Forests communities in transition: Eocene fossil sites from western and Arctic Canada

在过去的地质历史中，北美的热带森林与东亚和欧洲共享许多植物属(如松属、枫属、梧桐属和杜鹃属)。这些地理区域之间的交流在今天是不可能的，因为扩散走廊已经太冷了300-1500万年。然而，在过去的地质时期，气候变暖促进了它们之间的生物交换。化石记录提供了过去植物类群的存在和气候的初步记录。拟议的工作将集中在始新世早期(约5647.8年)，当时北美大部分地区支持热带动植物，中纬度年平均温度(MAT)约为20摄氏度，冬季无霜冻，甚至北极也有鳄鱼。这些温暖的高纬度早期始新世气候为动植物通过北极向北方扩散开辟了一条路线。不列颠哥伦比亚省的化石地点展示了北极以外加拿大始新世的唯一记录-从支持温带和热带生物群混合的森林的凉爽(MAT1012C)高地湖泊地点，到公元前和西澳太平洋海岸温暖(MAT 1520C)包括棕榈树的低地环境。拟议的研究计划有长期目标：(1)综合森林群落随时间的变化，即优势度、多样性和首次出现(物种起源)，包括化石地点内部和之间；(2)确定生物多样性的区域和时间格局，及其与气候变化的关系，即过去气候变化的生物后果和气候作为进化驱动因素。短期目标集中在：(1)McAbeefossil层和不列颠哥伦比亚省其他地方的目标遗址，以重建古环境；(2)完成对现有的寒武纪始新世遗址集合的分析；以及(3)对这些遗址进行系统分析，因为有机会扩大到包括不列颠哥伦比亚省的其他植物化石遗址，从而在时间和空间上扩大范围，涵盖不列颠哥伦比亚省的更多地区。不列颠哥伦比亚省的化石遗址将沿着层状平面进行采样，以隔离在时间上分开的森林社区。这些化石遗址使用放射性测量可测年的火山灰进行地层对比，将所有化石研究地点放在一个年代顺序中。通过记录收集到的每一个可识别的化石，我们将在生态时间尺度上重建气候、森林组成和多样性。对BC遗址丰富的化石叶、花和种子进行详细系统分析的目的是识别关键植物科和属，并可能澄清这些ETAXA的首次出现，因为这些始新世遗址富含重要的温带和亚热带植物科。这项研究将提供数据，帮助理解森林群落如何应对过去的全球变暖以及现代温带生态系统的出现。

North Americantemperate forests in the geological past shared many plant genera with eastAsia and Europe (e.g. Pseudolarix, Acer, Sassafras, and Trochodendron).Exchange between these geographic regions is not possible today as thedispersal corridors have been too cold for 3-15 million years. Climate warmingepisodes in the geological past, however, facilitated biotic exchange betweenthem. The fossil record provides a primary record of the presence of plant taxaand of climate in the past. The proposed work will focus on the early Eoceneepoch (ca. 5647.8 MYA) when much of North America supported a tropical faunaand flora, mid-latitude mean annual temperatures (MAT) were ca. 20C with mildfrost-free winters, and even the Arctic hosted alligators. These warm highlatitude early Eocene climates opened a northern dispersal route for plants andanimals via the Arctic. Fossil localities in British Columbia present the onlyrecord of the Eocene from Canada outside the Arctic - ranging from cool (MAT1012C) elevated upland lake sites that supported forests of mixed temperateand tropical biota, to warm (MAT 1520C) lowland environments on the Pacificcoast of BC and WA that included palms. The proposed research program has theselong term objectives: (1) Develop a synthesis of changes in forest communitiesthrough time, i.e., dominance, diversity and first appearances (origination oflineages), both within and between fossil sites; (2) Determine regional andtemporal patterns of biotic diversity, and its relation to change in climate,i.e. the biotic consequences of past climate change and climate as anevolutionary driver. Short term objectives are focused on: (1) the McAbeefossil beds and targeted sites elsewhere in BC to reconstructpaleoenvironments; (2) completion of analyses of existing collections of ArcticEocene sites; and (3) systematic analysis of these sites expanding asopportunity allows to include other plant fossil sites from British Columbia tobroaden the scope both temporally and spatially to cover more of BC. Fossilsites in BC will be sampled along bedding planes to isolate forest communitiesseparated in time. These fossil sites are stratigraphically correlated usingradiometrically datable volcanic ashes, placing all of the fossil study sitesinto a chronological sequence. By documenting every identifiable fossilcollected we will reconstruct climate, forest composition, and diversity atecological time scales. The objective for detailed systematic analyses of theBC sites rich record of fossil leaves, flowers and seeds will identify keyplant families and genera and potentially clarify first appearances of thesetaxa as these Eocene sites are rich in important temperate and subtropicalplant families. This study will provide data that helps understand how forestcommunities responded to past global warming as well as on the emergence ofmodern temperate ecosystems.