“Harvesting Small Trees for Bio-Energy”, and was presented during the 34th Council on Forest Engineering Annual Meeting, Quebec City, Quebec, Canada, June 2011. The article was authored by John Klepac, Bob Rummer and Jason Thompson, all of the US Forest Service. The operation studied consisted of 3-wheeled and 4-wheeled disc-saw feller bunchers, grapple skidders and whole-tree chippers. The research was carried out across various sites consisting of pine and hardwoods. Thinning consisted of removing the fifth row as well as selected trees in the stand. Stand density ranged from 1699 trees per hectare to 4202 trees per hectare. The combined mean DBH of all sites was 10.9 cm, with pine being 12.9 cm and the hardwood 6.9 cm. The stands ranged from 199 to 524 green tonnes per hectare.
Thinning productivity for the felling bunchers ranged between 15.5 and 20.6 tonnes per PMH (Productive Machine Hour) for thinning, and was 67.2 tonnes per PMH for clearfelling. Assuming a standard machine rate of $ 100 per PMH, the felling cost was $ 5.50 per tonne in thinning and $ 1.43 per tonne in clearfelling.
Skidder productivity averaged 26.6 tonnes per PMH with an average skidding distance of 340 m and payload of 3.1 tonnes (69.3 trees). Assuming a standard machine rate of $ 100 per PMH, skidding costs for both thinning and clearfelling was approximately $ 3.30 per tonne. Therefore, large cost reductions can be obtained by using clearfelled timber for bio-energy as opposed to thinning.
For a more complete account of the research, please access the article at http://www.srs.fs.usda.gov/pubs/ja/2011/ja_2011_klepac_001.pdf
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