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

点击翻译按钮获取中文摘要

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. 56-47.8 MYA) when much of North America supported a tropical fauna and flora, mid-latitude mean annual temperatures (MAT) were ca. 20°C 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 10-12°C) elevated upland lake sites that supported forests of mixed temperate and tropical biota, to warm (MAT 15-20°C) 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.