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REUTERS/Lucy Nicholson REUTERS/Lucy Nicholson

Due to drought, bark beetles, and devastating forest fires, at least 12 million California trees are dead, according to the U.S. Forest Service. That’s a conservative estimate, though; Gregory Asner of Stanford University recently concluded that roughly 120 million—about 20 percent of the state's forests—are doomed, even with a mighty El Niño.

A major question now is how to remove the trees that pose the highest risk to humans.

In California, roughly 30 percent of the population lives in what the U.S. Forest Service dubs the “ Wildland-Urban Interface,” where housing units are within or adjacent to naturally vegetated areas. Those are the areas where falling or flaming trees have the greatest impact on people.

Orange areas represent “Wildland-Urban Interface.” U.S. Forest Service

“Tree mortality across California’s forests is putting lives and critical infrastructure at risk, greatly increasing already dangerous wildfire conditions and exacerbating threats posed by falling trees,” Governor Jerry Brown wrote in a letter to U.S. Agriculture Secretary Tom Vilsack last week, after calling a state of emergency due to the “worst case of tree mortality” the state has ever seen.

Power lines, roads, and critical properties are vulnerable should a dried-out tree—or tree cluster, the prevailing pattern of the die-out— topple over or catch fire. In his emergency declaration, Brown mainly called attention to the tremendous infrastructure risk that the dying trees pose, and the coordination required to remove precarious trees from inhabited areas.

Under the declaration, state and local agencies are asked to work together to remove dead trees from “high hazard zones” (i.e., where people and structures are), and are permitted to circumvent some environmental regulations that would normally factor into the removal of trees on public property (a clause that has alarmed some environmentalists). In his letter to Vilsack, Brown also sought federal aid to remove the most precarious dead trees from private lands, and ordered the California Energy Commission to make use of some dead trees as biomass energy.

Looking ahead, however, protecting people from dying trees is going to take more than removing them. The Western U.S. will see more droughts like the current one, and we know tree mortality will accompany it. To reduce the volume of dead trees in the future, many scientists and fire experts have called for more prescribed fires—that is, regular, controlled, smaller fires to clear some of the brush, shrubs, and excess trees that fuel massive blazes. Relative to other parts of the U.S., California tends to shy away from prescribed fires because of strict air quality regulations, but it may be time to re-evaluate these priorities in extreme situations.

Of course, this is all to say nothing of the ecological tragedy represented by this loss of plant life. To ease future losses, we can stop worsening climate change, which scientists believe has contributed to the West’s extremely dry conditions.