Seemingly harmless earthworms are influencing the survival rate of sugar maple trees in Michigan, USA, according to researchers.
The invertebrates have spread throughout much of the Upper Midwest and digest the thick layer of leaf litter and other organic material, which is a feature of the forests there.
Sugar maple trees rely on the leaf litter to prevent their roots (the majority of which are in the top few centimetres of soil) from drying out.
“At this point, we don’t really know if earthworms are causing damage directly or making the soil and litter conditions so poor that drought and other things are getting to the trees,” says Tara Bal, a research assistant professor at Michigan Tech University.
Sugar maple dieback is increasing in this area and a range of potential causes are suspected, including drought, management practices and climate change.
Bal’s research discusses the correlation between increased earthworm activity and the subsequent levels of dieback.
The non-native earthworms were accidentally introduced from Europe and Asia when humans transplanted plants.
“Predictions are that within 100 years, 95 per cent of our sugar maple forests will be invaded by earthworms…forest managers will have to start thinking outside the box to keep forests and trees healthy and regenerating,” says Bal.