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（例如，假枝属、槭属、檫树属和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 - 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。化石记录提供了植物类群存在和过去气候的初步记录。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，冬天温和无霜，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，支持温带和热带混合生物群的森林，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。拟议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。过去气候变化对生物的影响以及气候作为一种进化驱动力。短期目标集中在：(1)McAbee化石层和不列颠哥伦比亚省其他地方的目标地点重建古环境；(2)完成现有北极始新世遗址的分析；(3)对这些遗址进行系统的分析，并在有机会的情况下扩大不列颠哥伦比亚省的其他植物化石遗址，以扩大时间和空间范围，覆盖更多的不列颠哥伦比亚省。不列颠哥伦比亚省的化石遗址将沿着层理平面取样，以隔离时间上分离的森林群落。这些化石地点使用放射性火山灰进行地层学对比，将所有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省遗址丰富的叶、花和种子化石记录进行详细的系统分析，将确定关键的植物科和属，并有可能澄清这些分类群的首次出现，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对过去的全球变暖做出反应，以及现代温带生态系统的出现

North American*temperate forests in the geological past shared many plant genera with east*Asia and Europe (e.g. Pseudolarix, Acer, Sassafras, and Trochodendron).*Exchange between these geographic regions is not possible today as the*dispersal corridors have been too cold for 3-15 million years. Climate warming*episodes in the geological past, however, facilitated biotic exchange between*them. The fossil record provides a primary record of the presence of plant taxa*and of climate in the past. The proposed work will focus on the early Eocene*epoch (ca. 5647.8 MYA) when much of North America supported a tropical fauna*and flora, mid-latitude mean annual temperatures (MAT) were ca. 20C with mild*frost-free winters, and even the Arctic hosted alligators. These warm high*latitude early Eocene climates opened a northern dispersal route for plants and*animals via the Arctic. Fossil localities in British Columbia present the only*record of the Eocene from Canada outside the Arctic - ranging from cool (MAT*1012C) elevated upland lake sites that supported forests of mixed temperate*and tropical biota, to warm (MAT 1520C) lowland environments on the Pacific*coast of BC and WA that included palms. The proposed research program has these*long term objectives: (1) Develop a synthesis of changes in forest communities*through time, i.e., dominance, diversity and first appearances (origination of*lineages), both within and between fossil sites; (2) Determine regional and*temporal patterns of biotic diversity, and its relation to change in climate,*i.e. the biotic consequences of past climate change and climate as an*evolutionary driver. Short term objectives are focused on: (1) the McAbee*fossil beds and targeted sites elsewhere in BC to reconstruct*paleoenvironments; (2) completion of analyses of existing collections of Arctic*Eocene sites; and (3) systematic analysis of these sites expanding as*opportunity allows to include other plant fossil sites from British Columbia to*broaden the scope both temporally and spatially to cover more of BC. Fossil*sites in BC will be sampled along bedding planes to isolate forest communities*separated in time. These fossil sites are stratigraphically correlated using*radiometrically datable volcanic ashes, placing all of the fossil study sites*into a chronological sequence. By documenting every identifiable fossil*collected we will reconstruct climate, forest composition, and diversity at*ecological time scales. The objective for detailed systematic analyses of the*BC sites rich record of fossil leaves, flowers and seeds will identify key*plant families and genera and potentially clarify first appearances of these*taxa as these Eocene sites are rich in important temperate and subtropical*plant families. This study will provide data that helps understand how forest*communities responded to past global warming as well as on the emergence of*modern temperate ecosystems.***