Author(s)

Barry J. Cooke¹, Jens Roland²

¹Natural Resources Canada, Canadian Forestry Service, Great Lakes Forestry Centre, Sault Ste. Marie, Canada.
²University of Alberta, Edmonton, Canada.

Using tree-ring analysis, we show that the dynamics of forest tent caterpillar [Malacosoma disstria (Hbn.)] outbreaks in Alberta, Canada shifted at the turn of the 20^th century from cyclic, synchronous behaviour 1850-1910 to complex, asynchronous behavior 1910-1993. This shift in dynamics coincided with the emergence in 1910 of a latitudinal gradient in outbreak stability and periodicity reflecting a similar gradient in the periodicity of winter temperatures. We postulate that the synchronizing strength of winter temperatures has diminished as a result of climate warming, and that any synchronizing strength due to inter-population migration has been superseded by regionalized patterns of periodic forcing caused by weak low-frequency variability in winter temperatures. We speculate that a decrease in polar vorticity at the start of the 20^th century led to increased meridional jet stream flow and more frequent arctic weather anomalies, resulting in a loss of synchronous decadal periodicity in outbreak occurrence. These changes in insect disturbance probabilities, including rising uncertainty, have profound consequences for forest disturbance risk management.

Dendroentomology, Forest Insects, Outbreak Cycles, Synchronization, Disturbance Ecology, Climate Change

Cooke, B. and Roland, J. (2018) Early 20^th Century Climate-Driven Shift in the Dynamics of Forest Tent Caterpillar Outbreaks. American Journal of Climate Change, 7, 253-270. doi: 10.4236/ajcc.2018.72017.