Serotiny in California Oaks

Abstract

Although prolonged seed retention, or serotiny, is believed to be an adaptation to highly variable environments such as the Mediterranean regions of California, no prior study has systematically investigated the prevalence of seed retention among California oaks (family Fagaceae), the dominant woody taxon in California foothill woodlands. We quantified the extent to which acorns were retained into and through the winter and spring within the canopy of five species of California oaks at Hastings Reservation, Monterey County. Significant serotiny was found in coast live oak (Quercus agrifolia) and, to a lesser extent, valley oak (Q. lobata), but was absent in blue oak (Q. douglasii), canyon live oak (Q. chrysolepis), and California black oak (Q. kelloggii). In both species where serotiny was observed, seed retention was primarily predicted by the size of the focal tree's acorn crop. In addition, serotiny in coast live oaks was more prevalent in dry years and when the overall acorn crop of coast live oaks was large. We found no evidence that acorn fall in these species is triggered by a specific environmental event. Prolonged seed retention in California oaks renders acorns available in the canopy to wildlife throughout the winter in some years with potentially significant effects extending beyond those of acorn abundance per se.