Logging Machinery Traffic Has Greatest Influence on Soil Chemical Properties in the Amazonian Rainy Season

In the forests of Amazonia each year, previously unentered stands are logged, which usually results in some degree of soil compaction. Consequently, the soil chemical properties in compacted areas are altered. The aim of this study was to determine how these changes may help or hinder site recovery in the context of seasonal variation and increased levels of compaction. To investigate these changes, an experiment was established in the Central Amazon. This consisted of tractor trails compacted at three incrementally increasing traffic intensities of one, three, and twelve machine cycles in the wet and dry seasons. Results revealed that elevated moisture in the wet season combined with heavy compaction from twelve machine cycles had the greatest impact on soil chemical properties. This was indicated by diminished total nitrogen, organic carbon, available phosphorus, cation exchange capacity, and elevated ammonium and Fe2+. Nevertheless, heavy compaction in the wet season led to lower Al3+ and higher base saturation, which could be beneficial for future site recovery. Study Implications: Annually, vast swathes of old-growth forest are logged for the first time in Amazonia. These areas require an extensive skid trail network to facilitate movement of logging machinery and subsequent log skidding. Skid trails always entail some level of soil compaction, especially in the heavily used primary skid trails. This compaction influences the soil chemical properties. Some impacts are only apparent in the wet season and may not be present in the dry season. Therefore, to reduce overall impacts to soil chemical properties, skid trail coverage should be planned to reduce the coverage of the logging site.