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We examined the effects of an alien species, Lehmann lovegrass (Eragrostis lehmanniana), on the semi-arid grassland ecosystems of the south-western United States. In order to evaluate these effects, we examined soil disturbance by animals in areas dominated by Lehmann lovegrass in comparison with areas dominated by native grasses. We measured amounts and types of faunalpedoturbation at paired plots in two different study areas, the Jornada basin in New Mexico and the Santa Rita Experimental Range in south-eastern Arizona. Area of soil disturbed and volume of soil turnover was significantly decreased on plots dominated by Lehmann lovegrass, at the Santa Rita Experimental Range but not on plots in the Jornada basin. At the Santa Rita, ground squirrels and attine ant activity was reduced the most of any other species in Lehmann lovegrass dominated pastures. Differences in the diversity of disturbances were inconsistent at both study areas indicating variable responses by taxa to dominance by an alien grass species. Variations among, within, and between study areas were attributed to site history as well as geographic and topographic position. The degree to which Lehmann lovegrass affects faunalpedoturbation appears to be related to the history of the site, specifically the time since the establishment of Lehmann lovegrass. (C) 2003 Elsevier Ltd. All rights reserved.