Study Site Location: Canyon de Chelly National Monument, Arizona.

Over time, saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) invasion has altered desert stream ecosystems, including channel narrowing and inhibiting or eliminating native understory plant communities. At Canyon de Chelly National Monument, the National Park Service has been aggressively removing these invasive tree species. Little is known, however, about best practices for reestablishing native understory plant communities after invasive tree removal. Our objective was to assess effective approaches for restoring native plant communities following removal of saltcedar and Russian olive in Canyon de Chelly. We conducted a randomized complete block experiment to examine the effects vertical mulch, seed mix diversity, and seeding rates on plant biomass and richness during the first three years after tree removal. We found vertical mulch strongly inhibited plant production and species diversity compared to non-mulched treatments. The effect of seeding rate depended, at least in part, on the diversity of species in the seed mix. Seeding commonly used perennial species at a standard seeding rate did not increase native vegetation biomass or richness relative to non-seeded treatments. The most effective restoration approach to encourage production and diversity of desirable species while limiting undesirable species during the first three years following tree removal appears to be seeding a diverse seed mix, containing both annual and perennial species, at a standard seeding rate and without mulch if there is a mature cottonwood overstory.