THE EFFECTS OF VEGETATION COVER AND WIND VELOCITY UPON SAND DUNE MIGRATION RATES IN THREE ACTIVE DUNE FIELDS OF THE SOUTHWESTERN UNITED STATES

Extending across several vegetation zones and four distinct desert systems, dune fields dominate the landscape of the southwestern United States. A vast majority of these fields are stabilized, yet several locations consist of active dunes. The role of vegetation has been recognized merely as a stabilizing agent; the interrelationship of vegetative cover and wind velocities and their effects upon migration rates has yet to be clearly documented in reference to North American dune fields. Given a direct relationship between aridity and vegetative abundance, this study focuses on three sites with variations in annual precipitation so as to produce a predictable variance of vegetative cover: Algodones Dunes Wilderness, near Yuma, Arizona; Great Sand Dunes National Park & Reserve, near Mosca, Colorado; and Monahans Sandhills State Park, near Odessa, Texas. Yuma, Mosca, and Odessa have, respectively, extremely arid, arid, and semi-arid climatic conditions (average annual precipitation of 76 mm, 228 mm, and 305 mm). Individual dunes were identified at all three sites and their movements tracked using annual photographs dating from 1989 to 1997. The migration rates were then plotted against ancillary wind shear and directional data. Results show the wind conditions correlated more strongly with the dune migration rates and directions as the abundance of vegetation decreases across the climatic gradient.