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

在过去的地质时期，北美温带森林与东亚和欧洲有许多共同的植物属（如pseudoolarix、Acer、Sassafras和Trochodendron）。这些地理区域之间的交换在今天是不可能的，因为散布走廊已经太冷了300万到1500万年。然而，过去地质时期的气候变暖事件促进了它们之间的生物交换。化石记录提供了过去植物分类和气候存在的初步记录。这项工作将集中在始新世早期（约5647.8亿年前），当时北美大部分地区都有热带动植物，中纬度年平均气温（MAT）约为20摄氏度，冬天没有温和的霜冻，甚至北极也有短吻鳄。始新世早期温暖的高纬度气候为植物和动物通过北极向北扩散开辟了一条路线。不列颠哥伦比亚省的化石地点提供了加拿大北极以外始新世的唯一记录-从凉爽（MAT 1012c）的高地湖泊遗址，支持混合温度和热带生物群的森林，到温暖（MAT 1520C）的卑诗省和西澳太平洋沿岸的低地环境，包括棕榈树。提出的研究计划有以下长期目标：(1)综合研究森林群落随时间的变化，即化石遗址内部和化石遗址之间的优势、多样性和首次出现（谱系起源）；(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。过去气候变化的生物后果和气候作为一个进化驱动因素。短期目标集中在：(1)mcabe化石层和BC省其他地方的目标地点重建古环境；(2)完成对现有北极—始新世遗址的分析；(3)对这些遗址进行系统分析，并适时将其他来自不列颠哥伦比亚省的植物化石遗址纳入其中，从而在时间和空间上扩大范围，覆盖更多的不列颠哥伦比亚省。不列颠哥伦比亚省的化石将沿着层理平面取样，以隔离时间分离的森林群落。这些化石地点在地层学上是相互关联的，使用梯度测量的火山灰数据，将所有的化石研究地点按时间顺序排列。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遗址丰富的叶、花和种子化石记录进行详细的系统分析，将确定关键植物科和属，并有可能阐明这些类群的首次出现，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，帮助了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.