Host-environment mismatches associated with forest trees injured by spruce beetles (Dendroctonus rufipennis) and aspen leaf miners (Phyllocnistis populiella) in Alaska

Spruce beetles and aspen leaf miners are prevalent in the forests of Alaska.  Although hosts of both pests are widespread, the distribution of spruce beetle is much more restricted than aspen leaf miner.  The widespread nature of both pests suggests that climatic factors play a dominant role in their distribution, but the concentrated distribution of the former suggests that the relative impacts of climatic conditions on the pest/host interactions differs between them.   We examined the influence of varying combinations of average annual temperature and precipitation on the large-scale incidence and distribution of trees injured by these insects.  Transition matrices were used to show spruce trees affected by the spruce beetle occur across much narrower climatic conditions than aspen trees injured by aspen leaf miner.  For both host species, healthy trees are found mostly in climatic zones with moderate to low temperatures and high precipitation; whereas, spruce beetle severity is most intense in zones of moderate temperatures and moderate precipitation.  This contrasting distribution defines an environmental mismatch.  Forests matched with favorable climatic conditions thrive; those that are mismatched can become vulnerable to spruce beetles.  In contrast, aspen leaf miner showed no restriction across climatic zones, and its distribution was apparently more dependent on host distribution than climatic conditions.