Seed addition with heterogeneous disturbances to increase native diversity in restored grasslands

Background/Question/Methods

The need for restoration of the tallgrass prairie biome is marked by critical declines of characteristic flora and fauna. Though restorations rarely approximate the diverse flora of remnant prairies due to poor native forb establishment, methods of enhancing forb diversity in existing restorations have been poorly investigated. We examine effects of multiple disturbance regimes on recruitment of native forbs sown into species-poor native grasslands at three restored tallgrass prairie research sites and evaluate the potential for mosaic disturbance management to increase plant community heterogeneity. Thirty-seven species of native forbs were sown into plots that were either undisturbed, summer burned, or subjected to one of the following disturbances in addition to summer burning: broad-spectrum herbicide, shallow disking, mowing, or annual spring burning. After collecting one year of pre-treatment data, species composition and abundance and light availability were monitored for three years following the experimental disturbances and seed addition.

Results/Conclusions

Native richness increased in response to sowing without disturbance, though disturbances further enhanced recruitment. Light availability was a strong predictor of recruitment, and site x treatment interactions indicated that the benefits of disturbance for enhancing native species richness were contingent upon the extent to which established vegetation restricted light availability at each research site. Herbicide application had the adverse effect of promoting colonization by exotic species when locally abundant in the surrounding landscape. We found significant differences in native forb community composition among treatments, but no singular treatment resulted in decisively superior establishment of sown species across sites. These findings, together with the variable structural requirements of grassland fauna, indicate that heterogeneous disturbance regimes within a single restoration site can enhance native forb diversity and the habitat value of restored grasslands.