conduit à une dispersion dirigée vers les pinèdes dans un paysage hétérogène. A une échelle plus fine, cette dispersion est aussi dirigée vers les pins isolés dans un milieu ouvert hétérogène. Cette dispersion peut ainsi conduire à une dynamique importante du hêtre dans les pinèdes alors que celle du chêne est limitée par sa faible survie

Dynamique du paysage et demographie des especes arborees dominantes (la régénération de Fagus sylvatica L. et de Quercus pubescens Willd. sur les Grands Causses )

MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF