Branch mass allocation increases wind throw risk for Fagus grandifolia

Abstract

AbstractWind is a major force of disturbance in forests throughout the world, causing trees to break or uproot and topple over, depending on tree morphology and growing conditions. Previous research has suggested that trees that are more massive or which have lower height–diameter ratios are less at risk to wind throw, but the influence of crown size and branching architecture has been more difficult to elucidate. In general, there has been more research on coniferous trees, which have more simplified and symmetrical crown structures, relative to broad-leaved, deciduous trees. Here, we modelled the probability of wind throw for American beech (Fagus grandifolia Ehrh.), a broad-leaved, deciduous species common in the eastern USA, for trees covering a broad range of sizes (5.6–79.8 cm, diameter at breast height), in two nearby stands, in an experimental forest in southwestern Michigan, USA, where a wind event occurred. After a major blow-down of more than 200 trees in one of the stands, a subset of trees was destructively sampled after the storm. Analysis of the characteristics of the wind-thrown versus non-wind-thrown, residual trees, indicated that a very large branch fraction of total tree mass was a key factor leading to toppling of the wind-thrown trees. This study provides new empirical data related to the characteristics of wind-thrown American beech trees and suggests a potentially important role for branch to stem mass ratios as a predictor of wind throw risk for this species and possibly other broad-leaved, deciduous tree species, with a deliquescent branching architecture.