Influences of animal activity on treeline position and pattern: Implications for treeline responses to climate change

The alpine treeline is a potentially sensitive indicator of vegetation response to climate change. However, there is not a generally accepted single hypothesis that explains treeline position and pattern at multiple scales. Recently a set of five hypotheses has been proposed for treeline explanations (Korner, 2003b). The impacts of animals are not explicitly included in any of these hypotheses, however, they can and should be included. In this review we discuss Korner's five hypotheses and explain how animal activity can be included within them to make them more applicable to treeline environments experiencing a changing climate. We utilize the conceptual model proposed by Cairns and Moen (2004) as an organizing framework for the inclusion of animal activity with existing hypotheses. Finally we suggest that the equivocal nature of treeline response to climate change may be in part related to animal activity.