Les résultats des projets CARBOFOR et ANR-QDiv : les questions qu'ils soulèvent, Les avancées apportées par le projet ANR-Climator -

Face aux changements climatiques, les gestionnaires forestiers se posent de nombreuses questions. Quel avenir pour les espèces actuelles ? Que prédisent les modèles ? Quelles successions envisager ? Que conserver et comment ?...Vincent Badeau fait ici le point sur les différents travaux entrepris pour identifier les relations entre la distribution des espèces et le climat, afin d'estimer comment ces distributions pourraient être modifiées en réponse aux différents scénarios climatiques. Il montre aussi qu'il est nécessaire de coupler différentes approches de modélisation pour espérer encadrer de façon satisfaisante les projections pour le futur

Leaf morphological differentiation between Quercus robur and Quercus petraea is stable across western European mixed oak stands

© INRA, EDP Sciences 2002Leaf morphology was assessed in nine mixed oak stands (Quercus petraea and Q. robur ) located in eight European countries. Exhaustive sampling was used in an area of each stand where the two species coexisted in approximately equal proportions (about 170 trees/species/stand). Fourteen leaf characters were assessed on each of 5 to10 leaves collected from the upper part of each tree. Three multivariate statistical techniques (CDA, canonical discriminant analysis; PCA, principal component analysis; MCA, multiple correspondence analysis) were used in two different ways: first on the total set of leaves over all stands (global analysis) and second, separately within each stand (local analysis). There was a general agreement of the results among the statistical methods used and between the analyses conducted (global and local). The first synthetic variable derived by each multivariate analysis exhibited a clear and sharp bimodal distribution, with overlapping in the central part. The two modes were interpreted as the two species, and the overlapping region was interpreted as an area where the within-species variations were superimposed. There was no discontinuity in the distribution or no visible evidence of a third mode which would have indicated the existence of a third population composed of trees with intermediate morphologies. Based on petiole length and number of intercalary veins, an "easy to use" discriminant function applicable to a major part of the natural distribution of the species was constructed. Validation on an independent set of trees provided a 98% rate of correct identification. The results were interpreted in the light of earlier reports about extensive hybridization occurring in mixed oak stands. Maternal effects on morphological characters, as well as a lower frequency or fitness of hybrids in comparison with parent species could explain the maintenance of two modes, which might be composed of either pure species or pure species and introgressed forms.Antoine Kremer, Jean Luc Dupouey, J. Douglas Deans, Joan Cottrell, Ulrike Csaikl, Reiner Finkeldey, Santiago Espinel, Jan Jensen, Jochen Kleinschmit, Barbara Van Dam, Alexis Ducousso, Ian Forrest, U. Lopez de Heredia, Andrew J. Lowe, Marcela Tutkova, Robert C. Munro, Sabine Steinhoff and Vincent Badea

Morphological variability of oaks (Quercus robur L, Quercus petraea (Matt) Liebl, Quercus pubescens Willd) in northeastern France: preliminary results

Morphological variability of oaks in Lorraine (northeastern France), was studied. Eight hundred oaks were sampled in 80 stands covering a broad range of ecological variability; 10 leaves, fruits and current-year shoots were collected per tree. Thirty-four morphological variables were measured and analyzed by factorial correspondance analysis. It is concluded that Q robur and Q petraea are clearly separated with a few morphologically intermediate individuals (3.5%). Q petraea is more variable than Q robur. Q pubescens and Q robur are totally isolated from each other, while Q petraea and Q pubescens form a continuum. Many variables discriminate between these 3 species; some of them have been little known prior to now (pilosity, presence of intercalary ribs). These results are compared with those from other parts of Europe.Variabilité morphologique des chênes dans le Nord-Est de la France; résultats préliminaires. Nous avons étudié la différenciation morphologique des chênes pédonculé, sessile et pubescent dans le Nord-Est de la France. L'échantillonnage a porté sur 80 populations provenant de stations représentant toute la gamme de variation des milieux de chênaies en Lorraine. Sur 10 arbres par population, 10 feuilles, infruiescences et rameaux de l'année ont été prélevés. Trente-quatre variables morphologiques ont été mesurées et analysées par analyse factorielle des correspondances. On observe une très nette séparation des chênes sessile et pédonculé, avec seulement 3,5% d'individus morphologiquement intermédiaires, ainsi qu'un isolement total du chêne pubescent et du chêne pédonculé. Par contre, les chênes sessile et pubescent forment un continuum. Le chêne pédonculé est moins variable que le chêne sessile. De nombreuses variables discriminent ces 3 espèces, dont certaines peu connues jusqu'alors (pilosité, présence de nervures intercalaires). Ces résultats sont comparés à ceux obtenus par ailleurs en Europe

Arboretums et dendrochronologie. L’exemple du dépérissement du cèdre à l’arboretum d’Amance et au domaine des Barres

National audienc

Warmer winters reduce the advance of tree spring phenology induced by warmer springs in the Alps

Mountain regions are particularly susceptible and influenced by the effects of climate change. In the Alps, temperature increased two times faster than in the Northern Hemisphere during the 20th century. As an immediate response in certain tree species, spring phenological phases, such as budburst and flowering, have tended to occur earlier. However, recent studies have shown a slowing down of phenological shifts during the last two decades compared to earlier periods, which might be caused by warmer winters. Indeed, cold temperatures are required to break bud dormancy that occurs in early fall; and dormancy break is a prerequisite for cell elongation to take place in spring when temperature conditions are warm enough. Here we aimed at evaluating the effects of winter warming vs. spring warming on the phonological shift along mountain elevation gradients. We tested the hypothesis that a lack of chilling temperature during winter delayed dormancy release and subsequently spring phonological phases. For this, we used eight years of temperature and phenological records for five tree species (Betula penctula, Fraxinus excelsior, Corylus avellana, Picea abies and Larix deridna) gathered with the citizen science program Phenoclim (www.phenoclim.org) deployed over the French Alps. Our results showed that for similar preseason (i.e. after dormancy break) temperatures, warmer winters significantly delayed budburst and flowering along the elevation gradient (+ 0.9 to + 5.6 days degrees C-1) except for flowering of Corylus and budburst of Picea. For similar cold winter temperatures, warmer preseasons significantly advanced budburst and flowering along the elevation gradient (- 5.3 to -8.4 days degrees C-1). On average, the effect of winter warming was 2.3 times lower than the effect of spring warming. We also showed that warmer winter temperature conditions have a significantly larger effect at lower elevations. As a consequence, the observed delaying effect of winter warming might be beneficial to trees by reducing the risk of exposure to late spring frost on a short term. This could further lead to partial dormancy break at lower elevations before the end of the 21st century, which, in turn, may alter bud development and flowering and so tree fitness