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Open AccessArticle

Effect of Bark-Stripping on Mechanical Stability of Norway Spruce

1
Latvian State Forest Research Institute ‘Silava’, Forest Tree Breeding and Adaptation, 111 Rigas street, LV-2169 Salaspils, Latvia
2
University of Applied Sciences and Arts, Faculty of Resource Mananagement, Büsgenweg 1a, 37077 Göttingen, Germany
*
Author to whom correspondence should be addressed.
Forests 2020, 11(3), 357; https://doi.org/10.3390/f11030357
Received: 28 February 2020 / Revised: 17 March 2020 / Accepted: 20 March 2020 / Published: 21 March 2020
(This article belongs to the Special Issue Natural Disturbance Dynamics Analysis for Forest Ecosystem Management)
The increasing effects of storms are considered the main abiotic disturbance affecting forest ecosystems. Bark-stripping damage from the growing ungulate populations, in turn, are among the main biotic risks, which might burden the stability of trees and stands. Therefore, the aim of our study is to estimate the effect of cervid bark-stripping on the mechanical stability of Norway spruce using a static tree-pulling test. For the test, eight damaged and 11 undamaged canopy trees were selected from a 40-year old stand (plantation with 1 × 3 m spacing) growing on mineral mesotrophic soil. The selected trees were bark-stripped 7–9 years prior to the experiment. Uprooting was the most frequent type of failure; only two trees broke at the stem. For the damaged trees, the resistance to pulling was significantly reduced (p-value < 0.001). Stem volume and presence of bark-stripping were the best linear predictors of the basal bending moment at the primary failure (irreversible deformation of wood structure) and secondary failure (collapse of the tree). A significant (p-value < 0.001) interaction between stem–wood volume and presence of bark-stripping was observed for primary failure, indicating a size-dependent reduction of stability of the damaged trees. Such interaction lacked significance (p-value = 0.43) for the secondary failure (mostly uprooting), indicating a decrease in stability irrespectively of tree size. Somewhat surprisingly, the decrease in the overall mechanical stability of the bark-stripped trees appeared not to be related to a direct reduction of the strength of the stems, but rather to physiological effects such as altered allocation of carbon, increased drought stress because of interfered hydraulic conductance of wood, or secondary infestation. The reduced stability also suggests that bark-stripped trees can act as the weak spots decreasing the collective stability of stands in the long term, thus increasing the susceptibility to storms. View Full-Text
Keywords: Picea abies; cervids; pulling test; wildlife damage; uprooting; wind damage Picea abies; cervids; pulling test; wildlife damage; uprooting; wind damage
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Krisans, O.; Saleniece, R.; Rust, S.; Elferts, D.; Kapostins, R.; Jansons, A.; Matisons, R. Effect of Bark-Stripping on Mechanical Stability of Norway Spruce. Forests 2020, 11, 357.

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