The impact of non-native earthworms on regenerating forest
communities in western Pennsylvania
John A. Gargasz and Cory M. Shoemaker
Department of Biology, Slippery Rock University

Abstract:
During the last glacial period, earthworms native to the Eastern United
States were extirpated, causing forest communities in Eastern North
America to develop without the presence of earthworms for at least the last
20,000 years. Now, non-native earthworms from Asia and Europe,
deliberately introduced through human actions, have invaded these forests.
This invasion potentially may affect these ecosystems’ composition and
function, although to date no research has assessed the impact of nonnative earthworms on forest communities of Western Pennsylvania. The
environmental impact of non-native earthworms varies by species, but
generally they change soil composition, alter carbon: nitrogen ratios, and
decrease phosphorus abundance. By altering the soil composition and
chemistry, these non-native earthworms have a cascading effect on forest
plant communities. This study specifically seeks to enumerate the impact of
non-native earthworms on new-growth forest communities across the
Eaton, T.H., 1942 Journal of the Washington Academy of Science
Header worm, Natural History Museum, London
Wisconsin glacial boundary in Pennsylvania.

Methods & Maps:

Sites will be selected by stratified sampling across three forest ages (Fig. 1)
1. Forests aged 20-30 years (3 sites)
2. Forests aged 40-50 years (3 sites)
3. Forests aged 60+ years (3 sites)
9 sites total
Three of the nine sites are located in a region covered during the most recent
glaciation (Wisconsin Glaciation)
At each site, three plots will be surveyed for
1. Earthworm diversity and abundance
2. Understory plant community composition
3. Overstory plant community composition
4. Abiotic conditions (disturbance, landscape features, etc.)

Purpose:

To analyze plant communities of different aged Western Pennsylvania forests and
how non-native earthworm species affect these communities.
We hypothesize that:
1. the presence of non-native earthworm species will change the composition of
these plant communities leading to the domination of non-native plants
2. Earthworm densities and plant communities will be correlated to the ages of
forests sampled and glacial history
3. Leaf litter layer will be affected by presence/composition of earthworm
community
4. Earthworm communities will affect plant community composition to include
understory, overstory, and non-vascular plant community components
Deliverables:
1. Characterize the earthworm community in regenerating woodlands of western
Pennsylvania
2. Link plant communities to earthworm communities
3. Describe impact of earthworm invasion on forest communities across glacial
boundary

*The authors gratefully acknowledge project support from a SRU FSRG