The Nature Conservancy began tallgrass prairie conservation and restoration efforts at Nachusa Grasslands in north-central Illinois (USA) in 1986. Over 34 years, the project has protected more than 275 acres of unplowed native prairie and planted approximately 2000 acres of prairie on former agricultural fields. Goals of the Nachusa Grasslands preserve include two central questions: 1) Are management practices sustaining plant diversity, including rare plants, in native prairies and 2) Do restored prairies support comparable levels of plant diversity and conservatism? Between 1994 and 1996, managers established 12 transects to evaluate and monitor plant community changes in both native and restored prairie units across the preserve. Transects included at least 10 quadrats (1m2 each) in which all observed plants were identified to species level. The transects were permanently marked and resampled in subsequent years. In this study, we synthesize the plant community data collected between 1994 and 2016, analyzing total plant species richness, native plant richness, proportion of native plants, and mean coefficient of conservatism. Due to differences in cover metrics used over the years, we considered species presence/absence only. We evaluated changes over time with regression analysis in R Studio.
Results/Conclusions
Most sites exhibited no statistical change in any of the metrics examined (P-values >0.05), indicating plant community richness and conservation value has been maintained across more than 20 years. Identity of native plants remained consistent and comprised >70% of the plant community across the sites. The cumulative number of native plants observed increased by approximately 20 species in two native prairies from 1994 until 2015 (P<0.05, R2=0.99 for both), showing native species respond positively to management. The overall proportion of native species did not change over this time interval, indicating non-native species also increased in these sites during the same time. However, non-native species encroachment did not negatively impact native species richness. The oldest planting on the preserve exhibited a 30% increase in native species presence across twenty years (P=0.002, R2=0.95), driven by continued over-seeding of native plants and aggressive control of invasive species. Native plants of high conservation value increased in two restored prairies and one native prairie (P<0.03, R2>0.78 for all). These data show management practices at Nachusa Grasslands sustain native plant communities, including species of high conservation value, in native prairie remnants. Prairie plantings also effectively restore diverse plant communities, reflecting native prairie richness.