Influence de la comp�tition herbac�e sur la croissance et l'architecture de jeunes Ch�nes rouges d'Am�rique (Quercus rubra L.) en plantation

Abstract

Résumé -De jeunes Chênes rouges d'Amérique plantés sur un sol d'origine agricole ont été soumis pendant quatre ans à deux niveaux extrêmes de compétition herbacée croisés avec deux niveaux de fertilisation initiale. Un suivi de la croissance et une analyse comparée du développement des arbres ont été réalisés sur les diverses composantes de la croissance en hauteur des arbres. La compétition herbacée se traduit par une diminution globale de la hauteur totale des arbres de 70 %, du nombre d'unités de croissance émises chaque année (polycyclisme) de 18 à 86 %, ainsi que du nombre d'entre-noeuds et de feuilles (-50 %) et de la longueur moyenne des entrenoeuds (-30 à 60 %) des unités de croissance. La fertilisation initiale n'a favorisé que la croissance en diamètre des plants désherbés. Par ailleurs, les plants enherbés montrent un nombre de branches par unité de croissance plus faible (-20 à -80 %), mais cette tendance s'annule ou s'inverse si ce nombre est rapporté à l'unité de longueur. Enfin, la mortalité des branches les plus anciennes est augmentée par la compétition pour la lumière. D'une manière générale, la compétition herbacée limite l'expansion des arbres et semble bloquer leur sé-quence de différenciation architecturale.architecture / Quercus rubra / croissance / morphologie / compétition herbacée Abstract -Influence of herbaceous competition on growth and architecture of young red oak trees (Quercus rubra L.) in plantation. Young red oak trees planted on a former agricultural soil have been submitted to two extreme levels of herbaceous competition combined with two levels of fertilization. The herbaceous competition is associated with a decrease of 70% of the mean total height and with a decrease of 18% to 86% of the number of growth units produced each year. It induced also a decrease of 50% of the growth units mean number of internodes and leaves and a decrease of 30% up to 60% in its mean internode length. Initial fertilization stimulated only diameter growth of weeded trees. The number of branches per growth unit is lower for non-weeded trees (between -20% and -80%), but not different or upper per length unit, and oldest branch mortality is higher in relation to light competition. In a general way, weeds competition tends to limit tree crown expansion and the expression of the architectural sequence of differentiation.architecture / Quercus rubra / growth / morphology / herbaceous competition Ann. For. Sci. 58 (2001)

Influence of herbaceous competitors on early growth in direct seeded Fagus sylvatica L. and Quercus robur L.

“…Two and three years following direct seeding, the shoot dry weight and leaf area had decreased to a similar extent in the treatments with vegetation. This is in line with several other studies [9,15]. However, the treatment's effect on seedling growth was not obvious until the second year after seeding.…”

Intra- and interspecific variations of polycyclism in young trees of Cedrus atlantica (Endl.) Manetti ex. Carri�re and Cedrus libani A. Rich (Pinaceae)

“…Polycyclism thus does not systematically have a positive effect on the total annual growth of Cedrus atlantica and C. libani individuals of different populations. This result differs from those obtained with Quercus rubra [14,26,38], Quercus petraea, Pinus contorta [37], Pinus pinaster [16,31], Pinus brutia [33], and Pinus halepensis [34] for which polycyclism generally leads to an increase in annual shoot length. In Cedrus libani, monocyclic annual shoots were longer than the first growth units of bicyclic annual shoots for the individuals at the more fertile site, and similar for those at the less fertile site.…”

“…For a same station, the differences in length between the first and second growth units related with year of growth. The differences in growth unit length according to type varied according to environmental conditions, unlike what was seen with young Quercus rubra [26] and Q. petraea [29,36], in which monocyclic annual shoots are generally the same length as the first growth units, which in turn are almost always shorter than the second growth units of bicyclic shoots.…”

Growth response to thinning in Quercus pyrenaica Willd. coppice stands in Spanish central mountain

“…Several studies throughout the Mediterranean area [2,3,7,9,17,20] led to possible alternatives to the current coppice situation, from the abandonment of silvicultural practices to a more intense level of management: reforestation, agricultural uses, establishment of pastures, new coppice systems, conversion to open woodlands, transformation 244 I. Cañellas et al to high forest, etc.…”