Hemlocks in Crisis: Agencies Mobilize in Defence of Iconic Tree

The Eastern hemlock is a force of nature in Nova Scotia by virtue of its age. Foresters past and present have ignored it in favour of more valuable spruce, pine and myriad hardwoods, allowing hemlocks to become the oldest member of our enduring forests, accounting for almost all of our remaining old growth.

While several plants and animals depend on these hemlocks because of their maturity, others rely on their expansive, closed canopies, which have the curious effect of shielding understories and streams from punishing sunlight year round, providing habitat for those creatures prone to coolness such as Brook trout and deer. They also protect the ground from an excess of snow, creating wildlife walkways even in the harshest of Januaries.

In the words of Parks Canada ecologist Matthew Smith, presently stationed at Kejimkujik National Park, “Hemlock forests really mediate climate and create these cool oases in the forest.”

Their importance to the ecology of eastern North America is difficult to overstate, especially now that they’re dying by the billions.

The Asian Aphid

The Hemlock Woolly Adelgid (HWA) is an aphid-like creature native to the forests of Asia, where it extracts water and nutrients from species of Asian hemlock evolved to handle this regular theft. Thousands of years ago, it’s believed, HWA was also introduced to the Pacific northwest, where it feeds on Western hemlocks and is held in check by predatory insects adapted to devour it.

In eastern North America, however, no such ecological balance has been struck. When HWA was introduced to Virginia in the 1950s it began an unchallenged spread north and east, thoroughly infesting New England and attempting two separate invasions of southern Ontario in 2011 and 2013, both of which were turned back by the careful application of pesticides.

This insect is a lethal parasite to the Eastern hemlock, which it drains to death in 4-10 years, and in mid-July of 2017 HWA was discovered in the forests of Weymouth, Nova Scotia. Since that initial finding, followup surveys by the Canada Food Inspection Agency have uncovered the widespread infestation of Digby, Yarmouth and Shelburne counties, with smaller pockets in Queens and Annapolis.

A Mounting Defence

“All detections have continued to be in those five counties in southern Nova Scotia,” said Ron Neville this past December, a survey biologist with the Canada Food Inspection Agency (CFIA).

Surveys undertaken by his and other agencies have looked closely at the hemlocks of New Brunswick, Prince Edward Island, Quebec and Ontario throughout 2018, but no additional signs of HWA have yet been found. In southern Nova Scotia, however, its destructive influence is already being seen. Along the Sissiboo River of Digby County and Tusket region of Yarmouth, hemlocks are dying.

In order to contain this infestation, CFIA has enacted a series of movement restrictions on several hemlock products leaving the five southern counties, including hemlock logs, bark chips, wood mulch, nursery stock, even decorative reefs. The movement of all firewood, regardless of species, is likewise restricted from leaving these counties. Products may only break quarantine with CFIA authorization, which requires that risk mitigation measures be in place. Anyone interested in moving their product is encouraged to contact CFIA.

“The restrictions are in place to prevent the long-distance spread of HWA by people,” said Neville. “Having the pest move more slowly gives us time to develop more effective management strategies.”

At the moment, there are no pesticides registered and available in Canada for use against HWA, depriving woodlot owners, private nurseries and conservation organizations of an important tool for the preservation of outstanding hemlock stands. Jon Sweeney is a research scientist with the Canadian Forest Service and among those remedying this problem.

“Right now there are no options,” he said.

The company Arborjet has applied to have their product IMA-Jet, with the active ingredient Imidacloprid, registered for use on HWA in Canada, against which it has already proven effective. Jon expects the application could be approved as early as spring, but until then he and colleagues have partnered with another company, BioForest, to test their product TreeAzin against HWA infested hemlocks on a private nursery in Meteghan, Nova Scotia. This insecticide, with the active ingredient Azadirachtin, is gentler than most, said Jon, in terms of environmental impact, and is already registered for use in Canada against the Emerald Ash Borer. It was injected into several large hemlocks this October, the results from which will be gathered come March.

While approval for both insecticides are proceeding apace, Sweeney expects them to be more expensive than the combination of imidacloprid and dinotefuran insecticides used to treat hemlocks in New York state. This combination protects the trees from HWA for five years and is relatively cheap, but is unlikely to receive approval from Canada’s Pest Management Regulatory Agency. Because IMA-Jet and TreeAzin may prove more expensive, landscape scale treatments for HWA might be cost prohibitive in Nova Scotia, and will have to focus on smaller hemlock stand until a long-term solution for HWA can be established.

The solution on hand in the eastern United States is the introduction of western insects which prey exclusively upon HWA, namely the beetle known as Little Larry (Laricobius nigrinus) and a species of Silver fly (Leucopis argenticollis), both slowly establishing themselves in selected states. Much like the testing of pesticides, predatory insects from Canada’s west coast are being considered for their safety and effectiveness if introduced to Nova Scotia, and the unique climatic factors at play. If suitable candidate species are identified, they may be introduced as a biocontrol which, in time, may permanently temper HWA.

“We still feel that biological pest control for HWA is really where management needs to move,” said Ron Neville. “There has been some work done in Nova Scotia to prepare for that type of initiative.”

Old Growth
Nova Scotian old growth, Coolen Lake.
Zack Metcalfe photo

In The Meantime

The Medway Community Forest Co-op resides in Queens County, and has been subject to restrictions on their wood. The insect has yet to be found on their land.

“There have been some added logistics to moving firewood, particularly as a large portion of our public clients reside in Lunenburg County,” said executive director Mary Jane Rodgers. “During the high season, when HWA is most active, we are required to cover our firewood that comes from hemlock sites, or if it is stored in our yard for a duration of 15 days before it is sold outside the restricted zone. Another step we take is tracking firewood through the CFIA movement certificates, ensure that our deliveries are well monitored if an outbreak were to occur elsewhere. So far these haven’t been too much of an inconvenience. CFIA is very responsive organization and has been very helpful throughout the process.”

She said the Co-op is considering a move to kiln-dried firewood as a new revenue stream in the near future. Since wood treated in this fashion can’t host invasive insects of any kind, it is a standard precaution among Canadian and American national parks, one undertaken in January of 2018 by Kejimkujik.

“In Nova Scotia, Keji and the neighbouring Tobeatic Wilderness Area certainly have some of the best examples of old growth hemlock forest, and some of the largest,” said the aforementioned Matthew Smith, who went on to say his trees boast 350-400 years of age.

“You walk through it and really feel what it was like in Nova Scotia prior to the harvesting of a lot of our old growth stands.”

On August 9 of 2018, HWA was discovered in a Keji campground and has since been uncovered at ten sites throughout the park. So far they are each relatively isolated. In order not to exacerbate the spread and to prolong the lives of their mightiest hemlocks, Keji switched from firewood supplied by the Medway Community Forest Co-op to kiln-dried firewood from the company Fiready in New Brunswick. They also enacted a firewood importation ban, where wood brought by visitors has to meet certain criteria, such as being kiln-dried itself and in its original packaging.

“It’s about slowing the infestation,” said Smith, “but it’s also about other invasive species, namely the nearby Emerald Ash Borer and Beech Leaf Weevil.”

Smith and his Keji colleagues are bracing themselves for the ecological impacts of HWA. Their trees have not yet started to die, which suggests their infestation is younger than those farther south, and they’re not sure at which pace the decline will occur, but they are well positioned to monitor the decline. Their facilities are surrounded by towering hemlocks which may begin to fall, and their visitor routinely favour hemlock trails, lined by cathedral-like groves. Consequently, the park may take a financial hit.

Smith encourages Nova Scotians to come see their outstanding old growth hemlocks, so long as these trees face an uncertain future.

Zack Metcalfe is a freelance journalist, author, and writer active across the Maritimes. This article was originally published with Atlantic Forestry Review.

2 Replies to “Hemlocks in Crisis: Agencies Mobilize in Defence of Iconic Tree”

  1. The Beech leaf weevil has devastated the Beaches here in HRM. We have about 100 within eyesight of our house, but no one seems to notice or care about that infestation.

  2. Take action fast, the Emerald Ash Borer has taken a lot of trees in Ottawa and Gatineau. It’s sad when walking ‍♀️ through the parks and see all the dead

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