Habitat loss and competition from non-native species are leading causes of declines in diversity. However, habitat restoration often targets on-the-ground management without resources directed toward applying or developing ecological theory.
The goal of this research is to identify plant interactions that determine establishment of native plant species at the seedling stage in order to develop the theoretical basis for restoration activities. Developing theories of seedling establishment and understanding the mechanisms that determine who lives and who dies is the first step in developing successful restoration techniques.
Working in upland prairies in western Oregon we examined factors that affect the establishment of plants of conservation concern. We test the hypothesis that seedling establishment of native plants of conservation concern is controlled by 1) competition with or 2) facilitation by associated vegetation, especially invasive grasses, forbs and mosses and interactions with bare soil and litter.
We seeded Lupinus oreganus, Erigeron decumbens, Sidalcea virgata and Iris tenax into 20 experimental plots at each of three sites that varied in community composition from a prior study on prairie restoration. We counted seedlings and estimated cover of grasses, forbs, mosses, and bare soil, as well as measured litter depth. We used linear regression to test for effects of associated vegetation groups and microsite conditions on seedling establishment.
Results/Conclusions
We found no evidence that competition or facilitation by other plant groups affected seedling establishment in the first year after seeding. However, litter depth was positively associated with seedling establishment of S. virgata (p=0.046, R2=0.106) at one site and L. oreganus at two sites (site 1, p=0.016, R2= 0.296; site 2, p=0.0518, R2=0.20). Average seedling establishment of Kincaid’s lupine and rose checkermallow was 11.8-28.4% and 15.2-22.6%, respectively, across all sites. Establishment of seedlings of these species was not significantly associated with cover of grass, forb, moss, or bare soil (p>0.28). Iris and daisy seedling establishment was very low (<1%); we were therefore unable to test for effects of community attributes on these species.
Competition and facilitation may have occurred simultaneously with a weak net effect or interactions with the live plant community may not be very important at the first year seedling stage. Litter appears to have a positive effect on seedling establishment of some species in these prairie systems. Interactions between native species and other community components may be stronger in the years after initial establishment, and we will test for these processes one year after seeding.