Fire suppression in historically oak-dominated forests of the eastern U.S. has facilitated the spread of fire-sensitive tree species, leading to low understory light. Oak (Quercus) species are competitively inferior under these conditions and often experience regeneration failure. Some researchers predict conversions of many forest stands from predominantly oaks to shade-tolerant, late-successional species such as red and sugar maple (Acer rubrum L. and A. saccharum Marshall, respectively). This would have numerous ecological and economical consequences, as many species depend on oak acorns for their survival, and oaks are a highly sought after, valuable timber species. In this study, we address a relatively unexplored consequence of this potential shift: how could interspecific differences in canopy and leaf characteristics between oaks and red maple affect nitrogen (N) and carbon (C) cycling via throughfall, stemflow, and leaf litter decomposition. Along two ridges in the southern Appalachians of eastern Kentucky, we tracked seasonal variations in chestnut oak (Q. montana L.), scarlet oak (Q. coccinea Muenchh), and red maple throughfall and stemflow quantity and quality following discrete precipitation events for a 2-yr period and assessed leaf litter decomposition, C, and N concentrations for 1 yr.
Results/Conclusions
Overall, throughfall quantity and quality were similar between species, but red maples generally produced 2-3x more stemflow with greater funneling ratios than either oak species. Total N inputs via stemflow were often greatest for red maple (e.g., ~ 1,600 mg m-2 compared to ~ 700 mg m-2 for oaks in summer 2006), but oaks usually generated higher C inputs (e.g., ~ 14,000-18,000 mg m-2 C compared to only ~ 7,000 mg m-2 C for red maple in fall 2006). Compared to oaks, red maple litter had initially lower lignin (11% compared to 14 and 20% for scarlet and chestnut oak, respectively), lower N concentration (0.4% vs. 0.5% for oaks), and a higher C:N ratio (116 vs. ~ 90 for oaks). Red maple leaf litter decomposed faster, with only 65% remaining after 9 mo compared to 78 and 87% for scarlet and chestnut oak, respectively. Thus, while the two oak species were similar with regard to potential avenues of N and C inputs, red maple consistently differed from the oaks. These findings suggest that a shift in canopy dominance as a consequence of altered disturbance regimes due to changing management objectives has important implications for ecosystem processes such as N and C cycling via species-specific differences in stemflow inputs and litter quality.
