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The aim of the study is to compare the forwarder grapple with a tilt function (tilt grapple) and the standard forwarder grapple, as well as to evaluate advantages and disadvantages of these grapples in thinning. Trials are conducted in 4 coniferous stands in North Western part of Latvia in state forests managed by the Joint stock company “Latvia State forests” (LSF). Two working methods are compared in the study. In the first method the forwarder is equipped with a grapple with the tilt mechanism and in the second method the standard grapple is used. Both methods are tested in the same stands. John Deere 810 D forwarder is used as a base machine. Forwarding is carried out by two operators with similar work experience in thinnings, however, with no experience with tilt grapples, and each operator performed with both work methods. A time study is carried out during the trials, the amount of extracted timber is accounted and damages of remaining trees are estimated. According to the study results consumption of productive work time to transport 1 m of logs to roadside is by 3 % smaller, if the tilt grapple is used, however, the difference is not significant. The impact of the operator on productivity is not statistically significant, too. According to the results of the study, the forwarding cost under conditions typical to the trials is 5.9 EUR·m, if tilt grapple is used, and 7.4 EUR·m, if the standard grapple is used. The amount of mechanical damages of remaining trees is smaller by 21 % in areas where tilt grapple is used. The total number of damaged trees in control sites (forwarding with standard grapple) conforms with average data in forests managed by LSF.

Increase of forwarding productivity and reduction of tree damages in thinning by use of loading grapple with tilt function