Released May 21, 2008
WOOSTER, Ohio — When emerald ash borer (EAB) attacks a forest, dead ash trees are not the only environmental mess this voracious pest leaves behind. Invasive plants waiting to take the place of the trees may have an even greater impact on EAB-infested ecosystems.
So say researchers with the Ohio Agricultural Research and Development Center (OARDC) and Ohio State University Extension, who are trying to figure out in a new study what will be the fate of forested lands in Ohio and elsewhere after they have been invaded by EAB, the exotic Asian insect that first made rather unpleasant news in Michigan six years ago.
The research and outreach project — titled “Responding to emerald ash borer impacts on forest structure and invasive plant colonization” — has been funded by a $500,000 grant from the U.S. Department of Agriculture’s (USDA) Cooperative State Research, Education, and Extension Service (CSREES). It began in 2007 and will run for four years.
Opportunity for invasive plants to colonize
According to OARDC and OSU Extension weed specialist John Cardina (one of the principal investigators in the project), in the process of killing native white, green, and black ash trees, EAB opens up gaps in the forest canopy, creating an opportunity for invasive plants to colonize the understory and trigger a cascade of changes in forest structure and dynamics.
“Killing the ash trees is bad enough, but this may not be the worst impact of emerald ash borer on eastern U.S. forests,” said Cardina, a professor in the Department of Horticulture and Crop Science. “These plants can change natural cycles, soil chemistry and degrade the ecosystem in many other ways. There’s also the question of what plants will win the battle for establishment in the gaps once occupied by ash trees. Will it be invasive plants or the seedlings of native trees such as oak, maple and cherry? The entire composition of the forest could be impacted in the long-term.”
Invaders
Invaders that have the potential to colonize ash-less forest gaps include those that were originally introduced as ornamental or soil-conservation plants, such as honeysuckle, buckthorn, multiflora rose and autumn olive.
“Right now you may not see a lot of invasive plants in the plots we are studying, but there are lots of potential invaders lurking on the edges,” Cardina pointed out. “They hadn’t had a chance to grow in the understory of the forest because there wasn’t enough light. But now that the ash trees are dying and the canopy is opening up, they will.”
Research
The project, said Dan Herms — an OARDC and OSU Extension entomologist who leads EAB-related research in Ohio — involves four specific objectives: quantifying the rate of EAB-induced ash decline and associated changes in forest structure and resource availability; quantifying changes in abundance, growth and reproduction of woody invasive plant species in EAB-impacted forests; using plant-demographic and forest-structure data to create models for predicting the future outlook of EAB-impacted forests; and developing and delivering educational curriculum and outreach activities that address the impacts of EAB on forest succession and spread of invasive plants.
To accomplish these objectives, researchers are analyzing forest structure and invasive-plant colonization at 59 forest stands (180 plots) located in southeastern Michigan and in northwest and southwest Ohio.
The Michigan sites are located in the Huron River watershed, both within (impacted forests) and just outside (non-impacted forests) the core zone of EAB-induced ash mortality in the state. The watershed encompasses extensive areas of public forested lands — including Kensington, Hudson Mills and Indian Springs metroparks, as well as Brighton, Highland, Island Lake, Pontiac Lake and Proud Lake state recreation areas.
Ohio study sites are located in a mixture of upland and riparian forests ranging in size from 15-acre private woodlots to 400-plus-acre stands in public lands — including Oak Openings Preserve Metropark in Toledo and Caesar Creek State Park southeast of Dayton. Only a small portion of the Ohio sites (those near the secondary EAB infestation zone in Toledo) are within impacted forests.
Having such a diverse study area — plots attacked by EAB up to seven years ago and experiencing 100 percent ash mortality, plots facing more recent infestation, and plots that have not yet been affected by the insect — will allow researchers to gain a better understanding of EAB’s ecological impact at different stages of infestation and post-infestation, leading to the study of responses of native and invasive plants to gap formation and changing resource availability; the creation of a model of ash decline; and the modeling of long-term effects of EAB on forest composition.
Much of the modeling work will be done by research ecologist Kathleen Knight, another project investigator, who works at the U.S. Forest Service’s Northern Research Station in Delaware, Ohio.
“Ash is probably the worst tree in our forest for this (die-off) to happen,” Herms pointed out. “It’s scattered in forests all over the state and grows in many different ecosystems, from wet riparian areas to dry upland sites. Other trees, such as red maple, concentrate in just one habitat. But because ash is present all over the place, EAB will impact forests everywhere.”
Ultimately, Cardina said, the knowledge generated by this project will translate into practices that those in charge of forest management can use to minimize the ecological impacts of EAB in Ohio and throughout eastern North America.
OARDC and OSU Extension are the research and outreach arms, respectively, of Ohio State’s College of Food, Agricultural, and Environmental Sciences. For more information about EAB research, log on to http://ashalert.osu.edu.
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http://www.ag.ohio-state.edu/~news/story.php?id=4640
Contacts: John Cardina, (330) 263-3644, cardina.2@osu.edu
Mauricio Espinoza, (330) 202-3550, espinoza.15@osu.edu
