In the Eastern US, fire is a natural process in Quercus (oak) forests. Fire promotes oak regeneration by reducing competition, preparing a suitable seedbed, and decreasing soil moisture. However, oak regeneration has declined since the early 20th century due to fire exclusion. In this study, we examined the effects of fire on tree regeneration over 25 years and asked: (1) Does tree regeneration vary under different fire regimes?, (2) Do the outcomes of prescribed fire differ on xeric, intermediate and mesic sites? and (3) Which limiting resources affect regeneration the most? From a study initiated in 1994, we re-sampled 45 1250m2 permanent vegetation plots across three fire treatments (unburned, annually burned, burned every three years) in two sites, Bluegrass Ridge and Young’s Branch, in the Wayne National Forest, OH. Pretreatment data was collected in 1995 and low-intensity prescribed burns were conducted during 1996-1999 followed by a mostly fire-free period. Tree seedlings were tallied and identified in sixteen 2m2 quadrats and saplings were tallied and identified in 312.5m2. Using linear mixed effects models and model selection using AIC, we examined if seedling and sapling density changed from 1995 to 2019 in relation to fire, light availability, soil nutrients, and soil moisture.
Results/Conclusions
There was a significant increase (p< 0.01) in total seedling density/ha on xeric sites in 2019 (mean=63,485) relative to 1995 (mean=27,013). For saplings/ha there was a significant increase (p< 0.03) on xeric sites in 2019 (mean=1,050) relative to 1995 (mean=1,003). There was no significant change in seedling or sapling density on mesic or intermediate sites or between fire treatments. In our model selection procedure, the change in (Δ) Quercus seedlings was negatively related to calcium and positively related to potassium while ΔAcer seedlings was positively associated with average litter depth and potassium. Time since fire and nitrates were positively related to ΔFraxinus seedlings. Ammonium and silt was positively related to ΔQuercus saplings, while nitrates was negatively and magnesium was positively related to ΔAcer saplings. ΔFraxinus saplings was positively associated with average litter depth. In Young’s Branch, Δsaplings was positively related to fire frequency and estimated nitrogen release and negatively related to calcium. Our results suggest that seedling and sapling density increased since 1995 on xeric sites, regardless of fire treatment, and fire had little effect on seedling and sapling regeneration for most species except for Fraxinus.