tree death

RVWithTito, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=8771491

It's not that hotter and drier summers kill trees by themselves.  But when winters are mild, creatures that kill the trees don't die, and continue to feast upon them. 

That appears to be at least part of what is happening to Douglas firs, particularly in Oregon.  Flatheaded fir borers have killed trees by the tens or thousands, by BLM counts. 

Bill Schaupp is an entomologist at the Forest Health Protection office of the U.S. Forest Service, and well-versed in tree-killing bugs. 

US Geological Survey

Gaze across the mountains of the Northwest these days and you may notice an unusual number of dead firs, pines and other conifer trees scattered among the green ones. Drought is usually considered the prime culprit. But recent research suggests the damage that has historically been done to conifer forests by routine dry spells is being compounded by climate change.