HUMAN IMPACTS ON THE DUNES NEAR LYNNDYL, UTAH

Most studies of the impact of off-road vehicles (ORVs) on American deserts have been conducted on nondunal desert landscapes or have emphasized ORV effects on dune wildlife only. Previous researchers have suggested that documented adverse consequences to desert plains and alluvial fans should be avoided by restricting ORV use to active sand dunes. The assumption that ORVs have no significant physical effect on active desert sand dunes, however, has not been adequately investigated. The research reported on here was undertaken to determine if selected dune variables differ significantly between dunes used and dunes not used by ORVs.

The Lynndyl dune field, located in west-central Utah about 200 km southwest of Salt Lake City, provides an excellent opportunity to study the effects of off-road vehicles on active desert sand dunes. About 40% of the 575 sq km dune field is administered by the Bureau of Land Management as a recreation area. Most of the recreation area is open to ORV use, which is seasonally intensive, but ORVs are prohibited from a designated natural region that covers about 17% of the total recreation area. The adjacent used and unused portions of the dune field have the same dune types, sand source, and climate.

Data on vegetation cover, water content, sediment compaction, and grain size distribution parameters were collected from multiple barchanoid dunes distributed between the used and unused portions of the dune field. Results show that the used dunes are significantly more compacted than the unused dunes, including when controlling for grain size differences between the two samples. In addition, variations in dune form and migration rates are explored with sequential aerial photographs.