Gravel and Grass Surfacing Reduces Soil Loss From Mountain Roads

Soil loss from forest roads was measured on two soils in the southern Appalachian Mountains. Losses from a roadbed without surfacing (bare soil) and later with grass cover were compared with those from roadbeds surfaced with different types and amounts of rock. In the first 2 months after construction in a deep sandy loam saprolite, soil loss rates were eight times greater from the bare soil site than from roadbeds with 15 to 20 cm of gravel. Loss rates declined in a 6-month period of light traffic and the cumulative loss during the first 8 months after construction was over 200 t/ha from the bare soil roadbed and less than 35 t/ha from roadbeds surfaced with graded crushed rock or large (7.5 cm) washed stone. Losses rose as logging traffic began and at the conclusion of the timber sale, roads were reshaped and ungraveled portions grassed. During logging, a site with a thin layer (5 cm deep) of crushed rock became heavily rutted and additional gravel was added. In the third year, erosion rates on this lightly graveled site approximately equaled those of bare soil, twice that of a grassed roadbed. Where the road was built with the B horizon of sandy clay loam, soil losses with 5 cm and 15 cm of gravel were intermediate between the high and low losses from similar surfacings on sandy loam saprolite. Differences in soil loss and trafficability persisted into the fourth year. Maintenance of forest roads disturbed stabilized road surfaces and contributed to soil losses. Forest Sci. 30:657-670.