A Preliminary Survey and Assessment of Rare Plant Communities of the Calcareous Tertiary of Mississippi and Alabama

Mississippi's Jackson Prairie and related limestone barrens of southwest Alabama are highly imperiled yet critical components of the North American Coastal Plain biodiversity hotspot. I here offer a preliminary, qualitative classification of plant communities associated with Eocene- and Oligocene-aged calcareous outcrops with an annotated checklist of associated species. A map of calcareous prairie patches from the past 30 years was constructed from satellite imagery, with reference to USDA soils data and geologic shapefiles. A total of 1393 patches were mapped spanning 2191.57 hectares. Site visits were conducted in the spring and summer 2021–2023 to ground-truth mapping and assemble species checklists for individual prairie and outcrop sites. Herbarium records, Element Occurrence Records, and iNaturalist observations were incorporated to examine current and historic presence of species. Documented here are 744 vascular plant species associated with 17 distinct community types, including grasslands, woodlands, and forests correlated with different substrates, disturbance regimes, and topographic positions, more specific than those included in the U.S. National Vegetation Classification. Long-term distributional trends are difficult to analyze due to lack of data and inconsistencies in historic records, but it is clear that the extent, quality, and diversity of all natural communities has declined, and that due to preservation bias a significant portion of the historic acreage of the Jackson Prairie represents likely extinct community types associated with more mesic, loamy, and acidic soils than current remnants.