The effects of selective timber harvesting in buffer strips along headwater channels using best management practices on runoff, turbidity and suspended sediment yield in an intensively cut eucalypt forest in southeastern Australia

Abstract

In a native forest on the south coast of New South Wales, Australia, five channels were instrumented with rain gauges and weirs to monitor rainfall, streamflow, turbidity, and suspended sediment yield over a seven and a half year period. After a five year calibration period, four of the catchments were harvested, while one remained as a control. In the harvested catchments there were two replicated treatments; selective harvesting in the 10 m buffers using Best Management Practices (BMPs), and no harvesting in the 10 m buffers.Results of the statistical analysis showed that harvesting had a significant impact on runoff and suspended sediment yield relative to the control, but did not have a significant impact on turbidity. There was no significant difference in post-harvest runoff, turbidity or suspended sediment yield between the treatments. In the treatment where there was no harvesting in the buffers, the significant increase in suspended sediment yield dissipated after 18 months and was accompanied by a hydrological recovery in peak flows toward pre-harvest values. In the treatment where there was harvesting in the buffers, there was no hydrological recovery in peak flows, nor was there a decrease in suspended sediment yields 18 months after harvesting.This lack of a hydrological recovery in the treatment where there was harvesting in the buffers had no significant effect on turbidity, hence the implementation of BMPs in the buffer strips along the ephemeral first-order channels were effective in maintaining the water quality status in an intensively harvested eucalypt forest. The implementation of BMPs outside of the selectively harvested buffers that are designed to reduce erosion on hillslopes and sediment delivery to streams were also effective in maintaining the water quality status in the same harvesting operation.