Time consumption and productivity of skidding Silver fir (Abies alba Mill.) round wood in reduced accessibility conditions: a case study in windthrow salvage logging form Romanian Carpathians

Abstract

Natural calamities (especially windthrows) may generate difficult work conditions in timber harvesting operations. When associated with the reduced accessibility conditions, the work conditions become even harder. This study investigates the time consumptions on specific work elements in timber skidding, develops time prediction models for timber skidding work elements and assesses the production rates for timber skidding in reduced accessibility stands where windthrow salvage cuttings were applied. Following a time study done for two skidders (TAF 690 OP and TAF 657) operating simultaneously in the same felling area, it has been found that, in average, in a delay free skidding cycle time, lateral winching accounted for a share of 26-33%, on-trail skidding accounted for a share of 64-71% and landing operations accounted for a share of 3%.Total delays accounted for 51% and 43% of the total work time in the case of TAF 690 OP skidder and TAF 657skidder respectively. Regression models for lateral winching (both skidders) revealed that the winching distance and the number of logs were the relevant predictors for the time consumption estimation (p<0.01), whereas in the case of on-trail skidding only the skidding distance was relevant (p<0.01). For the overall skidding operation (excluding landing operations) winching and skidding distances were found as relevant predictors (p<0.01) in case of TAF 690 OP, whereas the number of logs became an additional relevant predictor in case of TAF 657.In conditions of an average winching distance of 19.90 m and an average on-trail skidding distance of 980.32 m, the time study yielded a net production rate of 7.70 m3h-1 and a gross production rate of 3.75 m3h-1 in the case of TAF 690 OP skidder. By comparison, in the case of TAF 657 skidder, for an average winching distance of 22.86 m and an average on-trail skidding distance of 871.00 m, the net and gross production rates were of 5.61 m3h-1 and 3.20 m3h-1 respectively.