ORIGINAL PAPER Early Eocene plant diversity and dynamics in the Falkland flora, Okanagan Highlands, British Columbia, Canada Robin Y. Smith & James F. Basinger & David R. Greenwood Received: 25 May 2011 /Revised: 11 September 2011 /Accepted: 20 September 2011 /Published online: 21 October 2011 # Senckenberg Gesellschaft für Naturforschung and Springer 2011 Abstract The early Eocene fossil localities of the Okana- gan Highlands in British Columbia, Canada, and Wash- ington State, USA, span the Early Eocene Climatic Optimum, the warmest period of the Cenozoic, and reflect mild but equable upland climates (mean annual temperature <15°C, cold month mean temperature >0°C). The Okana- gan 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 rarefac- tion analysis of unbiased census collections from the Okanagan Highlands Falkland fossil locality, demonstrating levels of diversity similar to those documented at hyper- diverse 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, demon- strating 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. Keywords Fossil flora . Okanagan Highlands . British Columbia . Early Eocene Climatic Optimum . Diversity . Rarefaction Introduction Shellito and Sloan (2006) described the Eocene world as a “lost paradise,” when tropical vegetation extended well north of current ranges, and the poles were ice-free. Plant fossils yield information on terrestrial palaeoclimate that complements geochemical proxies and provide an indication of what the world can look like under very different global climate conditions. There is currently a particular interest in studying periods of Earth history that represent “greenhouse” climates (Royer 2008). One such key period is during the interval of peak Cenozoic warmth in the early Eocene, approximately 53–50 Ma, referred to as the Early Eocene Climatic Optimum (EECO; Zachos et al. 2001, 2008). The early Eocene fossil localities of the Okanagan Highlands in British Columbia, Canada, and Washington State, USA (Fig. 1) have received growing attention in recent years as sources of diverse and well-preserved plant and insect fossil assemblages that provide a window on this key interval of global warmth (e.g. Archibald and Mathewes 2000; Archibald et al. 2010; DeVore et al. 2005; DeVore and Pigg 2007; Greenwood et al. 2005; Smith et al. 2009). These sites, formed in similar lacustrine depositional Electronic supplementary material The online version of this article (doi:10.1007/s12549-011-0061-5) contains supplementary material, which is available to authorized users. R. Y. Smith (*) Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada e-mail: robin.smith@usask.ca J. F. Basinger Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada D. R. Greenwood Department of Biology, Brandon University, 270 18th Street, Brandon, MB R7A 6A9, Canada Palaeobio Palaeoenv (2012) 92:309–328 DOI 10.1007/s12549-011-0061-5