Yes, I have done a little bit of work on the treeline. A lot of my research focuses on the shrubline, which is the next line up as you move across the Arctic. As you move northwards, and also as you move up slopes and mountain ranges, you hit an elevational edge, which is where trees stop growing. Beyond that, large woody shrubs stop growing and then you end up with shorter plants, and eventually plants stop growing altogether.
One of the impacts of climate change is that those edges can be moving either northwards or upslope. You get taller vegetation, more woody vegetation and more carbon in that vegetation, but changes to the below-ground environment as well, and that can influence things like permafrost thaw and create some of those climate feedbacks. That changes the habitat for wildlife as well.