Ancient forests and climates of the Paleogene of Canada

古近纪-从6500万年到2400万年前（Ma）-是一个地质间隔，气候发生了重大变化，植物群落及其组成的各种物种随之演变。古近纪气候变化是由许多因素驱动的，包括大气中二氧化碳（CO2）水平的自然变化。在北美西部，早第三纪的植物群落从主要的亚热带森林类型转变为温带森林和开阔草原的混合，这在今天的北美东部更为典型。这一变化主要是由于全球气候从温暖和潮湿的转变，特别是在古新世晚期（61-55 Ma）和始新世早期（55-49 Ma），到渐新世（34 Ma）气候变冷和干燥，以及南极洲和格陵兰岛的冰盖在渐新世形成。该研究旨在利用加拿大西部保存完好的化石遗址，主要来自不列颠哥伦比亚省，重建古近纪早期始新世气候最佳时期（EECO）温暖气候的极端气候和森林生态系统。在古新世和早始新世时期，许多证据已经重建了大气中二氧化碳水平的2倍至5倍，但二氧化碳在EECO气候变暖中所起的作用仍然不确定。公元前化石遗址保存了许多树木和其他植物的各种各样的叶子，这些叶子是今天北美东部落叶林的典型特征，特别是温暖的东南部（例如棕榈），以及中国橡胶树（Eurobustsp.）和水杉（Metasequoia sp.），今天在东南亚发现的。此外，还存在一组昆虫，表现出在热带环境中预期的多样性。公元前始新世化石遗址提供了一个天然实验室，以研究生态系统如何应对过去的气候变化，以及探索有关落叶林进化和热带森林多样性起源的问题。

The Paleogene - from 65 to 24 million years ago (Ma) - was a geological interval of substantial climate change and consequent evolution of both plant communities and the various species that they were composed of. Paleogene climate change was driven by a number of factors, including natural changes in atmospheric carbon dioxide (CO2) levels. In western North America, over the Paleogene plant communities shifted from predominantly subtropical forest types to a mix of temperate forests more typical of eastern North America today, and open grasslands. This change was driven largely by a shift from globally warm and wet climates, especially during the Late Paleocene (61-55 Ma) and Early Eocene epochs (55-49 Ma), to cooler and drier climates by the Oligocene epoch (34 Ma) and the formation of ice caps on Antarctica and Greenland by the Oligocene. The research aims to use well preserved fossil sites in western Canada, principally from British Columbia, to reconstruct climates and forest ecosystems from the acme of warm climates during the Paleogene, the Early Eocene Climatic Optimum (EECO). During the Paleocene and Early Eocene epochs numerous lines of evidence have reconstructed atmospheric CO2 levels 2x to 5x present day levels, but uncertainty remains over the role CO2 played in warming EECO climates. The BC fossil sites preserve a diverse suite of the leaves of many of the trees and other plants that are today typical of the deciduous forests of eastern North America, and especially so the warmer southeast (e.g. palms), together with plant types such as the Chinese rubber tree (Eucommia sp.) and the dawn redwood (Metasequoia sp.), that are found today in southeast Asia. Also present are suites of insects exhibiting a diversity otherwise expected in a tropical setting. The BC Eocene fossil sites provide a natural laboratory to look at how ecosystems have responded to climate change in the past, as well as exploring questions about the evolution of the deciduous forests and the origins of tropical forest diversity.