CHANGES IN VOID DISTRIBUTION AND VOLUME DURING COMPACTION OF A FOREST SOIL

Bulk density and water retention measurements were conducted after 0, 1, 2, 4, 8, 16, and 32 trips with a rubber-tired skidder on a forest soil whose surface was formed from volcanic ash. Changes in these measurements were used to evaluate effects of traveling intensity with heavy equipment on some soil physical properties. Bulk density reached a maximum after four trips and remained statistically constant with additional trips. A parameter indexing the pore-size distribution, however changed after four trips. Compression of the soil during each skidder pass and elastic rebound thereafter was identified as the mechanism resulting in changes of the pore-size distribution while bulk density remained constant. Effects of heavy equipmet operation on the pore-size distribution and water retention properties should be recognized in forest management.