Invasive species wreaking havoc on ash trees nationwide
By Laci Gagliano
Sun Post Newspapers
They bear striking resemblance to an exotic green gemstone gleaned from the River Nile and could easily be mistaken for a stunning piece of jewelry. Beneath their slender, emerald sheath is yet another transfixing layer of shiny iridescence.
Visually, the emerald ash borer is a beautiful specimen, yet laced in the aestheticly pleasing beetle’s existence lies a destructively ravenous hunger for a common landscape fixture, the ash tree.
Emerald ash borers (EAB) are an invasive species native to parts of Asia, first discovered infesting U.S. trees in Michigan in 2002. The first Minnesota EAB infestation was discovered in 2009, and to date, have been detected in over half of U.S. states, especially throughout the Midwest and Great Plains, as well as in several Canadian provinces. Experts believe the insect was likely introduced to the U.S. in overseas cargo containing wooden packing materials originating in Asia.
The damage the emerald ash borer causes to ash trees is significant. Its life cycle begins as a less attractive larvae that hatches from eggs laid in the crevaces of the ash’s bark, then burrows under the bark, feeding just beneath it as the larvae tunnels its way across the bark’s underside. The tunnels created by the larvae destroys the tissues that circulate water and nutrients throughout the tree. Once they mature after about a year of feeding, the beetles bore their way back out of the trunk through tiny holes, and emerge to feed on other ash trees and produce new larvae. The amount of tunneling and boring the tiny beetles can accomplish reduces the tree’s remaining lifespan to just one to three years after the adults emerge. The entire course of killing the tree can take about two to four years, although a tree can lie dormant for up to five years after an infestation.
According to the DNR, Minnesota has around 1 billion ash trees throughout the state, and make up nearly 60 percent of the trees population in some communities. The Minnesota Shade Tree Advisory Committee (MNSTAC), which is developing legislation that would help fund EAB management efforts, estimates that approximately 2.65 million of the state’s ash trees are located within populated communities, and that one in five of those trees are at risk for an EAB invasion.
Emerald ash borers threaten communities with costly repurcussions. Federal studies have shown mitigation costs among all infected regions are in excess of $10 billion, including costs of cutting down dead trees and replacing them. Dead ash trees pose a risk of falling without warning, potentially damaging property or injuring people. The trees also absorb a substantial amount of stormwater, and the MNSTAC estimates that a loss of all of the urban ash trees in the state would result in an extra 1.7 billion gallons of water entering stormwater systems each year.
In wilderness areas, the trees’ demise in large numbers can mean threatening the ecosystems they’re a part of. Black ash is a type of ash commonly found in wet forests. If the ash is wiped out, that habitat could dry up and become covered in grass and shrubs, which could put the plants, animals, and insects that rely on both the ash trees and the wet habitat at risk.
The canopy of the ash trees begins to die away first as the tree is robbed of the water and nutrients required for survival. Woodpeckers also begin visiting infected trees frequently in search of the EAB. Gradually, long cracks in the bark start forming, and eventually, the tree’s entire foliage canopy dies off completely.
Minnesota is home to several native varieties of ash borers, which have natural predators to keep their numbers lower and to which ash trees have natural resistances built up. Similarly, emerald ash borers are not considered invasive in Asia for the same reasons. However, in the U.S., ash trees are not equipped to handle the volume of damage the EAB is capable of, and predation is not prolific enough to control non-native species’ numbers.
Quarantines are imposed on counties where infestation is rampant, meaning it is not legal to transport prohibited materials like ash wood chips, lumber, logs, waste, and firewood outside of the county of origin in order to keep the insect from spreading, which it easly accomplishes by flying from tree to tree.
Hennepin County is under a quarantine, as infestations have been discovered throughout the metro. The northwestern suburbs have all been impacted in some way, and cities are taking measures to attempt prevention and to most efficiently treat infected ash trees.
The best way to stop the spread of the emerald ash borer is to respect all local quarantines, only using firewood in the location it was purchased and not bringing it to or from any other region–or, as the DNR puts it, “don’t move firewood.”
Education efforts are being made by forestry and advocacy groups, and many local governments are studying the most effective and cost-efficient remedies and methods of prevention.
Entomologist Val Cervenka of the Minnesota DNR said some cities are taking the initiative to remove ash trees pre-emptively to breakup the pathways the insects have created. She also said people can take preventative measures with their own ash trees at home.
“People can hire professionals to inject a pesticide that kills the emerald ash borer and prevents it from attacking the tree. They would have to keep up that treatment every two to three years for the rest of the tree’s life.”
Cervenka said that some people elect to take down and replace ash trees with another type of tree, since ash is the only tree the ash borer attacks. Even in cities where infestations have not yet been detected, it’s crucial for people to be aware of the potential spread, which Cervenka said is just as likely from one city to the next.
“The impact on the Northwest Suburbs is going to be the same as anywhere across the state: we’re going to loose ash as a resource. A brand new infestation can pop up anywhere. People should just be aware that this is coming,” she said. “The Biggest way to prevent the spread is to not move firewood,” which Cervenka said includes any deciduous hardwood trees.
Cervenka pointed out that it’s helpful for people to be able to tell the difference between healthy and infested trees so that more infested trees can be identified, although she acknowledged it’s difficult to tell sometimes. She said the thinning canopy and increased presence of woodpeckers on an ash tree are strong signals that the tree may be infested.
Cervenka suggested that people visit the Minnesota Department of Agriculture’s website for more information on detecting infestations, as well as an interactive map that helps track the spread of the emerald ash borer at https://www.mda.state.mn.us/emeraldashborer.
Contact Laci Gagliano at [email protected]