Flowering and flower maturation in valley oak Quercus lobata
We investigated factors driving flowering and flower maturation and their effects on acorn production at both the annual and individual trees levels in a population of valley oak ( Quercus lobata ) in central coastal California, USA. Among years, female flower production was negatively correlated with rainfall, while warm spring temperatures and a large acorn crop the previous year decreased the proportion of flowers maturing into acorns. Among trees, individuals with greater access to ground water growing in warmer microclimates produced more catkins and more female flowers. In addition, male and female flower abundance were positively correlated even after controlling for tree size and resources, countering the hypothesis of a life-history tradeoff between investment in male and female flowering. Factors limiting pollen availability include weather-driven effects (both the pollination Moran effect and environmental vetos), phenological synchrony, and pollen coupling, factors that were difficult to distinguish. All three flower indices explained a significant proportion of variance in acorn production at both the annual and individual tree levels. Most important, however, was variation in female flower maturation, while both female and male flower abundance explained between one-quarter and one-third of variance in acorn production. Quercus lobata is not only a flower maturation masting species, but also a female flower and male flower masting species. The underlying drivers of flower initiation, fertilization, and flower maturation yield important insights into the factors influencing masting behavior in perennial plants and represent an area that can benefit from more empirical study.