Quantitative reconstruction of the Yiwu Jurassic Forest in Northwest China and high forest productivity in the Middle Jurassic

Forests constitute the dominant terrestrial ecosystems and play a critical role in global carbon cycling. However, the changing structure and function of forests through geological time remain poorly understood due to the scarcity of in situ fossil forests preserving detailed and physiologically important anatomical characters. On the basis of 78 in situ permineralized conifer stumps in the Yiwu Jurassic Forest of Xinjiang, China, we quantitatively reconstruct the forest using paleobotanical observations and ecological analyses. We found that this fossil forest has a random tree distribution with an average density of 126 trees per hectare, showing limited postestablishment competitive thinning; its estimated canopy height ranged from 10.47 to 43.95 meters, stand-level biomass was 276,192 to 386,946 kilograms per hectare, and a notable net primary productivity of 21.11 to 31.9 t/hm ² ·a, which is three times higher than that of modern temperate conifer forests. Elevated temperature and atmospheric p CO ₂ in the Middle Jurassic probably contributed to this high productivity. Our study indicates that tree density, canopy height, and biomass equivalent to modern forests had already emerged by the Middle Jurassic and that forests were functioning as major terrestrial carbon sinks.