THE IMPACT OF DIFFERENT CARRIAGES ON SOIL AND ROOTS - WHEELS AND TRACKS IN COMPARISON

Comprehensive field studies revealed distinct differences in soil structural changes and root damages by quality and extent, depending from traffic of wheeled or tracked machines. Surveys were done on skid trails from different sites in flat and sloped terrain. Beside midsized harvesters and forward- ers alternatively equipped with tracks on bogies, tracked harvesters were subject of the studies. Soil structural alterations were investigated by means of conventional soil physical methods and computed tomography. Registration and description of root damages were done using a new damage classification system (DCS). In general wheeled machines cause greater soil structural changes than tracked ones. Obviously, tracks are more soil gentle, especially on slopes. Bogie-tracks are more soil protective on slopes than on flat terrain, although their "compaction" level is somewhat lower than for wheels alone. Concerning dam- ages to main roots, wheeled machines mainly cause bark peeling while tracked ones and tracks on bogies severely affect the wooden body by cracking, splintering and breakage. Beside this, size and intensity of root damages are also correlated with carriage types. Polyurethane tracks as substitutes for steel tracks reveal results comparable to those of wheeled machines. Recommendations for the use of wheeled and tracked vehicles are given according to slope and stand conditions.