Predictions like this foreshadow a series of cascading effects that reach far beyond dead and dying trees. We can, the federal scientists say, expect an increase in bark beetles. Insect infestations are currently the most important biotic cause of tree mortality, killing hundreds of millions of trees throughout the West as temperatures have warmed and precipitation has declined.

Dead trees are more vulnerable to fire than green trees. The West has already seen fire seasons that start sooner in the spring and last longer into the fall, adding a total of 78 days beyond the average fire season four decades ago. Scientists predict an increase of up to 125 percent in the areas that burn in California.

More indirectly, the drought-killed trees will affect the water produced in the nation's forests and the 60 million people who depend on it, the Forest Service report states. As water quantities slow with less precipitation, a concentration of nutrients and sediments reduces the water quality.

Most ominously, the combination of dead trees, insect infestation and fire on forest ecosystems will likely release carbon – perhaps more, in some places, than forests store. This could culminate in a feedback loop that adds to global carbon accumulations, said Matt Jolly, a Forest Service researcher and fire ecologist whose study was published in Nature Communications.

The widespread die-off of trees is disquieting wherever it occurs, but it evokes particular anxiety in California, host to the tallest, most massive and oldest trees on Earth. The response demands looking beyond the immediate emergency to the long-term impacts of climate change, said James Vose, a Forest Service research ecologist. Something "quite large-scale" is happening in California, North America and across the globe. “This is and will continue to be a major challenge for forest and rangeland managers – certainly if the current drought continues or gets worse,” he said.

This article originally appeared on Water Deeply. For weekly updates about the California drought, you can sign up to the Water Deeply email list.

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