A hazards approach towards modelling pandora moth risk

Abstract

AbstractAim Pandora moth (Coloradia pandora Blake) is a phytophagous insect that produces a distinctive tree‐ring pattern in ponderosa pine (Pinus ponderosa Dougl. ex. Laws.) during outbreak cycles. This paper describes the spatial characteristics of the outbreak regions, determines whether the size of the 1989 outbreak was within the historical range of variability, and constructs a hazard map identifying the forests in Oregon that are susceptible to future pandora moth outbreaks.Location South‐central Oregon along the eastern flank of the Cascade mountain range in the High Lava Plains and Basin and Range Provinces.Methods We used dendrochronological records of 17 pandora moth outbreaks on 14 sites over 31,200 km2 area spanning 433 years. Using the site locations, we calculated minimum bounding polygons of adjacent recording sites to determine the relative size of each outbreak. Published literature on past pandora moth outbreaks and the environmental conditions of locally known outbreaks were used to create an outbreak hazard map using a geographical information system (GIS) model. Vegetation, climate, and soil layers were used to determine the potential susceptibility of Oregon forests to pandora moth.Results We found the area affected by past pandora moth outbreaks ranged in size from 12.4 to 3,391.5 km2. The 1989 outbreak covered 807.9 km2, which was well within the historical range of variability. The vegetation and soil layers greatly restricted the area susceptible to pandora moth while the climate layer seemed to have little effect in restricting the susceptible area.Main conclusions Pandora moth outbreaks did not increase in size over the last century as we have seen with spruce budworm outbreaks in this same region. Analysis of the environmental variables that are known to affect pandora moth outbreaks enabled us to produce a hazard map that predicts the suitable habitat for pandora moth. Temperature at the landscape scale did not restrain the range of pandora moth. The GIS model enabled us to propose areas susceptible to future pandora moth outbreaks providing a predictive model that can now be tested and refined with further sampling.