This undated file photo from the Colorado State Forest Service shows pine trees killed by beetles near Grandby, Colo. The U.S. Department of Agriculture warns in a report released Tuesd

 

              This undated file photo from the Colorado State Forest Service shows pine trees killed by beetles near Grandby, Colo. The U.S. Department of Agriculture warns in a report released Tuesd
This undated file photo from the Colorado State Forest Service shows pine trees killed by beetles near Grandby, Colo. The U.S. Department of Agriculture warns in a report released Tuesday that big changes are in store for the nation's forests as global warming increases wildfires and insect infestations, and generates more frequent floods and droughts. (AP Photo/Colorado State Forest Service, Jen Chase)