Extent and severity of damages caused to spruce roundwood by harvesting heads in standard versus debarking configurations
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Stump-site debarking has undergone a considerable shift from being common practice during the 1960s–1980s to now being almost exclusively used in eucalyptus plantations. By removing bark at the stump site, a high level of nutrients remains in the stand, and the debarked logs are less prone to act as a breeding environment for insects. With these two key advantages in mind, there has been a recent surge to adapt common harvesting heads so that they may be used for stump-site debarking of species other than eucalyptus. This study aimed to determine whether stump-site debarking affects the frequency, severity, and type of stem damage to Norway spruce (Picea abies [L.] Karst.) trees. Two harvesting heads (parallel and triangular-closing designs) were alternately operated in standard (non-debarking) and debarking configuration during winter and summer, all rest remaining equal. Damages were classified as either Type I or Type II, the former representing a depression of the wood surface caused by punctual or linear penetration of roller studs or splines and the latter referring to a larger-area gouge (fiber tear) resulting from roller slip or the delimbing knives cutting into the wood, often in combination. Results indicate that Type I Damages were significantly deeper under standard configuration (8.7 mm) than under debarking configuration (6.7 mm). Regarding Type II Damages, significantly longer damages (average of 238 cm), were caused by the triangular-closing head in debarking configuration as compared to damages caused with the standard configuration (69 cm). These results indicate that Type I Damages, under the tested conditions, are less severe with the debarking configurations but that Type II Damages could be problematic when considering the length of the gouges, as compared to standard configurations.
KeywordsDebarking heads Delimbing knives Feed rollers Harvesters Wood damage Softwood
The foundation of this work was derived from the Bachelor thesis of Mr. Andreas Schätzlein and the Master thesis of Mr. Florian Schramm. Technical assistance with field and laboratory analyses was kindly provided by Mr. Michael Miesl and Mr. Joachim B. Heppelmann. The authors also extent gratitude to the entrepreneurs and machine operators that participated in the study.
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