Eastern hemlock (Tsuga canadensis) as an alternate host for spruce budworm (Choristoneura fumiferana): dendrochronological evidence from Maine, USA

In northeastern North America, episodic eastern spruce budworm (Choristoneura fumiferana) outbreaks extensively defoliate balsam fir (Abies balsamea) and spruces (Picea glauca, Picea rubens, Picea mariana). We investigated eastern spruce budworm defoliation in eastern hemlock (Tsuga canadensis), a reported alternate host species, during previously documented outbreaks in Maine, USA. We compiled red spruce and hemlock tree-ring series from nine sites, seven of which showed synchronous radial growth reductions in spruce and hemlock during documented budworm outbreaks. Outbreak evidence varied among sites, but growth reductions were observed in six study sites during a 1914 outbreak. Synchronous growth reductions between spruce and hemlock suggest that when budworm defoliation occurred in spruce at a given site, hemlock typically experienced at least some level of defoliation. Relative budbreak synchrony with preferred host species may contribute to hemlock’s suitability as a host. This research is timely given the recent spruce budworm population increase in this region.