Examining Methodologies to Assess Abrasion in Tree Crowns

New methodologies were explored to determine if crown abrasion affects shoot elongation of preformed and sustained growth form species during stand development. Bud growth form differences can influence which species’ buds are abraded or broken upon impact with adjoining crowns affecting crown growth. Analysis of branch elongation, apical bud toughness and tree sway were investigated in this study. Branch elongation was measured on crowns where growth was inhibited by crowns of adjacent trees and on crowns where growth is uninhibited. Bud mass was also measured. Bud toughness by species’ shoot growth form was evaluated using a pendulum impact tester for the dormant and growing seasons. Crown movement was assessed by using 3-axial accelerometers in outermost points of crowns. Accelerometers logged the movement of branches in the tree crown over a period of time and were evaluated using local wind data during leaf-off and leaf-on. By using both the crown sway acceleration and associated bud toughness and mass data, possible force was calculated to evaluate the influence of crown friction. Branch elongation was greater for most species sampled on the exterior of the stand. Preformed buds are generally tougher in the dormant and growing season than sustained growth buds. Acceleration from wind gusts increased more rapidly as wind speed intensifies in the growing season when leaves are on the trees. Under the conditions of this study, more crown damage can occur with lower wind speeds during leaf-on. Crown friction and abrasion are contributors to crown and stand development patterns in mixed species stands, often allowing species with determinate shoot growth to stratify above trees with indeterminate growth.