Effect Of Simulated Grazing On Sediment Trapping By Single Plants: A Wind-Tunnel Experiment With Two Grassland Species In Mongolia

Vegetative cover suppresses dust storms in arid regions. Rearing livestock is a major industry in arid regions, and although livestock consume grass, the effect of their grazing on the ability of grass to trap sediments is not well understood. This study quantified the effect of plant clipping, a mimic of animal grazing, on sediment trapping by single plants in a wind-tunnel experiment. The study focused on two grass species, Stipa krylovii and Agropyron cristatum, which are native to the Mongolian steppe and are highly palatable for livestock. The two species were grown to a height of approximately 30 cm, and then single plants were placed in a wind tunnel. The frontal area of the plant was photographed before and during 5 min of wind blowing at a velocity of 8 m s(-1). The sediment that accumulated behind the plant was measured after the trial. The top 5 cm of the plant was then clipped away, and the plant was subjected to another wind-blowing trial. This experimental sequence was repeated until the above-ground part of the plant had been entirely removed. Although bending of S. krylovii in the wind was clearly apparent, bending ceased when the upper part of the plant body had been clipped away. Clipping reduced the frontal area, but there was little decrease in sediment accumulation until all of the above-ground biomass had been removed. These results indicated that sediment trapping by a single plant was likely attributable to the sheltering effect created by the lower part of the above-ground plant body; the flexible upper portion of the plant body apparently contributed very little to sediment trapping. The loss of the upper part of the bodies of grasses via grazing should therefore have little effect on sediment trapping when the plants are solitary or very sparsely dispersed.