Wyoming Fossils Reveal 100,000‑Year Recovery of Ancient Forests After Paleocene‑Eocene Warming

A new study published in *Science* shows that forests in southern Wyoming lost 60 % of their canopy during the Paleocene‑Eocene Thermal Maximum (PETM), a 56‑million‑year‑old period of rapid warming that mirrors today’s climate change. By analysing microscopic plant cuticles preserved in sedimentary rocks, researchers reconstructed the leaf‑area index—a measure of canopy density—across the PETM. The data reveal that the forests were at their densest just before the rapid temperature rise, likely due to rising atmospheric CO₂ from volcanic activity. As temperatures climbed by up to 11 °F (6 °C), heat and drought killed many trees, opening the canopy and allowing more sunlight to reach the forest floor. The altered canopy structure changed water flow and sediment deposition in the basin, as evidenced by a shift from fine soils to coarser river deposits. Recovery was slow; it took more than 100,000 years for canopy density to return to, and eventually exceed, pre‑warming levels. The study underscores that CO₂ fertilisation can boost growth only while temperatures and water remain within tolerable limits, offering a cautionary tale for modern forests facing rapid warming and increased drought.