Freezing-Rain- and Snow-Induced Bending and Recovery of Birch in Young Hemiboreal Stands

Abstract

Damage to birch (Betula spp.) trees after an extensive freezing rain and snowing event was assessed in hemiboreal stands aged from 2 to 30 years. Tree diameter, height, and stem bending were measured, stand age and time of thinning were obtained from inventory data, and the relative distance from a sample plot to the nearest adjacent stand was calculated. Stem bending was remeasured after one and three growing seasons to assess tree recovery potential. Stem damage was found for 31.0% of birch trees, with 93.7% of them bent. The probability of being bent was increased (p < 0.001) for trees of a lower social position within the stand and was higher in stands with larger growing stock (p < 0.05) and relative distance to the adjacent stand (p < 0.001). The probability of damage was significantly (p < 0.05) affected by recent tree removal, with decreasing susceptibility until five to six years after the last thinning. After one growing season, 31.3% of trees had less intense bending, and 8.2% had more intense bending compared with the initial assessment. A tree’s ability to recover stem bending to less than 15° was linked (p < 0.001) to its damage intensity, whereas the magnitude of the recovery was affected by both the damage intensity and the relative diameter (p < 0.001 and p < 0.01, respectively). The results indicate the importance of timely thinning that maintains a stable tree form and is performed considering the spatial planning of heterogeneity in the heights of adjacent stands to avoid damage at a young age.