Regeneration of virginia pine (Pinus virginiana) following southern pine beetle (Dendroctonus frontalis) outbreak in the Sipsey Wilderness, Alabama

We examined regeneration patterns of Virginia pine (Pinus virginiana) following a severe southern pine beetle (Dendroctonus frontalis) epidemic in the Sipsey Wilderness of the Bankhead National Forest, Alabama. Our findings illustrate how a passive approach to forest management, as mandated for such wilderness areas, can lead to considerable changes in the structure and species composition of protected ecosystems. P virginiana is an early-successional species and large mature stands are found within the wilderness. R virginiana reportedly needs direct sunlight and exposed soil to establish. Succession in surviving stands is leading to the establishment of hardwood forest. Because management to slow the beetle epidemic is prohibited in the wilderness, many stands of P. virginiana were killed. The resulting gaps may provide habitat for new P. virginiana recruitment, thus prolonging the existence of these stands in the forest. To determine how the epidemic has affected recruitment patterns of P virginiana, we surveyed existing or recently beetle-killed stands, designating four habitat types corresponding to the presence and absence of direct sunlight and exposed soil. Densities of small saplings were low within gaps, where sunlight is plentiful but exposed soil is uncommon. Small saplings were most dense where hiking trails crossed through gaps; such areas are small, but provide direct sunlight and exposed soil. No small saplings were found in the shade of surviving P. virginiana stands, even near trails. In another survey, we found that small sapling densities were positively correlated with gap size. Recruitment density in some of the gaps was sufficient to replace beetle-killed stands. Greenhouse experiments conducted to examine the importance of sunlight and exposed soil for germination and seedling survival unexpectedly revealed that R virginiana can germinate and survive in shade, below leaf litter, or in the presence of both. Inadvertently, the experiment suggested moderate amounts of shade and litter can facilitate germination when water availability is low. Altogether, our results suggest that P. virginiana is recruiting in gaps created by the epidemic, but this is confined to larger gaps. Over time, the distribution of P. virginiana in the wilderness will likely be no different than had the epidemic not occurred, as succession in the gaps and in mature unaffected P virginiana stands should lead to the same type of mature forest. (c) 2005 Elsevier B.V. All rights reserved.