Low cost prediction of time consumption for pre-commercial thinning in Finland

Abstract

The time consumption (TC) of pre-commercial thinning (PCT) varies greatly among sites, stands and forest workers. The TC in PCT is usually estimated by field-assessed work difficulty factors. In this study, a linear mixed model for the TC in PCT was prepared by utilizing forest resources data (FRD). The modelling data included 11 848 and validation data included 3035 worksites with TC information recorded by forest workers within the period of 2008–2018. The worksites represented a range of site and stand conditions across a broad geographical area in Finland. Site and stand characteristics and previous management logically explained the TC in PCT. The more fertile the site, the more working time was needed in PCT. On sites of medium fertility, TC in the initial PCT increased with stand age by 0.5 h ha yr. Site wetness increased the TC. PCT in summer was more time consuming than in spring. Small areas were more time consuming to PCT per hectare than larger ones. The between-forest worker variation involved in the TC was as high as 35% of the variation unexplained by the TC model. The coefficient of determination in validation data was 19.3%, RMSE 4.75 h ha and bias –1.6%. The TC model based on FRD was slightly less precise than the one based on field-assessed work difficulty factors (removal quantity and type and terrain difficulty): RMSE 4.9 h ha vs. 4.1 h ha (52% vs. 43%). The TC model could be connected to forest information systems where it would facilitate the predictions of the labour costs of PCT without field-assessing work difficulty factors.–1–1–1–1–1

Cost-efficient pre-commercial thinning: effects of method and season of early cleaning

“…We also found that the time consumption of EC depended on the elevation changes (H3b) and wetness of a site (H3c). Similar findings have previously been observed with elevation changes in Hämäläinen and Kaila (1983), and with wetness in Uotila et al (2020).…”

“…Depending on the cleaning method, the seasonal timing of EC could contribute to worktime consumption fluctuations of between 27 and 30%. Uotila et al (2020) found a similar difference in worktime fluctuations between seasons in cross-sectional data. In small cross-sectional data, Hämäläinen and Kaila (1983) also found that PCT in the spring was more productive than in the summer.…”

“…In the spring or autumn, when broadleaved trees are leafless, conifer crop trees, as well as terrain obstacles, can be seen easily. In cross-sectional data, the cutting work was also smoother in PCT in the spring or autumn than the summer (Uotila et al 2020). However, no controlled treatments confirm this finding.…”

“…In addition to the establishment of new seedlings, wetness increases the sprouting ability of broadleaves (Mikola 1942). Uotila et al (2020) demonstrated that worktime consumption in PCT increased with increased site wetness in cross-sectional data. However, the effect of site wetness on the time consumption of PCT has not been studied in controlled areas with precise worktime consumptions.…”

“…One of the key site-specific contributors to the establishment of broadleaves seems to be the wetness of the site (Uotila et al 2014(Uotila et al , 2020. In addition to the establishment of new seedlings, wetness increases the sprouting ability of broadleaves (Mikola 1942).…”