Pre-Dispersive Predation Influence on Natural Regeneration of Quercus robur L.

Quercus robur L. shows interannual variability in the production of acorns. This process is called “masting” and can generate some disadvantages for natural regeneration by reducing seed recruitment. Acorn production not only shows variability between years, but also among trees. Our aim was to estimate the percentage of acorn losses for pre-dispersive predation. For this, we have assessed the acorns reaching the ground for three years. Of all the acorns that the tree produces, only a proportion reaches the soil in viability to germinate and establish itself as a seedling. A significant number fall to the soil before completing their development, probably due to failures during this process or by self-regulatory mechanisms of the tree itself, which only keep the seeds that it can withstand according to the resources at its disposal. Another proportion is consumed by predators on the tree, and finally a significant number of acorns are predated by insect larvae. In the oak species, most of these such larvae are coleopteran of the genus Curculio and lepidopteran of the genus Cydia. In years of copious production, the acorns that reach the ground that are viable to germinate and establish themselves as seedlings ranges between 5% and 33%. The larvae damage is not only caused by the direct consumption of cotyledons and embryo but, even in cases in which the acorns remain intact, the larvae generate cavities and galleries in the seed, which facilitates the entry of fungi, bacteria, and other insects. In conclusion, pre-dispersive acorn predation by insects could place itself as one of the main constraints for natural regeneration of Quercus species.