Röjning på snö och röjning på barmark : effekter på produktivitet och kvarvarande bestånd

Sammanfattning: Approximately 4000-5000 hectares, of SCA´s forest land area in Västerbotten, are in need of pre-commercial thinning (PCT) every year. Within the management district, the areas annually treated with PCT must increase, in order to decrease the area with an urgent need for PCT. This can be done by employing more forest workers or entrepreneurs, by mechanized PCT or by an extended season for PCT. Positive experiences from a private forest owner, who started to carry out PCT when the first snow came and then continued for several months, gave an idea to investigate the possibilities to prolong the season of PCT. The purpose of this experiment was to compare PCT carried out when there was snow on the ground with PCT performed when there was no snow on the ground. The main questions addressed were dealing with the effect on the PCT productivity, the biological result and what the workers thought about performing PCT when the ground was covered with snow. The experiment was conducted in three Scots pine (Pinus sylvestris) dominated stands, which were in need of PCT through removal of deciduous trees. Within each stand, 20 plots (20'20 m) were marked out. The plots were ranked according to stand density and thereafter paired; the treatment times (winter and summer) were randomly assigned to the two plots in each pair. A time study of PCT was conducted, and two workers participated in the study. The results showed that: •no significant difference in time consumption, between PCT on snowy ground and PCT on ground with no snow, was found •the point of time for PCT did not affect the stand density after PCT •there was an interaction effect between workers and stand density; one of the workers was faster at a low stand density and the other was faster at a high stand density •stand density as well as worker and stand (structure) affected the time consumption •the mean diameter of the cut trees did not significantly affect the time consumption •in a comparison between SLA's performance prediction for motor-manual PCT and the workers time consumption did the performance prediction give a lower time consumption •the workers, who from the beginning were skeptic to perform PCT under snow conditions, afterwards changed their opinion and became more positive.