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

Annals of Forest Science, Nov 2002

Antoine Kremer, Jean Luc Dupouey, J. Douglas Deans, Joan Cottrell, Ulrike Csaikl, Reiner Finkeldey, Santiago Espinel, Jan Jensen, Jochen Kleinschmit, Barbara Van Dam, et al.

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

Ann. For. Sci. Leaf morphological differentiation between Quercus robur and Quercus petraea is stable across western European mixed oak stands Antoine Kremer 5 Jean Luc Dupouey 3 J. Douglas Deans 4 Joan Cottrell 1 Ulrike Csaikl 2 Reiner Finkeldey 0 Santiago Espinelg Jan Jensenh Jochen Kleinschmiti Barbara Van Damj Alexis Ducousso 5 Ian Forrest 1 U. Lopez de Herediak Andrew J. Lowe 4 Marcela Tutkova 2 Robert C. Munro 4 Sabine Steinhoffi Vincent Badeau 3 0 Swiss Federal Research Institute WSL , Zürcherstrasse 111, Birmensdorf , Switzerland 1 Forestry Commission (FC), Forest Research, Northern Research Station , Roslin, Midlothian, EH25 9SY, Scotland , U.K 2 Austrian Research Centre (ARCS) , Seibersdorf, 2444 , Austria 3 Institut National de la Recherche Agronomique (INRA), Unité d'Écophysiologie Forestière , 54280 Champenoux , France 4 Centre for Ecology and Hydrology , Edinburgh, (CEH), Bush Estate, Penicuik, Midlothian, EH26 0QB, Scotland , U.K 5 Institut National de la Recherche Agronomique (INRA), Unité de Recherches Forestières , BP 45, 33611 Gazinet Cedex , France - Leaf 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. - caractérise par une distribution bimodale, chaque mode correspondant à une espèce. La distribution de la première variable ne manisfeste pas de discontiunuité pouvant indiquer l’existence d’un troisième groupe, correspondant à des arbres avec des morphologies de type intermédiaire. Une méthode d’identification rapide basée sur les deux caractères les plus discriminants (nombre de veines intercalaires et longueur du pétiole) a été proposée et validée sur un autre jeu de données (98 % d’identifications correctes). La structure de la variation morphologique entre les deux espèces résulte sans doute de l’hybridation entre elles, et de l’hérédité des caractères morphologiques. 1. INTRODUCTION Morphological variation in mixed oak stands composed of Quercus petraea and Quercus robur has been of general interest in Europe for decades. The two species commonly coexist in mixed stands and foresters need rapid “easy to use” morphological screening methods which would help to discriminate between the species [ 9, 10, 14 ]. Dendrologists require classification criteria for taxonomic purposes [ 3, 17, 18, 22, 25 ]. Forest biologists and ecologists seek unambiguous traits which could be used for studying introgression between these two interfertile species [ 15, 28, 29, 34 ]. The vast amount of literature devoted to morphological variation in mixed oak stands demonstrates the debate that has been raised. In addition to efforts to define the most appropriate morphological traits to be assessed [ 2, 26, 30, 31 ], investigations have been conducted on relevant statistical methods [ 11, 12, 20 ]. However these reports have not led to general agreement on the methods and traits to be used for distinguishing Quercus petraea from Q. robur, mainly because no comparative studies were conducted across different countries. Key issues in the controversy were also the sampling and (...truncated)


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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, Vincent Badeau. Leaf morphological differentiation between Quercus robur and Quercus petraea is stable across western European mixed oak stands, Annals of Forest Science, 2002, pp. 777-787, Volume 59, Issue 7, DOI: doi:10.1051/forest:2002065