Influence of the Tree Decay Duration on Mechanical Stability of Norway Spruce Wood (Picea abies (L.) Karst.)

Abstract

Wood properties have an influence on the safety around the tree itself as well as on actual possibilities of using wood. The article focuses on the wood properties of the Norway spruce (Picea abies (L.) Karst.) in reference to the time since the tree has decayed. The study was conducted among mature tree stands of spruce in Białowieża Forest, where over the last 10 years there has been a weakening of spruce tree stands due to water deficiency which has contributed to the gradation of the European spruce bark beetle (Ips typographus). The study focused on spruce wood of living and healthy specimens as well as the wood of standing trees which has decayed between one and five years before the sample was collected. The findings indicate a gradual decrease in wood properties as time passed since the physiological decay of the tree. Significant differences in the decrease of mechanical wood properties have been observed in trees which had been decayed for 3 years and they should be considered life and health hazard for people and animals.

What Happens to Wood after a Tree Is Attacked by a Bark Beetle?

“…If white rot and brown rot fungi cause a wood mass loss, as the wood density decreases, so do its mechanical properties [45]. This effect was shown in research [21], where the mechanical properties gradually decreased with increasing duration of degradation processes due to fungi. However, Kržišnik et al [22] in their research compared only the effect of blue-stained wood on its properties; the differences in the density of control and blue-stained samples were not statistically significant.…”

“…In the case of the mechanical properties of bark beetle-infested wood, changes in these properties over a longer time horizon (i.e., over a period of several years) may be caused by the action of fungi. In their study, Jelonek et al [21] dealt with changes in the mechanical properties of bark beetle-infested Norway spruce wood after the beetles had left the stump for several years. Research has shown a declining trend in average values of modulus of rupture (MOR), as well as modulus of elasticity (MOE).…”

“…A statistically significant decrease was demonstrated only three years after tree infestation, where after three years the MOR decreased from 89.85 MPa to 68.93 MPa and the MOE decreased from 10.679 GPa to 7.269 GPa. Based on these results, the authors stated that stands that have been infested with bark beetles and fungi for three or more years are potentially dangerous for tourists in forests and further suggested that the wood of these trees can be further used in industry for up to two years after bark beetle infestation [21]. Norway spruce wood still meets the standard required strength properties for timber after the first or second year after infestation by bark beetle and can be used for construction purposes.…”

“…However, because of the development of wood-decaying and wood-staining fungi, the time for which wood from bark beetle-infested trees can be used is automatically limited in time. Jelonek et al [21] suggested that spruce wood from stands in Białowie ża Forest can be industrially used within two years of bark beetle infestation. However, the degree of fungal infestation of wood depends on wood moisture, which is strongly affected by local climatic conditions.…”

“…It is obvious that in the region where certain tree species are most affected by bark beetles, the properties of the wood of these tree species are investigated, and in other regions where bark beetles attack other tree species, the properties of those other tree species are investigated. For these reasons, research in Central and Eastern Europe deals mainly with spruce (Picea abies, Picea obovata Ledeb) [21][22][23] and in North America mainly pine (Pinus ponderosa Douglas ex C.Lawson, Pinus taeda L.) [24][25][26][27].…”