Does the shelterwood method to regenerate oak forests affect acorn production and predation?

Abstract

The shelterwood system is one of the primary methods currently used to encourage regeneration of oak forests; yet, little is known about its influence on acorn production and predation. We compared acorn production, and predation by insects and mammals in stands of red oak ( Quercus rubra L.) that were regenerated by the shelterwood method (50% canopy removal) to that of uncut (control) stands in the first year of production after the harvest treatment. In each plot, we measured stand and tree characteristics and estimated acorn production by using both acorn traps and a visual crown survey to place trees into productivity classes. Acorns collected in traps were examined to record the external and internal conditions, percentage of cotyledon damaged and the presence of insects. Exclusion cages were used to quantify acorn predation by mammals in harvested and control plots. Oaks in the shelterwood plots produced more acorns than oaks in uncut stands if the acorn crop was rated by the crown survey method, but not when production was measured with acorn traps. We found no evidence that the shelterwood method influenced acorn predation by insects or mammals. Visual examination of the exterior of the pericarp indicated that insects attacked 44% and 47% of the acorns in harvested and control plots, respectively. Most of the damage produced by insects was attributed to pip galls (cynipid wasps) and acorn weevils ( Curculio sp.), which in most cases damaged more than 75% of the cotyledon. Squirrels and chipmunks were the primary mammals responsible for removing 50% of the acorns in the fall-spring whereas mice took 33% of the acorns. Use of the shelterwood method in conjunction with leaving the best acorn producers can be used to create the desired stand structure while maintaining or increasing acorn production and oak regeneration potential in the stand.