Interactive Effects of White-Tailed Deer, an Invasive Shrub, and Exotic Earthworms on Leaf Litter Decomposition
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Interactive Effects of White-Tailed Deer, an Invasive Shrub, and Exotic Earthworms on Leaf Litter Decomposition Michael B. Mahon,1,2*
Melany C. Fisk,1 and Thomas O. Crist1
1
Department of Biology, Miami University, 700 E High St, Oxford, Ohio 45056, USA; 2Present Address: Department of Biological Sciences and Environmental Change Initiative, University of Notre Dame, 721 Flanner Hall, Notre Dame, Indiana 46556, USA
ABSTRACT Herbivore overabundance and species invasions could alter decomposition rates in temperate forests, with consequent effects on carbon sequestration, nutrient retention, and other ecosystem processes. At local scales, herbivores, invasive plants, and soil macroinvertebrates can be important drivers of decomposition, but interactive effects among these different groups are unknown. We tested for the effects of white-tailed deer, Amur honeysuckle, and earthworm activity (manipulated via mesh exclusion) on litter decomposition rates and loss of litter nitrogen (N) in five hardwood forest sites in southwestern Ohio. Each site consisted of a 20 9 20-m deer exclosure paired with a deer access plot; honeysuckle was removed from half of each plot. Effects of earthworm activity were tested using paired litter boxes of fine mesh (0.25 mm; earthworms excluded) or coarse mesh (10 mm; earthworm access). Restriction of earth-
Received 25 September 2019; accepted 18 January 2020
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00485-9) contains supplementary material, which is available to authorized users. Author Contributions: MBM, MCF, and TOC conceived and designed the experiment; MCF contributed field methods; MBM conducted fieldwork and specimen ID; MBM and TOC performed statistical analyses; MBM and TOC wrote the manuscript; comments from MCF improved the manuscript. *Corresponding author; e-mail: [email protected]
worm activity in fine mesh treatments slowed litter decomposition and increased retention of N in the litter layer compared to coarse mesh. Deer access interacted with mesh treatments, with faster decomposition occurring in deer access, coarse mesh treatments relative to others. Greater earthworm biomass in deer access plots relative to deer exclosure plots corresponded with more rapid litter decomposition. Honeysuckle presence did not affect litter decomposition, but did increase litter N retention. The interactions between deer and earthworm activity indicate that reductions in deer populations may slow litter decomposition rates, increasing complexity of habitat structure at the soil surface, which relates to habitat for plants and animals. Key words: earthworms; Odocoileus virginianus; Lonicera maackii; litter disappearance; temperate deciduous forest; above–belowground interactions.
M. B. Mahon and others
HIGHLIGHTS Earthworm activity accelerated leaf litter decomposition. Deer exclosure slowed decomposition by reducing earthworm biomass. Honeysuckle had little effect on litter mass loss, but altered litter N dynamics.
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