Intense or prolonged herbivory by large mammals can change forest composition and alter successional trajectories by limiting tree seedling survival and growth. But herbivory is often only one of many stressors for seedlings. Maritime live oak forests on the southeastern U.S. coastal barrier islands feature long-lived southern live oak (Quercus virginiana) and sand live oak (Q. geminata) trees. Deer and feral hog herbivory, changes in water availability on the coast, and legacy effects from the history of agriculture may be contributing to limited oak seedling survival and sapling recruitment. We conducted an exclosure experiment across 4 barrier islands to determine the effect of these potential stressors on oak seedlings. Deer and hog fences were constructed on each island within 2-3 forest types with different land use histories. Quercus virginiana and Q. geminata seedlings were planted within fenced and unfenced plots. Natural oak seedlings were counted and measured (stem diameter and height). Planted seedlings were surveyed and stem diameter, height, herbivore damage, and water stress (measured by browning and leaf drop after a short summer drought) were recorded. We evaluated the effect of type of fencing, forest type/land use history, and water stress on planted seedling growth and survival.
Results/Conclusions
After one year, naturally occurring seedling abundance increased within fenced areas, suggesting herbivory is limiting natural recruitment. Planted seedlings of both species within fences showed increased growth and survival, with high and intense herbivory observed in unfenced plots. Differences in seedling growth and survival of both species were not related to land use history but rather to microsite conditions of higher light intensity and related water stress, and subsequent lower growth and survival. Quercus geminata seedlings showed increased growth and survival compared to Q. virginiana after a summer drought period. Our results indicate that fencing is an appropriate conservation strategy to increase the abundance of natural seedlings and the survival and growth of planted seedlings, and that herbivory and water stress may be stronger proximate factors for oak seedling survival than legacy effects from historic agriculture. Sand live oaks, with their lower water requirements, may be a more appropriate species for restoration planting, particularly in light of projected future climate conditions.