Western Spruce Budworm Outbreak History

Western spruce budworm (Choristoneura occidentalis Freeman) outbreak history was reconstructed for the Sacramento Mountains of south -central New Mexico, at the southern limit of the species distribution range. Six host tree -ring width chronologies (Douglas -fir and white fir) and three non -host control chronologies (ponderosa pine) were used for this reconstruction spanning from 1800 to 1990. Both the host and non -host species had similar climatic response so the non -host chronologies were confidently used as climatic controls. Up to eight defoliation events were documented within individual stands and at least seven major regional outbreaks were identified among the stands back to 1800. At least five major outbreaks occurred in the twentieth century: 1890s1900s, 1910s1920s, 1940s, 1960s, and 1980s. The 1960s and 1980s outbreaks were verified by Forest Service aerial and ground survey records. These recent outbreaks seemed to have been more synchronous among the different stands than outbreaks that occurred in the 19th century. There were similarities between this outbreak history and an outbreak history reconstructed for northern New Mexico, a distance of about 340 km to the north. The regional -scale pattern identified in these histories lends support to a hypothesis that past logging and fire suppression has changed western spruce budworm dynamics.