Determinants of tree sway frequency in temperate deciduous forests of the Northeast United States

Trees are the most common cause of utility damage and power outages during storms in the northeastern United States. Previous studies on tree sway and risk of wind-throw have largely been conducted in heavily managed coniferous stands, while relatively little is known for northeastern mixed temperate deciduous forests. The objective of this study was to identify factors determining tree sway frequency in northeastern forests. To this end, we monitored the fundamental vibrational frequency (FVF) of 39 trees representing nine different tree species on 3 sites in southern New England over one year, and regressed those measurements against 25 potential predictor variables. Results showed that four predictors were significant across all sites and species. The height to the base of the live crown, as well as tree slenderness, defined as diameter-at-breast height divided by tree height squared (DBH center dot H-2), were significant. Previous studies on coniferous trees support the significance of slenderness. The other two predictors accounted for the presence or absence of foliage and whether temperatures were above or below freezing. These findings highlight the relationship of tree shape and FVF, and indicate the relationship is similar between excurrent (e.g., coniferous) and decurrent (e.g., northeastern broadleaves) species when they are grown in closed canopy situations, regardless of species mix or location. Given this relationship, and our understanding of the relationship of FVF to wind-firmness, forest management practices designed to effect slenderness and tree shape have the potential to increase wind-firmness and reduce tree-related storm damage to utility infrastructure.