 Within affected regions, epidemics did not recur regularly.In 1965, Blais obtained further evidence from the radial growth on basal disks of balsam fir, white spruce, and black spruce (susceptible species), and non-susceptible white pine in the Laurentide Park, Quebec.He concluded that outbreaks occurred in 1704, 1748, 1808, 1834, 1910, and 1947.