The overabundance of white-tailed deer (Odocoileus virginianus) and the presence of invasive plants, such as Amur honeysuckle (Lonicera maackii), have strong effects on deciduous forest ecosystems of eastern North America. Deer and Amur honeysuckle reduce abundance and richness of seedlings, saplings, and herbaceous plants in the forest understory. Increased abundance of exotic earthworms has been linked to deer and invasive plant presence. Asian and European earthworms have detrimental effects on ecosystems processes through decreasing soil nutrient availability and total soil carbon and increasing soil horizon mixing in forest soils. We hypothesized that removal of deer and invasive honeysuckle would reduce the abundance of invasive earthworms and increase standing litter biomass. We analyzed invasive earthworm abundance and leaf litter biomass from five sites in southwestern Ohio from 2011 to 2015. The sites consisted of a 20x20-m deer exclosure paired with a control plot, each with a split-plot removal of honeysuckle. All earthworms were sampled using the hot mustard extraction technique following collection of leaf litter.
Results/Conclusions
Deer removal had a significant negative effect on earthworm abundance. Additionally, fewer earthworms were found in the exclosures as the study progressed. We found no effect of the honeysuckle treatment on earthworm abundance. Deer removal had a significant positive effect while honeysuckle removal had a weak positive effect on standing litter biomass. In addition, earthworm abundance and deer treatment had an interactive effect on standing litter biomass. This result indicates that earthworms reduce standing litter biomass at a higher rate when deer are present. Our results show that deer presence may increase earthworm invasion and earthworm effects on ecosystem processes, such as decomposition. Additionally, our study provides further insight into interactions between above- and below-ground organisms, as well as potential effects of those interactions on ecosystem processes. The direct and indirect effects of deer on standing litter biomass and earthworm abundance potentially have cascading effects on other invertebrate communities, nutrient cycling, and soil formation in forest ecosystems.