Biological, chemical and mechanical characteristics of "Wulstholz" as a response to mechanical stress in living trees of Picea abies [L.] Karst.

In the present study, the biological, chemical and mechanical wood properti es of "Wulstholz" as a response to mechanical stress of spruce trees (Picea abies [L.] Karst.) were investigated. "Wulstholz" is formed locally on the compression side of overstressed tree trunks after slip planes were initia ted. It is characterized by an increased xylem production leading to bulges . The S2-layers of "Wulstholz"-tracheids are thicker than the corresponding cell wall layers in normal wood, and the cell lumen diameter is significan tly reduced. The tracheid length decreases gradually from an average of 4 m m to 2.5 mm compared to normal wood, and the tracheids conspicuously are sh ifted against each other longitudinally. "Wulstholz" contains a higher conc entration of lignin than normal wood, whereas the concentration of glucose in the hydrolysates is reduced. The hemicelluloses-concentration, particula rly the mannose-content, is significantly higher compared to normal wood. T he compression strength and the modulus of elasticity, despite a higher den sity, are significantly reduced in "Wulstholz" in comparison to normal wood . But due to the specific anatomical and chemical properties, "Wulstholz"-t racheids can be deformed and compressed considerably without fracturing. Th e investigations demonstrate that "Wulstholz" can restabilize wind-exposed trees.