Insect herbivore damage on latitudinally translocated silver birch (Betula pendula) - predicting the effects of climate change

Boreal forests might be challenged by increased herbivory pressure in the future due to global warming, since warming is predicted to increase the abundance of herbivorous insects and to lead to shifts in their distribution towards higher latitudes where they might face more palatable food sources. We studied the effect of the latitudinal translocation of silver birch (Betula pendula Roth) on herbivore damage to 26 micropropagated genotypes originating from six populations ranging from 60 to 67 degrees N in Finland in two growing seasons, 2011 and 2012. The genotypes were planted at three sites located in southern (60 degrees N), central (62 degrees N) and northern (67 degrees N) Finland. The genotypes translocated to lower latitudes from their latitudes of origin were experiencing higher intensity of herbivore damage compared to the genotypes translocated to higher latitudes in 2011, but not in 2012. All genotypes were experiencing herbivore damage by local herbivores of each study site. These results suggest that, as many herbivore species are predicted to shift their ranges towards higher latitudes, they can feed on novel host plant genotypes and may face more palatable food sources than at their present range. This suggests that future climate change will increase herbivore damage to young silver birch. Increased herbivory, in turn, might affect the growth of birch and therefore should be considered when making predictions about the boreal forest composition in the future.