Question: What is the effect of shrubs on herbaceous species richness at three spatial scales: quadrat, site, and region? Location: Prepuna, subtropical semi-arid Andes. Methods: At eight sites, we recorded the presence of herbaceous species in spaces beneath shrubs/small trees and in open areas. At the quadrat scale, the average species number per quadrat was calculated and compared between the two microhabitats (shrubs/open). At the local (site) scale, all quadrats of each site were pooled according to microhabitat, and all sites were then combined for the regional analysis. Results and conclusions: We found greater herbaceous species richness below shrubs at all three spatial scales considered. Several species were found exclusively associated with the shrub undercanopy. This effect seems to depend more on greater inventory diversity at the different scales than on greater differentiation diversity in the herbaceous communities associated with shrubs. Facilitation seems to be responsible for the increase of species richness beneath shrubs, but further experimental study is needed to obtain insight into the underlying mechanisms.