Trees and seasonal wind gust maxima in Ireland: acclimation and minimal factors of safety

Abstract

ABSTRACT Daily maximum high gust wind speeds at Dublin, Ireland over a recent 30-year period were analysed. Maximal and mean storm gusts are compared to those occurring in the growing season period of xylogenesis in relation to thigmomorphogenetic acclimation of temperate trees to their wind environment and to the maintenance of notional minimal factors of biomechanical safety against major failure in storm winds. Maximal annual gust probabilities are estimated, and the correlation between the highest mean growing season gusts and extremum storm gusts is discussed. Successful acclimation to the mean highest 5% of growing season gusts is conjectured to confer a notional minimal factor of safety against major failure – in extremum winter storm gusts – of ~4. Tree risk assessment may be improved by shifting focus from “defects” to factors of inadaptation, which preclude or compromise a tree’s ability to maintain minimal factors of safety relative to its wind environment.