Conclusions on the Impacts of Logging at Danum

Abstract

AbstractDuring logging, road and skid trail crossings of streams acted as key points of sediment input to stream channels. Slope stability was disturbed in places, with minor soil slumping. In the logging period, woody debris inputs to streams increased; clay rich sediment built up on the channel floor, and the stream water remained turbid, even at low flows. After logging, some of the consequent changes to streamflow and sediment transport are short-lived, but exceptional rainfalls can mobilize sediment that had accumulated during logging and create high one-day sediment yields. Such post-logging impacts of extreme events indicate how the legacy of logging operations persists and how the scars in the forest landscape can be reactivated. The log haulage and transport infrastructure, especially abandoned dirt roads and their drainage, can create problems for many years after the forest has been left to recover. A key issue is the persistence of extensions to the drainage network created by skid trails that crossed streams; or gullies that took roadside runoff into stream head hollows. Landslides created by collapse of road embankments remain highly significant sediment sources in the largest storm events, providing major initial inputs and subsequent additional inputs during later heavy rainfalls. Sediment sources decline to the few remaining bare patches on abandoned roads, nearby landslides and a few extremely compacted former log-landing areas. Most stream channels returned to gravel beds, but after the most extreme storms large pulses of clay-rich sediment from former landslides again encumber channel beds. Many biotic indicators of forest recovery show that many plant and animal species regain their number, the abundance of different species varies and there can be a significant shift in species adaptation. On the other hand, in the highly compacted areas caused by logging, soil bulk density remains high, suggesting that the treatment of skid trails, log landing areas and main access roads after logging is crtical for a full recovery of the rainforest.KeywordsDelayed responsesDrainage networkSediment productionRecovery indicators