PS 81-142 - Continued mortality and crown dieback during an 8-year fire free interval and its influence on canopy openness and oak recruitment in an upland oak-dominated forest in the Daniel Boone National Forest

Friday, August 16, 2019
Exhibit Hall, Kentucky International Convention Center
Jordan N Winkenbach, Forestry and Natural Resource Sciences, University of Kentucky, Lexington, KY, Mary A. Arthur, Department of Forestry, University of Kentucky, Lexington, KY and Wendy Leuenberger, Department of Integrative Biology, Evolution and Behavior, Michigan State University, East Lansing, MI
Background/Question/Methods

The ecological and economic importance of oak species (Quercus) is hard to overstate, especially in Kentucky where 76% of forested land area is oak-hickory mixed hardwoods. Oak regeneration in eastern forests has been hampered by removal of periodic fire and the continued ‘mesophication’ of eastern forests. This study examines an oak-dominated forest after an 8-year fire-free interval following a decade of repeated fire with 3 treatments; Frequent (burned 5 times), Less Frequent (burned 2 times), and a control. Previous work from this study found that crown dieback and mortality continued after initial burning. This could have important implications for future stand structure and regeneration, particularly if seed-producing oak trees continue to experience crown decline and mortality. However, canopy openings created by latent mortality could also provide an improved light environment for suppressed oaks in the understory to be recruited into larger size classes. 93 permanent plots were remeasured during the summer of 2018 and compared with data collected after the last prescribed fire in 2010.

Results/Conclusions

During the fire-free interval tree mortality was 17% and did not vary significantly across treatments. Probability of crown dieback was significantly higher in the Less Frequent treatment for both midstory (10-20 cm DBH (diameter at breast height); p=0.008) and overstory (>20 cm DBH; p = 0.046) trees. Canopy cover ranged 69-99% and was significantly lower in the Frequent treatment (p= 0.0006) and on drier sites (p= 0.0026). Stems recruited into the sapling layer (2-10 cm DBH) were 6.9% oak, all found on burned sites (Frequent, Less Frequent). Mesic species dominated by sassafras (S. albidum) and red maple (Acer rubrum) comprised 70% across all sites. Sapling recruitment was significantly higher on burned sites and on sites with a more open canopy (p<0.001). Recruited midstory stems were 5.4% oak and dominated by red maple (34%). Midstory recruitment was significantly higher on sites with a more open canopy (p<0.001). Continued decline and mortality of oak trees was not found in the study area and the significant increase in canopy openness in the Frequent treatment is aligned with management goals for prescribed burning. Additionally, the presence of oak regeneration (n=48) on burned sites is noteworthy because at the start of the fire free interval there were zero oaks found in the sapling layer. However, the large recruitment response of mesic species in both the sapling and midstory layer presents a substantial hurdle for ongoing oak management.