Timber construction in torrent control with Norway spruce and silver fir: wood quality and colonization with decay fungi during the first years
2014
Rickli, C., Eidgenoessische Forschungsanstalt für Wald, Schnee und Landschaft WSL, Birmensdorf (Switzerland) | Graf, F.
Timber is widely used for protection measures in torrent control. However, life span of woody constructions such as timber check dams is limited due to fungal decay. Only sparse scientific information is available on the long-term behaviour of timber structures and the colonisation with decay fungi. Related to this, in practice a controversial discussion has been going on if either Norway spruce (Picea abies) or silver fir (Abies alba) is more enduring and if bark removal increases resistance against fungal decay. In order to going into this matter, a series of 15 timber check dams built in 1996/1997 has been monitored. The constructions were alternatively realised with Norway spruce and silver fir, half of them each with remaining and removed bark, respectively. The scientific investigations included the documentation of colonisation with rot fungi and the identification of decayed zones with a simple practical approach as well as based on drilling resistance. Colonisation by decay fungi started three years after construction (e.g. Gloeophyllum sepiarium), two years later first parts with reduced wood resistance were detected. The protection measures were still fully functional sixteen years after construction although decay was found on all check dams but two. Wood quality was markedly better in watered sections compared to the occasionally dry lateral abutment sections, without showing clear differences in decay between logs of Norway spruce and silver fir. However, both the practical approach and the drilling resistance measurement suggest more defects on logs without bark. Further investigations and sound statistical analysis are needed to confirm the observed trends.
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