In the northern high latitudes, vegetation distribution and carbon cycling have been continuously changed in the past and could change more rapidly as the climate warming. The purpose of my PhD dissertation is to quantify the uncertainty in modeling vegetatidynamics and to assess the effect of permafrost on vegetation dynamics and carbon cycling in the northern high latitudes under different levels of warming conditions. The uncertainty in current modeling of vegetation dynamics is considerably large. The first part of this study is to assess how high-latitude vegetation may respond under various climate scenarios during the 21st Century with a focus on analyzing model parameters induced uncertainty and how this uncertainty compares [...]