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Thursday
Jun302011

Exotic forest pests: the danger is real

Fresh from the Woods

By Joe Rankin

Forests for Maine's Future Writer

 

June 2011

 

Around the turn of the last century a serial killer sneaked into the United States. An immigrant from Asia.

 

It likely came over with a load of lumber from Europe. Like many serial killers it specialized in a particular type of victim, in this case the American chestnut tree.

 

The first dead showed up in 1904 on Long Island. Within four decades the chestnut blight, a deadly fungus, a relative of yeasts, molds and mushrooms, had wiped out four billion specimens of what was perhaps the most valuable and important tree species in eastern North America.

 

The chestnut blight is a cautionary tale, and not the only one.

 

Dutch elm disease, which came from Asia via Europe, devastated American elms, which had gracefully shaded the streets of cities and villages across the continent, within a matter of decades after it entered the country in the 1930s on crates made of infected wood.

 

Today, as researchers and plant geneticists and breeders continue to develop disease resistant varieties of the chestnut and the elm in hopes of bringing them back to forest and street, the country's forests face new threats from more recently arrivals from afar. Maine, with a $2 billion plus forest products industry and an outdoor recreation-based tourism industry valued at another $1 billion, has a right to be concerned.

  Dave Struble, to his right is a map showing the spread of the emerald ash borer

In 2002 Maine State Entomologist Dave Struble said in an interview that exotic pests posed perhaps the biggest threat to the Maine woods. A decade later he hasn't changed his mind. Far from it.

“When it comes to dealing with exotic pests we are in the swamp well over our boot tops,” Struble said recently.

 

Of the half dozen exotic forest pests Struble was worried about 10 years ago, one, the hemlock woolly adelgid, a sap sucking bug, has made its way into Maine after virtually wiping out the majestic hemlocks of the southern Appalachians.

 

Meanwhile, the voracious emerald ash borer and the Asian long-horned beetle are chewing and drilling their way in this direction, despite efforts by governments and scientists to halt them. Other aggressive exotics on the watch list: the pine shoot beetle, the winter moth, the Sirex woodwasp, the brown spruce long-horned beetle, the balsam woolly adelgid, and the disease known as Sudden Oak Death.

 

The ash borer, a bright green beetle from Asia, kills all species of ash trees. The borer was first found in Michigan in 2002 and since then has spread an average of 50 miles a year. It has made its way to New York's Hudson River Valley. The Asian long-horned beetle, which came to the U.S. from China in the early 1990s or before, prefers maples but will feast on a smorgasbord of hardwoods. It has attacked trees in several U.S. cities, including Chicago and New York City; and infested thousands of trees in Worcester, Mass, with new infested trees being found in Worcester almost daily.

 

Both these pests can be spread by moving firewood. For that reason Maine officials last year banned out-of-state firewood and began conducting “firewood exchanges” on the Maine Turnpike. Only a few weeks ago one of those exchanges intercepted firewood from the Worcester area. A good save, that. But nobody's letting their guard down.

 hemlock woolly adelgid

As a veteran of the forest pest wars, Struble knows that stopping invasives is nearly impossible.

 

“I think eventually most of these diseases and pests will get here,” he says somberly. Struble, who has been Maine's point man on the forest pest front since 1988, remembers a boss once telling him, “you have a morbid job. You always lose.”

 

Maybe not always, but invasive exotics, whether weeds, animals, fish, insects, microbes, birds or fungi have a won-loss record any athlete or politician would envy. Transplanted accidentally or on purpose into a new world where the normal checks and balances don't apply, invasives, by definition, run rampant, wiping out or elbowing aside native species.

 

Think the European starling, the imported fire ant, Japanese knotweed, Eurasian water milfoil, kudzu, the multiflora rose, the Burmese python in Florida, Russian olive, Japanese barberry, the common pigeon, the cane toad, the varroa mite that kills honeybees. The list goes on, and on, and . . . on. And that's just North America. Every continent has its own invasives. And some of theirs came from us.

 

Some exotic forest pests can be controlled, usually at horrendous expense and with spotty success. Most can't. Some end up endemic in an ecosystem: occasionally problematic, but not as devastating as they could have been.

 

The gypsy moth, a native of Europe, was introduced to the Boston area in the late 1860s and has been spreading since. The caterpillar defoliates trees. It killed so many white oaks in the southern part of Maine that that species never really did recover, said Struble. Populations of the moth still occur in Maine. However, outbreaks have been largely suppressed by a fungus that showed up in gypsy moth populations in southern New England in the late 1980’s and spread throughout the region.

Asian long-horned beetle 

The browntail moth, an import from Europe at the end of the 1800s, was a serious problem for decades in Maine and elsewhere in New England, but has since been in decline due to natural controls. Although populations are greatly reduced from its heyday, it remains a sporadic serious problem locally in Maine and Cape Cod.

 

The hemlock wooly adelgid is spread by birds as well as movement of infected nursery stock, making it virtually impossible to contain. It is now settled into coastal Maine, said Struble, but apparently isn't as virulent as in areas farther south. Maine's legendary winters may be helping. Temperatures of minus 30 degrees and below will kill all the adelgids, and even minus 10-15 can knock back populations of the fuzzy little bugs. Researchers are now developing “risk maps” that will show where the adelgid is expected to be a real problem, said Struble.

 

But there is a wild card: global warming. Warmer temperatures encourage the spread of many insects and diseases, or exacerbate their outbreaks. Warmer winters and hot dry summers in the Rocky Mountain region contributed to the recent devastating outbreak of the mountain pine beetle, a native pest, which has killed hundreds of thousands of acres of lodgepole pines from Mexico to Canada.

 

No one knows what will happen when the emerald ash borer and the Asian long-horned beetle find their way to the vast hardwood forests of the North Woods.

 

Past experience has shown that spraying, quarantines and cutting down infested or infected trees only go so far at containing exotic forest pests.

 

“What we are doing is buying time. The question then is what we do with the time we have. To sit back and simply enjoy it would be simply irresponsible,” said Struble.

 

Continued research, particularly on pests and diseases of the forest pest, so-called bio-controls, is a must, he said. There is a lot of ongoing research in other states on bio-controls of the emerald ash borer, for instance, including on a ground-nesting native wasp that feeds the beetles to its larvae. Maine is seeking to use the wasp, which is harmless to humans, as a way to monitor for emerald ash borer since the wasps are easier to find than the bugs themselves. Maine is also researching spraying a virus to control browntail moth and is cooperating on regional projects developing bio-controls for hemlock woolly adelgid, said Struble.

 

“We are still flailing and moving forward,” Struble said. “This is like wrestling with a bear: you can't quit when you get tired; you quit when the bear can't take it anymore. Surrender is not a viable survival option."

 

While some woodland owners shrug off the threat of forest invasives, saying it's not an issue yet, others tend toward panic even when the potential threat hasn't arrived. Neither of those responses is warranted, said Struble.

 

“You want to be vigilant, you do want to be concerned. People should be looking,” he said.

Tom Doak, the executive director of the Small Woodland Owners Association of Maine and a former chief of the Maine Forest Service, agrees.

 sudden oak death

He said when hemlock woolly adelgid came to Maine he got calls from people who wanted to know if they should cut all the hemlocks in their woods. “I said, it's here. But nobody knows what's going to happen in this climate. You shouldn't panic. But, if you have a lot of hemlocks and have the opportunity to reduce that amount, it might be a prudent thing to do,” Doak said.

 

Similarly, Struble and Doak say if your woods are full of ash trees, you might at least take a look at how you would get to them if you needed to harvest them. “You want to be prepared to do that, but don't cut right yet,” said Doak.

 

“A lot of it is helping people be more aware of what is going on, but not overreacting when they hear something,” Doak said. “Just be prudent about it.”

 

“I do agree that the important thing is to do what we can with the time we have. And the job of the government is to make that time as long as possible. And that's why the government should be aggressive in extending that time” by working out regional quarantines and funding research, Doak said.

 

Doak said he worries that, given the level of the threat, the federal and state governments aren't doing enough. “Exotic pests are the greatest threat to the Maine woods. The potential is real. But I don't think there are enough resources put into this issue right now. I don't know where I would reallocate, but there's a very real possibility of not having the resources here,” Doak said.

 

The budget for the Maine Forest Service's Forest Health and Monitoring Division, the division Struble heads, is just under $1 million, about half of which goes to forest health issues, said Struble. In 1973 the division had 29 people. Now it has about eight positions, one of which is vacant. “I'm not certain I'm going to be able to fill it,” he said.

 emerald ash borer

Meanwhile, Struble and Doak agree that one of the keys to minimizing any eventual infestation of an exotic pest is through maintaining a healthy, diverse forest. Forests made up largely of one or a few species are more vulnerable because pests can spread more easily. In northern Maine in the 1970s and 1980s the spruce budworm, a native pest, spread rapidly through vast swaths of spruce and fir.

 

Oh, did we mention that Struble said Maine is due for another spruce budworm “event” within the next 10 years? How severe it will be no one knows, or whether by that time its effects will be complicated by exotics. That's the thing: there's no such thing as a “foreseeable future.”

 

 

Fresh from the Woods is produced by Forests for Maine's Future, a collaboration of the University of Maine, Maine TREE Foundation, the Small Woodland Owners Association of Maine and the Maine Forest Service.