Paper Reviewed
Axelson, J.N., Smith, D.J., Daniels, L.D. and Alfaro, R.I. 2015. Multicentury reconstruction of western spruce budworm outbreaks in central British Columbia, Canada. Forest Ecology and Management 335: 235-248.

In setting the stage for their study, Axelson et al. (2015) report that since the early 1900s, documented western spruce budworm (WSB) outbreaks in the Douglas fir forests of British Columbia have resulted in the defoliation of over 5.6 million hectares of forested land located primarily in the southern interior of the province, citing the study of Maclauchlan et al. (2006). And they further note that this finding has led to what they call "an anecdotal perception" that the western spruce budworm is expanding its range northward in response to a warming of the climate. However, they also write that in the southern interior of the province, "tree-ring studies show that over the last 500 years WSB outbreaks have occurred repeatedly, with a mean return interval of approximately 33 years," citing the studies of Campbell et al. (2006) and Alfaro et al. (2014), which facts suggest that this "anecdotal perception" is likely not correct.

In further exploring this recurring decadal-scale phenomenon, therefore, the four Canadian researchers studied eleven Douglas fir host chronologies and two regional Pinus non-host chronologies to reconstruct WSB outbreaks over a 435-year period in the central interior of the province -- the Cariboo Forest Region -- where "standard dendrochronological techniques were used to develop tree-ring chronologies at each site and the program OUTBREAK was used to detect outbreak periods."

This work revealed the occurrence of 12 WSB outbreaks that began in the early 1600s and had a mean return interval of approximately 32 years, thereby demonstrating, in the words of Axelson et al., that "outbreaks observed over the last 40 years in this region are not unprecedented and offer no support for the perception that the WSB has been expanding northward into the Cariboo Forest Region."

References
Alfaro, R.I., Berg, J. and Axelson, J. 2014. Periodicity of western spruce budworm in Southern British Columbia, Canada. Forest Ecology and Management 315: 75-79.

Campbell, R., Smith, D. and Arsenault, A. 2006. Multi-century history of western spruce budworm outbreaks in interior Douglas-fir forests near Kamloops, British Columbia. Canadian Journal of Forest Research 36: 1758-1769.

Maclauchlan, L., Brooks, J. and Hidge, J. 2006. Analysis of historic western spruce budworm defoliation in south central British Columbia. Forest Ecology and Management 226: 351-356.