A review of exotic earthworm observations in the Canadian boreal forest and taiga zones

Abstract

Over the past few decades there has been increasing concern that boreal forests could convert from a carbon sink to a carbon source, thus accentuating the effects of climate change. Although forest fires are generally regarded as mainly responsible for causing boreal forests to transition to a carbon source, other factors, such as the activity of exotic earthworm species, could also play an important role. Invasive and exotic species of earthworm can affect nutrient cycling, biodiversity, and forest dynamics. In this context, greater knowledge of the distribution of exotic species of earthworm could help researchers to understand the likely changes in the ecosystems that they have colonized. Herein, we report the results of an exhaustive literature review of the presence of exotic species of earthworm in the Canadian boreal forest and taiga zones. We identified 230 sectors containing 14 earthworm species (11 exotic, two native, and one putative native) in six provinces and three territories across Canada’s boreal forest and taiga zone. We also report 23 as-yet unpublished observations from the province of Quebec. We noted the presence of earthworms in environments (acid soils, harsh climate) that were historically considered inadequate for their survival. This suggests that the portion of Canada’s boreal forests suitable for the presence or colonization of exotic species of earthworm is larger than was previously believed. This study represents the first compilation of locations with exotic species of earthworm in this large northern area. Factors that could affect their distribution and potential effects on boreal ecosystems are also discussed. We also report that several earthworm species seem to be overcoming the previously assumed limitations of temperature and soil pH.