In the last decade the forests of the eastern San Juans have been devasted by pine beetle kill. Pine beetles burrow under the tree bark and introduce a blue stain fungus that blocks water and nutrient transport within the tree, thus killing it. The beetles are a natural part of the forest, normally playing an important role of attacking old and weak trees, thus aiding development of younger trees.
However, what's not natural is this kind of widespread annihilation of entire forests that's happening these days. This is yet another alarming sign of the effects of climate change. As average temperatures rise, the forests experience less and less prolonged deep freezes during the winters which are necessary to kill the beetles and keep their population in check. Milder winters, hotter drier summers, and a century of forest fire suppression have all combined to weaken the forests, allowing the pine beetles to continue to spread until the forest is almost totally wiped out. The unprecedented outbreak of beetle kill in the last decade is happening throughout not only Colorado but across much of the West, in what might be the largest forest insect blight ever seen in North America.