Stephen Stirling | NJ Advance Media for NJ.com

An extinction-level event is slowly unfolding in New Jersey, one that will profoundly change the state's landscape, do upwards of $2.7 billion in damage and potentially dampen property values in towns across the state.

The perpetrator is the size of a penny, and, at this point, there is little that can be done to stop it.

The emerald ash borer has decimated ash tree populations across the midwest as it slowly plods its way across the country. It's spread to at least half of New Jersey and experts seem resigned to the fact that the state's ash trees' days are numbered as a result.

Ash trees are one of the most prolific flora in New Jersey. The federal government estimates there are at 24 million ash trees growing wild in New Jersey and state foresters believe there could be just as many lining the streets and backyards of state municipalities.

But because the torpedo-shaped green beetle is virtually undetectable before its larvae hollow out the inner bark of their host tree, promising a swift death, there's little that can be done to stop its spread.

Foresters say it appears all but inevitable that ash trees, at least in the common context we know them today, will be all but a memory in New Jersey before long.

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That sounds pretty dire. What gives?

Well, it is. Various species of ash represent at least 2.5 percent of the state's tree population, according to federal data. That's almost certainly an underestimation because there are few records for how municipalities and developers used ash trees in plantings over the last several decades. Anecdotally we know they did — a lot.

The emerald ash borer is also an expert at guerrilla warfare. Adults can fly and can move relatively undetected from tree to tree. Its larvae bore into the vital life systems of trees and are hard to spot until it's too late.

"The emerald ash borer is a pretty bad insect in comparison to other forest threats," said Rosa Yoo, a state regional forester with the state Department of Environmental Protection. "The key thing is to be prepared. We know it's going to come through and it's going to kill nearly all of them."

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Why are we so sure?

History, mostly. New Jersey's history is littered with examples of invasive pests and viruses having devastating impacts on our floral ecosystem.

"The most prolific tree in New Jersey forests used to be chestnut before a virus wiped them out," said Eric Olsen, director of Land for The Nature Conservancy in New Jersey. "We had some volunteers find one or two recently on our land and tag them just so we could see them when we're out here."

More recently, the asian long-horned beetle wreaked havoc on New Jersey maple trees. While it was declared largely eradicated in 2013, it continues to flare up in Middlesex and Union counties.

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Why can't we eradicate the emerald ash borer?

The problem goes back to detection. While insects like the asian long-horned beetle leave clear calling cards early, the emerald ash borer does not. Its larvae primarily affect the inner bark of ash trees and by the time a tree shows symptoms of damage, it's well on its way to death.

"It's very difficult to detect at low levels," Yoo said. "By the time a tree starts to show problems, it's often too late."

Extensive efforts to control or wipe out the emerald ash borer have been carried out across the country, but to very little effect thus far. Michigan, where the bug was initially discovered, has essentially written off their ash populations after statewide quarantine efforts failed to halt the beetle's spread.

It's estimated Michigan alone has lost 50 million trees to the pest.

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Photo Courtest of EmeraldAshBorer.info

So what is this thing again?

The emerald ash borer is an exotic beetle species native to Asia. It was first discovered in the United States in Detroit in 2002 and likely arrived in wood packing materials.

Adult beetles are a vibrant green, true to their name, about the size of a penny and mostly harmless. They nibble on ash tree leaves and cause little damage.

The beetle's larvae are the problem. Emerald ash borer larvae burrow into tree bark and feast, disrupting the host tree water and nutrient transport systems. Typically, a tree infested will only survive for two to three years.

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Where is the emerald ash borer now?

The emerald ash borer has been positively identified in ten New Jersey counties to date. But Yoo said they have likely spread much farther than current data shows.

"Our maps should be viewed as broad brush strokes. You can kind of assume that the detections are the oldest affected areas, those that are going to be some of the hardest hit," she said. "When you think of all the highways, railway corridors — all these linear pathways they have to travel. Those are just new paths for (emerald ash borers) to take and infect new trees."

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What does an ash tree look like?

Ash trees are ubiquitous in New Jersey, but it's often difficult to tell them apart from other species of tree. The most common characteristics are diamond-patterned bark, compound leaves of five, seven or nine leaflets and paddle-shaped seeds.

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Where are ash trees found in N.J.?

Ash trees are everywhere in New Jersey. In the wild, they are clustered in the forests of northern and central New Jersey. The Great Swamp National Wildlife Refuge has one of the most densely packed clusters of ash trees in the state.

But the trees are also found in many yards, towns and large developments in the state — data that is not included in the map above. The map shows modeled density of ash trees found in the wild in New Jersey.

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Why did the ash tree become so popular among developers and municipalities?

Ash trees, for many years, were some of the cheapest planting trees available. As a result, they became popular choices for municipalities purchasing street trees and developers looking to landscape when suburban sprawl became king in the 1980s and 1990s.

Some towns have entire streets lined with ash, a fact that they will likely come to regret in short order.

"Now would be a great time to do before-and-after photos," said Jason Grabovsky, a professor of ecology evolution and natural resources at Rutgers University. "You could see entire neighborhoods that suddenly look like moonscapes in a year or two."

The map above shows that the state's outer-ring suburban counties grew precipitously during the later half of the 20th century. Most ash trees were likely planted during this time.

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Did you say $2.7 billion?

In 2003, the U.S. Department of Agriculture estimated the value of wild ash trees in New Jersey to be approximately $2.7 billion. If those trees die, that's the best guess we have at what that loss will look like.

But the cost to municipalities or homeowners is far more difficult to calculate. For one, we don't know how many ash trees exist on government, residential or commercial properties around the state. Uprooting and replacing a dead tree will also cost more than just letting one die, so the costs to New Jersey residents could be significant.

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Will N.J. have any trees left?

Plenty. New Jersey's diverse ecosystems will be able to handle the loss of the ash tree should it be completely decimated.

"We're actually pretty fortunate that we don't have any stands that are 100 percent ash," Yoo said. "They're generally mixed with other species."

The Great Swamp stands to be particularly affected, but has their own active "strike team" for dealing with invasive species. Yoo said our natural diversity could be instructive for communities with high concentrations of ash.

"It's an opportunity to start thinking about your trees more, about what you have and grouping different species together," she said. "The (eastern ash borer) isn't going to be the last pest we deal with, so now is an opportunity to position ourselves better for the future."

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Why should you care?

There's a good to likely chance you have at least one ash tree on your property and an even better chance that your municipality or local developers have planted them in recent decades. The promised mass death of the trees could have a chilling effect on property values in communities that do not replace them quickly.

Additionally, scores of dead or dying trees are a significant safety hazard. When in all likelihood a significant storm impacts a region with a deteriorating ash population, strong winds could produce a massive treefall event, endangering lives and property.

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What can you do?

Yoo recommends trying to identify ash trees on your property and hiring a tree expert to go over options with you. There are treatments that prevent against emerald ash bore, but more often than not the best option is to remove and replace an existing tree.

"Nobody really has the luxury to sit and wait. The emerald ash bore doesn't care," she said. "Your window of time to do anything really is very small at this point. You have two to four years to figure it out."