Deaths in our forests

Hemlock stands falling victim to voracious insects

SUNDAY HERALD NEWS, AUGUST 29, 2004
Story and photos by GREGORY J. RUMMO

IF STEPHEN KING had written the opening to this article, it might go something like this: She had been a matriarch, standing tall and strong for the last 80 years.  Despite living through the Great Depression, two world wars and numerous frigid winters in the northeast, she had somehow managed to weather these storms. But one day, she caught a bug from Asia and slowly, her youthful vigor ebbed as the life was literally sucked out of her. During those last years, her limbs grew weak and became brittle. Her skin began falling off in chunks, exposing the raw red flesh underneath. It was as though she was suffering from Leprosy. When we finally called in the surgeon he said there was little he could do.  In a last act of mercy, we cut her body up in sections, and ran her limbs and trunk through a wood chipper.

            It's a sad day when a big tree dies—especially when it's in your own backyard. But the 100-foot hemlock we had cut down several years ago one bright spring day was no anomaly. It was one among many in our neighborhood that suffered a similar fate over the past 20 years.  All had fallen prey to an infestation of bugs which biologists have been seemingly powerless to thwart.

            This fall, as the leaves of the deciduous forests undergo their autumnal color transformation as a prelude to them dropping off the trees, a plague of insects called the hemlock woolly adelgids (HWA) continues its slow and silent defoliation of the hemlock forests in the eastern United States. Here in New Jersey, that means predominately Sussex, Morris, Passaic, Bergen, Warren, Hunterdon and Somerset counties.

            Most of the hemlocks at risk—14,225 acres out of a total of 26,000—are located in Sussex County, New Jersey's northernmost county bordering New York State. But you don’t have to drive that far to see the devastation.

You can take a short walk through my neighborhood in northern Morris County on the Passaic County border. Here around Lake Edenwold—the tiny 4-acre lake that laps at my backyard—there is ample evidence of the defoliation. Scattered among the maple, oak and other hardwoods in the woods, in people's backyards and along the lake's shoreline are the pale gray spikes that once were healthy eastern hemlocks (Tsuga canadensis). In their prime, these trees had graceful sweeping limbs covered with soft, green needles. They created dense shade and provided nesting sites for a number of song birds such as the blackburnian warbler, black-throated green warbler and the blue-headed vireo, all of which prefer the seclusion of hemlock forests to raise their young. The dense shade underneath the trees also shielded Kikeout Brook and its now virtually extinct population of native brook trout from the hot summer sun, preventing the small stream from becoming a simmering consommé during the months of July and August.  

            But now these once majestic trees—former centurions of a forest primeval—are little more than dry, rotting corpses; home for another year or two perhaps to a pileated woodpecker or a wood duck until the next gale barrels through and snaps the trunks in half, leaving the stumps to endure a more humiliating fate; to a colony of carpenter ants or termites.

The hemlock woolly adelgid is native to the Far East; Japan and most likely China, where it is common but innocuous. They are kept in check by natural predators. But here, there are no natural predators hence; they are insidious, feasting freely on hemlocks without any challenge to their voracious appetite. HWA attack a hemlock in its petiole, the small stem that joins the needle to the twig. Existing in three stages; eggs, crawlers and adult females (all HWA are females), they lay their eggs in the winter months from December to February. They hatch beginning sometime in April into first generation crawlers. It is the crawlers, or nymphs, which do most of the damage during the growing season.

            They are Lilliputian demons, microscopic vampires, attacking and sucking the life out of the hemlocks. They accomplish their dirty work by injecting a long, flexible hypodermic-like tube called a stylet bundle into the base of the hemlock's needles. The stylet bundle works its way into the tree's xylem, and once there, it zeroes in on these cells where a hemlock stores its food. Then, the little bugs go to work, turning on the suction and siphoning out the tree's stored food supplies. If the infestation is left unchecked, the hemlock slowly starves to death over a period of several years.

            The HWA problem, which started in southeastern Pennsylvania in the 1950's, first came to light in New Jersey almost 20 years ago. In the mid-1990s, Mrs. Denise Royle, a graduate student at Rutgers University did extensive work on a project identifying areas of New Jersey's hemlock forests and their relative health by utilizing infrared satellite images dating back to 1984 and comparing them to images made in 1994. Working together with George Koeck, a Regional Forester with the N.J. Forest Service, she used the Geographic Information System (GIS) to calculate the total acreage of remaining hemlock in the state and identify the degrees of HWA caused defoliation. Entire tracts of hemlock forest, more than 50 acres in Sparta Glen for example, were almost completely defoliated as biologists stood by helplessly and watched.

            When I first wrote about the HWA infestation in New Jersey in 1995, I spoke to Koeck at length. At that time his prognosis for the future of the hemlock forests was ominous. “For all practical purposes, the hemlock forests in New Jersey are doomed,” he told me in a telephone interview.

            The problem, he explained was finding a cost-efficient way to kill the adelgids. While HWA infestations on ornamental size hemlocks can be easily checked using either dormant oil spray, a commercially available insecticide called Merit or insecticidal soap, it is the forests of 100-300 year old trees that would be next to impossible to treat by any means due to the sheer physical size of each tree, the acreage involved and the inaccessibility of hemlock stands. You can't run a 10-mile length of garden hose into Waywayanda Gorge and effectively spray a 300-year old hemlock. And aerial spraying with an insecticide such as Merit, while often effective, kills other beneficial insects including aquatic species which then impacts fish and birds higher up on the food chain.

            But there appeared to be a ray of hope in the late 1990s.

In Japan, hemlocks are not at risk to adelgid infestations because of a natural predator, a beetle known as Pseudoscymnus tsugae. It has the peculiar culinary penchant of dining almost exclusively on the hemlock woolly adelgid. Studies were underway to introduce this predaceous species to attack and kill the HWA or interrupt its life cycle. Dick Reardon, an entomologist with the USDA Forest Service explained that in 1990, a population of these beetles was imported from Japan by Mark McClure, a scientist with the Connecticut Agricultural Experimental Station. Experiments began in the laboratory shortly thereafter and the results were encouraging. By 1997, large numbers of the beetles had been reared for release into infested hemlock stands in the eastern U. S. 

            “They are a real good mortality agent on HWA and we are seeing positive results in places like Connecticut, where we released the beetles on individual trees in field plots of hemlock,” Reardon told me when I spoke to him in 1998. It was his hope that the beetles would be reared en masse and subsequently released in the dozen or so states where HWA infestations were the worst, New Jersey being among them.            

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A year later, such a program was well underway in New Jersey. Mark Mayer, an entomologist with the New Jersey Department of Agriculture, was overseeing the mass rearing and releases of Pseudoscymnus tsugae at the Department of Agriculture Philip Alampi Beneficial Insect Laboratory in Ewing Township. In 1999, a total of 140,000 beetles were produced. 65,000 were released in 13 sites and an additional 67,500 shipped to other states. The remaining beetles were held as rearing stock. By early 2000, the state Department of Agriculture had produced 230,000 beetles with more than 140,000 released in 1998 and 1999 in places like the Newark Watershed around Clinton Reservoir and in the Hemlock Ravine in Waywayanda State Park's northwest corner. More releases were planned for later that year.

            It was quite literally aliens pitted against predators in a miniature War of the Worlds that was playing out in the state’s hemlock forests. But the prognosis still wasn’t good. In 2000, Mayer told me, “We are in a race, but the adelgid is way ahead.”

            But four years later in 2004, there may now be cause for some rejoicing. Brad Onken, a Forest Entomologist and HWA Program Coordinator with the USDA Forest Service out of Morgantown West Virginia is hoping that New Jersey’s hemlocks may not all be doomed to extinction.

            One of the reasons has been the weather; two successive colder than normal winters. Who could forget the way we were forced to hunker down in our homes last January for three weeks straight, bemoaning the arctic blast that sent the mercury plummeting into the single digits?  Those frigid temperatures were freezing the hibernating adelgids to death. “This [was] quite a blessing for us as it offer[ed] an opportunity for established predators like P. tsugae… to be better positioned to build in numbers naturally,” Onken explained. 

But it wasn’t just meteorological serendipity that worked in the hemlock’s favor. Two new predators of the HWA were introduced into the environment. Laricobius nigrinus, a native to British Columbia, was released in 5 other states and there are plans to conduct releases elsewhere this fall including New Jersey.

The New Jersey Department of Agriculture Beneficial Insect Lab has also begun rearing a second lady beetle predator, Scymnus sinuanodulus, a native of China. The plan is to begin releasing them in New Jersey and other states where there are HWA infestations next spring.

            “The search for additional HWA natural enemies in China and elsewhere where HWA originates will continue until we have exhausted all opportunities,” Onken explains. “Our goal is to establish a complex of HWA natural enemies throughout the infested region to provide long term control of HWA.  This is not a quick fix but offers a self perpetuating means of limiting outbreaks of HWA.  We are focused on very host specific (meaning the predators only feed on adelgids) natural enemies so the risk of collateral damage to native species is minimal.”

            Onken concedes the battle to save the hemlocks is a race against time. “In the southern region such as the Great Smokies, the clock is ticking faster. They have not had the winter mortality of HWA as occurred in the Northeast and HWA has been spreading like wild fire over the last couple of years throughout the southern Appalachians.  This area contains some of the oldest and largest hemlocks in the East and the timeframe to get this under control before we lose this resource is down right scary.”

            In the battle of alien versus predators, I’m rooting for the predators. But even if the predators are capable of keeping the adelgid population in check, the adelgids have a huge head start. Onken sounds an ominous note: “We do stand to lose [the hemlocks] as an ecological component of eastern forests.”

            Not even Stephen King could conjure up a more frightening scenario.n

Photos of HWA infested hemlock and three predator beetles courtesy of US Forest Service. For additional information, visit the US Forest Service’s Hemlock Woolly Adelgid website.

Gregory J. Rummo is an author and a syndicated columnist. His second book, “The View from the Grass Roots—Another Look,” was published in August. Copies may be purchased on the Internet from the publisher. A limited number of autographed copies are available directly from the author at GregRummo.com.