BIOTIC RESPONSES OF OKANAGAN HIGHLANDS PLANTS TO DISTURBED HABITATS IN A HIGH ELEVATION FLORA

The suite of floras present within the Okanagan Highlands are preserved in lacustrine sediments deposited in syntectonic grabens associated with uplifted core complexes. This unusual setting captured a rare glimpse of upland plant communities present in Washington State northward into British Columbia after the Paleocene-Eocene Thermal Maximum (PETM, ~ 55. 5 Ma) and Eocene Thermal Maximum (ETM, ~ 53. 2 Ma). How Okanagan Highlands plants adapted to their upland environment and disturbed habitat can be assessed by integrating morphological clues from the fossils with physioecological data from their modern temperate relatives. Some plants document strong abiotic selection for adaptations linked with mean annual temperature and seasonal thermal amplitude. Evidence for shoot differentiation and leaf flushes is evident in such taxa as Cercidiphyllum and Zizyphoides. These plants produce short shoots and dimorphic leaves, features that strongly suggest complex responses to light and temperature signals expected in seasonal regimes. Modular adjustments for temperate climates also are linked with the cost of reproduction. For example, in the temperate deciduous buckeyes (Aesculus) resources essential for vegetative growth and maintenance are diverted to be invested into fruits and seeds. Buckeyes further adjusted resource allocations to evolve a drought-deciduous habit favorable for inhabiting chaparral. Besides modular adjustments, evolutionary mechanisms ranging from vegetative reproduction to complex breeding systems and hybridization have also been selected for in these high elevation, disturbed habitats in some groups such as Rosaceae. The Okanagan Floras provide a rare opportunity to think of both modular plant responses and a variety of specialized reproductive mechanisms within an evolutionary and paleoecological framework.