Impact of Hemlock Woolly Adelgid on Forest Ecosystems

The hemlock woolly adelgid (Adelges tsugae) is an invasive sap-sucking insect that has precipitated widespread mortality of eastern and Carolina hemlock (Tsuga canadensis and Tsuga caroliniana) across eastern North America. By feeding on tree reserves, it induces defoliation, crown dieback and eventual tree death, leading to the loss of a foundation species integral to microclimate regulation, soil chemistry and habitat structure. Canopy thinning increases light penetration, soil temperature and moisture fluctuations, which in turn accelerate decomposition rates and alter nutrient cycling. As hemlock stands transition to early-successional hardwood communities, carbon dynamics shift from net sequestration to net emission, with implications for regional carbon budgets. Hydrological regimes are also affected: reduced canopy interception increases streamflow and elevates nutrient leaching. Biotic assemblages respond rapidly; understory plant diversity often increases in the short term but community composition becomes homogenised as non-native and generalist species colonise. Canopy loss cascades through arthropod, avian and microbial communities, reshaping food webs and ecosystem functioning. Climatic factors, particularly winter temperature minima, influence adelgid survival and range expansion, while human-mediated movement has accelerated its spread. Together, these ecological processes underscore the global significance of adelgid-driven hemlock decline and highlight the urgency for integrated management strategies, including biological control, silvicultural treatments and refined predictive modelling to safeguard the remaining hemlock forests and their ecosystem services.

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Impact of Hemlock Woolly Adelgid on Forest Ecosystems publication trend

The graph below shows the total number of articles in impact of hemlock woolly adelgid on forest ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Foundation species: A species that exerts a dominant influence on ecosystem structure and function, often supporting characteristic microclimates and biological communities.

Ovisac: A protective casing produced by some insects, including the hemlock woolly adelgid, that encloses and safeguards eggs during development.

Biological control agent: A natural enemy, such as a predator or parasitoid, deliberately introduced or augmented to suppress populations of a target pest species.

Successional dynamics: The sequence of changes in species composition and ecosystem structure over time following a disturbance or loss of dominant vegetation.

References

1. The Past, Present, and Future of the Hemlock Woolly Adelgid (Adelges tsugae) and Its Ecological Interactions with Eastern Hemlock (Tsuga canadensis) Forests. Insects (2018).
2. Mortality and Recovery of Hemlock Woolly Adelgid (Adelges tsugae) in Response to Winter Temperatures and Predictions for the Future. Forests (2017).
3. Impact of the introduced predator, Laricobius nigrinus, on ovisacs of the overwintering generation of hemlock woolly adelgid in the eastern United States. Biological Control (2020).
4. Changes in canopy structure and ant assemblages affect soil ecosystem variables as a foundation species declines. Ecosphere (2015).
5. A foundation tree at the precipice: Tsuga canadensis health after the arrival of Adelges tsugae in central New England. Ecosphere (2012).
6. Rebound of Adelges tsugae spring generation following predation on overwintering generation ovisacs by the introduced predator Laricobius nigrinus in the eastern United States. Biological Control (2020).
7. Response of macroarthropod assemblages to the loss of hemlock (Tsuga canadensis), a foundation species. Ecosphere (2011).
8. Foundation Species Loss and Biodiversity of the Herbaceous Layer in New England Forests. Forests (2015).
9. Loss of foundation species revisited: conceptual framework with lessons learned from eastern hemlock and whitebark pine. Ecosphere (2019).