Abstract
Post-disturbance salvage logging mitigates economic loss after windthrow, and the value of salvaged timber is strongly linked to its quality and dimensions. We studied the occurrence of wind-induced damage of aspen in the hemiboreal forests of Latvia based on data from the National Forest Inventory and additional measurements. Individual tree data from three re-measurement periods were linked to follow a tree condition (live, broken, uprooted) and to link tree characteristics to a respective snag. Three linear models were developed to assess factors affecting the snapping height. An assortment outcome was calculated for undamaged and salvaged trees using the bucking algorithm, and timber value was calculated at three price levels. Wind-induced damage occurred for 3.4–3.6% of aspen trees, and among these, 45.8–46.6% were broken. The mean height of the broken trees was 27.3 ± 0.9 m, and it was significantly higher (both p < 0.01) compared to the height of undamaged and uprooted trees. The tested models indicated tree height as the main explanatory variable for relative snapping height, with higher trees having a lower point of the stem breakage. The other significant factor was the forest type group, indicating that trees growing on dry mineral soils had lower relative snapping height than trees growing on drained mineral soils. Stem breakage significantly (p < 0.001) reduced the volume of assortments, as compared to the volume of undamaged trees. Relative volume loss of sawlogs showed a logarithmic trend with a steep increase up to snapping height of 6 m, and it correlated tightly (r = 0.83, p < 0.001) with relative value loss of the total stem. Timber value loss had a strong, positive relation to tree diameter at breast height and fluctuated by 0.4% among different price levels. The mean volume reduction was 37.7% for sawlogs, 11.0% for pallet blocks, and 8.9% for technological wood.
Highlights
European forests encounter increased severity and frequency of natural disturbances [1]that have substantial negative socio-economic consequences [2,3], especially in regions that are highly dependent on the forest sector
Stem breakage occurs at the point where opposite sides of its cross-section experience compressive and tensile stresses that exceed the resistance of stem fibers [16]
The other significant factor was the forest type group, indicating that trees growing on dry mineral soils had lower relative snapping height than trees growing on drained mineral soils (Figure 2b)
Summary
European forests encounter increased severity and frequency of natural disturbances [1]that have substantial negative socio-economic consequences [2,3], especially in regions that are highly dependent on the forest sector. European forests encounter increased severity and frequency of natural disturbances [1]. The wind is among the key disturbance agents [4,5], accounting for about half of the recorded damage in European forests over the last two centuries [1]. Post-disturbance salvage logging, i.e., removal of fallen and damaged trees, is conventionally done to mitigate economic loss after windthrow [11,12]. Revenue from salvage logging is usually substantially lower than could be obtained from undamaged trees, as storms affect forests that have not reached target cutting age/dimensions, and stem damage limits the possibility of obtaining the highest-graded assortments. Breakage has the strongest negative economic effect on revenue [15]. In real trees, deviations of leaning or non-circular stems, crown shape asymmetries, stem defects, and other individual traits occur, which makes the presumption of uniform wood properties infeasible
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