Worming their way into your forests?
Eisenhauer, N., Stefanski, A., Fisichelli, N. et al. (2014). Warming shifts ‘worming’: effects of experimental warming on invasive earthworms in northern North America. Sci Rep 4, 6890. https://doi.org/10.1038/srep06890. PDF.
Summary
Rising temperatures can facilitate the northward spread and establishment of invasive species that were previously limited by cold conditions. Yet, complex interactions between temperature and moisture variables can also hinder invasive species range expansion, for example through drought-related stress. Therefore, to assess climate change related invasion risks more accurately, more information is needed on the interactions between environmental drivers of invasive species spread.
Eisenhauer et al. (2014) used a soil warming experiment to examine how potential interactions between temperature and soil moisture content affect the density and biomass of invasive earthworms. They found that under both closed- and open- canopy conditions, warming treatments had a neutral or positive effect on earthworm densities but only when soil moisture was high. Decreases in earthworm densities were associated with a temperature-related decrease in soil moisture and were driven by changes in the density of worms living belowground, with surface-dwelling earthworms largely unaffected.
Given projections for hotter climates with more varied rainfall, the authors suggest that climate change is unlikely to increase the spread of exotic earthworms, unless warming conditions are coupled with increases in rainfall or earthworm spread is facilitated by human actions such as release of exotic earthworms used as fishing bait. This study highlights the importance of examining interacting environmental variables at a local scale when evaluating the risk of invasive species spread under current or future climate change.
Take home points
The impact and direction of warming on exotic earthworm density and biomass depends on soil moisture conditions.
Under both closed and open canopy, warming had a positive or neutral effect on earthworms when soil moisture content was high but a negative effect when soil moisture conditions were low.
Projected climate changes in North America are expected to produce unfavorable abiotic conditions for exotic earthworms, due to predicted hotter and drier conditions, with more varied rainfall.
Exotic earthworm spread may still be facilitated by warming conditions if local climate rainfall patterns increase moisture availability or if humans transport earthworms to new invasion sites.
Management implications
Knowing how both temperature and water availability in your local area is expected to vary with climate change will help predict shifts in invasive earthworm populations in the future.
On the ground surveys of exotic earthworm densities will help infer present invasion patterns and provide baseline data for current and future management.
Informing the public, particularly anglers using earthworm baits, about the potential negative consequences of invasive earthworms can help reduce human-mediated spread of earthworms to new invasion sites.
Keywords
Climate extremes; Range Expansion; Impact studies; Earthworms; Soil moisture content; Temperate-Boreal Forest Ecotone