Yorkshire Philosophical Society

Event Information

“The collapse of tropical forests” during the Permian-Triassic Mass Extinction: new research

Dr. Zhen Xu (Jane), Research Fellow, University of Leeds

Image: Pre-extinction tropical seed fern with complex vein system

Abstract:

Although flowering plants had not yet evolved, equatorial regions in the late Permian were already covered by lush forests dominated by unusual plants called gigantopterids. Giant lycophyte trees up to 50 metres tall formed the canopy, while tree ferns, seed ferns, horsetail ancient relatives and some gymnosperms created complex and diverse ecosystems. This world collapsed during the Permian–Triassic Mass Extinction, triggered by massive volcanic eruptions. Our research shows that the loss of forests greatly reduced Earth’s ability to store carbon, leaving atmospheric CO2 high for millions of years and creating a prolonged “super-greenhouse” climate. This ancient event offers an important warning: if modern tropical forests collapse under rapid warming, the climate system could take geological timescales to recover.

We are holding this free Cafe Scientifique session on Wednesday 6 May 2026 with doors open from 7pm, talk starting at 7.30pm at City Screen Basement, Coney Street, YO1 9QL   Lift access available. No Booking necessary.

Please buy a drink in the basement bar, take your seats and be ready for a presentation and Q and A.

Member’s report:

Dr Xu (Jane) gained a degree in geology and a doctorate in geobiology from China University of Geosciences (Wuhan) and moved to the University of Leeds in 2023 as a Research Fellow in the School of Earth and Environment.

She focussed her talk on the ‘Great Dying’, the Permian-Triassic mass extinction event 252 million years ago, when most marine and terrestrial life became extinct. Great volcanic eruptions – the Siberian Traps – persisted for hundreds of thousands of years at a time when almost all the Earth’s landmass was joined in one great continent of Pangea. The very large volume of basaltic lava can be measured today and erupted through carbon-rich sediments which caused a rapid increase in the carbon dioxide in the Earth’s atmosphere, forming greenhouse conditions and temperature increases too sudden for life to adapt or evolve. This persisted for about five million years.

Jane wanted to focus on two aspects: Why did it take so long for the atmosphere and vegetation to recover?

Small lycopod plant and seed fossils have been found in the South China area from almost immediately after the mass extinction event. How did they survive when all the tall tropical forests were wiped out?

Jane described the tropical flora towards the end of the Permian: peat bogs and large forests of giant club mosses and horsetails absorbing and burying carbon, producing coal deposits as in the Carboniferous Period beforehand. A coal gap of several million years after the extinction event shows that this had all disappeared from the tropical continent.

Reconstructing deep time vegetation dynamics based on plant fossil data and climatic sedimentary records and simulating biogeochemical–climate feedbacks using an Earth System model SCION (Spatial Continuous Integration recently developed at the University of Leeds) and working with others at the University, she had shown that the loss of forests sequestrating carbon had produced a tipping point from which the Earth was unable to respond. Only as the forests re-established themselves from polar regions and the organic carbon cycle restarted that Earth slowly began to ease out of the super greenhouse conditions. There have been recent discoveries of Early Triassic fossils of exceptional plant life from an area of South China which had then been islands off the mainland. These have been dated to just after the extinction event and are mainly very small lycopod gymnosperms and ferns. Jane has undertaken research on possible adaptations of photosynthesis that would explain their survival.

C3, C4 and CAM are the three systems of photosynthesis. C3 is used by most staple crops and flowering plants, these make up around 95% of all plant species on the planet. They photosynthesise by capturing sunlight during the day, splitting water into energy and oxygen.

C4 plants utilise a specialised pathway, which enhances their ability to fix carbon dioxide (CO₂) and minimise photorespiration allowing them to adapt to hot and dry environments.

CAM (Crassulacean Acid Metabolism) plants are a specialised group of plants adapted to extremely arid conditions. CAM plants are highly efficient in their use of water, with pores that open through the night and close during the day. Examples are cacti, succulents and pineapples.

Focussing on one order, she and her team collected data from 485 identifiable and measurable lycophyte sporophyll specimens from different regions and geological ages including living species.

Quoting from one of her team’s papers:

“Early Triassic lycophytes are closely related to modern Isoetales (Quillworts), a group characterized by exceptional ecophysiological flexibility. Their carbon isotope signatures resemble those of extant Isoetes that use crassulacean acid metabolism (CAM) photosynthesis, indicating a similar physiological strategy in deep time. Coupling these results with climate simulations suggests that CAM photosynthesis could have conferred a substantial advantage under Early Triassic super greenhouse conditions. Together, our findings identify CAM physiology as a potential mechanism enabling plant survival and ecosystem recovery following Earth’s largest mass extinction.”

She was now exploring the possibility of a mechanism for plants switching to CAM photosynthesis to survive these major increases in temperature and aridity.

The questions afterwards reflected the audience appreciation of her overview of so many areas of study and her perseverance in having her research published.

Paul Thornley

Links:

https://environment.leeds.ac.uk/see/staff/12660/zhen-xu-jane-

https://www.nature.com/articles/s41467-025-60396-y#change-history

https://www.nature.com/articles/s41559-026-03026-0#author-information

https://www.nature.com/articles/s41467-018-07945-w