Origins and Adaptations of California Hardwoods 1 Philip

California's flora of hardwood trees has evolved from a mixture of Arctotertiary and Madro-tertiary progenitors under selective pressures of drought and low nutrient availability. Plant growth form and evergreen vs. deciduous leaf duration are important aspects of morphological adaptation to Mediterranean-climate conditions. Architecture and phenology of below-ground tissues may be at least as important as that of aboveground tissues. Physiological responses at both the whole plant and tissue levels are important aspects of adaptation in hardwoods, and these can be seen in comparative drought tolerance and xeromorphy of wood anatomy. In comparison to hardwoods, the conifer species which dominate most California forests exhibit a much more conservative mode of adaptive variation in canopy architecture, leaf retention, and drought response. California hardwoods exhibit a remarkable range of ecological tolerance. In comparison to the conifers which dominate most California forests, hardwoods possess a far broader range of morphological, physiological and phenological adaptations to their environments. These adaptations can be seen in their canopy architecture, root architecture, photosynthetic capacity, tissue water relations, adaptation to low nutrient soils, leaf phenology, and hydraulic architecture of the xylem. ORIGINS OF CALIFORNIA HARDWOODS AND HARDWOOD