Effects of road decommissioning on stream habitat characteristics in the South Fork Flathead River, Montana

Previous studies have demonstrated the negative effects of roads on stream characteristics important for fish survival; however, few have examined whether decommissioning reverses these adverse impacts. We examined the relationships between the percentage of fine sediment in stream substrate and roads and looked at whether decommissioning had measurable effects on stream habitat in the Flathead National Forest, Montana. We conducted habitat surveys and substrate coring in 12 streams encompassing three watershed treatment types: (1) roadless areas, (2) areas with roads in use. and (3) areas with decommissioned roads. Significant positive correlations were found between the percentage of fine sediment in substrate and various measures of road impact (road density, roads in use, and number of stream crossings). Watersheds with roads in use had higher percentages of fine sediment than those without roads and those with decommissioned roads. Watersheds with high levels of vegetative regrowth on decommissioned roadbeds had a lower percentage of fines in stream sediment. Decommissioning efforts that enhance regrowth may improve stream habitat, although significant effects of these manipulations are difficult to detect through spatial comparisons. Future studies using either before-after or before-after-control designs to evaluate the effects of decommissioning practices on fish and wildlife habitat and populations are needed.