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Silva Fennica 1926-1997
Acta Forestalia Fennica

Articles by Dirk Jaeger

Category : Research article

article id 10447, category Research article
Marian Schönauer, Stephan Hoffmann, Martin Nolte, Dirk Jaeger. (2021). Evaluation of a new pruning and tending system for young stands of Douglas fir. Silva Fennica vol. 55 no. 2 article id 10447.
Keywords: thinning; time study; Pseudotsuga menziesii; body posture; heart rate; OWAS; physical workload; young stand
Highlights: Electric pruning shears combined with workflow re-organization reduced time demand for pruning; Thinning by chainsaw was more productive than using the clearing saw Husqvarna 535FBX, which on the other hand showed lower physical workload; Overall cost savings through the use of the new system were quantified at 6%.
Abstract | Full text in HTML | Full text in PDF | Author Info

In Germany, management restrictions for Norway spruce (Picea abies (L.) H. Karst.) due to climate change lead to increasing interest in Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) as a potential substituting species. However, Douglas fir requires cost-intensive silvicultural treatments, such as periodic thinnings and, in particular, pruning. In order to improve the efficiency of such treatments, a new tending system with an adapted two-step work system was analyzed. The new system, using electric pruning shears and the backpack clearing saw Husqvarna 535FBX ‘Spacer’, was compared to the conventional three-step work system, using handsaw and chainsaw and characterized by tree selection previously conducted as an independent work step. Time and motion studies to determine productivity and costs, as well as ergonomic analysis through heart rate measurements and posture analysis were conducted. Overall, the new system was found to be more productive and to have lower costs, with 8.9 trees per scheduled system hour (4.17 € tree–1), compared to the conventional system with 8.1 trees per scheduled system hour (4.44 € tree–1). Ergonomic improvements with the new system could be mainly observed during the felling of competing trees, when the level of heart rate reserve was reduced by 9.3 percent points, compared to the conventional system. However, significant advantages in reducing unfavorable body postures expected for the ‘Spacer’ could not be confirmed. Since time savings within the new system were mainly attributed to the adaptation of workflow and the use of the electric shears during pruning, it should be considered to replace the ‘Spacer’ within the new system by light chainsaws for best results under the conditions investigated.

  • Schönauer, Department of Forest Work Science and Engineering, University of Göttingen, Göttingen/Germany E-mail: (email)
  • Hoffmann, Department of Forest Work Science and Engineering, University of Göttingen, Göttingen/Germany; School of Forestry, University of Canterbury, Christchurch/New Zealand ORCID E-mail:
  • Nolte, Forest Education Center FBZ / State Enterprise Forestry and Timber NRW, Arnsberg/Germany E-mail:
  • Jaeger, Department of Forest Work Science and Engineering, University of Göttingen, Göttingen/Germany E-mail:

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