43 research outputs found
Search for top-down and bottom-up drivers of latitudinal trends in insect herbivory in oak trees in Europe
International audienceAim: The strength of species interactions is traditionally expected to increase toward the Equator. However, recent studies have reported opposite or inconsistent latitudinal trends in the bottom-up (plant quality) and top-down (natural enemies) forces driving herbivory. In addition, these forces have rarely been studied together thus limiting previous attempts to understand the effect of large-scale climatic gradients on herbivory. Location: Europe. Time period: 2018â2019. Major taxa studied: Quercus robur. Methods: We simultaneously tested for latitudinal variation in plantâherbivoreânatural enemy interactions. We further investigated the underlying climatic factors associated with variation in herbivory, leaf chemistry and attack rates in Quercus robur across its complete latitudinal range in Europe. We quantified insect leaf damage and the incidence of specialist herbivores as well as leaf chemistry and bird attack rates on dummy caterpillars on 261 oak trees. Results: Climatic factors rather than latitude per se were the best predictors of the large-scale (geographical) variation in the incidence of gall-inducers and leaf-miners as well as in leaf nutritional content. However, leaf damage, plant chemical defences (leaf phenolics) and bird attack rates were not influenced by climatic factors or latitude. The incidence of leaf-miners increased with increasing concentrations of hydrolysable tannins, whereas the incidence of gall-inducers increased with increasing leaf soluble sugar concentration and decreased with increasing leaf C : N ratios and lignins. However, leaf traits and bird attack rates did not vary with leaf damage. Main conclusions: These findings help to refine our understanding of the bottom-up and top-down mechanisms driving geographical variation in plantâherbivore interactions, and indicate the need for further examination of the drivers of herbivory on trees
Search for top-down and bottom-up drivers of latitudinal trends in insect herbivory in oak trees in Europe
AimThe strength of species interactions is traditionally expected to increase toward the Equator. However, recent studies have reported opposite or inconsistent latitudinal trends in the bottomâup (plant quality) and topâdown (natural enemies) forces driving herbivory. In addition, these forces have rarely been studied together thus limiting previous attempts to understand the effect of largeâscale climatic gradients on herbivory.LocationEurope.Time period2018â2019.Major taxa studiedQuercus robur.MethodsWe simultaneously tested for latitudinal variation in plantâherbivoreânatural enemy interactions. We further investigated the underlying climatic factors associated with variation in herbivory, leaf chemistry and attack rates in Quercus robur across its complete latitudinal range in Europe. We quantified insect leaf damage and the incidence of specialist herbivores as well as leaf chemistry and bird attack rates on dummy caterpillars on 261 oak trees.ResultsClimatic factors rather than latitude per se were the best predictors of the largeâscale (geographical) variation in the incidence of gallâinducers and leafâminers as well as in leaf nutritional content. However, leaf damage, plant chemical defences (leaf phenolics) and bird attack rates were not influenced by climatic factors or latitude. The incidence of leafâminers increased with increasing concentrations of hydrolysable tannins, whereas the incidence of gallâinducers increased with increasing leaf soluble sugar concentration and decreased with increasing leaf CÂ :Â N ratios and lignins. However, leaf traits and bird attack rates did not vary with leaf damage.Main conclusionsThese findings help to refine our understanding of the bottomâup and topâdown mechanisms driving geographical variation in plantâherbivore interactions, and indicate the need for further examination of the drivers of herbivory on trees.</p
Victims or perpetrators: contribution and response of insects to forest diebacks and declines
International audienceUnprecedented forest declines and diebacks are expected worldwide in response to global change. Insects can trigger or contribute to these disturbances, which can in turn have either beneficial or detrimental retroactive cascading effects on insect communities. However, we are still unsure of the effects that pests will have on these disturbances in the future, and new biodiversity and pest management strategies still need to be put into place. Several recent contributions to Annals of Forest Science address these issues
SantĂ© des forĂȘts et biodiversitĂ©
International audienceForest diebacks are likely to increase in response to climate change, with increased frequency and intensity of droughts in some parts of the world (including Europe) already visible in forests. The progressive deterioration of the state of health of a stand is accompanied by the appearance / increase of certain habitats / certain resources, potentially favorable to certain organisms (opportunities for (temporary) resurgence for taxa currently under threat) and unfavorable to other species (risks of loss of ecosystem services). The impact of forest dieback on biodiversity has been poorly studied, and we approach it here via two research projects: BUCHE and Climtree. The BUCHE project is a methodological project on diebacks and pests, with secondary results on forest biodiversity, led in the forest of Vierzon, an oakwood that has experienced repeated diebacks (1920, 1940, 1980, 2000 - 2004 ). Since 2016, we have conducted a sampling of certain groups of saproxylic insects in dendromicrohabitats modified by dieback (canopy & sap runs) for the study of links between dieback and biodiversity. Despite the fact that we used a limited design, we observed positive dieback effects on saproxylic taxa (dependent on deadwood), in quantitative & qualitative terms. This exploratory work remains to be extended on a larger scale (more plots and forests), and on more varied taxonomic / functional groups. The Climtree project focuses on the effects of silver fir dieback on the biodiversity in Pyrenean forests. The average defoliation index of fir trees, a species highly sensitive to water deficit, has increased in the southern limit of its range since 2000, especially in the Pyrenees. As part of our sociological study on the response of local forest stakeholders to the decline of the fir forests following climate change, a typology of landowners was constructed. On the other hand, our ecological study analyzes the response of biodiversity to dieback through a sampling design in 2 regions of the Pyrenees. According to the initial results, the structure of fir stands is affected by the level of decline, and to a lesser extent by salvage logging, but this does not significantly change the biodiversity. In conclusion, forest changes through dieback result in habitat and resource changes with potentially large impacts on a major reservoir of biodiversity. The direction and intensity of the changes are, however, still difficult to predict and vary according to the functional / taxonomic groups and the forest.Les dĂ©pĂ©rissements forestiers ne sont pas des phĂ©nomĂšnes nouveaux mais risquent de s'accentuer en rĂ©ponse aux changements climatiques : augmentation de frĂ©quence et d'intensitĂ© des sĂ©cheresses dans certaines parties du globe (dont l'Europe) avec des consĂ©quences dĂ©jĂ visibles sur les forĂȘts. La dĂ©tĂ©rioration progressive de l'Ă©tat de santĂ© d'un peuplement s'accompagne de l'apparition / augmentation de certains habitats / certaines ressources, potentiellement favorables Ă certains organismes (opportunitĂ©s de rĂ©surgence (temporaire) pour des taxons actuellement menacĂ©s) et dĂ©favorables Ă d'autres organismes (risques de perte de services Ă©cosystĂ©miques). L'impact des dĂ©pĂ©rissements forestiers sur la biodiversitĂ© a Ă©tĂ© peu Ă©tudiĂ©, et nous l'abordons ici via deux projets de recherche : BUCHE et Climtree. Le projet BUCHE est un projet mĂ©thodologique sur dĂ©pĂ©rissements et ravageurs secondaires, avec des rĂ©sultats « collatĂ©raux » sur la biodiversitĂ© forestiĂšre, dans la forĂȘt de Vierzon, une chĂȘnaie qui a connu une succession rĂ©pĂ©tĂ©e de dĂ©pĂ©rissements (1920, 1940, 1980, 2000 - 2004). Depuis 2016, nous y conduisons un Ă©chantillonnage de certains groupes d'insectes saproxyliques dans des dendromicrohabitats modifiĂ©s par les dĂ©pĂ©rissements (canopĂ©e & suintements de sĂšve) pour l'Ă©tude des liens entre dĂ©pĂ©rissement et biodiversitĂ©. Sur un dispositif limitĂ© (spatial & temporel), nous observons des effets du dĂ©pĂ©rissement positifs sur les taxons saproxyliques (dĂ©pendant du bois mort), en termes quantitatifs & qualitatifs. Ce travail exploratoire reste Ă approfondir sur un dispositif plus large (plus de parcelles & de massifs forestiers), et sur des groupes taxonomiques / fonctionnels plus variĂ©s. Le projet Climtree porte sur les effets du dĂ©pĂ©rissement du sapin sur la biodiversitĂ© des sapiniĂšres pyrĂ©nĂ©ennes. Le dĂ©ficit foliaire moyen du sapin pectinĂ©, une essence trĂšs sensible au dĂ©ficit hydrique, augmente dans la limite sud de son aire de rĂ©partition depuis 2000, notamment dans les PyrĂ©nĂ©es et le massif central. Dans le cadre de notre Ă©tude sociologique sur la rĂ©ponse des acteurs forestiers locaux au dĂ©pĂ©rissement de la sapiniĂšre consĂ©cutif au changement climatique, une typologie des propriĂ©taires a Ă©tĂ© construite. D'autre part, notre Ă©tude Ă©cologique analyse la rĂ©ponse de la biodiversitĂ© au dĂ©pĂ©rissement de la sapiniĂšre via un plan d'Ă©chantillonnage dans 2 rĂ©gions des PyrĂ©nĂ©es. D'aprĂšs les premiers rĂ©sultats, la structure de la sapiniĂšre est affectĂ©e par le niveau de dĂ©pĂ©rissement, et dans une moindre mesure par les coupes de rĂ©cupĂ©ration mais cela modifie peu la biodiversitĂ©. En conclusion, les mutations forestiĂšres via un dĂ©pĂ©rissement entraĂźnent des changements d'habitats et de ressources avec des impacts potentiellement forts sur un rĂ©servoir majeur de biodiversitĂ©. L'orientation et l'intensitĂ© des changements sont toutefois encore difficilement prĂ©visibles et variables selon les groupes fonctionnels / taxinomiques et le massif forestier
Les Agriles, des joyaux tueurs dâarbres â deuxiĂšme partie
International audienceLes agriles sont gĂ©nĂ©ralement des parasites de faiblesse qui rĂ©vĂšlent le stress subi par des hĂŽtes affaiblis. Ils colonisent des branches cassĂ©es comme des troncs dĂ©pĂ©rissants et se maintiennent ainsi facilement Ă un niveau endĂ©mique dans les houppiers et le sous-Ă©tage. Les forestiers et des arboriculteurs dâEurope, dâAmĂ©rique et dâAsie redoutent nĂ©anmoins leurs dĂ©gĂąts
Les Agriles, des joyaux tueurs dâarbres â premiĂšre partie
International audienceInsectes chatoyants, les agriles prĂ©sentent une exceptionnelle diversitĂ© taxinomique malgrĂ© un aspect relativement uniforme et des cycles biologiques peu diversifiĂ©s. Câest leur penchant immodĂ©rĂ© pour les arbres affaiblis, mais vivants, qui les rend redoutables, dâautant plus que les changements climatiques et la mondialisation leur permettent dâĂ©largir leur spectre dâhĂŽtes et dâen croquer bien au-delĂ de leurs aires dâorigine respectives, avec de graves consĂ©quences Ă©cologiques et Ă©conomiques
ForĂȘts en crise et biodiversitĂ© : menaces et opportunitĂ©s: Effets des crises sanitaires et de leur gestion sur la biodiversitĂ© forestiĂšre
International audienceLe nombre de signalements de grands dĂ©pĂ©rissements forestiers dans le monde a Ă©tĂ© multipliĂ© par trois depuis une quinzaine dâannĂ©es. Depuis une dĂ©cennie, les forĂȘts dâEurope de lâouest connaissent des dĂ©pĂ©rissements plus frĂ©quents, sur de plus grandes surfaces et avec un taux de mortalitĂ© plus fort, en raison de dĂ©ficits hydriques rĂ©pĂ©tĂ©s. Dâune sĂ©vĂ©ritĂ© marquante par rapport au rĂ©gime rĂ©gional de perturbations naturelles, ces crises sanitaires contemporaines affectent la dynamique de la mosaĂŻque forestiĂšre et peuvent modifier le rĂ©gime rĂ©gional de perturbations naturelles jusquâĂ mettre en pĂ©ril la rĂ©silience forestiĂšre. A travers lâanalyse de la littĂ©rature internationale (et notamment de plusieurs mĂ©ta-analyses rĂ©centes) et des rĂ©sultats de plusieurs cas dâĂ©tude (chĂȘnaies de la rĂ©gion Centre val-de-Loire, sapiniĂšres pyrĂ©nĂ©ennes, pessiĂšres bavaroises) explorĂ©s par des projets INRAE en cours, nous observons comment les processus de dĂ©pĂ©rissement complexes et Ă©volutifs affectent la structure des peuplements dans plusieurs contextes forestiers.Les dĂ©pĂ©rissements se traduisent par une transformation profonde de diffĂ©rents compartiments de lâĂ©cosystĂšme forestier. La surface terriĂšre des arbres morts augmente avec lâintensitĂ© du dĂ©pĂ©rissement, tout comme le volume et la diversitĂ© du bois mort, et la densitĂ© de certains dendromicrohabitats Ă ontogenĂšse rapide (branches morts du houppier, coulĂ©es de sĂšve, champignons saprolignicolesâŠ). Le profil de bois mort est significativement modifiĂ©, au profit des gros bois morts, et lâhĂ©tĂ©rogĂ©nĂ©itĂ© du stock de dendromicrohabitats accrue. La dĂ©foliation partielle de la canopĂ©e a des effets sur la quantitĂ© et la qualitĂ© de feuillage, mais aussi sur les conditions abiotiques, avec des changements de moyenne et dâamplitude des valeurs.Les dĂ©pĂ©rissements ont ainsi des consĂ©quences sur les habitats, par la quantitĂ© et la qualitĂ© des ressources trophiques et des conditions de vie pour la biodiversitĂ© forestiĂšre. Un panorama des cas dâĂ©tude nationaux et internationaux nous montre des rĂ©ponses contrastĂ©es des guildes biotiques. Pour les guildes favorisĂ©es par les pulses de ressources associĂ©s aux Ă©pisodes de dĂ©pĂ©rissements, les crises sont favorables Ă la rĂ©surgence dâespĂšces rares dont le renforcement des effectifs accroĂźt la dĂ©tectabilitĂ©. En sus de leurs multiples effets locaux, les dĂ©pĂ©rissements Ă large Ă©chelle affectent la composition des paysages forestiers et induisent des effets rĂ©gionaux sur la biodiversitĂ© locale.Les peuplements dĂ©pĂ©rissants font souvent lâobjet de travaux de rĂ©coltes « sanitaires » ou dâexploitation des « produits accidentels » (« salvage logging »), dont lâimpact Ă©cologique est significatif sur les conditions dâhabitat, avec des effets dĂ©lĂ©tĂšres sur de nombreux groupes typiquement forestiers, et des effets positifs sur les espĂšces de milieu ouvert, induisant ainsi un changement des communautĂ©s dont la composition sâĂ©loigne des assemblages forestiers. Pour ne pas sacrifier les bĂ©nĂ©fices des perturbations sur la biodiversitĂ©, et dans le respect des Ă©quilibres Ă©conomiques et phytosanitaires, une sylviculture de rĂ©tention peut ĂȘtre rĂ©flĂ©chie pour profiter de la crise, en visant des rĂ©coltes sanitaires sĂ©lectives. Des simulations fondĂ©es sur des donnĂ©es empiriques montrent un effet de seuil autour de 75% de surface dĂ©pĂ©rissante non exploitĂ©e, une valeur variable selon les groupes, pour le maintien dâau moins 90% de la diversitĂ© spĂ©cifique des espĂšces forestiĂšres
Face aux effets du changement climatique sur les forĂȘts de la rĂ©gion Centre-Val de Loire : les plantations de pin maritime comme solution ?
International audienceLes effets du changement climatique se font de plus en plus sentir sur les forĂȘts françaises ; ils sont surtout dĂ©sormais visibles : des arbres dĂ©pĂ©rissent. Les forĂȘts de la rĂ©gion Centre-Val de Loire ne sont pas Ă©pargnĂ©es : lâemblĂ©matique chĂȘne (pĂ©donculĂ© et dĂ©sormais aussi sessile) est concernĂ©, tout comme le pin sylvestre et plus encore le chĂątaignier. La sĂ©cheresse en est une cause mais sans ĂȘtre la seule. Cela se vĂ©rifie notamment dans la forĂȘt de Vierzon, qui constitue un « terrain dâĂ©tude privilĂ©giĂ© pour les scientifiques » tant les dĂ©pĂ©rissements sont nombreux ; elle est aussi lâun de nos sites dâĂ©tude. Notre communication se fondera sur les recherches conduites dans le cadre du projet Plantaclim qui, selon son intitulĂ©, vise à « Maximiser les services des (re)plantations forestiĂšres dans le contexte du changement climatique ». Nous nous appuierons sur lâanalyse de donnĂ©es spatiales, des observations de terrain, des inventaires floristiques et entomologiques, ainsi que sur des tĂ©moignages : ont Ă©tĂ© interrogĂ©s 25 acteurs de la filiĂšre forĂȘt-bois (surtout 5 avec qui les effets du changement climatique ont Ă©tĂ© davantage abordĂ©s) et 4 autres acteurs du territoire (dont association de protection de la nature) ; se sont ajoutĂ©s des Ă©changes rĂ©guliers avec les partenaires socio-Ă©conomiques du projet (dont ONF et CNPF). Pour les acteurs forestiers, face aux dĂ©pĂ©rissements, la plantation apparaĂźt comme une solution, dâailleurs encouragĂ©e par les pouvoirs publics (plan de relance) et, mĂȘme si des essais sont rĂ©alisĂ©s avec de nouvelles essences, ce sont pour lâheure les pins maritimes qui profitent de la dynamique. Mais peuvent-ils constituer une solution pour lâensemble de la rĂ©gion Centre-Val de Loire ? AprĂšs avoir exposĂ© le cadre mĂ©thodologique de notre recherche, nous analyserons les regards portĂ©s par les acteurs interrogĂ©s. Nous retracerons ensuite les dynamiques des plantations de pin maritime et nous nous intĂ©resserons, dans un 3e temps, aux (dis)services rendus par ces derniĂšres et notamment Ă la biodiversitĂ© associĂ©e. Nous montrerons ainsi que cette solution nâa pas vocation Ă ĂȘtre gĂ©nĂ©ralisĂ©e Ă lâĂ©chelle de la rĂ©gion et ne peut valoir que localement, sur le plan biophysique autant que sociĂ©tal
Plantaclim, an interdisciplinary project to study the ecosystem services provided by forest plantations
International audienceThe area of forest plantations is increasing around the world. This is particularly evident in the case of fast-growing plantations, which are helping Asian countries such as Vietnam to accelerate their forest transition. Of course, these artificial stands, often planted with exotic species, must be treated with caution. Yet they are particularly encouraged in the current context of accelerating climate change. They appear to be a means of mitigation, through the sequestration and storage of carbon and/or the avoidance of CO2 emissions through the production of local bio-sourced materials, replacing other more energy-intensive materials (concrete, etc.). They are also a way of adaptation, by allowing the introduction of species from regions with a climate similar to that expected in the region where they are introduced. Thus, forest plantations will play an increasingly role and we consider that it is important to study them, to know better the services (and disservices) they provide. It is the objective of Plantaclim, an interdisciplinary research project funded by the Centre-Val de Loire region and led by UMR CITERES (2021-2024). Alongside UMR CITERES, 14 partners (4 academic and 10 socio-economic) took part.The team focused on forest plantations of the Centre-Val de Loire region, using the example of maritime pine and poplar plantations. Both are expected to remain in place despite climate change, and the area of maritime pine is even growing, mainly replacing dying Scots pine. To study these plantations and their (dis)services, the project comprised 4 main tasks.We began by making an inventory of these plantations and the services they provide (Task 1), and selected 6 study sites. Within these, we selected 56 pairs of plots, combining poplar plantations and subnatural woodlands or pine and oak stands of different ages, for the surveys. The particularity of the project was indeed to compare native stands and plantations (for soil and plant biodiversity).We then studied the environmental (Task 2) and socio-economic (Task 3) characteristics of the studied plantations, in order to gain a better understanding of the support, provisioning and cultural services associated with these plantations. We thus analyzed the characteristics of their soils, the associated plant and entomological biodiversity, the advantages and obstacles for the entire forest-wood sector (from tree planting to wood processing), leisure activities and the representations of these plantations by stakeholders, local residents and users.In the task 4, the results were crossed on a spatial basis. This task was also an opportunity for researchers and local stakeholders involved in the project to discuss ways of improving these plantations, taking into account climate and socio-economic changes, while ensuring that they meet society's expectations, limit negative impacts on the environment and landscapes, and promote the use of local bio-sourced materials, in order to help secure the future of the industry in the region, by making it part of a sustainable approach
Effets à court et moyen terme du dépérissement forestier sur les habitats et les ressources ainsi que sur les communautés de coléoptÚres saproxyliques
International audienceNatural disturbance regimes are changing with the anthropogenic climate change. These modifications induce pressure on worldwide ecosystems. As a result, forest ecosystems are facing droughts and pest outbreaks, among other disturbances. We conducted three case studies in European forests to investigate the consequences of forest dieback on the habitats and resources as well as on the saproxylic beetle communities. We observe that forest dieback generated a large increase in deadwood amount. It also changed the profile of tree-related microhabitats, with an increase in fruiting bodies of saproxylic fungi in our three case studies. Furthermore, by promoting deadwood, forest dieback had positive effects on individual abundance and species richness of saproxylic beetles. We also showed in a case study that forest dieback had positive impact on the functional richness of saproxylic beetles, mainly at the landscape scale. However, the increase in deadwood, as a resource pulse, and the beneficial effects on saproxylic beetles may only be short to medium term. Moreover, species associated with declining habitats and resources due to forest dieback could be negatively affected. Therefore, major efforts to study ecosystems as a whole and over time must be made to better prepare for future changes