View Our Woods
See Us On:
« Good reviews for online forestry program | Nature photography: A new way of seeing the woods »
Saturday
Jan262013

Spruce budworm: Coming again soon?

 

By Joe Rankin

Forests for Maine's Future Writer 

It was a hot July day in the 1970s. Dave Struble was back home in Island Falls, on a day off from his job as a regional entomologist for the Maine Forest Service. But it was too hot to do much, and he suggested to his Spruce budworm larva (Photo: Maine Forest Service)wife, Pat, that they drive to Houlton to the drive-in. At least, he said, they would be outdoors and there might be a breeze.

Struble, now the Maine state entomologist, doesn’t remember what movie was playing. Perhaps that’s because they didn’t see much of it.  “You could barely see the screen because there were so many moths flying around the projector.,” he said. Among them were spruce budworm moths. Lots of them.

 The last major spruce budworm epidemic in Maine was getting into full swing. It was an outburst of insects that would eventually defoliate millions of acres of northern Maine forest, give birth to a widespread and vigorous spray program, and set timberland owners scrambling to log vast tracts of spruce and fir before it became worthless.

The fear is that it will happen again, and soon. The budworm has been on the march in Quebec for several Eastern spruce budworm moth (Photo: U.S. Forest Service)years and has defoliated millions of acres there. Watching that unfold, the Maine Forest Service is beginning to plan for an infestation here.

“A lot of factors involved in dealing with an outbreak would be hard to solve conclusively if a plan was constructed too far in advance of an outbreak,” said Douglas Denico, the chief of the Maine Forest Service. “That said, it is time to develop a plan to deal with what likely lies ahead. We are in the early stages of piecing such a plan together, with this year dedicated to completion of a draft. Some issues pose major policy decisions which can be pointed out in a plan but need resolution within state government.”

The Pest

The spruce budworm, Choristoneura fumiferana, is an endemic native pest, not an foreign invasive like the much feared Asian long-horned beetle or the emerald ash borer. It evolved with the conifers of the boreal forest. There are an estimated 40 species and many more subspecies just in North American. There are western species and eastern species. There are Asian species that live in the Siberian taiga.

 The spruce budworm is the immature stage of a nondescript grayish-brownish moth.

 Contrary to its name, the spruce budworm doesn’t actually like to feast on spruce. It prefers balsam fir, though it will eat spruce trees as well. It prefers white spruce over red and black. But it’ll eat those too, particularly if they’re mixed in with the others.

Like other moths, it grows through various stages in its life cycle -- an egg, several versions or instars of larvae, Budworm damage (Photo: Maine Forest Service)a pupal stage, and, finally, the adult moth. It is as a larva that it is damaging to trees, eating the needles and developing buds. Needles severed at the base turn brown, giving the tree a rusty cast. Growth is measurably reduced after a tree loses half its new needles for two to three years in a row.  Dieback and death follow one to three years later.  Whether a tree dies or recovers depends on the severity of the outbreak, and the health and vigor of the tree. 

When the defoliation is bad enough it can be mapped from the air, looking like a big rust stain on the landscape.

There are probably always a few spruce budworm moths in any given chunk of forest. But the moth is subject to periodic population explosions. No one knows what propels them, whether it’s climate or the age of the forest. Both have been suggested. Such population explosions are part of the biology of many species. Think lemmings, for instance.

The budworm has natural predators, among them several species of warblers, such as the bay-breasted, the Cape May, and the Tennessee. They undoubtedly help keep numbers down in normal years, but when conditions precipitate an outbreak, they can’t begin to keep up.

The first known spruce budworm outbreak was documented in Maine in 1807, and there was another in 1878, according to the U.S. Forest Service. There was an outbreak in the years between 1910 and 1920 and waves of them since, said Struble. The regional outbreak in the 1950s and 1960s touched the state, but only lightly. Then there was the one that began in the mid 1970s and lasted, again, about 10 years.

In 1973 and 1974 the moths were devastating the forests in Quebec and clouds of the moths were wafting across the state. The moths can fly, of course, but are generously helped by wind. A powerful storm front can sweep them hundreds of miles. Even the larvae can travel, carried on the filaments they spin. Struble (Graph: Maine Forest Service)remembers how, about the time of the drive-in episode, a couple of his colleagues fishing  on their day off came across huge numbers of budworm moths dying on the water -- 12 miles off the coast.

The past

The Maine Forest Service monitored budworm numbers using light traps. Contractors would empty the traps and package up the catch to send to Augusta. There Maine Forest Service workers separated out the target moths from the non-target species and counted them. On any given year there were 17 to 25 trap sites.

In 1961 the traps yielded an average of 44.9 months. By 1978 the average had rocketed to 12,900. 

During the height of the last budworm epidemic Maine was spraying millions of acres of timberland a year in an effort to blunt the infestation and give timberland owners time to salvage doomed trees. It was controversial because of the chemicals used. Early on it was DDT, later it was carbamate insecticides, including Sevin. Still later, in the 1980s, the spray program switched to the natural insecticide Bacillus thuringiensis or Bt, a bacterium that attacks the gut of the caterpillar that ingests it. Although environmentally gentler than the Budworm egg mass (Photo: Maine Forest Service)chemical pesticides, Bt isn’t without its side effect: the bacterium doesn’t just kill budworm larvae, non-pest species are also susceptible.

The spray program was massive. From 1954 through 1967 the Maine Forest Service treated just over 1.2 million acres total. But beginning in 1970 things started to ramp up: 210,000 acres one year, then 500,000, 470,000, 2.2 million. It reached its zenith in 1976, when planes sprayed more than 3.5 million acres. In all they treated 18.5 million acres between 1954 and 1985.  

And it was massively expensive. Between 1954 and 1982 the spruce budworm project cost $60.9 million in landowner, state and federal money. In 1979 alone costs totaled $11.3 million, according to Maine Forest Service figures.

The biggest expenditures were on aircraft, insecticide and personnel. In 1983, for instance, some $1.4 million was spent on spray planes, almost $1.8 million on insecticide, and more than $1.1 million on personnel. While the spruce budworm control program had a cadre of year round employees, that number swelled in the warmer months. In 1982, to pick one year, the Maine Forest Service had 146 positions tied to the project, most fairly short-term. Seasonal employees worked in the field, collecting samples and in the lab tallying larvae and egg mass samples as well as counting moths.

Also controversial was the massive salvage that followed the outbreak. The budworm did its worst in virtually pure stands of spruce and fir. When loggers went in after the timber they generally clearcut. There was no reason to leave trees that were going to die anyway, and mature spruce and fir that grew together rarely would survive high winds once thinned.

Budworm-killed trees from the air (Photo: Maine Forest Service)In the end the outbreak simply faded away. By 1985 the light traps were yielding an average of 600 moths. A year later it was 60. By 1990 it was 4.4, said Struble. 

The return

Many forest entomologists say that the budworm will come back. You can bank on it. The question is when. The answer could be -- soon.

Quebec has seen populations of spruce budworm increase steadily since 2006. By 2010 it covered almost 1.5 million acres, according to Natural Resources Canada. The outbreak began unusually far north, on the north shore of the St. Lawrence River. Four years later it had reached the lower St. Lawrence near Rimouski.

Struble, who keeps in close touch with his counterparts in Quebec, said that by 2012 the budworm had affected 5.6 million acres in Quebec, with two million acres severely defoliated. “The whole pattern of defoliation in Quebec is a geometric progression,” he said. “We are in a curve going up.” Last year was the first that the Quebec government has been able to map defoliation on the south side of the St. Lawrence by air, he said. 

A map of the outbreak put out by Quebec’s Ministry of Natural Resources and Wildlife shows the defoliation for 2012 in red. It looks eerily like a huge flame burning to the north of the St. Lawrence, with a handful of burning embers scattered on the south side of the river.

“The problem is expanding to our north,” said Struble. “Quebec is spraying, but they are not spraying enough to affect the overall dynamics of the outbreak. They’re taking their high priority areas where they’re trying to harvest . . .  and spraying that to manage their losses. They are not spraying as much acreage as they have heavy defoliation in a given year. They’re not keeping up with it. I don’t know that they can afford to keep up with it.”

In neighboring New Brunswick province researchers have found some late-stage larvae of the budworm, but so far there’s no full-fledged outbreak in that province, he said. 

Based on what’s happening in Quebec, Struble predicts a 1950s to 1960s outbreak in Maine “very early in the next three to five years” but “not the big one. There may be some patches of serious defoliation, but not a blanket of death.” However, “add eight to 12 years on top of that and you could be back in a 1970s type of outbreak.”

He bases that prediction partly on the fact that Maine’s spruce and fir forest isn’t quite as mature as it was going into the last outbreak. But it’s getting there. In a few more years it should prevent a ripe target. 

The future

How bad will the next outbreak be? No one really knows. How will the trees react? No one knows. How will the state and the landowners react? Good question.

Struble said when there is another outbreak he doubts that there will be a huge spray campaign this time around. For one thing spraying is expensive.Translate the millions spent on the last budworm spray campaign into today’s dollars and see if you don’t gulp hard.  And land ownership patterns have changed in the past four decades.

In the 1970s the bulk of it was in the hands of giant paper and timber companies. The paper companies had their own mills. Salvaged spruce and fir could be turned into pulp and paper by the companies that owned the trees. But paper companies sold their lands to investment groups. There’s almost no vertical integration Looking up through budworm-killed trees. (Photo: Maine Forest Service)anymore. No more built-in markets for raw logs. While paper use is down, there are markets for pulp. But the market for spruce and fir lumber is heavily dependent on homebuilding, which is down right now. Who knows what it will be in three to five years, much less 15 to 18.

Given all that, Struble questions whether the new forestland owners would be willing to contribute to a multi-year spray campaign. The private logging road network in Maine’s eight northern and easternmost counties was expanded tremendously during the last budworm outbreak to facilitate salvage operations. For the most part it’s still there. Whether the new owners will undertake salvage operations of threatened timber is a question, he said. The answer will likely depend on whether the market for it is there. 

Denico, the MFS chief, said that the question of whether there will be a spray program of some kind this time around “is one of the major policy questions to resolve. Given our lead time on the outbreak, salvage may be the major option taken with spray used as a backup.”  

The “availability of markets may heavily influence the direction taken,” said Denico, adding “In any event, it will be a fascinating debate.”

The area of Maine covered by spruce and fir forests is down somewhat from four decades ago. But “budworm has the potential to do a tremendous amount of economic damage across the northern half of the state,” Struble said.

A team of University of Maine researchers agrees with that assessment. In a 2011 paper published in the Journal of Forestry, they concluded that spruce and fir are an important part of forest stands across more than half the forested area in the state. Those trees “represent a merchantable standing volume of almost 5.5 billion cubic feet” that is “susceptible to substantial SBW-induced mortality and growth loss.” 

The researchers used a computer program developed by the Canadian Forest Service to look at potential effects of a spruce budworm outbreak on two widely separated Maine townships, one in northern Maine, one in southeastern Maine. Since forest conditions and landownership patterns have changed so much since the last outbreak, it’s hard to use past experience as a guide, they said. Given that, they said there would be a “clear benefit” to land managers of employing the software to get a township-by-township analysis of potential SBW impacts in preparation for the next SBW outbreak.” 

There are other questions as well. How will climate change affect the spruce budworm’s life cycle and its effect on Maine’s forests?

“I really don’t exactly know,” said Struble. There is a sense among some scientists that a warming climate could nudge the budworm epidemic farther north, he said. “But I don’t know why the southern edge wouldn’t stay where it is.” 

Joe Rankin is a forestry writer who lives in New Sharon.