Spatial patterns of forest insect outbreaks across the Pacific Northwest

Insects play several important roles in forest ecosystems including serving as natural enemies, pollinators, and nutrient cyclers. However, outbreaking species can cause damage beyond the limits of forest tolerance. Forest insect outbreaks can be extremely catastrophic events that lead to large scale tree mortality over a relatively short period of time, causing cascading negative effects including reductions in wildlife habitat and increased carbon emission. Insects are also strongly affected by climate and changes in climate because many of their physiological processes are regulated by temperature. Consequently, warming temperatures have critical ramifications to insect populations, including more frequent and/or more intense outbreaks. We used historical aerial detection survey data (1960-2015) from the coniferous forests of Oregon, Washington, and British Columbia to quantify the spatial dynamics of bark beetles, folivores, and their interactions across local and regional scales, and to measure how these dynamics have changed through time. Among bark beetles, the degree of regional spatial autocorrelation has increased over the past two decades, indicating that outbreaks have become larger in spatial extent, more clustered, and thus more contiguous across the landscape, It is important to note that these patterns are being driven largely by Dendroctonus ponderosae. In contrast, the degree of spatial autocorrelation among folivores has remained fairly constant through time. This research highlights the importance of identifying ecologically important interactions to better mitigate the consequences of forest insect outbreaks.