HELENA, Montana — Ponderosa pine and pinyon forests in the American West will die at an increasing rate as the world grows warmer, becoming less and less resilient when they are weakened by higher temperatures, according to new projections.

Although these forests now withstand short droughts, warming temperatures increasingly stress the forests, which means they will no longer survive the shorter droughts they once endured.

And future droughts will be hotter as the planet warms.

“We’re saying that if the climate warms a little more, things don’t get a little different, they get very different,” said Henry Adams, a plant biologist at Oklahoma State University and lead author of a new paper, published in Environmental Research Letters in a special edition of the journal titled “Focus on Tree Mortality in a Warming World.” “You get an acceleration in the rate of mortality.”

“Long droughts are what it takes to kill trees,” Dr. Adams said. “As you crank up the heat though, the time it takes to kill trees is less and less.”