OOS 13-5 - Mediterranean climate, fire and plant evolution

Tuesday, August 8, 2017: 2:50 PM
Portland Blrm 254, Oregon Convention Center
Jon E. Keeley, Western Ecological Research Center, U.S. Geological Survey, Three Rivers, CA

In the early 1970s the National Science Foundation funded IBP project comparing California and Chile focused on the hypothesis that similar mediterranean-type climates (MTC) would select for structurally and functionally similar ecosystems. Mild winter temperatures during the rainy season contribute to substantial biomass production and the summer drought favors shrublands and also converts biomass into available fuels for wildfires. High intensity crown fires are common in these shrublands and this talk addresses the question of shrub evolution and fire adaptations in relation to the Cenozoic origin of the MTC in California, and contrasts this with what is known of Chilean climate, plants and fire. It has long been accepted that the MTC was relatively new, originating only within the last 1-2 million years. However, more recent evaluations have concluded that the MTC developed far earlier and was in place by the mid-Miocene. Origins of chaparral shrub taxa were evaluated from dating the earliest plant macro-fossils.


Most chaparral genera were present in the Eocene under an aseasonal climate, however these taxa were adapted to fires through vigorous postfire resprouting. This early origin is consistent with other structural and physiological traits related to tolerance of summer drought that predate the MTC. These shrubs are adapted to tolerating soil drought regardless of whether it is MTC summer drought or winter drought or imposed by substrate and aspect. An important change associated with the MTC is coupling of drought with high temperatures greatly increased the extent of drought-prone soils and concomitantly the expansion of shrublands. This had a profound impact on fires since it increased fuel continuity and predictability of fires. Ceanothus and Arctostaphylos, apparently originated in the Miocene and have radiated widely after the development of the MTC and it’s hypothesized that this was driven by adaptation to this unique niche of predictable fires. These two large genera are dominated by species that have adapted their reproduction to the immediate postfire environment by production of dormant seeds that require fire for germination. These obligate seeding species represent one of the clearest adapations to the MTC. Comparisons will be made with the role of fire in the Chilean matorral.