Plant community response to regional sources of dominant grasses in grasslands restored across a precipitation gradient

Background/Question/Methods

Guidelines for ecological restoration generally advocate using locally-sourced plants, but there is uncertainty regarding whether local sources will be best adapted to future environmental conditions.  Restoring communities with high genetic diversity would increase the potential for adaptation and species survival in an uncertain climate future.  The effects of using non-local genotypes or a mix of plant sources on the assembling plant community, however, are poorly known.  The objective of this study was to evaluate whether different regional sources of two dominant prairie grasses (Andropogon gerardii and Sorghastrum nutans) differentially effect diversity of restored plant communities.  Three reciprocal common gardens experiments were established across a climate gradient characterized by a two-fold increase in annual precipitation from central KS to southern IL.  At each site, plots were seeded with regional sources of the focal grasses from central Kansas (CKS), eastern Kansas (EKS), southern Illinois (SIL), or a mix of seed from all three regions (MIX).  All plots were also seeded with the same suite of subordinate species.  Species composition and diversity were measured during the 4^th year of restoration.

Results/Conclusions

The effects of dominant grass source on cover and diversity of the plant community varied among sites.  In Illinois, non-dominant species in locally sourced (SIL) plots had significantly lower cover than in CKS and EKS plots (P=0.01).  The SIL source plots contained lower diversity than CKS and EKS plots and lower richness than MIX plots (P=0.011).  In eastern KS, there was no difference in the cover of functional groups or diversity among sources (P>0.05).  In central KS, MIX plots had marginally significantly higher cover of C3 forbs than the local (CKS) plots (P<0.10); no variation in diversity occurred among differently sourced plots (P>0.05).  Overall, summed cover of the two dominant grasses was lowest relative to that of the other regional sources when planted furthest from their local environment.  In the eastern portion of the gradient, where light availability tends to be most limiting to plant growth, the cover of dominant species reduced the diversity of the plant community.  The use of seed mixes with high regional diversity (mixed sources) did not significantly compromise the cover or diversity in restorations across the climate gradient and could be a potential restoration strategy to ensure long-term adaptability to future climate conditions.