Herbivory-mediated responses of selected boreal forests to climatic change

Recent efforts to project vegetation responses to climatic warming have emphasized the tight linkages between climate and vegetation distribution. Here we provide several examples indicating that the direct effects of climatic warming on boreal vegetation can be qualitatively different than the indirect effects mediated by climatic responses of herbivores. These herbivore-mediated vegetation responses to climatic warming will likely vary regionally. In southern Fennoscandia, we project that the climatically induced changes in animal populations should enhance the density of spruce at the expense of pine and broadleafed trees. In northern Fennoscandia we project reduced herbivory on broadleafed trees and increased herbivory on pine, leading to an increase in broadleafed trees and spruce and a reduction in pine. Climatic warming in interior Alaska may reduce herbivory on broadleafed trees and increase herbivory on evergreen spruce, thus reinforcing the impact of increased fire frequency.