Influence of canopy density on architectural development of young sessile oak, Quercus patraea (Matt.) Liebl. (Fagaceae) during forest regeneration

The growth and branching patterns of the main axis of 6-year-old sessile oa k, growing in a natural regeneration in the north of France, were analysed each year retrospectively according to three increasing canopy density cond itions: large gap, small gap, and dense canopy. Increasing gap size is asso ciated with an increase in the total height, basal diameter, branching prob ability, and global polycyclism rate of the trees. At the growth unit or an nual shoot level, from dense canopy to large gaps these botanical entities also show an increase in their total length, number of nodes, polycyclism, and branching rate as well as mean number of branches and mean internode le ngth. A discussion of our results revealed some endogenous features of grow th and branching patterns in young sessile oak trees. It is also shown that increasing canopy density generally tends to reduce the expression of the endogenous architectural sequence of differentiation of young sessile oak t rees. Young trees growing below dense canopy thus seem to be "delayed" in t heir sequence of differentiation and appear to be in a "waiting" status, wh ereas young trees growing in large gaps exhibit an architecture very simila r to trees growing in nurseries under nonlimiting growth conditions.