How do thinning and burning treatments influence the canopy carbon balance of southern Ohio's mixed-oak forests?

Wildfire suppression in the last 80 years has resulted in increased fuel loads in Western US forests. Questions remain as to how fire suppression impacts the structure and function of Eastern forests. Principal among those is the role of fire in oak regeneration. The Ohio Hills Fire and Fire Surrogate (FFS) Study is a factorial, replicated experiment designed to explore how prescribed fire and fire surrogate treatments might improve oak regeneration and growth.  We wanted to investigate the impacts of these treatments on forest canopy function and potential carbon gain of the most common tree taxa at the site.  Leaf nitrogen content (N_mass, %) and specific leaf weight (SLW, g ∙ m^-2) are two important traits that are closely linked to plant photosynthetic performance. The objective of this study was to understand how N_mass and SLW of seven canopy tree taxa (Quercus alba, Q. coccinea, Q. prinus, Q. velutina, Carya spp., Acer rubrum, and Liriodendron tulipifera) responded to thinning (T) and/or burning (B) treatments and different landscape and soil properties in southern Ohio.  In 2003, leaf samples were collected along a vertical canopy gradient from trees in treatment plots (T, B, TB, control) in three FFS-OH locations. Treatment impacts were detected on SLW for most species at the tree crown base.  N_mass of most species did not respond to treatments.  PnET-II sensitivity analyses suggested these subcanopy changes in SLW increased the annual net primary production by 3 to 7%.  Regression tree analyses indicated that landscape features and soil properties had a minor influence on N_mass and SLW.  Inter-species differences accounted for most of the variation in both leaf traits. It has long been understood by foresters that thinning increases stand productivity, but our study quantifying altered leaf traits and modeling canopy productivity provides a mechanism for this observed increase.