Pathogens, herbivores, and phenotypic plasticity of boreal Vaccinium vitis-idaea experiencing climate change

Climate warming is occurring at a rapid rate in the boreal forest; mean winter temperature has increased about 48C in Alaska over the last 40 years and about the same increase is predicted over the next 40 years. Warming temperatures tend to increase the number and kinds of herbivores and pathogens. How will boreal plants to respond to these abiotic and biotic changes? To address these questions we used common gardens and reciprocal transplants of Vaccinium vitis-idaea at sites with contrasting abiotic conditions near Fairbanks, Alaska. Plant morphology, chemistry, resistance to pathogens and herbivores, and survival were all strongly influenced by the destination environment (planting site and block within site), and less by the site of origin for the seed. Overall, seedlings survived significantly better at the summer cold site, which was buffered from drought as a result of its northern aspect, presence of sphagnum moss and permafrost (86.4% survival versus 48.5%). However, this cool damp site had more stem-killing consumers, the pathogens Phomopsis columnaris and Exobasidium vaccinii and mammalian browse, all of which became more common over the three years of the study as the plants became larger. Taken together, these results suggest that the seedling stage is likely to be vulnerable to droughts, except at sites with thick moss cover, which results in greater duration of summer moisture. Thus, as the climate warms, seedling growth will be restricted to those sites where the adult stages will later suffer from more stem-killing pathogen attack and mammalian browse.