Globally widespread forests first arose in the Pennsylvanian subperiod, some 300 to 320 Ma, populated by bizarre tree-sized club mosses, ferns, sphenophytes, and gymnosperms (1). At this time, most of Earth’s landmasses were fused together as Pangaea, gripped by the late Paleozoic ice age, and subject to glacial–interglacial cycles (2). The compacted remains of the forests that densely covered this partially frozen supercontinent are widely preserved, and in the best-explored tropical realm form economic coal measures (3). Knowledge of the so-called Pennsylvanian coal forests has been literally mined from Earth’s surface through 200 y of hard labor in the coalfields of Appalachia, the Ruhr, and South Wales, among many other places (3). These hard-won fossil discoveries reveal that primeval vegetation choked almost every conceivable terrestrial environment from boggy deltas (3) to rugged mountain terrains (4). Especially tantalizing is the localized preservation of whole forested landscapes, allowing scientists to walk for miles through the coalified stands of upright fossil trees (5). Yet, despite being entombed with such remarkable fidelity, Pennsylvanian forests remain deeply mysterious ecosystems, lacking even remotely close living relatives for comparison. In PNAS, Matthaeus et al. (6) develop sophisticated vegetation–climate models that elegantly fuse traditional fossil data with fundamental plant physiology to bring these long-dead forests back to life. Quite unexpectedly, their wide-ranging findings identify frost tolerance as a key factor in controlling Pennsylvanian forest dynamics and distribution, with episodic frost dieback disturbing cycles of runoff, erosion, and weathering at a global scale. They further hypothesize that enhanced frost tolerance, which arose in early conifers, may have simultaneously conferred drought adaptation, paving the way for conifer dominance in the hot and arid Mesozoic that followed the cool Paleozoic.
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Early online date||26 Oct 2021|
|Publication status||Published - 2 Nov 2021|