Effects of burning and timber harvest treatments on oak and maple populations in temperate mixed forest

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Emily M. Booth and Brent J. Sewall, Department of Biology, Temple University, Philadelphia, PA, J.D. Lambrinos and Shannon Henry, Forest Management Section, Fort Indiantown Gap National Guard Training Center, Annville, PA

Background/Question/Methods
Forests in eastern North America have been shaped extensively by clear-cutting and decades of fire suppression, leading to high stem densities, depauperate understories, and an increasing prevalence of fire-intolerant tree species. Native upland oak ecosystems, which are well adapted to fire, have increasingly been replaced by encroaching maple, birch, and other mesic tree species. However, little research has been completed in eastern North America within the context of frequent fires, especially when combined with the effects of silvicultural treatments on xerophytic oak and mesic hardwood tree populations. Our objective was to evaluate the ways in which prescribed burning and timber harvest treatments affect the recruitment of oak and maple species into the community and overstory. We studied managed stands of temperate mixed coniferous and broadleaf forest at Fort Indiantown Gap National Guard Training Center, a military training area in the Appalachian Mountains of southeastern Pennsylvania. Stem densities for three age classes (adult, sapling, and seedling, defined by size) and adult and sapling basal area (BA) were collected from 1510 forest inventory plots in 2003, and 1049 plots in 2013-2014. We used model selection and generalized linear mixed models with zero-inflation to examine the impact of burning and timber harvesting on oak and maple trees in each age class.
Results/Conclusions
Oaks and maples responded differently to prescribed burning and timber harvest in each age class. In adult oaks, plots that were both burned and harvested had similar adult oak stem density but smaller BA compared with untreated plots, suggesting attrition of larger trees and recruitment of smaller trees to the adult age class with treatment. By contrast, plots that were both burned and harvested were associated with lower adult maple densities and BA than plots with either treatment alone or no treatment, especially where the overstory had a greater percentage of maple trees. In oak saplings, plots that were both burned and harvested had similar densities but greater BA than untreated plots. Burning resulted in lower maple sapling densities and BA. Oak seedling densities were lower in harvested plots, and there was no relationship of burning or harvest on maple seedling densities. Our results indicate that in northeastern temperate forests, timber harvest may favor maple seedlings over oak seedlings, but at sapling and adult age classes the combined treatments of prescribed burning and timber harvest could be effective in limiting the replacement of oaks by encroaching maples.