Using Landsat to Assess the Relationship Between Spatiotemporal Patterns of Western Spruce Budworm Outbreaks and Regional-Scale Weather Variability

Western spruce budworm is a defoliator of coniferous forests of North America. Past research has shown that climate is a principal driver of budworm outbreaks, though the underlying relationships are not well understood. We utilized Landsat time series to investigate the relationships between spatiotemporal patterns of budworm outbreaks and weather variability. Landsat-based maps of budworm infestations from (1995-2013) were produced and used to describe patterns of the most recent budworm outbreak in British Columbia. Superposed epoch and regression analysis were used to explore relationships between outbreak patterns and annual temperature and precipitation anomalies. We found that western spruce budworm outbreaks were preceded by autumn precipitation deficits that were 12% lower than the long-term average, and co-occurred with summer precipitation up to 20% below the long-term average. Spring temperatures shortly before outbreaks were 0.7.degrees C lower than normal, whereas winter temperatures during outbreaks were above average by 0.5.degrees C. We concluded that the most recent outbreak of western spruce budworm in British Columbia co-occurred with distinct weather patterns that probably facilitated budworm population development and synchronized host-herbivore phenology. Although Landsat has been used to map insect disturbances, our study demonstrated its usefulness for understanding landscape-to regional-scale drivers of budworm outbreaks.