Caractérisation de la tolérance à l'ombrage des jeunes semis de hêtre et comparaison avec les essences associées

Abstract

Beech is considered to be a shade-tolerant species, at least while it is juvenile. It is nonetheless quick to take advantage of clearings in the canopy to grow significantly faster. In this article, the authors compare the functional features connected with photosynthesis and light interception of cultivated beech seedlings subjected to various levels of light with those of accompanying species. They show that none of these features taken alone is able to account for these species' degree of shade-tolerance. However, for individuals to be able to survive in weak light conditions, it is essential for the annual carbon balance on the scale of those individuals (including losses by all organs through respiration) to be positive. Combined features such as ratio of the leaf area to total biomass, or moreover, the per biomass unit light interception efficiency for a given illumination, are indicators of that balance and hence of the degree of shade-tolerance. The value of these two indicators however decreases as a function of seedling size and at an increasing rate when growth is intense. On this basis, slow growth is in itself a characteristic of shade-tolerance. In the article, the authors develop this idea and match it up against a set of data derived from their experiments.