It has long been believed that global climate change would spur the northern advancement of boreal forests into the tundra. However, this study, led by scientists at the University of Oxford and the Arctic Centre at the University of Lapland, shows instead that low shrubs on the tundra are rapidly growing into trees. Willow and alder in particular have shown this trend in the last 50 years.
The study was conducted on Russia's northwest Arctic coast. As Dr. Marc Macias-Fauria, lead author on the study, states: "Previously, people had thought that the tundra would be colonized by trees from the boreal forest to the south as the Arctic climate warms, a process that could potentially take centuries. But what we've found is that the shrubs that are already there are transforming into trees in just a few decades."
More information on the study can be found here.