Invasive Earthworms in Northern Scandinavia

An increasing number of species are appearing outside their natural habitat, mostly due to human activities, but also because of climate change. These species often harm native biodiversity and greatly affect the functioning of ecosystems. Some of these invasions are easily visible, while others are hidden – right beneath our feet in the soil. Invasive earthworms are one of them.

Earthworms generally beneficial

Earthworms are generally valuable organisms that deliver beneficial ecosystem services to crop production. However, earthworm activities may be less beneficial in other environments such as boreal forests. Since the last glaciations, the great forests of the northern regions evolved largely without earthworms. Nevertheless, invasive burrowing earthworms are now spreading rapidly in these forests and heavily affect their environment – but how? And how widespread are they?

Mapping earthworm distribution and unraveling their impact

This project aims to map past, current, and potential future distribution of burrowing earthworms in Sweden, whilst also evaluating the potential effect of these earthworms in Swedish boreal forest soils in which they are not (yet) present. One of the specific goals is to unravel how earthworms may change soil functions (such as carbon storage), and how earthworms interact with other organisms, like fungi, bacteria, and plants.

Field experiment simulating future climate

To test the above-mentioned goal, researchers of the project have established an experimental garden in the forest near Lunsen and Krusenberg, 5 km south of SLU’s campus in Uppsala. This garden contains mesocosms (experimental boxes) with soil turfs from forests near Gällivare, Norrbotten. The forested location provides a similar forest-microclimate for the turfs like in their original environment, while the warmer climate in this lower latitude mimics expected climate change impacts.

The mesocosms contain turfs from a variety of sites: from nutrient poor pine forests with lichens, crowberry and heather, to nutrient richer spruce and birch forests along rivers, with herbaceous plant cover. Each turf has at least one small tree, either pine, spruce, or birch. Including these saplings are essential to keep an (almost) untouched microbial community with tree-associated ectomycorrhizal fungi in the mesocosms.

Measurements occur continously

Earthworms will be placed in the boxes during early summer 2024. Since earthworms are already widespread in forests around Uppsala (unlike in the north), potential escape of them will not pose risk for the surrounding environment. Until their introduction, plant roots and microbial communities can heal from damages caused by cutting during turf collection and the long drive from Gällivare to Uppsala.

Throughout the succeeding two years, temperature and moisture sensors will monitor soil conditions continuously in the mesocosms, and carbon dioxide emissions will be measured regularly. The researchers will occasionally collect soil samples, in which soil properties will be analysed, including DNA and RNA analysis of the microbial communities.