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In arid regions, overstory plants may influence establishment and persistence of understory species. Identifying relationships between overstory and understory plants may increase success of revegetation efforts. This research considered whether three desirable grasses native to the Sonoran Desert, Arizona cottontop (Digitaria californica), plains lovegrass (Eragrostis intermedia) and bush muhly (Muhlenbergia portern), differ in density or cover under overstory species compared to open areas. Selection of sites in southern Arizona (two or three per species) was based on abundance of study species and elevation. Density and cover of Arizona cottontop and plains lovegrass was highly variable between canopied and open areas among sites. Bush muhly had greater density and cover under canopies at all sites. No association was noted between precipitation or elevation and density or cover ratios. Identifying understory species well-adapted to shaded sites may aid in determining the best use of existing vegetation for revegetation in this region. (C) 1997 Academic Press Limited.