Branch Elongation, Bud Durability, and Wind-Generated Crown Movement Associated with Crown Abrasion in Deciduous Trees

Abstract

Trees that grow in close proximity to other trees are subject to crown and branch abrasion, causing mechanical injury. The loss of branch tips and buds through abrasion can affect the architecture and growth of tree crowns. This research quantifies the impacts of crown abrasion between neighboring trees of several deciduous species and how crown abrasion may influence stand dynamics. Tree interactions were evaluated during the dormant and growing seasons to determine how wind-generated movement affects crowns under foliated and un-foliated conditions. Branch elongation was measured in tree crowns where growth was both inhibited and uninhibited by adjacent trees. Bud durability was evaluated by growing season for species with determinate and indeterminate shoot growth forms using a pendulum impact tester. Crown movement during wind events was assessed by using three-axial accelerometers in the outermost points of tree crowns. Accelerometers logged the movement of branches in the tree crown. By using both the crown sway acceleration and associated bud durability and mass data, the possible force necessary to break or abrade buds and branches was calculated at different wind speeds. Branch elongation was greater for most species on the exposed side of the crown that was not affected by adjacent trees. Preformed buds from the determinate growth form were determined to have greater durability than sustained growth or indeterminant buds. Acceleration from wind gusts increased more rapidly as wind speed intensified in the growing season when leaves were on the tree than in the dormant season. This research suggests that crown abrasion contributes to the development of mixed species stands by reducing crown size and growth therefore allowing slower-growing species with determinant growth to stratify above faster growing trees with indeterminant growth.