Animals and Money: Canada’s Earthworm Crisis

Forests, as well as forest soil, act as a major carbon reservoir¹ and altering these ecosystems can influence their ability to store atmospheric CO₂. Earthworms, which are invasive in boreal forests of Canada, have an immense influence on the ecosystem and ecological communities because they alter forest soil. As a result, earthworms have a substantial influence on the carbon cycle, which could have negative effects on Canada’s ecosystem, climate, and even economy. 

As ecosystem engineers, earthworms play an important role in regulating physical, chemical, and biological processes in underground ecosystems. They are involved in decomposition processes, nutrient cycles, water regulation and carbon sequestration, greatly affecting soil properties². By degrading organic matter and molecules, produced by plants and animals, earthworms provide small organic compounds and mineral nutrients, such as nitrogen, which plants need to thrive³. Since earthworms mix the soil, they influence the soil structure, infiltration of water, and distribution of nutrients⁴.
In Canada, however, the delicate chemical equilibrium of soil and organic matter is threatened by invasive earthworms. Native earthworms in North America have been extinct for 12,000 years due to extensive glacier formation⁵. Since then, North American ecosystems have developed and adapted in the absence of earthworms and their soil-forming properties. With the European settlement, earthworms were introduced once again in the boreal forests of Canada. Here, the earthworms’ otherwise beneficial decomposition efforts instead throw the ecosystem off balance. Invasive earthworms lead to a decline of organic matter and a reduction in nutrients in the soil⁶. Additionally, less invertebrates live in soils invaded by earthworms⁶. Earthworms therefore interfere with carbon storage in boreal forest soil, allowing more to be released into the atmosphere⁵. The impact invasive earthworms have on carbon storage and consequently the climate can be measured through the Kyoto Protocol. The Kyoto Protocol is an agreement to combat greenhouse gas emissions, which places economic value on carbon emissions. Lower carbon emissions are thereby more economically profitable¹. The Earthworm's impact on forest carbon stocks therefore has an economic significance for the Canadian government. The carbon stocks in Canadian boreal forests have an economic value of 744 USD per hectare¹. Roughly half of the total carbon is bound in subterranean biomass⁸. In total there is 270 million hectares of Canadian boreal forests⁷. For the subterranean biomass of the forest area this adds up to carbon stocks worth 100 billion Dollars. However, forest soils that are inhabited by earthworms bind less carbon - up to 94% less, depending on the soil type⁵. 

In 2019 10% of boreal forests were inhabited by invasive earthworms. Based on these numbers, carbon worth up to 9,4 billion dollars could not be stored in the forest soil due to earthworm invasion, a significant cost to the Canadian economy.This carbon gets shifted into mineral carbon stocks but also into CO₂ that is released into the atmosphere. Invasive earthworms therefore not only have a substantial economic impact. The introduction of Earthworms affects the immediate environment and could potentially contribute to climate change. 

Hedda Wern

Issue 14 (PDF)