At the height of California’s fierce wildfire season, the Sierra Nevada and North Coast forests are choked with tens of millions of dead trees, from gnarly oaks to elegant pines that are turning leafy chapels into tinderboxes of highly combustible debris.

Ground crews wielding chain saws, axes and wood chippers are braving the intense summer heat in the Sierra’s lower elevations, where most of the pine trees have died. The devastation and danger are greatest in the central and southern Sierra Nevada, where the estimated number of dead trees since 2010 is a staggering 66 million.

Scientists say rarely is one culprit to blame for the escalation in the state’s tree deaths, and the resulting fire hazard. Rather, destruction on such a broad scale is nearly always the result of a complex convergence of threats to forest ecosystems.

Chief among them is a severe, sustained drought in the Sierra Nevada that is stressing trees and disabling their natural defenses. Climate change is raising temperatures, making for warmer winters. No longer kept in check by winter’s freeze, bark beetle populations are growing. Separately, a nonnative, potent plant pathogen is thriving in the moist areas of the North Coast, introduced to California soil by global trade. Opportunistic fungi are standing by, ready to finish the kill.

Factor in human shortcomings — poor or absent forest management, a failure to clear out ignitable dead wood, the darker temptation of arson, unchecked carelessness — and you have a lethal recipe.

From The New York Times: http://www.nytimes.com/2016/08/30/science/california-dead-trees-forest-fires.html?_r=2