Physiological and evolutionary ecology of oaks (Quercus): Functional traits in relation to habitat, environmental stress and global change (Florida)

Indirect gradient analysis of an assemblage of 17 sympatric oak species in northern central Florida revealed that species' distributions are strongly controlled by soil moisture, nutrients and fire dynamics. Environmental variables in habitats of each species were quantified, and several hypotheses concerning expected relationships among species-level traits and environmental factors within species' habitats were tested. Relationships among traits and habitat factors were also examined in an evolutionary context using independent contrasts based on a molecular phylogeny of these 17 oak species. Finally, life history traits, allometric relationships and habitat factors were explored as predictors of species' responses to elevated CO₂ under contrasting nutrient or light regimes.; Maximum transpiration rate and maximum hydraulic conductivity were positively correlated with the soil moisture in species' habitats, but only when calculated on a sapwood area basis rather than a leaf area basis. This indicates that species have adjusted their allometry in relation to water stress. In a study of northern red oak, drought response was found to change with ontogeny.; Leaf lifespan was negatively correlated with maximum photosynthetic rate (mass basis) and specific leaf area, although there was no relationship between leaf lifespan and the soil nutrient availability in species' habitats. The broader climatic distributions of species are better predictors of leaf lifespan than local habitat factors. Life history traits including seed mass, maximum height, and basal area increment were positively correlated with nutrient availability. Finally, evergreen oaks were more tolerant of freezing-induced xylem embolism and chilling-induced photoinhibition than deciduous oaks.; Habitat breadth of species was an important predictor of plant responses to elevated CO₂ such that generalists tended to be more responsive to CO₂ than specialists. In a three year study of red oak, allometric relationships between leaf area and whole plant biomass changed over time and under contrasting light regimes, explaining to a large extent differences in biomass enhancement ratios of plants grown under elevated CO₂.; Some traits, such as the period of canopy foliation and vulnerability of stems to freezing, were significantly conserved throughout evolution, while other traits, including soil moisture and nutrients in species habitats, were highly convergent throughout evolution. The result is that closely related species are more likely to occur in contrasting habitats than expected by chance. Correlations among traits and habitat factors were generally robust when using phylogenetically independent contrasts based on an independent molecular phylogeny. Therefore, we provide evidence for correlated evolutionary change in life history traits and hydraulic properties with habitat factors, suggesting that oaks have specialized to succeed in particular habitats.