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