Date of Award


Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Forest Resources


Robert W. Rice

Second Committee Member

Andrew F. Egan

Third Committee Member

Jeff Benjamin


An empirical time study was conducted to compare productivity and cost (stump to truck), effects on the residual trees and on the soil of four yarding methods - a forwarder following an in-woods processor, and a farm tractor, bulldozer, and rubber- tired cable skidder following manual felling - in a group selection harvest of a mixed hardwood stand in Maine.

A sensitivity analysis was applied to study differences between yarding machines costs in two different scenarios, one for old machines and other for new machines. Results indicated that the total machine cost and yarding cost for old machines were lower than the new machines. For old machines, the yarding cost was lowest for the forwarder method ($2.52/m3) and highest for the skidder method ($5.21/m3). In the case of new machines, the yarding cost per unit was lowest for the forwarder method ($5.67 m3) and highest for the skidder method ($14.80 m3).

The farm tractor, bulldozer and skidder methods were associated with greater numbers of damaged trees per meter of yarding trail length. The skidder method resulted in the highest number of trees with bole damage, while forwarder caused the lowest. The tractor method resulted in the most root damage and the forwarder method resulted in the largest trail width. In addition, the bulldozer method resulted in the largest number of damaged boles per 100 m2 of near trail space, while the forwarder method was associated with smallest number of damaged boles per 100 m2.

The bulldozer and forwarder systems were associated with the highest and lowest soil bulk density measured in machine tracks, in trail centerlines, and harvested group selection units vs. adjacent untrafficked areas, respectively.

While, overall, the forwarder was considerably more productive, caused only slightly more residual stand damage, less soil compaction, and was less expensive on a cost per cubic meter basis. However, it's larger size, wider turning radius, and high capital investment, especially when coupled with an in-woods processor, and moving costs suggest caution when considering a forwarder, especially for the harvest of relatively small nonindustrial private forests characteristic of much of the region.