CONTRIBUTORY FACTORS TO SOIL SPATIAL VARIABILITY IN AN ULTISOL .2. RETENTION OF LIVING TREES INSITU FOLLOWING LAND CLEARING

The effect of retaining living trees in situ following manual land cle aring on soil physical properties was studied in a Typic Kandiudult in southern Cameroon. Soil compaction in the surface 100 mm was greatest with complete clearing and least under forest, with retention of livi ng trees resulting in soil compaction levels which were intermediate t o both the former. Soil compaction in the surface 100 mm also increase d with increasing distance from the tree trunk (or tree stump with com plete clearing). Both the above observations were attributed to a comb ination of high root density, high macrofaunal activity, high ground c over, high organic matter content and low traffic under forest and at the base of trees or tree stumps. Increasing soil compaction also occu rred with increasing depth, and was attributed to the existence of few biopores in the subsoil horizons. Absence of biopores was thought to be due to low root densities in the subsoil caused by a combination of low macroporosity, low air porosities during the wet season and low p H. In comparison to sub-humid and semi-arid ecologies, therefore, the beneficial effects of retaining living trees in situ following land cl earing at this site were less.