Multi-Century Reconstruction of Pandora Moth Outbreaks at the Warmest/Driest Edge of a Wide-Ranging Pinus Species

Pandora moths (Coloradia pandora subsp. davisi Barnes and Benjamin) have been observed to reach epidemic populations on the Kaibab Plateau, resulting in relatively small, localized defoliation events of ponderosa (Pinus ponderosa Lawson). We reconstructed the historical pandora moth outbreak regime using tree rings and forest health records to explore how exogenous factors, climate, and fire, are related to outbreak dynamics close to the driest range of ponderosa pine. We collected eight tree-ring chronologies dating back 400 years, geographically dispersed around the plateau, and inferred past outbreaks by comparison with non-host tree-ring chronologies, weather records, and historical observations. Eleven outbreaks were detected between 1744 and the present, many of them occurring at all the sites. Outbreaks were found to be synchronous, typically lasting 10 years at 25-year intervals. Interruption of the frequent fire regime that prevailed prior to 1880 was associated with a shift to shorter, less frequent outbreaks. Dry to wet oscillations in climate were correlated with outbreak initiations. Pandora moth outbreaks appear to have been an intrinsic part of the Kaibab Plateau’s forest ecosystems, though more research is needed to understand outbreak effects on the ecosystem and future directions of the moth–host relationship under climate warming.