Outbreak record characteristics for regional records used in this study and the inter-regional record presented in this paper for the 1700–1990 common period.

Regions are as follows: BC = central British Columbia, WA = northern Washington, MT = western Montana / eastern Idaho, ID = western Idaho / northeastern Oregon, OR = north-central Oregon, CO = southern Colorado, NM = northern New Mexico, All = synchronous outbreak record (years with outbreaks recorded in three or more regional records). Species are: PSME = Douglas-fir, ABGR = grand fir, ABCO = white fir. Area sampled is a very approximate estimate based on published site descriptions.