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Crown architecture in Quercus petraea and Q. robur: the fate of buds and shoots in relation to age, position and environmental perturbation
1 Gatersleben, Germany 2 Gwynedd, Wales
Shoot and bud dynamics of peripheral crown portions of mature pedunculate and sessile oak trees (Quercus robur L., Q. petraea (Matt.) Liebl.) were monitored over almost three vegetation periods. The formation and shedding of buds and extension units (eus) was mapped in the form of simplified drawings. Branches were additionally subjected to manipulative treatments simulating herbivore (defoliation at different times, loss of certain bud types) and abiotic damage (artificial acid rain) and the effects on branch architecture analysed. Branch characteristics, such as branching order and age structure, had a large influence on the growth and dynamics of peripheral branch portions, even greater than that of the manipulative treatments, with the exception of spring defoliation and shoot tip removal, which led to increased shoot shedding. In order to quantify the observed changes in crown structure with time, new measures were introduced: the shedding ratio corresponds to the number of shed eus divided by the total number of eus present and produced since a given starting point. The vitality ratio was defined as the total number of eus produced in 1 year, divided by the total number of eus shed during the same time. The vitality ratio could thus be – on a small scale – the quantitative measure of Roloff's vitality classes (Roloff, 1987, 1988, 1989).
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