Climate change has already reshaped North American forest pest dynamics: Insights from multidecadal process-based modelling

Ongoing anthropogenic climate change has the potential to modify the population dynamics of forest pest insects by shifting the distribution of suitable climate conditions for their development. We used processed-based temperature-driven physiological models to assess the impact of changing climate conditions between 1951 and 2022 across North America on eight important forest pest insects, namely western spruce budworm, eastern spruce budworm, spongy moth, hemlock woolly adelgid, mountain pine beetle, southern pine beetle, spruce beetle and emerald ash borer. Our analyses revealed substantial changes in climate suitability resulting in pronounced northward and elevational shifts for most pest species although the magnitude and spatial patterns of these shifts varied both geographically and among species. We also showed that shifts in highly suitable conditions were more important at the colder edge (either northern or upper elevation) than at the warmer boundaries for several species, either driven by the Arctic amplification or elevation-dependant warming. Our results indicated that both the total area and the host tree biomass exposed to highly suitable climate conditions have increased for many pest species over the last decades, further exposing ecosystems to elevated risk. Our analyses also identified areas (e.g., western Canada) that are increasingly exposed to overlapping, potentially cumulative and interacting, biological disturbances. We also showed that climate change has already contributed to increasing the climatic suitability and geographic spread of exotic forest pest species in North America. Changes in climate suitability over the past seven decades across North America likely represent early signals of continued and potentially accelerating shifts under ongoing anthropogenic climate forcing. In this context, efforts to limit the expansion of pest populations under future climate change scenarios will be key to mitigating their cultural, ecological and economic impacts.