Urban Forest Ecology: Earthworms Implicated in Sugar Maple Decline

Dr. Tara Bal
Dr. Tara Bal examining earthworm activity in leaf litter.

Whoa. Worms can cause a lot of problems, as we’ve been exploring on the blog with regard to the organic matter over-consumer, Asian jumping worm. A Michigan Tech study entitled “Evidence of damage from exotic invasive earthworm activity was highly correlated to sugar maple dieback in the Upper Great Lakes region” points to … just that. That is, the way in which earthworms (which, due to glacial scraping in the past, are not native in Michigan or in New York) are directly and indirectly contributing to or causing maple decline, which has affected urban forests as well as exurban ones.

Michigan Tech did a great summary of the research and here is the abstract for the study, published in the journal Biological Invasions. The lead author is Dr. Tara Bal, who wrote her dissertation about sugar maple decline in the Upper Great Lakes Region.


Sugar maple (Acer sacharrum Marsh.) in the western Upper Great Lakes region has recently been reported with increased crown dieback symptoms, prompting investigation of the dieback etiology across the region. Evaluation of sugar maple dieback from 2009 to 2012 across a 120 plot network in Upper Michigan, northern Wisconsin, and eastern Minnesota has indicated that forest floor disturbance impacts from exotic invasive earthworms was significantly related to maple dieback. Other plot level variables tested showed significant relationships among dieback and increased soil carbon, decreased soil manganese, and reduced herbaceous cover, each of which was also be correlated to earthworm activity. Relationships between possible causal factors and recent growth trends and seedling counts were also examined. Maple regeneration counts were not correlated with the amount of dieback. The recent mean radial increment was significantly correlated with various soil features and nutrients. This study presents significant evidence correlating sugar maple dieback in the western Upper Great Lakes region with earthworm activity, and highlights the need for considering the impacts of non-native earthworm on soil properties when assessing sugar maple health and productivity.