Exotic Earthworm Communities as Drivers of Soil Carbon Dynamics in Northern Temperate Forests.

Abstract

This research applies community and ecosystem ecology principles to answer previously unresolved questions regarding changes in forest soil carbon dynamics in response to exotic earthworm introductions. Here, I describe four separate studies completed in northern temperate forests at the University of Michigan Biological Station. These studies (1) characterized the spatial and temporal variability in the species composition of exotic earthworm communities across a forest landscape, and (2) evaluated key factors that contribute to variation in exotic earthworm community impacts on soil carbon content, chemistry, and redistribution. Specifically, this dissertation makes the following conclusions:

1. Exotic earthworm species distributions show spatial variation associated with leaf litter and soil properties, and have expanded across upland forests over decadal time scales.

2. Exotic earthworm species present on site represent three ecological groups, which vary in burrowing and foraging activity. Variation in the species composition of exotic earthworm communities thereby results in community-specific impacts on all major components of soil carbon budgets.

3. Leaf litter degradation and transport are key processes by which earthworm communities influence soil carbon budget components. Leaf litter degradation is primarily driven by the foraging activity of one ecological group; while leaf litter redistribution in the soil profile is determined by the volume and connectivity of burrow systems created by the composite earthworm community. The subsequent fates of litter-derived carbon and nitrogen (gaseous and leachate loss, retention in the soil profile) in earthworm-invaded soils are strongly influenced by soil texture.

4. The alteration of multiple soil carbon processes by earthworm activity can lead to minor shifts in the net soil carbon budget, though shifts in soil carbon chemistry may have long-term implications for rates of soil carbon turnover.

Importantly, the establishment of fundamental baseline data (in the form of soil C budgets) to compare earthworm community impacts on soil C content, and evaluation of earthworm species distribution following regional spread across the landscape, will contribute to the growing literature on biological invasions in north temperate forests of the Midwestern and Northeastern U.S. and advance our general knowledge of exotic earthworm invasions and their impacts.