Wildfire alters oak growth, foliar chemistry, and herbivory

Fire is a major disturbance factor influencing the formation and maintenance of oak (Quercus)-dominated forests of eastern North America. Fire suppression practices have resulted in declining oak dominance, and caused the loss of oak seedlings due to poor light regimes and vegetative competition. Both wildfires and prescribed fires can alter forest stand composition and influence succession. Fire can also cause physiological changes in plants, potentially influencing growth, competition, and susceptibility to herbivory. Fire may impact herbivore populations directly by altering habitat and abundance, or indirectly through alterations in food supply. The objective of my study was to assess the effects of a naturally occurring wildfire on chestnut oak (Q. prinus L.) seedling growth, foliar chemistry, and suitability to a generalist herbivore, the gypsy moth (Lymantria dispar L.). I sampled chestnut oak seedlings four times for phytochemical analysis throughout the post-fire growing season, and sampled once to assess suitability for caterpillar performance and to measure seedling growth. Chestnut oak seedlings sampled from burned sites had significantly higher foliar nitrogen and water content than seedlings sampled from non-burned sites. Seedlings from burned sites had transient declines in foliar carbohydrate concentrations, and also had higher initial tannin levels. Although seedlings from burned sites were smaller with respect to stem diameter and height, they grew more with respect to absolute growth rate, leaf area, and biomass, than their non-burned counterparts. In spite of the differences in leaf chemistry, there were no significant differences in the growth or development of gypsy moth caterpillars fed foliage from burned versus non-burned seedlings.