First, the good news about the bark beetles that have been ravaging western forests for almost a decade: A new report indicates they may finally have eaten themselves out of house and home after killing conifers on some 42 million acres of forests at prime fish and wildlife altitudes.

Now the bad news: The same report showed evidence that warm winters have allowed the bugs to push into higher altitude areas where cold temperatures once held them back.

The U.S. Forest Service report said aerial surveys showed beetle-killed trees on 3.8 million acres of public down, the second consecutive year of a decline, and less than half of the nine million trees killed in 2009.

Researchers say while pine and spruce beetle outbreaks are cyclical in the west. Traditionally their advances were stopped because the bugs could not withstand winter temperatures that dropped well below zero for long periods of time – routine in the mountain West, until recently.

The beetle kills have last vast tracts of dead and dying forest across prime public fish and wildlife property during the onset of severe and prolonged drought – also linked to climate change.

Those dead trees have left an arguably record amount of fuel on forests floors, increasing the likelihood and severity of wildfires.

Foresters say it will take decades, if not longer, for forests to recover, and because of warming some areas will never return to their historic plant regimes but covert into different habitat.