LTREB: Phenology and Masting in California Oaks

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The proposal will investigate the proximate factors leading to highly variable and spatially synchronized seed production in a wind-pollinated, obligate outcrossing tree species, the valley oak (Quercus lobata). This phenomenon, known as mast-fruiting or masting behavior, is believed to be driven by either environmental forcing or pollination coupling. Environmental forcing postulates that trees use weather as a cue to determine the resources they devote to reproduction in a particular year. Pollen coupling assumes that pollen is limited and that fertilization efficiency is dependent on pollen production by nearby trees. This proposal will test these hypotheses using long-term data on acorn production by Q. lobata collected on a statewide scale combined with detailed data on individual phenology, microclimate, overall pollen abundance, and the fate of female flowers. The project will collect statewide data on acorn production, a highly variable food resource important to both game and non-game wildlife. The project focuses on a tree species of considerable conservation interest because of development, habitat conversion, apparent lack of regeneration, and susceptibility to future climate change. The work proposed here will help to emphasize the key role Q. lobata and oak woodlands in general play as a natural resource important both to wildlife and to ecosystem function. The extensive dataset on seed production by forest trees that will result from this research will be made electronically available, first in summary form and ultimately as metadata, for future researchers interesting in using the data to examine patterns and test hypotheses regarding the ecology and evolution of masting behavior.