Broad and local-scale patterns of exotic earthworm functional groups in forests of National Wildlife Refuges of the Upper Midwest, USA

Abstract

The National Wildlife Refuge System is the world's largest network of lands set aside specifically for wildlife conservation. For refuge planners and managers tasked with maintaining ecological integrity and wildlife habitat, many uncertainties exist. In forests in the Upper Midwest, for instance, exotic earthworms are impacting ecosystem structure and function, but their community composition and effects on refuges is unknown. We examined the association of earthworm functional group abundance and community composition within upland forests of refuges with broad scale patterns of anthropogenic land use and local scale differences in forest characteristics. Patterns of anthropogenic land cover, including proportion of the land, mean patch area, and largest patch index, were strongly correlated with the biomass of epi-endogeic earthworms. Earthworm community diversity, however, was inversely related to patterns of dominating anthropogenic land cover, and increased under high ratios of natural to anthropogenic lands in the surrounding ecoregion. Within forests, earthworm community composition could be partially explained by variables representing both dispersal opportunities and habitat suitability. In general, heavily-invaded forests had low conifer dominance, high silt content, high basal area, greater amounts of anthropogenic cover within 500 m, and were closer to roads and farther from agriculture. However, the relationship between local forest characteristics and biomass differed greatly among earthworm functional groups and between refuges dominated by natural lands and those dominated by anthropogenic lands. For refuges with high earthworm loads and well developed earthworm communities, managers may be confounded in restoring historic conditions and may need to look at multiple tools, including artificial regeneration, to mitigate for current earthworm effects. In refuges seemingly in earlier stages of earthworm invasion, future planning and management should be tempered by potential effects observed in those refuges in more anthropogenic landscapes.

Campsites, forest fires, and entry point distance affect earthworm abundance in the Boundary Waters Canoe Area Wilderness

“…Whether measured in terms of biomass or density, earthworms were consistently more abundant on islands with campsites as compared to those without. This result corroborates the findings of previous studies showing that human activity influences the distribution and abundance of non-native earthworms (Hendrix et al, 2008;Shartell et al, 2015). These include correlations with road proximity (Cameron & Bayne, 2009) and boat launches (Cameron, Bayne & Clapperton, 2007) and their spread through use as fish bait (Keller et al, 2007).…”

Ecological Predictors and Consequences of Non-Native Earthworms in Kennebec County, Maine

“…As we predicted, earthworms were most-likely to be present near roads. These findings are congruent with other studies that suggest that earthworms are generally found closer to roads, especially older roads, along forest edges, near logging sites, or near other human disturbances (Beausejour et al 2014, Bohlen et al 2004a, Cameron and Bayne 2009, Gundale et al 2005, Holdsworth et al 2007, Randsom et al 2015, Sackett 2012, Shartell et al 2015. In Maine, I interpret the fact that distance to roads is the only significant predictor in our model as evidence Forest size, forest composition, and pH were not statistically significant predictors for worm presence; however their inclusion in the best-fit model indicates that they are important factors in predicting the presence of earthworms at a site.…”

Earthworm diversity and distribution in district Mandi, Himachal Pradesh of Northwest Himalaya, India

“…Epi-endogeic earthworms, consuming leaf litter and top mineral soil, were found in all land use types except in grasslands. Shartell et al (2015) [64] opined that epi-endogeic worms had strong association with human impacted habitats and ability to coexist with other functional groups. Anecic functional group of earthworms was not found in any of the land use types under the present study that were either degraded or highly disturbed.…”