End Permian to Middle Triassic plant species richness and abundance patterns in South China: coevolution of plants and the environment through the Permian–Triassic transition

This study reviews plant species richness and abundance change from the End Permian to Middle Triassic in South China and examines the co-evolutionary relationship between the flora and the environment through this critical interval in the history of terrestrial biotas. A normalized macro-fossil plant record, that considers only one taxon per whole plant, is produced. This identifies four broad phases of plant evolution. Phase 1 is marked by pre-extinction floras that demonstrate a long-term decline of species richness beginning in the Late Permian (lower Changhsingian) that culminates in the distinct End Permian Plant Crisis (EPPC) at the end of the Changhsingian. Other evidence for the health of the flora, including palynology, biomarkers, wildfire proxies, soil erosion and weathering proxies show a drastic loss of plant abundance (biomass) and increase of wildfire frequency (suggestive of increasing seasonal aridity) during the EPPC. A Phase 2 survival interval, during the Changhsingian–Griesbachian transition, has a severely impoverished plant assemblage consisting of opportunistic lycopods and a short-lived holdover flora. Phase 3 (Late Griesbachian–Smithian) saw the modest recovery of species richness as several groups began to radiate, notably conifers and ferns. Diversity increases substantially and persistently during the succeeding Phase 4 and sees the dominant lycopods/herbaceous bryophytes of Phase 3 replaced by conifer-dominated floras. Plant abundance recovery began earlier than the resumption of coal formation which only initiated in the Anisian following its disappearance during the EPPC. Only in the Late Triassic did the flora recover to a level comparable to that seen in the Permian. The flora of South China thus took ~15 million years to completely recover from the profound environmental and climatic effects of the Permo-Triassic mass extinction.