Croissance de l'erable a sucre et du hetre a grandes feuilles selon la position sociale dans le peuplement

La reconstitution de la croissance et du développement de l’érable à sucre et du hêtre à grandes feuilles, appartenant à trois classes sociales différentes, a été effectuée à partir de l’analyse de 51 tiges. D’après les résultats obtenus, la différenciation sociale des arbres dans le peuplement d’étude était déjà terminée à l’âge de trente ans, et la hiérarchie qui en a résulté était pratiquement fixée. Parmi les grandeurs dendrométriques du peuplement, on peut identifier le volume comme une grandeur très sensible et indicatrice de la position sociale de l’arbre dans le peuplement.

Following an experimental thinning, 28 sugar maples and 33 beeches were sampled and divided into three social classes The study was carried out in a mixed hardwood seedling stand in the Temiscouda-Restigouche section (L.6, Rowe, 1972) of the Quebec province in Canada. Diameter, height and volume growth measured by stem analysis are described here. Mean ages for the three classes defined are comprised between 40 and 43 years at the time of thinning, but significant differences in diameter and height already exist. In fact, differentiation of trees into classes (and therefore stand hierarchy) are fixed after 30 years, i.e. when the stand reaches a dominant height of 10 meters. Height competition, mostly between the first 2 classes, still exists long after the best classes dominate the weakest ones in diameter or volume growth. Relative increments are expressed as ratios of the first class for the lowest two classes. It can be noticed that, while relative height increment for class three still has a value of at least 68 p. 100, relative diameter and volume increments are as low as 22 and 7 p. 100 respectively. Consequently, the best dendrometrical indicator found for expressing the social class of a tree is volume. Relative diameter of lower classes (two and three) decreases more than relative height, probably as a result of competition for light. Therefore, diameter is more appropriate than height for practical differentiation of trees social classes. Height and diameter increments for the first classes of the two species are similar from 20 to 40 years of age. Volume growth for both species is also comparable up to 40 years. Further studies are proposed to relate yield classes to crown dimensions, to establish relative importance of the 3 classes at different ages of the stands, and to study distribution of trees in thinned stands.