The distribution and establishment of non-native earthworm populations and their impact on organic layer thickness in the Acadian Forest

The distribution and impacts of non-native earthworms are poorly documented in Atlantic Canada meaning that we have limited knowledge of the relationship between earthworms and forest properties. To address this knowledge gap, we surveyed earthworms and sampled the soil organic horizon in 41 forest stands located in New Brunswick to investigate their relationship with forest properties and impact on organic horizon thickness and carbon content. We found earthworms at 39% of the sites that we surveyed. Earthworms were more common in hardwood stands than softwood stands, at low elevations, and near current or historical human activity. Sites with earthworms had thinner organic horizons and less carbon. A simple two-pool Lotka-Volterra model described the relationship between earthworm abundance and organic horizon carbon well. The model predicted that earthworm invasions take about a decade to reach numbers typical of invaded sites and half a century to reach carrying capacity. Together these data suggest that, despite their long-term regional presence, much of the Acadian Forest that is not adjacent to human activity remains unimpacted and vulnerable to the effects of non-native earthworms.