An Assessment of the Phenology, Dendrochronology and Genotypes of a Mixed-species Community of Oaks at Pepperwood Preserve, California
Wendy Herniman, Steward at Pepperwood Preserve, Sonoma County, California
The phenology, dendrochronology and genotypes of a small multi-species community of oaks in an area of mixed hardwood forest in Pepperwood Preserve, California were investigated in order to compare similarities and differences between species (Quercus agrifolia, Quercus douglasii, Quercus garryana, Quercus kelloggii and their hybrids).
Phenological and dendrochronological studies found that generally there were no significant differences between the species of oaks, so that phenophase onsets of bud burst, flowering and fruiting were similar, as were tree-ring width growth rates.
The long-lived oak trees in this community were found to be Quercus agrifolia (over 540, 260, 214, and 158 years old) and Quercus kelloggii (211, 199, and 175 years old), followed by Quercus hybrids (200, 80 and 60 years old) and Quercus douglasii (175, 160, and 62 years old), with Quercus garryana being generally much younger (85, 76 and 75 years old).
Genetic sequencing results highlighted the influence of scrub oaks, both Quercus berberidifolia and Quercus john-tuckerii, on the genealogy of this community and its ancient origins. The genetic sequencing results showed that the red oaks, Quercus section Lobatae, were unhybridised, but that the situation was far more complex for the white oaks, Quercus section Quercus, where hybrids were in the majority. This finding affirms the concept of oak communities, especially white oaks, being a ‘syngameon’ of species, whereby a community’s evolutionary potential and adaptability to changing conditions is enhanced by interbreeding between those species.