Cover and density of winter annual plants on the perimeters of ant nests were compared with those of adjacent reference sites in three habitats at Jornada LTER, New Mexico, USA. There was a distinct floristic assemblage of winter annual plants on ant nest perimeter in comparison to reference sites. Descurainia pinnata, Lesquerella gordonii, Malacothrix fendleri and Eriogonum abertianum were strongly associated with ant nest perimeters and had higher cover on ant nest perimeters.
The floristic assemblages and cover were least affected by presence of harvester ant nests in the grama grassland habitat and most affected in the basin slope mixed habitat. Soil chemical analyses did not show large generalized differences in nutrient contents. However, there were higher concentrations of NO3-N and inorganic P on ant nest perimeters and also, there were different ratios of resources (e.g., water and N and P availability) due to ant soil disturbance on ant nest perimeter. Floristic assemblage could be determined by a fortuitous juxtaposition of clumped seeds at beginning of winter, by intra and interspecific competition of winter annual during February and March, and mediated by ant clipping at the end of April and May. There were no significant differences in below ground biomass between ant nest perimeter and reference sites. This many be due to intense clipping of annual plants by ants on nest perimeters in April.