COMMUNITY DYNAMICS OF PENNSYLVANIAN PEAT SWAMPS AND THE NATURE OF THE CARBONIFEROUS RAINFOREST COLLAPSE

The Phillips Coal Ball Collection (PCBC) is one of the largest paleobotanical datasets in existence, representing plant occurrences from over 50,000 Pennsylvanian coal balls. A subset of these coal balls (carbonate concretions of peat found in coal deposits) span the duration of the Pennsylvanian (323-299 Ma), represent 25 coals from North America, Europe, and northern Africa, and preserve tropical lowland peat-generating wetland (“peat swamp”) floras in exquisite detail, allowing unprecedented paleoecological study of these communities. Long-term ecological stability in peat swamp communities across the Pennsylvanian, disrupted by a floral turnover interval (the “Carboniferous Rainforest Collapse”) at the end of the Desmoinesian stage, has previously been observed. To further investigate these trends, we calculated Bray-Curtis and Chao dissimilarity values between each coal in the dataset and performed principal component and detrended correspondence analyses on the entire dataset. No geographic patterns are discernable between coal floras in the dataset, but temporal patterns are visible; namely, a trend of increased dissimilarity between coals with increasing temporal separation and a shift from lycopod-dominated to fern- and pteridosperm-dominated communities at the end of the Desmoinesian stage. The temporal patterns we recover elucidate interesting trends in the recolonization of lowland swamp environments from floras in refugial habitats after flooding during interglacial periods. The protracted nature of the floral shift in the late Desmoinesian sheds further light on the duration and dynamics of the Carboniferous Rainforest Collapse.