A method to evaluate needs and efficiency of formative pruning of fast-growing broad-leaved trees and results of an annual pruning

The aim of this study was to characterize the form of high-value broad-leaved trees objectively and easily in order to quantify how they need to be pruned to obtain a straight cylindrical bole. We also followed the evolution of the tree form with and without pruning. For this purpose, we devised a rating system based on form defects, that is, all secondary shoots borne by the main stem that could durably affect its straightness and (or) cylindrical form, and their seriousness, i.e., degree and persistence of the deformations they produce on the main stem. Using this system, we describe wild cherry (Prunus avium L.), sycamore (Acer pseudoplatanus L.), and ash (Fraxinus excelsior L.) in agroforestry plots. Most of the trees were pruned yearly, while some were left unpruned as controls and to monitor the natural evolution of form defects. We found that the method allows the species to be classified for their pruning needs in terms of two parameters: the seriousness of the most frequent defect(s) and the number of defects added each year to the tree. We show how these criteria can be used to design appropriate pruning strategies according to species and to evaluate labor time. Some ways to improve the description method are proposed. The results of the annual formative pruning applied to trees are also reported and discussed.