Changes in distribution for individual species is expected to lead to shifts in forest assemblages and tree species may rearrange into novel communities.Major shifts in overstory species composition may not be observable until well into the 21st century because of the long time frames associated with many ecosystem processes and responses to climate change. These shifts, however, may become more apparent along ecotones where boreal species reach the southern edge of their range. Major stand-replacing disturbance events, forest management, and human activities all have the potential to strongly influence how forests change in response to changing climatic conditions. Additionally, non-native species may also be to take advantage of shifting forest communities and unoccupied niches if native forest species are limited.