Utilization of red oak acorns in non-bumper crop year

Abstract

Utilization of acorns from individual red oaks Quercus rubra Fagaceae) was examined in the tree canopies during fall and from the ground beneath the canopies during winter in a Missouri oak-hickory forest. The goal of the study was to determine whether vertebrates show preference for acorns from individual trees on the basis of acorn or crop characteristics. Seed production, percentage of crop which was viable, maldeveloped, or infested by insects, average seed weight and tannin content of mature, viable acorns were measured for 11 red oak adults. Behavioral observations were conducted in September and October during the peak period of seed fall. Over winter removal was determined by counting the number of acorns removed from 3x3 m plots underneath the trees' canopies between December and mid-April. Canopy removal of acorns was surprisingly low-an estimated average of 52 acorns per tree compared with a mean estimated crop size of approximately 1,200 mature acorns. Over winter, approximately 50% of the acorns were removed from ground plots (range 7% to 93.1%). Number removed corresponded more to the density of nuts rather than to seed and crop characteristics. The low rate of acorn utilization by canopy visitors contrasts with other studies in the literature and may have been due to 1) the fact that this study was done in a relatively homogeneous forest where high density of conspecifics reduces the impact on any one individual or 2) perhaps an unusually low density of birds and mammals.