An assisted succession model using sainfoin

Background/Question/Methods

Assisted succession involves the use of an intermediate crop to “capture” a site away from weedy species prior to community diversification with native species.  We propose the use of sainfoin (Onobrychis sativa) as an assisted succession species in crested wheatgrass (Agropyron cristatum) and cheatgrass (Bromus tectorum) stands. Crested wheatgrass and cheatgrass are difficult to diversify with natives, this may be due to their documented ability to facilitate negative feedbacks on native plant reestablishment.  A successful assisted succession species will be competitive with the invasive species it is displacing.  Here we test one aspect of the competitive ability of sainfoin to tolerate possible negative soil feedbacks. If crested wheatgrass and cheatgrass create negative soil feedbacks, can sainfoin alleviate those negative feedbacks and in turn facilitate the growth of native species?  We grew crested wheatgrass, cheatgrass, and sainfoin for three generations in heat-treated and non heat-treated soils.  The fourth generation we added three native species; prairie clover (Dalea purpurea), prairie coneflower (Ratibida columnifera), and black-eyed Susan (Rudbeckia hirta) commonly found in reclamation seed mixes. We then compared total biomass of all species to determine the effects of soil modification on the growth of each species.

Results/Conclusions

Sainfoin and the three native forbs had significantly higher biomass in non heat-treated soils regardless of the pre cultivator species.  This suggests that the presence of soil biota may be an important factor in enhancing the biomass of native plants and sainfoin.  Crested wheatgrass and cheatgrass had significant differences in biomass in response to the pre-cultivator species. Both species had higher biomass when grown in sainfoin modified soils, suggesting negative feedbacks between the two species. Native forbs and sainfoin growth were not inhibited by feedbacks from crested wheatgrass and cheatgrass modified soil.  The difficulty in establishing native plants into crested wheatgrass and cheatgrass may be more a result of direct competition than negative soil feedbacks.  Our results suggest that sainfoin can be effectively used to capture sites from invasives. Plots are currently being established to evaluate our ability to diversify sainfoin stands with native species.