The researchers studied how a type of tree population near the top of a mountain in China has changed over the past 100 years. They found that the number of trees has increased significantly, but the treeline itself hasn't moved much higher up the mountain. The trees on the shady side of the mountain grow differently than those on the sunny side. Despite the area getting warmer, the treeline hasn't shifted much. This shows that factors other than just temperature affect where trees can grow at high altitudes.