The objective of this research was to compare the performance of a small (92 horsepower) grapple skidder with that of a large (185 horsepower) grapple skidder in corridor thinning applications in southern pine plantations. Comparisons included (1) time and production, (2) residual stand damage, (3) soil compaction, (4) cost, and (5) the impact of tree size on productivity. The large grapple skidder was found to be (1) more productive, (2) associated with slightly more residual stand damage, (3) associated with less soil compaction, (4) less expensive on a cost per ton of production basis, and (5) more sensitive to variation in tree size than was the small grapple skidder. The results of this research suggests that large grapple skidders are capable of excellent performance in corridor thinning of southern pine plantations. / Master of Science

Study objectives were 1) to identify successful mechanized thinning and prelogging systems currently operating in the South, 2) to document system characteristics contributing to their success, and 3) to determine which factors affect levels of residual stand damage from thinning operations. The first objective was accomplished by a South-wide industry survey. The latter two objectives were realized through in-depth field studies of selected systems. The survey indicated three system types used on small-tree operations. Feller-buncher/grapple skidder/hydraulic loader systems comprised the majority of operations described. No predictable relationships between system type and tree size were apparent, so examples of the most common type were chosen for detailed study. Three thinning and three prelogging systems were selected, covering a range of ownership patterns and physiographic regions. Information was obtained pertaining to each system's application; crew organization and background; equipment spread and descriptions; performance; and special considerations provided by landowners or timber buyers. Residual stand damage cruises were conducted at each thinning operation's job site. Case-by-case analyses and comparisons between systems based on economic and productivity criteria resulted in a number of recommendations. These suggestions represented system characteristics seen as keys to the success of the operations studied. The recommendations focused on desirable contractor and crew characteristics, equipment selection decisions, job layout, minimization of residual stand damage, and methods of landowner/timber buyer support for small-tree operations. / M.S.