Effects of a selective thinning on wind loading in a naturally regenerated balsam fir stand

Abstract

Recent trends in forest management promote the development of stands with a complex structure involving the use of partial cuts of various types. Partial cuts can increase the risk of wind damage but prior research on wind damage has largely focused on simple stand types and new modeling approaches are needed for these more complex stands. The present study looked at how the wind loading distribution in a naturally regenerated balsam fir (Abies balsamea (L.) Mill.) stand is modified by a local selective thinning. Two anemometers placed at canopy height and 2/3 canopy height, and strain gauges attached to the trunks of balsam fir trees allowed us to measure the wind-induced turning moments experienced by a sample of trees. A localized thinning was implemented around 2/3 of the sample trees in the second year of the experiment. Competing trees were removed within a 3.5 m radius of residual trees. Results show a dominant effect of the selective thinning at the tree scale but with an additional effect at the stand scale. The stand scale effect is likely linked to a change in wind profile within the canopy. A distance-independent competition index was useful in explaining the wind load distribution within the stand. Trees experiencing more competition were exposed to the largest increase of turning moment after the selective thinning. This study confirms the potential of competition indices for wind damage modeling in heterogeneous stands.