Influence of rocky landscape features and fire regime on vegetation dynamics in Appalachian Quercus forests

Question: How do interactions between rocky landscape features and fire regime influence vegetation dynamics? Location: Continental Eastern USA. Methods: We measured vegetation, disturbance and site characteristics in 40 pairs of rocky and non-rocky plots: 20 in recently burned stands, and 20 in stands with no evidence of recent fire (‘unburned’ stands). Two-way analysis of variance (ANOVA) was used to assess the main and interaction effects of fire and rock cover on plant community composition. Results: In burned stands, rock cover had a strong influence on vegetation. Non-rocky ‘matrix’ forests were dominated by Quercus, and had abundant ground cover and advance regeneration of early and mid-successional tree species. Burned rocky patches supported greater density of fire-sensitive species such as Acer rubrum, Sassafras albidum and Nyssa sylvatica and had little advance regeneration or ground cover. Quercus had fewer fire scars and catfaces (open, basal wounds) on rocky patches, suggesting that rocky features mitigate fire severity. In unburned stands, differences between rocky and non-rocky patches were less distinct, with both patch types having sparse ground cover, little tree regeneration, and high understorey densities of relatively shade tolerant A. rubrum, N. sylvatica and Betula lenta. Conclusion: Under a sustained fire regime, heterogeneity in rock cover created a mosaic where fire-adapted species such as Quercus dominate the landscape, but where fire-sensitive species persisted in isolated pockets of lower fire severity. Without fire, species and landscape richness may decline as early-mid successional species are replaced by more shade tolerant competitors.