PARTITIONING GENETIC AND ENVIRONMENTAL COMPONENTS OF PHENOLOGICAL VARIATION IN QUERCUS DOUGLASII (FAGACEAE)

Abstract

Oaks (genus Quercus) often display a large range of phenotypic variation across many of their traits. The contribution of genetic and environmental sources, and their interaction, to this variation can be partitioned experimentally using common garden plantings in which several genotypes are grown in a single location and the phenotype of interest is measured. Due to their slow growth and complex genetic structure, oaks have rarely been grown to maturity in experimental conditions that would allow partitioning phenotypic variation in this traditional way. Here we present results from trees growing in two established experimental gardens of Quercus douglasii Hook. & Arn. planted in 1991. Data from these common gardens are combined with additional data collected at the original provenance populations that served as acorn source locations. We surveyed phenological progression through the spring at both garden and field sites and found significant associations between fall and spring minimum temperatures and spring phenology, represented here as the date of bud break. A genetic component of phenological variation associated with the provenance sites was identified at both common gardens and accounts for 16.4% of the total variation observed among trees, while 68.2% of the variation can be attributed to environmental plasticity, plus a genetic × environmental interaction that accounts for about 1% of bud break variation. We discuss the implications of these components of phenological variation in Blue Oak, especially with respect to climate change, local adaptation, restoration, and assisted gene flow.