PS 14-106
A seven-year study of the impact of temperature and individual variation on flowering and leaf phenology in a savanna population of valley oak, Quercus lobata Née
The impact of climate on flowering is an increasing concern because mounting evidence indicates that climate warming is causing changes in the timing of leafing and leafing-out which are influencing many ecological processes including: exposure to spring frost, availability of leaves for herbivorous insects, exposure of acorns to seed predators, pollen availability, and seed production. We are studying valley oak, an ecosystem foundation species of California that has experienced significant loss of coverage due to landscape transformation. Here, we address three questions: (1) Do early and later flowering valley oak individuals show a reduction in acorn production? (2) Do the same individuals flower early and late across years, suggesting a heritable component to flower timing? (3) Does year-to-year variation in climate shape the onset of budburst, leafing out, and flower emergence in our population? The study site is an oak savanna at the University of California Sedgwick Reserve, administered by UCSB. During winter and spring of 2007-2013, we monitored dates of budburst, emergence of male catkins and female flowers, and leaf elongation in 100 Quercus lobata adults
Results/Conclusions
Our findings indicate that onset of bud burst and flowering varies extensively within a population and across years. We observed that 10% of the trees with early budburst and 10% with late budburst had lower acorn production than the middle 80% of the trees. Secondly, we found a significant correlation on rank order of dates of first and median budburst and first male catkin flower across trees from year to year. Finally, we found that these dates were shaped by temperature. This study provides evidence that timing of flowering may have a genetic basis and that selection against early and later flowering trees favors the synchronization of flowering. We also find that the date of first flowering is inversely correlated with synchrony of flower production across years. The findings of this research illustrate that climate warming will affect (i) the timing of leaf phenology, which may affect the insects that feed on the leaves; (ii) the synchrony of flower production, which will affect reproductive fitness of individual trees; and (iii) the abundance of acorns that will affect the insect and wildlife populations that depend on acorns as a resource. Thus, our study adds to the growing evidence that the disruption of phenology caused by climate change may have demographic effects on the focal tree species and cascading effects on the ecosystem.