Rahul Somvanshi
Two periods of extreme greenhouse warmth drove the biggest changes in land-plant diversity during the past 120 million years, according to a new study in Nature Plants. The finding helps explain why flowering plants, conifers, ferns and mosses changed so dramatically in deep time—but it does not mean modern warming will produce a similar recovery on a human timescale.
The researchers compiled more than 60,000 fossil pollen and spore records and used statistical methods designed to account for uneven fossil sampling. Their reconstruction covers about 130 million years and draws on records from high-latitude southeastern Australia and tropical regions of northeastern Africa and northern South America.
Two greenhouse intervals reshaped plant communities
The study found that most turnover—both the disappearance of pollen and spore types and the appearance of new ones—occurred during the two warmest intervals in the record. Cooler periods showed less change. The authors conclude that extreme greenhouse climates were closely associated with major floristic turnover across several plant groups, not flowering plants alone.
Flowering plants became especially prominent from the middle Cretaceous, about 100 million years ago, when they began displacing older plant groups that had dominated land ecosystems. But the new analysis also identified responses by conifers and their relatives, ferns and mosses at both high and low latitudes.
The result does not say heat simply creates more biodiversity. The researchers describe a much more disruptive process: warm intervals eliminated previously important diversity while creating conditions in which new, related plant forms emerged. Each ancient interval lasted a few million years.
What does this mean for today’s climate change? The study is a warning against treating ancient diversification as reassurance. Today’s human-driven warming is much faster than the greenhouse phases examined in the fossil record. Extinction can occur quickly, while the evolution of replacement species takes geological time.
The paper also tested other possible explanations, including interactions among plant groups and geographic isolation. Those factors may matter, but the climate pattern explained the broad turnover signal better in the authors’ analysis. The Nature Plants study therefore adds long-term evidence that climate can reorganise plant ecosystems at a planetary scale.
For present-day conservation, the practical point is direct: losing existing plant species is not offset by the possibility that new species could eventually evolve. Protecting habitats and reducing greenhouse-gas emissions determine whether today’s ecosystems remain intact for the species that depend on them.
