This past summer, wildfires raged across Canada, with a record-setting 15 million hectares (roughly 5% of the country’s total forested area) being burned across all 13 provinces and territories. It is understood that hotter, drier summers resulting from climate change are increasing the frequency and severity of forest fires globally. At the same time, land and water managers have been reflecting on the “Summer of Invasives”. A novel invasive pathogen causing oak wilt was sadly detected for the first time in Canada, while sightings of spotted lanternfly and grass carp were reported in Ontario (both) and Quebec (the latter). Hemlock woolly adelgid spread to additional locations within Ontario. While wildfires were at the forefront of environmental challenges in Canada in 2023, new biological invasions raised a quieter alarm. As it turns out, climate change can exacerbate and be exacerbated by both.
Historically, we’ve been able to rely on our long, cold Canadian winters to prevent many invasive insects from establishing here, but this might be changing. In warmer winters induced by climate change, insect eggs may have a better chance of overwintering and hatching the following spring. Current research is showing that spotted lanternfly eggs can survive at temperatures of –20°C, making it possible for this destructive agricultural pest to establish in southern Ontario, Quebec and British Columbia. Sleeper species, which are non-native species that are present at low population levels but not currently posing societal or ecological problems, could “wake up” (I.e., increase their populations and spread) when climate conditions become more favourable for them. Sirex woodwasp is an example of a sleeper species that has been limited to parts of Ontario and Quebec and could threaten pine plantations in the future. Even native insects are expanding their range and becoming invasive in new regions. Mountain pine beetle, a species that is native to parts of British Columbia, exploded in population and spread into northern Alberta after several milder winters. Finally, diseases that keep some insects, like spongy moth, under control are less impactful in warmer temperatures.
While climate change facilitates the establishment and spread of invasive species, we ought to consider the latter as potential climate change accelerants, too. Healthy forests are carbon sinks, meaning they capture and store carbon dioxide (CO2) that would otherwise be in the atmosphere contributing to climate change. The destruction of mature trees, whether by wildfire or invasive pests or pathogens, releases this stored CO2 back into the atmosphere, transforming the carbon sink into a carbon source. The previously mentioned mountain pine beetle is both expanding its range due to climate change and potentially turning forests from carbon sinks into carbon sources as they explode in population and kill pine trees.
Invasive species also blunt our ability to adapt to climate change. Emerald ash borer has decimated hundreds of thousands of ash trees since it was first found in Canada. Not only are they removing an important forest tree species that contributes to CO2 storage, but they also continue to destroy many street trees in towns and cities that provide shade and cooling – a relief during hotter summers. Hemlock woolly adelgid attacks and kills hemlock trees. Hemlocks are important in riparian areas as they prevent soil erosion and shade streams, maintaining crucial cold-water habitat.
Climate change enables further biological invasion while invasive species are exacerbating the impacts of climate change. Furthermore, warmer temperatures and droughts stress native trees and forests, making them less resilient towards attacks from novel pests and pathogens. With new research showing that biological invasions are as costly as natural hazards, we must reckon with the catastrophic threat posed by invasive species. Successful adaptation to a changing climate depends on it.
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