Factors limiting the growth of indigenous tree seedlings planted on degraded rainforest soils in Sabah, Malaysia

Abstract

During selective logging of tropical rainforest in Malaysia, the topsoil is removed from log landings and skid trails by bulldozers. The exposed subsoil is compacted, nutrient-poor, low in organic matter, drought-prone and hot. Vegetation on log landings and skid trails recovers extremely slowly. Tree seedlings planted on these degraded areas perform much less well than those planted in adjacent manually disturbed areas. An experiment was set up to investigate whether soil factors reduced early tree growth. The treatments used were: digging to reduce soil compaction; fertilizing to replace lost nutrients; mulching to reduce soil temperatures and evaporation rates; replacement of topsoil. Two pioneer tree species ( Macaranga hypoleuca and M. gigantea) and two dipterocarp species ( Dryobalanops lanceolata and Shorea leprosula) were planted in treated plots. Fertilizing of seedlings resulted in a dramatic improvement in height, basal diameter and dry weight increments of all species 6 months after planting. Digging improved seedling growth slightly, but mulching had little effect. This suggests that nutrient deficiency is the most important factor limiting early tree growth on degraded soil. Topsoil replacement resulted in growth as good as that of fertilized seedlings. The topsoil plots also contained 35 times more volunteer plants than any other treatment. Pioneer tree seedlings grew significantly faster than dipterocarp seedlings.