The Relative Importance of Crown Position and Vigor in Determining the Growth and Mortality of Sugar Maple Trees

In northern hardwood forests, selection silviculture aims to remove low-vigor trees that are likely to die or grow slowly to increase the growth of the remaining high-vigor trees, particularly those afforded more exposure to direct light. However, few studies have quantified the relative importance of crown position and vigor in determining growth and mortality. In this article, we did so for the most common species, sugar maple (Acer saccharum Marsh.), and we quantified the difference in growth and mortality between each of four crown classes to determine whether fewer classes can be used to describe competition-related variation in growth. Our results show that mortality is primarily determined by vigor, competition reduces growth more than the defects used to assess vigor, and there is only a modest difference in growth between dominant and co-dominant trees, indicating that these two classes can be merged because they are effectively released, unlike trees that are surrounded by competitors. Based on these results, we conclude that stand improvement should not be prioritized over crown spacing, and that tree markers should release surrounded trees to whatever extent possible, including as many trees as possible and low-vigor trees where necessary.