Freeze tolerance influenced forest cover and hydrology during the Pennsylvanian
Abstract
Throughout Earths natural history, forest distribution is restricted by the various eco-physiological limits of era-appropriate plants. As forest distribution alters Earth surface processes, accounting for major forest-limiting factors into deep time will improve characterization of those eras and prediction of Earth System behavior in the future. During Earths penultimate icehouse (the late Paleozoic ice age [LPIA]), glacial-interglacial cycles subjected plants to oscillating, contrasting stressors. We combine climate modeling and ecosystem-process modeling to simulate arboreal vegetation in the late Paleozoic ice age. We then compare the resulting hypothetical distributions to the fossil record in light of plant physiological principles. Using GENESIS V3 GCM simulations, varying pCO2, pO2, and ice extent for the Pennsylvanian, and fossil-derived leaf C:N, maximum stomatal conductance, and specific conductivity for several major Carboniferous plant groups, we simulated global ecosystem processes at a 2 spatial resolution with Paleo-BGC. Based on leaf water constraints, Pangaea could have supported widespread arboreal plant growth and forest cover. However, these models do not account for the impacts of freezing on plants. According to our interpretation, freezing would have affected plants in 59% of unglaciated land during peak glacial periods and 73% during interglacials, when more high-latitude land was unglaciated. Comparing forest cover, minimum temperatures, and paleo-locations of Pennsylvanian-aged plant fossils from the Paleobiology Database supports restriction of forest extent due to freezing. Many genera were limited to unglaciated land where temperatures remained above 4C. Freeze-intolerance of Pennsylvanian arboreal vegetation had the potential to alter surface runoff, silicate weathering, CO2 levels, and climate forcing. As a bounding case, we assume total plant mortality at 4C and estimate that contracting forest cover increased net global surface runoff by up to 6.1%. Repeated freezing likely influenced freeze- and drought-tolerance evolution in lineages like the coniferophytes, which became increasingly dominant in the Permian and early Mesozoic.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.B53C..05M