Ancient forests and climates of the Paleogene of Canada

古近纪--从6500万年前到2400万年前--是一个气候显著变化和植物群落及其组成的各种物种随之进化的地质时期。古近纪气候变化是由许多因素驱动的，包括大气二氧化碳(CO2)水平的自然变化。在北美西部，古近纪植物群落从主要的亚热带森林类型转变为今天北美东部更典型的温带森林和开阔草原。这种变化在很大程度上是由于全球暖湿气候的转变，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)，气候变得更凉爽和干燥，以及渐新世在南极和格陵兰岛形成冰帽。这项研究的目的是利用加拿大西部保存完好的化石遗址，主要是来自不列颠哥伦比亚省的化石遗址，从古近纪，即早期始新世气候最佳时期(EECO)的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，许多证据已经重建了大气二氧化碳水平，是现在水平的2倍到5倍，但对于二氧化碳在东半球气候变暖中所起的作用，仍然存在不确定性。公元前化石遗址保存了一套多样化的树木和其他植物的叶子，这些树木和其他植物现在是北美东部落叶森林的典型，特别是温暖的东南部(如棕榈树)，以及中国橡胶树(杜仲属)等植物类型。以及今天在东南亚发现的黎明红杉(水杉属)。此外，还出现了成套的昆虫，表现出热带环境下原本预计会出现的多样性。公元前始新世化石遗址提供了一个自然实验室，可以研究生态系统过去是如何应对气候变化的，以及探索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.