Assessing competitive potential of native forbs from cheatgrass dominated habitats

Background/Question/Methods

In western North America, reseeding with native plants is often hindered by Bromus tectorum L. (cheatgrass), a ubiquitous invader. Natives growing in B. tectorum dominated habitats are thought to be either remnants from once uninvaded habitat or adapted for competition with the invasive plant. If they are competitors, these species would be ideal candidates for use in reseeding projects. Early germination, a high germination percentage, and rapid vegetative growth rate are key to the success of B. tectorum. A series of laboratory investigations were conducted to identify native plants with similar germination and early growth characteristics to B. tectorum, and the ability to compete with B. tectorum. Seeds were collected from B. tectorum and ten native forb species growing in invaded habitats in and around Zion National Park, UT and Montrose, CO. Germination response was tested with and without pre-treatment, at four temperature regimes representing early spring in the Zion area. Five species with high germination rates were included in a greenhouse competition study. The greenhouse experiment tested which native species can avoid being suppressed by low and high density B. tectorum competition, and whether native forbs can suppress growth and reproduction of B. tectorum target plants.  

Results/Conclusions

Bromus tectorum germination reached 100 percent within seven days over all treatments and temperatures. Two native annual forbs, Cryptantha ambigua (Boraginaceae) and Lotus humistratus (Fabaceae), had germination percentages that did not differ from B. tectorum under several conditions. An additional three species had maximum germination percentages between 50 and 73 percent. The remaining five species had maximum germination percentages below 50 percent. The species with maximum germination percentages over 50 percent: C. ambigua, L. humistratus, Penstemon palmeri (Plantaginaceae), Machaeranthera tanacetifolia (Asteraceae) and Eriogonum leptophyllum (Polygonaceae) were seeded in the competition experiment. Forb species differed in emergence time and percent, which mirrored results from the germination experiment. Forbs species also differed in growth rate and competitive ability in the competition experiment. Species with high germination rates that can suppress, or avoid being suppressed by B. tectorum should be considered in revegetation of burned sites where B. tectorum may remain in the seed bank or disperse into the site from adjacent habitats.