Herbivory effects on Quercus durandii, Quercus fusiformis and Quercus texana

Recruitment failure, defined as the failure of juvenile plants to reach maturity, has been described for many plant communities and is becoming a major concern for conservation biologists and land managers. Many different species of Quercus (oak) in North America exhibit recruitment failure. Previous studies have reported high Quercus juvenile densities, indicates that seed production, seed germination, and seedling recruitment were not a problem in the past. Light intensity has been shown to be a potential factor affecting regeneration in Quercus communities. The browsing of Quercus species by herbivore populations is a common occurrence; however the amount or impact of foraging pressure on sensitive oak communities is likely largely unknown. In some studies, it has been shown that the herbivore communities depend heavily on the newly emerged seedlings and saplings as late summer, fall, and winter browse. The current study used four simulated herbivory treatments to determine the effects of herbivory on three Quercus species (texana, fusiformis, and durandii) within the Kerr Wildlife Management Area, west of Kerrville, Texas. The simulated herbivory treatments were 0, 33, 66, and 100% of the total stem length removed. In addition, the natural herbivory level was also evaluated. Results indicate similar responses by the

three species to the simulated herbivory treatments. Juvenile mortality increased and the measured growth parameters decreased with increasing removal of stem (increasing herbivory pressure). The natural herbivory treatment showed that there is a general preference for Q. texana by the herbivores, and that foliar nitrogen and chlorophyll were lowest in Q. texana. Results indicate herbivory may play an important role in determining the replacement dynamics of some Quercus communities, particularly when the herbivory pressure is high. In addition, the effects of herbivory in combination with other factors, such as light levels, may further reduce the recruitment potential of these Quercus species at lower herbivory pressures. If the goal of managers is to increase the recruitment of juvenile Quercus into the adult populations, the herbivory pressure should be considered.