Wetland-Dryland Vegetational Dynamics in the Pennsylvanian Ice Age Tropics
International journal of plant sciences
Premise of research. The Late Paleozoic Ice Age was the last extensive pre-Pleistocene ice age. It includes many climate changes of different intensities, permitting examination of many and varied biotic responses. The tropical Pennsylvanian Subperiod, usually visualized as one vast wetland coal forest, in fact also was dominated, periodically, by seasonally dry vegetation that, in turn, covered most of the central and western Pangean supercontinent. Equatorial wetland and dryland biomes
... ted during single glacial-interglacial cycles. This recognition changes understanding of the Coal Age tropics; examination of their spatiotemporal patterns indicates that these vegetation types responded differently to global environmental disturbances and long-term trends and points to potentially different underlying controls on evolutionary histories of their component lineages. Methodology. This study is based on the published literature and on examination of geological exposures and fossil floras, mainly from North America but also from other parts of the world. Pivotal results. Wetlands and seasonally dry habitats were equally part of the Coal Age Pangean tropics. They dominated these landscapes at different times, under different climatic regimes. Wetland vegetation was likely forced into refugia during seasonally dry (subhumid to semiarid) parts of glacial-interglacial cycles; it reemerged/reassembled during wet (humid to perhumid) periods. Seasonally dry vegetation resided permanently in areas of western and central Pangea and in microhabitats within the Central Pangean Mountains. Both floras had lower biodiversity than modern floras in similar habitats. The wetland flora species pool was more phylogenetically disparate than any modern vegetation. In contrast, seasonally dry floras were dominated by seed plants. These biomes responded differently to acute environmental changes and chronic long-term aridification. Conclusions. From ecological or evolutionary perspectives, the present-day world is but one possibility. Lower-diversity worlds such as the late Paleozoic, with a rich spectrum of environmental variations, offer insights into relationships between organisms and environments that expand understanding of these phenomena and enlarge our sense of what is possible or probable as we look to the future.