Développement des plants de hêtre (Fagus sylvatica L) dans une régénération naturelle, équienne, âgée de 18 ans

Dans une régénération naturelle de hêtre, équienne, âgée de 18 ans, le développement des plants est étudié en analysant la morphologie de leur tige principale, sous 3 éclairements : à la lumière, en demi-lumière et à l'ombre. La régénération est pluristrate dans les 2 premiers cas et monostrate dans le dernier. La structure se dessine tôt et son caractère mono- ou pluristrate apparaît rapidement. La stratification a une influence sur le développement des plants à l'âge de 18 ans ainsi que sur leur croissance annuelle et cumulée, chaque année pendant 18 ans. Les reclassements des individus seront examinés dans un prochain article.Growth of young beeches (Fagus sylvatica L) in an even-aged, 18-year old natural beech regeneration. In an even-aged 18-year old natural beech regeneration, the growth of young plants has been analysed using only the main stem under 3 daylight intensities: full-light, half-light, and shade. The structure shows 3, 2 and 1 layers respectively under these light conditions (table I). The variations in total height and root collar diameter had 2 components in full-light and in half-light only, ie among- and within-layers (figs 1, 2 and 3). In full-light, the height variations were responsible for the differences among the layers and those of root collar diameter for the differences within the layers, fig 1. In half-light the variations in height and root collar diameter were simultaneously responsible for the differences among and within the layers (fig 2). The structure appeared early with a single or several layer(s) (fig 8). The annual and multiannual growth exhibited 3 periods: establishment, differentiation, and regression or stabilisation, (figs 5, 6, 8 and 9). In full-light where differentiation is best between the layers, stratification had an influence on the vigour of the seedlings and to some degree on their shape, but not in half-light (fig 10). The layers may be considered as reflecting social status in full-light where the height is regulated by stratification. The classification of seedlings according to their total height over the 18-year period will be analysed in a subsequent paper