Early Eocene plant diversity and dynamics in the Falkland flora, Okanagan Highlands, British Columbia, Canada

Abstract

The early Eocene fossil localities of the Okanagan Highlands in British Columbia, Canada, and Washington State, USA, span the Early Eocene Climatic Optimum, the warmest period of the Cenozoic, and reflect mild but equable upland climates (mean annual temperature 0°C). The Okanagan Highlands region has been identified as a centre of temperate plant family diversification in the northern hemisphere during the early Eocene. Here, we test the hypothesis of mid-latitude high diversity through rarefaction analysis of unbiased census collections from the Okanagan Highlands Falkland fossil locality, demonstrating levels of diversity similar to those documented at hyperdiverse Eocene sites in South America when adjusted for sample size. An explanation for this diversity may lie in the upland character of the Falkland site, as altitudinal gradients provide a mosaic of microhabitats through interacting effects of topography and climate. Fine-scale trends are also examined within the Falkland site, demonstrating a shift in plant community composition over time to a more diverse flora, although the dominant taxa persist through the section in varying levels of abundance. Intra-site patterns in plant community structure and composition are attributed to a combination of environmental factors, including disturbance and microhabitat diversity.