Freeze tolerance influenced forest cover and hydrology during the Pennsylvanian

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 118; no. 42; pp. 1 - 12
• Main Authors: Matthaeus, William J., Macarewich, Sophia I., Richey, Jon D., Wilson, Jonathan P., McElwain, Jennifer C., Montañez, Isabel P., DiMichele, William A., Hren, Michael T., Poulsen, Christopher J., White, Joseph D.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 19.10.2021
• Subjects: Biological Sciences; Carbon dioxide; Carboniferous; Climate; Climate Change; Climate Models; Conservation of Natural Resources - methods; Drought resistance; Earth surface; Ecosystem; Environment models; Forest growth; Forests; Fossils; Freezing; Glacial periods; Glaciation; Global climate models; Hydrology; Ice ages; Intolerance; Leaves; Mesozoic; Paleobiology; Paleozoic; Pangea; Permian; Physical Sciences; Physiology; Plant fossils; Plant growth; Plant physiology; Plants; Runoff; Simulation; Specific conductivity; Stomata; Stomatal conductance; Surface runoff; Trees - physiology; Vegetation; carboniferous; runoff; modeling; freezing; forest cover
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2025227118

The distribution of forest cover alters Earth surface mass and energy exchange and is controlled by physiology, which determines plant environmental limits. Ancient plant physiology, therefore, likely affected vegetation-climate feedbacks. We combine climate modeling and ecosystem-process modeling to simulate arboreal vegetation in the late Paleozoic ice age. Using GENESIS V3 global climate model 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° 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 Pennsylvanianaged plant fossils from the Paleobiology Database supports restriction of forest extent due to freezing. Many genera were limited to unglaciated landwhere temperatures remained above −4 °C. 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 −4 °C 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.