Tree species composition is thought to be a major controlling factor affecting decomposition processes beneath tree canopies via direct effects on litter quality and indirect effects on microclimate and the decomposer community. Savanna-like ecosystems offer a unique opportunity for testing hypotheses regarding the relationships between above-ground tree species and decomposition processes, because individual trees and their canopies are typically non-overlapping. Understory plant species can also exert an influence on decomposition processes, and in cases where understory plants are invasive species, such influences can represent an alteration of function from that found in the native habitat. The objective of this study was to simultaneously examine the influence of three tree species, blue ash (Fraxinus quadrangulata), chinkapin oak (Quercus muehlenbergii), and shagbark hickory (Carya ovata), and an invasive shrub, Amur honeysuckle (Lonicera maackii), on decomposition dynamics in a savanna ecosystem in central Kentucky. Single- and mixed-species litterbags were placed under savanna trees and in the surrounding savanna vegetation matrix, and litter decomposition rates, litter C and N, and microarthropod abundance were assessed over a period of two years. Litter pickups occurred at 1.5, 3, 6, 12, and 24 months. Results/Conclusions
Preliminary data show that litter from the invasive honeysuckle breaks down much more rapidly than the litter of all three tree species, as expected based on initial lignin and C:N concentrations (C:N: 29.3 honeysuckle, 34.5 hickory, 37.4 ash, 47.7 oak; % lignin: 17.6 honeysuckle, 17.0 ash, 25.4 oak, 27.4 hickory). Oak and hickory litter had lower decay constants than ash, reflecting differences in initial lignin content and litter C:N. While all three tree species’ litter appears to break down more rapidly in the presence of honeysuckle, this effect is especially pronounced with hickory litter, suggesting an interaction between canopy species and honeysuckle. In single-tree species litterbags, N was immobilized for at least the first year, with only ash litter beginning to release N at 6 months. In single-species honeysuckle litterbags and mixed-litterbags (honeysuckle + individual tree species litter), however, N release occurred immediately. Both litter quality and microenvironment (tree canopy and open savanna) appeared to have some effect on microarthropod abundance. If the effects of invasive species on certain ecosystem processes are strongly influenced by over-story species, this could suggest a novel approach to understanding the vulnerability of ecosystem processes to invasions of honeysuckle and potentially other invasive species.
