How Bark Beetle Attack Changes the Tensile and Compressive Strength of Spruce Wood (Picea abies (L.) H. Karst.)

Abstract

Since 2014, forestry in the Czech Republic has been significantly affected by a bark beetle outbreak. The volume of infested trees has exceeded processing capacity and dead standing spruce (Picea abies) remain in the forest stands, even for several years. What should be done with this bark beetle wood? Is it necessary to harvest it in order to preserve the basic mechanical and physical properties? Is it possible to store it under standard conditions, or what happens to it when it is “stored” upright in the forest? These are issues that interested forest owners when wood prices were falling to a minimum (i.e., in 2018–2019) but also today, when the prices of quality wood in Central European conditions are rising sharply. To answer these questions, we found out how some of the mechanical properties of wood change in dead, bark beetle-infested trees. Five groups of spruce wood were harvested. Each of these groups was left upright in the forest for a specified period of time after bark beetle infestation, and one group was classified as a reference group (uninfested trees). Subsequently, we discovered what changes occurred in tensile and compressive strength depending on the time left in the stand and the distance from the center of the trunk. When selecting samples, we eliminated differences between individual trees using a CT scanning technique, which allowed us to separate samples, especially with different widths of annual rings and other variations that were not caused by bark beetle. The results showed the effect of log age and radial position in the trunk on tensile and compressive strength. The values for tensile strength in 3-year infested trees decreased compared to uninfested trees by 14% (from 93.815 MPa to 80.709 MPa); the values for compressive strength then decreased between the same samples by up to 25.6% (from 46.144 MPa to 34.318 MPa). A significant decrease in values for compressive strength was observed in the edges of the trunks, with 44.332 MPa measured in uninfested trees and only 29.750 MPa in 3-year infested trees (a decrease of 32.9%). The results suggest that the use of central timber from bark beetle-infested trees without the presence of moulds and fungi should not be problematic for construction purposes.

Differential Energy Criterion of Brittle Fracture as a Criterion for Wood’s Transition to the Plastic Deformation Stage

“…The use of acoustic emission methods [48,49] and other modern methods [11,50,51] contributes to a better understanding of the physical aspects of brittle fracture and plasticity of wood, as well as other materials at various stages of their deformation [52,53]. The input data for calculations according to the proposed model uses the concept of stiffness but not the modulus of elasticity and other physical constants of the material, so the modeling technique (under some constraints) is indifferent to the defects and features of wood, which, considered as a structure in accordance with [4].…”

Computed Tomography as a Tool for Quantification and Classification of Roundwood—Case Study

“…In Lowe et al the authors analyze the effect of infestation of spruce wood by common insects on the mechanical properties of such wood. The computed tomography technique was used to correctly assess the extent of damage and cut out the test specimens [39]. Authors Boscaini et al represent a new method for efficient localization of defects in CT scans of logs of valuable wood assortments [40].…”

Towards an Integrated Approach to Wildfire Risk Assessment: When, Where, What and How May the Landscapes Burn

“…Seidl et al [272] estimated that climate change will increase the damage from windstorms, bark beetle (Ips typographus) attacks, and wildfires up to +0.91× 10 6 m 3 of timber per year until 2030. However, in the last decades, massive bark beetle outbreaks and wildfires have already occurred at an unprecedented scale and in unusual regions [273][274][275]. While fire-related disturbances barely occurred in Central Europe from 1986 to 2016 [276], wildfires have started to become an emerging threat [277].…”