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.

Abstract

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.

Crazy Worms Addendum

Cornell Cooperative Extension just came out with a helpful bulletin about Asian jumping works, aka crazy worms. It includes images showing how to tell apart invasive European worms and the more damaging crazy worms, and advice on how to prevent their spread. Limited research on potential predators to hope control this pest shows that Eastern red centipedes and other arthropods may be the best bet.

And here’s a time-lapse video that shows what the worms, Latin name Amynthas agrestis, do to organic matter—gobble it up and leave behind a small volume of overly aggregated castings that dry out quickly. It’s not good.

See prior post for more info, and thanks to horticulturist Laura Wyeth for this additional info.

NYC Parks Director of Forestry-Brooklyn Andrew Ullman on Containing Oak Wilt

owleaves1NYC Parks Director of Forestry for Brooklyn Andrew Ullman shares news of oak wilt containment efforts in that borough.

The image at left shows how oak wilt appears on the leaves of white oak (A) and on red oak (B). The leaves fall prematurely, with some green still present, from the affected trees.   

Andrew Ullman:

To date, there has only been one confirmed case of oak wilt in NYC (Brooklyn) though there are several known outbreaks on Long Island. Oak wilt was first confirmed in Brooklyn in Green-Wood Cemetery during the fall of 2016. It should be noted, this tree was on private property and therefore not under the jurisdiction of NYC Department of Parks and Recreation (NYC Parks). NYC Parks has sampled about a dozen trees that are presenting possible oak wilt symptoms. We are currently awaiting the results from the lab and expect to have them within the next few weeks.

The potential impacts on NYC’s urban forest are significant. Citywide, there are nearly 90,000 street trees in the oak genus. Oaks make up roughly 13% of our street trees, and there are many more oaks growing in our parks and natural areas. Oak wilt, caused by Ceratocystis fagacearum, is a lethal vascular wilt fungi. Symptoms include wilting, defoliation, and ultimately death of the host tree. The disease is transmitted by root grafts or insects and affects host trees in a manner similar to Dutch elm disease.

After the confirmed case of oak wilt in Brooklyn, NYC Parks created a proactive inspection program to inspect trees within the boundary established around the confirmed infection site. Parks has inspected all of the oaks trees growing on the streets and in our parks within that boundary. Between NYC Parks inspectors and our friends at Trees New York, we looked at more than 3,000 oak trees as part of this program. We have also created a contract specifically for managing oak wilt. The work completed under this contract will aid us in our efforts to control the spread of oak wilt if we do find it has spread beyond the initial infection site.

Additionally, we are working closely with NYSDEC, Green-Wood Cemetery, and Cornell University’s Plant Pathology Lab to coordinate response and share information. Finally, we are also limiting non-emergency work on oak trees during the growing season to limit the likelihood of spreading the disease.

Please see as well a previous post about preventing the spread of oak wilt with DEC Oak Wilt Operations Coordinator Jennifer Kotary.