The first maps of the Earth's forests plotted by scientists at Royal Holloway, University of London after creating a database of more than two thousand fossilised forest sites from the Cretaceous period, when dinosaurs were at their peak. The patterns of vegetation, together with information about the rate of tree growth, support the idea that the Earth was stifling hot 100 million years ago. High temperatures and possibly more atmospheric carbon dioxide caused forests to extend much closer to the poles and grow almost twice as fast as they do today. The findings have obvious implications for understanding the long-term effects of global warming.
Just before the dinosaurs went extinct the forests changed as angiosperms – flowering plants – made an appearance. "Flowering trees similar to present-day magnolias took off, bringing color and scent to the world for the first time," says Peralta-Medina. The angiosperms gradually spread over habitats previously dominated by the conifers; by the end of the Cretaceous they are the most common tree species.
As well as mapping the fossil forests, the team gathered measurements of tree rings from samples of fossil trees and from earlier studies, and found that Cretaceous trees grew twice as fast as their modern counterparts, particularly nearer to the poles.
The reason for this baking hot climate seems to have been extremely high levels of carbon dioxide in the atmosphere - at least 1000 parts per million (ppm) compared to 393 ppm today.
"If carbon dioxide concentrations continue to rise unabated, we will hit Cretaceous levels in less than 250 years," explains Falcon-Lang. "If that happens, we could see forests return to Antarctica."
More information: Peralta-Medina, E, Falcon-Lang, HJ, 2012. Cretaceous forest composition and productivity inferred from a global fossil wood database. Geology 40(3) doi: 10.1130/G32733.1