River bar vegetation mowing response in the Middle Rio Grande

Abstract

The Bureau of Reclamation routinely mows vegetation on side bars along the Rio Grande to assist with river flow management. To address the question of how such mowing affects vegetation composition and structure, three bars in the middle Rio Grande near Albuquerque, New Mexico were selected in 1994 for an experimental mowing program. Three 50-foot-wide strips on each bar were left unmowed, with the area between the strips mowed as usual. This mowing pattern was repeated in 1995 and 1996. In August 1996, vegetation composition, abundance and structure were measured under the two conditions of the treated bars and at one additional bar with no history of mowing. Species composition and abundance were compared among sites and treatments using ANOVAs and canonical discriminant analysis. The greatest negative effect was on the native cottonwood where there were significant declines of 70-90 percent on some sites with respect to cover, stems and individuals. Mowing also reduces the exotic Russian olive cover by 50-70 percent on sites where it is dominant. Although cover may decline, Russian olive often responds by resprouting and creating vigorous multiple-stemmed individuals. Coyote willow was affected less by mowing; at the site with the most willow cover (Belen), declines in both cover and the number of individuals were only about 32 percent. This relatively higher mowing tolerance may reflective coyote willow's greater adaptativeness to natural disturbances such as flooding. What is clear however, is that regardless of what shrubs are dominant, cottonwood is always the most negatively affected by mowing.

Parent Publication

• Rio Grande ecosystems: linking land, water, and people: Toward a sustainable future for the Middle Rio Grande Basin

Citation

Muldavin, Esteban; Milford, Elizabeth; Chauvin, Yvonne. 1999. River bar vegetation mowing response in the Middle Rio Grande. In: Finch, Deborah M.; Whitney, Jeffrey C.; Kelly, Jeffrey, F.; Loftin, Samuel R. Rio Grande ecosystems: linking land, water, and people: Toward a sustainable future for the Middle Rio Grande Basin. 1998 June 2-5; Albuquerque, NM. Proc. RMRS-P-7. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 139-150.