Effects of prescribed fire and native forb seeding on low quality grasslands in Texas and Oklahoma

Whitney Behr, Carolyn V. Whiting, Kyle M. Simpson, Elinor M. Lichtenberg, Shalene Jha and Norma Fowler, Integrative Biology, University of Texas at Austin, Austin, TX

Background/Question/Methods
Many grasslands have lost species diversity due to human-driven processes such as overgrazing, row cropping, soil erosion, fire suppression, and invasive species. Prescribed fire is a common restoration practice in grasslands but burning alone may not be sufficient to restore native plant diversity. Native seeding is another common practice to restore lost species. The effects of these practices are not easily generalizable across sites with different land histories, so we tested the effectiveness of these practices on sites with different land histories across a 470 km latitudinal gradient extending from central Texas to southern Oklahoma.
Two plots were burned during the dormant season (January-March) in 2018 at ten low-quality grassland sites. After the prescribed burns, a mix of twelve native forb species was seeded in one of the two burned plots at each site. Plant species abundances at these sites were sampled in June and September for two years following burning and seeding treatments to determine 1) if burning alone could change the plant community composition, structure, or richness, 2) if the burning + seeded plots showed greater improvement than the burn only plots, and 3) if this latitudinal gradient affected plant community responses at our sites.
Results/Conclusions
Prescribed fire alone did not have a detectable effect on the composition of the plant communities at any of the ten sites over the two years we monitored.
Abundance of seeded species was significantly higher in the burn + seed plots than in either the burn or control plots in the second year. Only two of the twelve seeded species (Asclepias viridis and Chamaecrista fasciculata) were detected in the seeded areas during the first year following treatment. Six of the twelve seeded species (two above, plus Coreopsis tinctoria, Gaillardia pulchella, Monarda citriodora, and Centaurea americana) were detected in the seeded areas during the second year.
The expected pattern of increased species richness at lower latitudes was not detected. Instead, species richness was highest at our northernmost sites. This may be explained by invasive grass abundance, which was inversely related to latitude.
Our results demonstrate that single fires conducted during the dormant season may not be effective restoration practices for degraded grassland communities. Despite the variety of land histories across our sites, the plant communities generally responded to burning and seeding, making our results potentially useful for informing restoration practices in a wide variety of degraded grasslands.