Decomposition of leaf litter controls carbon storage potential and nutrient cycling in eastern temperate forests. Changes to decomposition rates in temperate forests due to species invasions may adversely affect carbon sequestration, nutrient retention, and other ecosystem services provided by these forests. While decomposition is influenced by abiotic factors (e.g. temperate and soil moisture) at broad spatial scales, at local scales the biotic interactions among herbivores, invasive plants, and soil macroinvertebrates are important drivers of decomposition. White-tailed deer, Amur honeysuckle, and invasive earthworms have been found to accelerate decomposition of leaf litter in eastern forests, but it is unknown if they have additive or synergistic effects on litter decomposition. We tested for the effect of the removal of white-tailed deer, Amur honeysuckle, and earthworms on percent mass remaining from five sites in southwestern Ohio in 2016. The sites consisted of a 20x20-m deer exclosure paired with a control plot, each with a split-plot removal of honeysuckle. Earthworm treatments were paired litter samples with 0.25mm mesh in earthworm exclusion samples and 6mm mesh in control samples. We predicted that the removal of deer, honeysuckle, and earthworms would having additive effects in slowing decomposition rates compared to controls with all three taxa present.
Results/Conclusions
We found a positive effect of earthworm removal on decomposition rates and a weak positive effect of deer removal, but we saw no effect of honeysuckle removal on decomposition rates. Our results indicate that the invasion of exotic earthworms into temperate forests may reduce the carbon storage capacity of these systems. Moreover, the invasion of these earthworms and the overabundance of white-tailed deer showed additive effects on decomposition rates in temperate forests. The lack of a measurable effect of honeysuckle may be due to moderate levels of invasion in our sites; areas with high levels of honeysuckle invasion may see stronger effects on decomposition rates. The increase of decomposition may deplete crucial leaf litter habitat for mammals, amphibians, and invertebrates in these forest systems earlier in the year. The cascading effects of these taxa, in conjunction with warming temperatures, could accelerate the loss of soil carbon in eastern temperate forests.