Posted: Mar. 24, 2014 11:41 pm Updated: Mar. 27, 2014 11:42 pm
By BRUCE A. SCRUTONbscruton@njherald.com
Unlike an ancient Greek who committed suicide by drinking hemlock, there is a tiny insect known as the hemlock woolly adelgid that spends its entire life drinking only the sap of the hemlock tree to the point that, over the past few decades, it has desiccated hundreds of acres of forest in this region.
Foresters and ecologists have now invited their own specialist to dinner — a species of beetle, laricobius nigrinus, with its own exclusive dinner taste, the woolly adelgid.
And dinner time for the beetle is not a summer barbecue, as is common with most other insects, but a banquet hall surrounded by the cold and snow of winter.
But the tolerance by beetle and adelgid of the cold only goes so far, said Richard Evans, ecologist for the Delaware Water Gap National Recreation Area who has been studying, and fighting, the hemlock woolly adelgid for more than 20 years.
“I’d say we’ve seen maybe a 90 percent die-off of the hemlock woolly adelgid because of the unusual cold of this winter,” he said. “So, there was a silver lining to the weather.”
Asked about control of the smaller insect because of the cold, he said, “It could bring the infestation under control for a year or two, which would give the hemlocks a chance to recover, grow more healthy.”
The tiny adelgid, which is less than 1/16-inch long, gets its “woolly” first name because it builds a covering that resembles a small tuft of wool. A tree infected with the insect shows these white specks on the underside of the new growth at the ends of its branches.
It is because the adelgid feasts on the new growth at the ends of the branches that hemlocks don’t die suddenly, but over the course of a few years, unable to replace with new growth the needles that have grown old and fallen off.
Unlike some other hemlock forests in the eastern part of North America — the tree ranges from northeast Alabama up the Appalachians to the St. Lawrence River valley — which can be several hundred years old, the hemlock forests in the national park and northwestern New Jersey are only about 150 years old — “teenagers in the prime of their life,” Evans said.
The woolly adelgid apparently came to this country as a hitchhiker from Japan in the early part of last century but wasn’t considered a widespread pest until the last 20-30 years.
Evans said the pest was first discovered in the national recreation area in 1989, “and in the last 25 years, has spread everywhere.” Its destruction also can be seen in Tillman’s Ravine in Stokes State Forest and in other hemlock stands between Stokes State Forest and High Point State Park. Hundreds of hemlocks that had shaded Sparta Glen, a municipal park in Sparta,were decimated by the insect in the 1990s to the point where park visitors were warned of the danger of falling dead trees.
Evans said about 40 percent of the hemlocks within the park have been killed by the infestation, with a mortality rate of up to 60 percent in some areas.
Rosa Yoo, assistant regional forester with the state Department of Environmental Protection, said the state has about 26,000 acres of hemlock forests “and all are at some level of infestation.”
The Beneficial Insect Lab, a division of the state’s Department of Agriculture, produced the nigrinus species of the beetle and, working with the National Park Service, began releasing the beetle a few short years ago in the Van Campen Creek area of the park on the border between Sussex and Warren counties.
“We released about 12,000 of the beetles,” Evans said, “and it’s showing great promise. They have spread miles from where we released them.”
The nigrinus species is native to North America, but was limited to the northwest in Washington and Oregon with a more cold-tolerant strain in Idaho.
The beetles released here were bred from that Idaho strain.
About a year ago, a second species, Laricobius osakensis, found natively around the area of Osaka, Japan, was released in the southern areas of the hemlock range where much more damage has been caused by the adelgid.
Research there has shown osakensis is even more voracious than nigrinus, but likely won’t be released up here because it is not as cold-tolerant as its cousin, Evans said
Yoo said the nigrinus beetles released in areas of the state forests in Sussex County are “also moving and reproducing, so it seems to be working.” The beetles are about three millimeters long, according to Cornell University,
She said the full effects of the beetles “can take a few years to bring this under control, but I have hopes.”
While the beetles are chomping their way through adelgids in Van Campen, at Raymondskill Falls, the park service is working on other remedies for an area where more than 1,200 hemlocks had to be cut down because they had died and become a hazard.
There, the paths that people use to reach viewpoints of the falls are lined with fencing nearly eight feet tall, creating what are known as exclosures, meant to keep the deer out of several acres of land. The intent is to allow the forest to regenerate itself.
While adelgids suck up the sap in new growth, deer eat away at the lower canopy of trees and eat sprouting hemlocks down to the ground.
A hemlock forest is great cover for deer, providing shelter from wind and storm and a ready food supply. But an overpopulation of deer keeps the forest from regenerating itself.
Hemlocks are very shade-tolerant and require stands of hardwoods to provide that shade to protect young trees from the summer sun.
In an interesting example of how varying species adapt, the hemlocks get the sun they need for growth in the winter when the leaves of the hardwoods have fallen, opening the canopy to the sky.
The exclosures, it is hoped, will keep deer out of that area for next generations of hemlocks to get a foothold.
Hemlocks are a long-lived species, with some individual trees estimated to be from 500 to 800 years old.
Their dense shade, especially in ravines with streams at the bottom, provide the aquatic environment essential to clear water and good trout streams.
Evans, who was trained as an aquatic ecologist, said it was the relationship between the hemlock forests and water courses that drew him to the effort to save the forests.
“If we didn’t do something (with saving the hemlocks), then the streams would die,” he said. “I’ve grown to love the forests. If we do something to save them now, they will persist for hundreds and hundreds of years.”
Both Yoo and Evans said there is also research ongoing to find strains of hemlocks that are actually resistant to the woolly adelgids.
“Research has found some trees actually defend themselves by producing a chemical,” said Yoo. She said further research is needed to determine if the chemical is being produced by the tree or is absorbed by the tree from its environment.
Since the first adelgids were found 25 years ago, the park service has been using a variety of chemical insecticides, some injected directly into the trees, to test effectiveness of different treatments.
Along the hiking paths that travel through most of the hemlock groves in the park, trees sport different colored paint spots, each color signifying a different year and type of treatment.
Evans is optimistic about how research, especially with the beetles, is progressing.
“It looks very promising. If you asked me four, five years ago about the outlook for the hemlocks, I don’t know what I would have said,” he answered. “I’m more hopeful now than I was then. I think in the long term, we will have healthy hemlock forests for all to enjoy.”