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Riparian plant communities often represent the most diverse communities in temperate zones. Also, many studies have shown that riparian communities can be susceptible to overgrazing by wild ungulates and livestock. At the Valles Caldera National Preserve in north-central New Mexico, we tested the effects of ungulate grazing on riparian plant community diversity and composition. To do this, exclosures were erected at various riparian sites: each site included exclosures excluding all ungulates (UE), exclosures excluding only livestock (LE), and control plots excluding no ungulates (C). Baseline species diversity (1/?) data were collected in 2002 (UE = 8.87, LE = 7.55, C = 9.18), exclosures were erected in 2004, were surveyed yearly through 2008, and were resurveyed in 2014. Diversity initially increased for all treatments, peaking in 2007 (UE = 11.15, LE = 9.93, C = 12.49). In 2008, diversity began to decrease, and had decreased to levels lower than the baseline data by 2014 (UE = 7.18, LE = 7.48, C = 8.89). Initially, UE plots had the greatest diversity, but after 2006, C plots' diversity became highest and remained highest through 2014. While LE plot diversity was lowest at the outset, by 2014 LE and UE diversity indices nearly converged. We suggest that higher disturbance from grazing in control plots contributed to their higher diversity.