Insect and Disease Impacts on Blue Oak Acorns

Abstract: We studied the impacts of diseases and arthropods on acorns and naturally occurring seedlings of blue oak, Quercus douglasii, in northern California. Damage levels were always significantly higher in acorns collected from the ground than those picked from the tree. Accurate assessments of damage levels could only be made by dissecting acorns, since external symptoms were frequently absent from acorns with severe damage to the embryo. Levels of insect and disease damage to acorns varied significantly between locations and between trees. Foliar feeding by several types of insects had no apparent effect on the survival of natural blue oak seedlings over 3 years. Water stress appeared to be the primary factor affecting seedling survival. Although many seedlings survived the complete loss of their shoots and resprouted, repeated resprouting was associ-ated with increased mortality. Overall seedling mortality after 3 years was 25 percent, but ranged from 5 percent to 65 percent at different plots. We suggest that blue oak seedlings are adapted to persist for a number of years beneath mature trees and may constitute an important source of advance regeneration