A reporter from Discovery channel came by last summer looking for Global Warming damage to the permafrost. I showed him where the aspen and paper birch were invading the black spruce forest as much as 100 yards in the past 30 years. He left with a look of despair on his face.
Paper birch or white birch. My impression was the paper, or brown, birch trees (of which I have several dozen) were not very tolerant of the dryer air at the higher latitudes.