In Western rangelands, invasion by the exotic annual grass Bromus tectorum is altering fire regimes, community composition, and ecosystem function. Communities with well-established perennial grasses may be more resistant to invasion by B. tectorum, making post-disturbance restoration with native perennial grasses desirable. However, restoration with these later-succesional species is often unsuccessful. Greater restoration success may be achieved with seed mixes that mimic natural succession in Great Basin systems, which includes native annuals as a key component of the post-disturbance community. In a greenhouse competition experiment, seedlings of the native perennial grass, E. multisetus, were grown with high and low density of two native annual forbs (8 or 4 seedlings of Amsinckia tesselata or Mentzelia veatchiana) or an annual forb mix (1 or 2 seedlings, depending on density treatments, of each A. tesselata, M. veatchiana, Cryptantha pterocarya, and Eriastrum sparsiflorum). Half of the pots were grown with competition from B. tectorum. We recorded the number of green leaves on E. multisetus plants at 9, 12, and 15 weeks after planting. All plants were harvested after 15 weeks, when some of the species were becoming senescent. Aboveground biomass of each target plant was placed in one bag and aboveground biomass of competitors in separate bags sorted by functional group (annual forb or annual grass).

Results/Conclusions

Growing with competitors decreased the size of E. multisetus, however the largest decrease in size was found when grown with B. tectorum and A. tesselata. In contrast, E. multisetus grew best with M. veatcheana, regardless of density. When in competition with B. tectorum, E. multisetus performed best when M. veatchiana was also present. These results support the idea that the presence of certain native annual forbs can enhance the establishment of E. multisetus in B. tectorum invaded rangelands.