After Forest Fire, A Warming Climate Interferes With Tree Regeneration As the warming climate makes extreme fires more likely, some iconic tree species are not growing back like they used to. Ecologists say this could transform vast areas of western forests.

After Forest Fire, A Warming Climate Interferes With Tree Regeneration

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STEVE INSKEEP, HOST:

One reassuring fact about wildfires, like the ones now burning in the West, is that they're part of nature. Fires clear out forest land for new growth. Though it is devastating if the flames destroy homes or endanger people, you can usually expect the forest to come back - or at least you could expect that. What if it doesn't because of climate change? Michael Elizabeth Sakas of Colorado Public Radio followed up on a fire from years ago.

MICHAEL ELIZABETH SAKAS, BYLINE: After a quick hike off a steep dirt road, forest ecologist Marin Chambers stands surrounded by grasses, shrubs and blackened bare trees. This burn patch is from the 2002 Hayman fire northwest of Colorado Springs. The ground is dry, crunching under Chambers' feet.

MARIN CHAMBERS: What we're seeing is a very large high-severity burn patch, where the vast majority of the trees have died.

SAKAS: These 18-square miles burned hot and fast in a single day, part of what - until last month - was the biggest fire in Colorado recorded state history. It was driven by how dense the forest was because of past fire suppression, that combined with high winds and extreme drought. Nearly 20 years later, there's something missing. Where are the new trees?

CHAMBERS: In areas that are really far from surviving trees, we're not seeing trees regenerate in large numbers. Some regeneration may be occurring, but certainly not enough to recreate a forest in the near term.

SAKAS: Chambers and her colleagues at Colorado State University have found that forests are struggling to grow back some of the state's most iconic species, like ponderosa pine and Douglas fir. Baby trees can't thrive in the increased heat and drought brought on by climate change.

CHAMBERS: We're standing out here. It's very hot and dry. You know, imagine being a ponderosa pine seed trying to grow out here. It's a pretty intense environment.

SAKAS: If there is forest regeneration, it happens in bands along the forest edge, where surviving trees can drop their seeds. But Chambers says even that isn't happening at lower elevations, where it's hotter and drier. She's not sure this area of the Hayman fire will ever reforest. Research has found that, instead, it could convert to grassland. Camille Stevens-Rumann, also with Colorado State University, says there can be lots of benefits to having patches of grasslands between forested areas, but not something this big.

CAMILLE STEVENS-RUMANN: I think what we really are sad to see is when we have those huge expanses where we're talking about tens of thousands of acres that have transitioned from forest to grasslands.

SAKAS: One major concern is that trees sequester carbon. Fewer trees mean less stored carbon, which means more warming, which we just heard makes it harder for trees to regrow. Stevens-Rumann has studied a large range of burned forests across the West. She's found that in many places, trees that have been there for a century or two are not coming back.

STEVENS-RUMANN: We're really moving away from the suitable climate for tree regeneration to happen.

SAKAS: But she wants to emphasize that Colorado is not losing all of its forests. She says it can sound dire, but many places do still have abundant tree regeneration, even if they are different species or at higher elevations as the climate warms.

STEVENS-RUMANN: That gives me hope for these landscapes. And I think part of what we all have to accept in this new and changing world is that these ecosystems are going to look different than the ones that maybe we have grown fond of in the past.

SAKAS: Stevens-Rumann says she likes to see it this way. This isn't a goodbye to forests altogether; it's more of a we'll see you farther up the hill, hopefully.

For NPR News, I'm Michael Elizabeth Sakas in Denver.

(SOUNDBITE OF MESSAGE TO BEARS' "RUNNING THROUGH WOODLAND")

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