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

北美洲温带森林在过去的地质历史中与东亚和欧洲共享许多植物属(例如松属、枫属、梧桐属和杜鹃属)。*这些地理区域之间的交流今天是不可能的，因为*扩散走廊已经太冷了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分类群的存在和过去气候的初步记录。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物和植物区系，中纬度年平均温度(MAT)约为20摄氏度，温和的无霜冻冬季，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(1012摄氏度)高地湖泊遗址，到公元前和西澳太平洋海岸包括棕榈树的温暖(1520摄氏度)低地环境。拟议的研究计划有这些长期目标：(1)综合森林群落随时间的变化，即化石地点内部和之间的优势度、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模式，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)McAbee化石床和不列颠哥伦比亚省其他地方的目标地点，以重建*古环境；(2)完成对北极*始新世地点现有集合的分析；以及(3)对这些地点进行系统分析，因为*机会允许包括不列颠哥伦比亚省的其他植物化石地点，以*在时间和空间上扩大范围，以涵盖BC的更多地区。公元前的化石遗址将沿着层状平面进行采样，以隔离在时间上分离的森林群落。这些化石地点使用*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块可辨认化石，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的植物科和属，并可能澄清这些*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 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.***