Community attributes along a perturbation gradient in a shortgrass steppe

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Abstract
We constructed a perturbation (response) gradient that encompassed several types of disturbances (causes) affecting shortgrass steppe communities, and that was confounded by time scales of initiation and duration. The objectives were to (1) examine the type of disturbance and the relative magnitude of response in relation to the history of the shortgrass steppe, and (2) determine which attributes of the plant communities displayed relationships across the perturbation gradient, rather than across traditional successional ‐ time gradients.Comparisons of disturbance types indicated that long‐term heavy grazing by cattle resulted in plant communities which differ less from communities resulting from other disturbances than did long‐term ungrazed sites. The removal of grazers from this system promoted attributes of earlier serai stages. Water addition, below‐ground grazing by white grubs, and water‐plus‐nitrogen enrichment had distinct and large impacts on community composition. Nitrogen enrichment resulted in additions but not losses of species. The shortgrass steppe has a high degree of adaptation to both short‐term drought and aboveground grazing. Belowground grazing and semi‐aridity may be considered antagonistic pressures on the community.Community attributes that displayed a relationship with increasing level of perturbation were decreasing dominance and increasing diversity, and fluctuation in species composition during short‐term wet/dry cycles. The level of perturbation was related to negative impacts on the two primary species and a corresponding increase of other warm‐season species, but was not related to densities of any other species, life‐form, or functional group.