COMPARISON OF 2 THINNING SYSTEMS .2. STAND AND SITE IMPACTS

During the winter of 1991, a side-by-side comparison was made between two popular thinning systems: a feller-buncher, grapple skidder, loade r/slasher system and a harvester, forwarder system. A first commercial thinning was conducted in an 18-year-old loblolly pine stand. Test ar eas were cruised prior to thinning and remeasured after operations wer e completed. The target basal area per acre was successfully met by th e forwarder system but not by the skidder system. Individual tree dama ge was recorded during plot remeasurement. The skidder system scarred 25 trees per acre versus 10 trees per acre with the forwarder system. Ground disturbance was recorded by two samples. One focused on skidder and forwarder trails where the area in various levels of disturbance was measured along with soil bulk density. The other sample was a syst ematic survey covering the entire study area and gave an overall sampl e of ground disturbance levels. The skidder system had more disturbed area and compacted the soil more than the forwarder system.