Aspects of precommercial thinning

• Main Author: Fällman, Karin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2005
• Subjects: Not in use; please see Agris categories; Northern Sweden
• Online Access: https://pub.epsilon.slu.se/912/; https://pub.epsilon.slu.se/912/1/avhandling_KF.pdf

Precommercial thinning (PCT) in young forests in Sweden has been an important part of the silvicultural system since the 1950s. However, the annual area treated with PCT has decreased since the 1990s. At the same time the relative cost of PCT compared to both harvesting and regeneration has increased. The objectives of the work underlying this thesis were to examine the attitudes to PCT among private forest owners, and to evaluate alternative and potentially more cost-effective methods for PCT. The private forest owners’ attitudes to PCT were assessed by a questionnaire, which showed that they were interested in their forest and wanted to perform PCT. However, it was often neglected or postponed, usually because lack of time and secondly the cost of the operation. The forest owners seem to have many objectives for their forestry in addition to financial considerations. There were also significant differences between male and female forest owners, for instance the female forest owners claimed to have less knowledge regarding forestry and PCT-issues than male forest owners. Several alternative PCT-methods were evaluated by field experiments, all with a randomised complete block design. One study focused on PCT through topping i.e. cutting the secondary stems at a higher level above ground than in traditional PCT, in a naturally regenerated birch (Betula)-dominated stand. Topping proved to be an attractive alternative, since the main stems in the topped treatments grew as well as the main stems on traditionally treated plots. Furthermore, it gave better results in terms of stem and branch properties. A point cleaning experiment (cutting competing trees within a certain radius of each main stem) in a planted Scots pine (Pinus sylvestris) stand showed that a single point cleaning operation gave worse results in terms of growth and stem quality variables, then a single traditional PCT. The findings are consistent with traditional recommendations to perform a subsequent PCT operation after point cleaning. The last study examined the effects of several variants of PCT, with differing tree selection criteria, in a typical planted Scots pine young stand in northern Sweden. The results showed that PCT was a profitable measure even if all planted stems were removed, raising the possibility that silvicultural cost-effectiveness could be optimised by retaining some of the natural regeneration and reducing the number of seedlings that are planted accordingly.