Assessing the Guidelines for Pre-Harvest Clearing Operations of Understory in First Thinnings: Preliminary Results from Stora Enso in Finland

The objective of this study was to analyze forest industry professionals’ opinions of the utility of pre-clearance work prior to the first-thinning operations. A total of 153 interviews were conducted with three groups of professionals (forest machine entrepreneurs, harvester operators and logging officers) with a response rate of 80%. In general, the respondents agreed that the occurrence of understory would hinder the cutting work if the softwood tree understory density exceeded 1,152 trees/ha and a height of 1.42 m. The corresponding values for broadleaved trees were 1,669 trees/ha and a height of 1.86 m. The respondents stated that trees eligible for logging should be pre-cleared within a circular area with a mean radius of 1.24 m, and the stump height of cleared trees should not exceed 10.8 cm. In intermediate areas (i.e., outside of the circular areas) understory trees exceeding a height of 1.96 m should be pre-cleared. Pre-harvest clearing should be conducted, on average, 9.2 months prior to the logging operation. The results indicated significant differences between the opinions of the respondents concerning the understory density, the height that would hinder cutting and the most convenient pre-harvest clearing method. As a result of this research, pre-clearance guidelines, based on the best-practice knowledge of the professionals, was launched at Stora Enso company in Finland. Because the study results were based on subjective knowledge, they should be validated by long-term empirical data collection and continuing analysis of the effect of understory trees on the efficiency of a forest machine operator.