SOIL COMPACTION AND TOPSOIL REMOVAL EFFECTS ON SOIL PROPERTIES AND SEEDLING GROWTH IN AMAZONIAN ECUADOR

The effects of soil compaction and topsoil removal on soil physical an d chemical properties, and growth of planted trees were investigated. The study was conducted during an oil extraction project in tropical m oist forest on a Typic Paleudult in Amazonian Ecuador. The forest was being cleared by bulldozers that compacted the subsoil and scraped awa y the topsoil. Compaction and topsoil removal resulted in a 70% increa se in bulk density, with a 23% increase caused by subsoil compaction a lone. There were also significant decreases in organic matter, nitro e n and phosphorus content, total porosity and base saturation, and an i ncrease in cation exchange capacity. Both compaction and topsoil remov al caused a decrease in macroporosity of the subsoil and reduced water availability. Seedlings of each of three mature canopy tree species ( Cedrelinga cateniformis (Fabaceae), Caryodendron orinocense (Euphorbia ceae) and Virola elongata (Myristicaceae), were planted in undisturbed soil, compacted subsoil and uncompacted subsoil. Growth responses to soil compaction and topsoil removal, measured over 9 months, were not consistent among species. Height growth was reduced in all species but diameter growth decreased only in Cedrelinga cateniformis. Subsoil co mpaction reduced height growth and increased mortality of only one spe cies, and topsoil addition to compacted subsoil did not generally incr ease growth. Fertilization had the most consistently positive effect o n growth. The results of this study confirm that many soil physical an d chemical factors are altered by compaction and topsoil removal, but do not reveal clear effects of these changes on tree seedling growth. Although the most consistent result was reduced height growth in compa cted subsoil with topsoil removed compared with undisturbed soil, this decrease cannot be attributed consistently to either soil compaction or topsoil removal.