Ancient forests and climates of the Paleogene of Canada

古近纪——6500万年前至2400万年前——是一个气候发生重大变化的地质时期，植物群落及其组成的各种物种随之进化。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，在古近纪，植物群落从主要的亚热带森林类型转变为温带森林（更典型的北美东部）和开放草原的混合。这种变化的主要原因是全球气候从温暖潮湿，特别是在晚古新世（61-55 Ma）和早始新世（55-49 Ma），到渐新世（34 Ma），气候变冷和干燥，以及渐新世在南极洲和格陵兰岛形成冰盖。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，从古近纪，早始新世气候最佳（EECO）时期温暖气候的顶峰重建气候和森林生态系统。在古新世和始新世早期，许多证据都重建了大气中二氧化碳水平，是现在水平的2倍到5倍，但二氧化碳在变暖的EECO气候中所起的作用仍然不确定。不列颠哥伦比亚省的化石遗址保存了许多树木和其他植物的叶子，这些树叶是今天北美东部落叶森林的典型，特别是温暖的东南部（如棕榈树），以及今天在东南亚发现的中国橡胶树（杜仲属）和黎明红杉（水杉属）等植物类型。此外，还出现了一组昆虫，它们表现出了热带环境中应有的多样性。不列颠哥伦比亚省始新世的化石遗址提供了一个自然实验室，可以研究过去生态系统是如何应对气候变化的，也可以探索有关落叶林的进化和热带森林多样性的起源的问题。

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.