In the Forests of the Sierra, Rocky, and Cascade Mountain

In the forests of the Sierra, Rocky, and Cascade Mountain ranges the pine beetle has killed large numbers of whitebark pine trees. In some areas up to 100,000 trees are falling daily. The beetles have survived and multiplied due to warmer winters. The entire ecosystem is affected and the tree species are threatened. Which major threat to biodiversity below is most likely the cause?

A) Habitat destruction
B) Global climate change
C) Hunting and poaching
D) Overexploitation for resources
E) Predator control