Eastern Hemlock Trees: The Invasive Species Epidemic in Nova Scotia

By Jessica Harmon, SMU Service Learning Student

Eastern Hemlock and the Woolly Adelgid

Nova Scotia is filled with deep emerald forests that are a part of the province’s many ecological and characteristic traits. The Eastern Hemlock (Tsuga canadensis) is a species that is an integral part of Nova Scotia’s old-growth forests and surrounding ecosystems. Throughout the province, the Eastern Hemlock is seeing a significant decline in numbers. According to Nature Trust Nova Scotia (2024), we are at risk of losing eastern hemlock in places such as the Kejimkujik National Park forever without rapid intervention. They are currently at major risk for regional extinction due to the Hemlock Woolly Adelgid (Hemiptera: Adelgidae). The Hemlock Woolly Adelgid (HWA) is an insect that was accidentally introduced to eastern North America from southern Japan. Its first sighting report was in 1951, and it has been slowly increasing its range since its arrival (Limbu, S., Keena, M. A., & Whitmore, M.C., 2018). HWA is browning-orange in colour and aphid-like insects as adults, and appear like black, wingless insects with a waxy coat as juveniles, while their eggs are found in small white clusters (Nova Scotia Invasive Species Council, 2021). These crawler insects will settle near the base of the eastern hemlock’s needles and remain there for the rest of their lives. They will insert themselves through the plant tissue and into the host’s storage cells where it will feed on the tree's starch. This will cause hemlock to lose its needles and can kill a century-old tree in as little as 1-3 years (Doccola, J., Hascher, W., Aiken J., & Wild, P, 2012). Luckily, the province of Nova Scotia has developed a strategy to help these valuable Eastern Hemlocks in their recovery using a heavily researched method of chemical injection into the tree. The province has created an opportunity of environmental stewardship for the community to be involved in this strategy alongside trained scientists. Keep reading for information on how to get involved below. All are welcome!

Eastern Hemlocks in Pockwock, NS (Jessica Harmon, 2024).

Ecological Importance of The Eastern Hemlock

The tall, dark, softwood eastern hemlock stands have been a part of a long forest history in Mi’kma’ki for thousands of years (Nature Nova Scotia, n.d). Eastern hemlock trees are one of the most abundant tree species in North America (Limbu, S., Keena, M. A., & Whitmore, M.C., 2018). They are majorly distributed from the southeastern coast of Canada such as Nova Scotia to parts of Georgia, Alabama, and Minnesota (Limbu, S., Keena, M. A., & Whitmore, M.C., 2018). The eastern hemlock can often reach over the age of 500 years and over 30 meters tall. They are a foundational species as they play a major role in the rare old-growth forests and their surrounding ecosystems (Nature Nova Scotia, n.d).

Eastern hemlocks are a shade-tolerant species, meaning that they can thrive in a shady environment with an abundance of taller, older trees in their stand. They are known for their skills to stabilize water and temperature in the soils, keeping nearby streams cool. These skills allow the hemlocks to create a cool and moist climate for the soil, which results in a slow rate of nitrogen cycling, enabling a diverse habitat for both terrestrial and aquatic organisms. There are no other known tree species that could replace the ecological functions of the hemlock (Limbu, S., Keena, M. A., & Whitmore, M.C., 2018).

In addition, the eastern hemlock provides important shelter for wildlife in the winter as they trap warmth from the earth and use their large canopies to catch snow and freezing rain (Nova Scotia Nature Trust, 2024). While the winter seasons come with lower levels of light and colder temperatures, the species can lower their respiration rate (Briggs, G, 2021), as well as their rates of photosynthesis on extremely cold days (Burkle, L.A., & Logan, B.A, 2003) which assists neighbouring tree species to grow and thrive in the toughest of winter days having more access to the sunlight.

The Solution – Tree Injection

Nova Scotia has been working with a scientific chemical solution founded by decades of research to inject the sick eastern hemlock trees against the invasive HWA. Although spray applications on the species are more commonly used in other parts of the world, there are more advantages of tree injections in terms of longer-term protection. This treatment looks to be a better economical and efficient solution as the treated tree may only need re-treatment every 2-3 years, or up to 6 years with a high-rate treatment (Doccola, J., Hascher, W., Aiken J., & Wild, P, 2012). The procedure is followed through by small amounts of chemical pesticides that are injected into the tree’s lower trunk. From there, the tree can transport the treatment to the affected tissues within the canopy (Nature Nova Scotia, n.d). It is important to treat the hemlock trees promptly, if the HWA affects the trees’ ability to transport the treatment, the tree will unfortunately die.

You Can Get Involved!

HWA affects eastern hemlocks on both private and public land. The province has embraced funding for the treatments through the federal Department of Environment and Climate Change fund (Nature Nova Scotia, n.d). However, the majority of Nova Scotia is private land, which leaves more hemlock stands vulnerable to death. The province launched a fundraiser in 2023 to treat these sick trees on private land (Nature Nova Scotia, n.d). The province has also launched a provincial HWA Action Program to protect the highest-priority old-growth hemlock stands in Nova Scotia (Nova Scotia Nature Trust, 2024). The Nova Scotia invasive species council (NSISC) is another great source to help identify and prevent further spread of the woolly adelgid in our communities (Nova Scotia Invasive Species council, 2021). Community stewardship programs welcome individuals with varying levels of experience to participate. These initiatives invite anyone interested to join and receive a series of training sessions on proper tree injection techniques. Volunteers are then guided to these high-priority forests to deliver treatment to large quantities of hemlock trees. You will gain the skills of tree identification, forest management, tree injection, and get to spend time with some of Nova Scotia’s best ecological researchers and environmental scientists!

Click here to learn more about tree injection volunteering.

Eastern Hemlocks in Pockwock, NS (Jessica Harmon, 2024).

Summary

The eastern hemlock is a vital species for newly developing forests as well as old-growth forests and must be protected from the hemlock woolly adelgid. Eastern hemlocks are important to the diversity and sustainability of a forest as they can stabilize the soils for many types of organisms, as well as help neighbouring species in the harshest of cold weather. HWA can live their lives in the base of the hemlock’s needles, killing them rapidly all over the province. Luckily, the province’s stewardship shines with tree injection strategies which invite the provincial community to be a part of saving the hemlock trees. Make sure to stay up to date with the hemlocks, and we hope to see you out there!

References

Briggs, G. (2021). Hemlock. Mine Library. https://milnepublishing.geneseo.edu/botany/chapter/hemlock/#:~:text=It%20may%20gain%20so me%20advantage,and%20water%20transport%20is%20restricted.

Burkle, L. A., & Logan, B. A. (2003). Seasonal Acclimation of Photosynthesis in Eastern Hemlock and Partridgeberry in Different Light Environments. Northeastern Naturalist, 10(1), 1–16. https://doi.org/10.2307/3858668.

Doccola, J., Hascher, W., Aiken, J., & Wild, P. (2012). Treatment Strategies Using Imidacloprid in Hemlock Woolly Adelgid (Adelges tsugae Annand) Infested Eastern Hemlock (Tsuga canadensis Carrière) Trees. Arboriculture & Urban Forestry, 38(2), 41–49.

Grant, T. (2023). New tools to save Nova Scotia’s hemlocks come into use as a species continues to decline. CBC News. https://www.cbc.ca/news/canada/nova-scotia/eastern-hemlock-woolly-adelgid-bark-spray-pestici de-kejimkujik-1.7003127.

Limbu, S., Keena, M. A., & Whitmore, M. C. (2018). Hemlock Woolly Adelgid (Hemiptera: Adelgidae): A Non-Native Pest of Hemlocks in Eastern North America. Journal of Integrated Pest Management, 9(1), 1-. https://doi.org/10.1093/jipm/pmy018.

Nature Nova Scotia. (n.d). Save Our Hemlocks: Fighting Hemlock Woolly Adelgid. Nature Nova Scotia.https://naturens.ca/actions/saveourhemlocks/#:~:text=Beyond%20the%20beauty%20and %20magical,hemlock%20forests%20are%20under%20attack.

Nova Scotia Hemlock Initiative. (n.d). Nova Scotia Hemlock Initiative: Keeping the Legacy Alive. https://www.nshemlock.ca.

Nova Scotia Invasive Species Council. (2021). Hemlock Woolly Adelgid. Nova Scotia Invasive Species Council. https://nsinvasives.ca/hemlock-woolly-adelgid/.

Nova Scotia Nature Trust. (2024). Hemlock Wooly Adelgid (HWA). Nova Scotia Nature Trust. https://nsnt.ca/hemlock-wooly-adelgid-hwa/.