Ph.D. Candidate, Northwestern University; Chicago Botanic Garden

Light, Soil, Fire, and Seeds: Investigating the Environmental Gradients that Drive Restored Oak Woodland Plant Community Diversity

Once widespread across the Midwestern, U.S., Quercus woodlands have been degraded by land use changes, fire suppression, and invasive species. Previous research shows that gradients of light, soil, and fire structured diversity in predegraded woodlands. However, we know less about the processes structuring diversity in woodlands being restored through native seed addition. This study addresses how the gradients of canopy openness, soil nutrients, and fire frequency influence plant communities being restored with native seeds. We surveyed plant community diversity, canopy openness, soil properties, and determined burn rate and seeding history in seven woodland restorations across Cook County, IL. We found that the seeded status of a plot and canopy openness interacted in their effect on species richness, such that there was a significant relationship between canopy openness and species richness in unseeded plots, but not in the seeded plots (p= 0.03*). We also found that the abundance of non-sown species increased with canopy openness (p= 0.004*) and decreased with increasing burn rate (p= 0.02*). In contrast, there was no relationship between sown species abundance with the gradients of canopy openness or burn rate. These findings suggest that native seed addition can influence the role that canopy openness and burn rate play in driving plant community diversity. Additionally, this work suggests that the differing responses between the sown and non-sown species are important to consider. A better understanding of how plant communities restored through native seed addition respond to environmental gradients will help guide restoration practices in this highly threatened ecosystem.