San Diego Union-Tribune: Bugs and diseases are killing trees at an alarming rate across the West, from the spruce forests of Alaska to the oak woodlands near the San Diego-Tijuana border. Several scientists said the growing threat appears linked to global warming. That means tree mortality is likely to rise in places as the continent warms, potentially altering landscapes in ways that increase erosion, fan wildfires and diminish the biodiversity of Western forests. It also could prompt new approaches …