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A threat to hemlocks

April 8, 2015
By SHAUN KITTLE - Outdoors Writer (skittle@adirondackdailyenterprise.com) , Lake Placid News

LAKE PLACID - A fungus infestation in the 1900s almost wiped out American chestnut trees, and now scientists are worried the same thing could happen to eastern hemlocks in the Adirondacks.

In the late 1800s, a New York City nursery owner imported Japanese chestnuts to offer his customers an exotic tree for their yards. In doing so, he also unwittingly imported a pathogenic fungus called Cryphonectria parasitica, which hitched a ride on the trees.

Japanese chestnuts were resistant to the fungus, but their American counterparts were not. Soon, the resilient tree that once dominated hardwood forests along the East Coast was reduced to scattered populations of saplings.

Article Photos

Adirondack Mountain Club government relations and conservation associates Paul Gallery, left, and Cathy Pedler inspect an eastern hemlock tree near the Adirondak Loj for signs of hemlock woolly adelgid, an invasive insect that’s decimating hemlock stands in other regions.
(News photo — Shaun Kittle)

Scientists with the SUNY College of Environmental Science and Forestry have been working on a genetically modified strain of American chestnut that can resist the fungus, but so far none of the specimens has made it beyond the laboratory.

The fact that importing a tree could introduce something devastating to a native species wasn't even considered 100 years ago, but today's scientists have a better handle on the impact of invasive species.

In the Adirondacks, The Nature Conservancy's Adirondack Park Invasive Plant Program was implemented to deal with the invasives that are already here while launching pre-emptive strikes against species that are knocking on the region's door.

Of particular concern now is the hemlock woolly adelgid, an insect from Japan related to aphids that uses its long mouth parts to draw nutrients from eastern hemlock, western hemlock and Carolina hemlock trees. It does this by penetrating the bark, usually at the base of a needle.

Unlike balsam woolly adelgid, which has been present in the Adirondacks for at least 10 years and doesn't seem to be of grave concern, hemlock woolly adelgid is potentially devastating to eastern hemlocks, a stately evergreen with soft, flat needles and tiny cones.

"West Virginia right now is being decimated by hemlock woolly adelgid," Quirion said. "There are vast expanses of dead hemlocks."

A hemlock responds to the insect intrusion by blocking off its own circulation, essentially creating a dam that stops the flow of water and nutrients to the insect.

That also stops the flow of water and nutrients to the needles, causing them to die. After several years of this, the tree dies too. The process can be slowed by cold temperatures, so it could take as many as 10 years for an infested tree in the Adirondacks to die.

"I'm not going to beat around the bush," APIPP coordinator Brendan Quirion said. "The American chestnut was lost through the chestnut blight. We're in a situation like that. We could lose this species if we don't take action."

Hemlocks are a "foundation species" in the Adirondacks, which is an ecologist's way of saying the tree helps create favorable conditions for other species. Quirion said some bird species exclusively use hemlocks for nesting and food, and the shade they provide along stream banks is essential to brook trout, which need cool water to thrive.

A lot of non-native species show up as their range expands north, a trend scientists typically attribute to a warming climate. That makes them relatively easy to track.

Plotting where hemlock woolly adelgid is found doesn't help as much because the insect travels on wind, birds and other animals, so it can appear anywhere.

Over the last 20 years, the insect has been found in southern portions of New York state, especially in Broome, Tioga and Chemung counties, and it's also been spotted in isolated areas in Long Island, western New York and parts of the southern Catskills.

Quirion said the invasive insect could already be in the Adirondacks, and a map depicting eastern hemlock stands here shows what he means - the tree is present throughout the Park, and a bird carrying a hemlock woolly adelgid could land on any of them.

Since the insect reproduces both sexually and asexually, that's all it would take for the insect to gain a foothold.

"In Japan, there's a spruce the insect uses in its life cycle, and when that spruce is present it's able to reproduce sexually," said Cathy Pedler, a government relations and conservation associate with the Adirondack Mountain Club (ADK). "Here, it's not present, so it reproduces asexually, which makes it even harder to control. Each generation is like a carbon copy of the last one. If it were reproducing sexually, there'd be certain things that would limit how many offspring it would produce."

The threat of the insect is the reason the Backcountry Forest Monitors project came into being last year. Participants in the program are trained in how to look for evidence of the insect. Last year, volunteers adopted 22 hemlock stands. So far this year, 27 more have been adopted.

The process is simple: Investigate the underside of a hemlock's branches, where the needles meet the twigs, and then document the findings on the iMap Invasives online database.

Several white, woolly dots, which are produced by the insect to protect itself from the elements, could mean the tree is infested. The dots can also sometimes be found in caverns in the bark.

Paul Gallery, a government relations and conservation associate with the ADK, said spider mites also leave a woolly substance, but they are often found on the surface of the bark, not in the deep cracks.

Gallery pointed that out in a hemlock stand located just off of the trail to Street and Nye mountains, near the Adirondak Loj.

"These dots are much smaller, but they're kind of similar to what it would look like," Gallery said. "The adelgid is basically just looking to get at the cambium through these deep crevices."

Pedler said there are plenty of other species of concern, like Asian longhorn beetle and emerald ash borer, and they will be included in upcoming workshops.

"Hemlock woolly adelgid is the one we're most concerned about because of how insidious it is, of how devastating it is to control when there doesn't seem to be any resistance to it in our hemlocks," Pedler said.

Different kinds of chemical treatments are available, with the most expensive protecting a tree for seven years.

Biological controls are also being studied, including a beetle that preys on the insect. A combination of a beetle and chemical treatments were successfully used to eliminate hemlock woolly adelgid from Zoar Valley in western New York.

Quirion, Gallery and Pedler were among those leading a Backcountry Forest Monitor program workshop at the Adirondak Loj on March 28. The next workshop will focus on the Lake Champlain basin, with more to come throughout the Adirondacks this summer.

"If anyone sees a dead or dying expanse of trees, we want to know about it, no matter what species it is," Quirion said. "If you see trees dying off in abundance, report it to someone so we can make sure it's not an invasive species like this."

 
 
 

 

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