California lost more than 36 million trees in the last year alone

JUANA SUMMERS, HOST:

Many of California's trees, its pines, oaks and especially firs, are dying. A recent survey of the state's forests found more than 36 million trees died in the last couple of years. NPR's Nathan Rott reports on what's driving that loss.

NATHAN ROTT, BYLINE: Jeffrey Moore has been doing aerial surveys for the U.S. Forest Service, flying low over western forests to check on their health, for decades. This most recent survey...

JEFFREY MOORE: That was something I hadn't seen since 2016, back at the height of the last exceptional drought period that we had here in California.

ROTT: Red trees, yellow, dead and dying. Moore and his team found four times the number of dead trees in this survey than they did in the year previous. Most were firs - think your classic Christmas tree conifer.

MOORE: We have two different primary species of fir here in California

ROTT: Red firs, which typically live at higher elevation and are resilient to drought - it's not good, Moore says, that those are dying - but also white firs, which typically live at lower elevations and tend to grow really fast. About a third of the dead trees Moore and his team found were white firs, and he says that's not necessarily bad. Typically, white firs are the kinds of species that are cleared out with regular wildfire, leaving more nutrients and water for bigger trees like pines. But now, we humans regularly put out wildfires, aggressively. And...

MOORE: Since we've removed fire from these systems, those little trees, those little fir trees are now big trees. Big trees need lots of water.

ROTT: Add a historic Western megadrought...

MOORE: And something's got to give.

ROTT: Jon Wang is an assistant professor at the University of Utah who published research last summer showing that many of California's dying forests are not coming back.

JON WANG: And the way climate change affects these forests, primarily, is by making the atmosphere hotter. And the warmer it gets, the more water that each of these trees needs.

ROTT: Thirsty trees are more susceptible to disease, to pests and wildfires, and it's harder for forest to recover in those new conditions.

WANG: It's always kind of shocking because it's really, you know, sad to see these forests that have been such an iconic part of California's landscape to really see them start to decline.

ROTT: But he says it shouldn't come as a surprise. The drought has been well documented. Climate warnings are everywhere and die-offs, sadly, are likely to continue.

Nathan Rott, NPR News. Transcript provided by NPR, Copyright NPR.