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California’s new megafires are taking a toll on wildlife habitat, researchers find » Yale Climate Connections

California’s long-toed salamanders are one of the species threatened by rising rates of extreme fire in the state. Named for the unusual length of one of its hind toes, this salamander is typically dark gray or black with yellow or green markings on its back and measures up to three inches long from snout to vent.

During massive California wildfires in 2020 and 2021, about 14% of the long-toed salamander’s range in the affected areas were burned by high-severity fire — the most of any species studied as part of a broader investigation into the toll of these fires on the region’s wildlife habitat.

A recent article in the peer-reviewed journal PNAS found these fires, which burned more than 19,000 square kilometers, largely in California’s Western Cordillera ecoregion, burned the habitat of more than 500 vertebrate species. More than 100 species experienced high-severity fire that burned between 5 and 14% of their range in the study area. So the new research offers an important lens on the potential impacts that hotter, bigger, climate-change-fueled fires may have on wildlife and ecosystems.

Why today’s fires may create more challenges for wildlife

Fire is a normal part of many ecosystems and it serves an important role, from helping increase forest heterogeneity — which involves a forest composed of trees of various sizes, ages, and species in varying configurations — to creating features wildlife can use, like meadows and downed trees that can be used by cavity nesters. Yet the 2020 and 2021 fires were so massive that “there is simply no frame of reference for understanding population responses to the scale and severity of the fires seen,” according to the PNAS article authors. “It is unlikely that many species have adaptations to survive these fire events.”

So what is it about these fire events that could potentially make them harder on some species, including salamanders and some other vertebrates, than the fires of yesteryear? Gavin Jones, research ecologist for the U.S. Forest Service for Rocky Mountain Research Station and one of the authors of the PNAS paper, says the issue is largely about the fires’ severity.

“The thing to be focusing on is how the fires burned, in particular, how much of the fires burned at high severity and what the patch characteristics of those high-severity areas were,” Jones says

A fire’s severity is classified by the way it changes the area after the fire is out. A high-severity fire is generally defined as one that leaves behind at least 70-80% mortality in overstory trees.

According to the report, the scale of the 2020 and 2021 megafires in California was “unprecedented in the modern record” with the 19,000 square kilometers burned 10 times more than the historical average. The researchers found that more than 9,000 square kilometers burned at high severity, with most of this occurring in large patches that “exceeded historical estimates of maximum high-severity patch size.”

Fires normally burn in a patchwork manner, with different patches of severity. But the megafires created a more problematic kind of patchwork.

“Historically, you would almost never get a patch of high-severity fire that’s larger than 100 hectares (1 square km),” Jones says. “Much more commonly, you would get a one- or 10-hectare patch of high-severity fire in these forests.” Smaller patches of high-severity fire can have some ecosystem benefits, such as adding diversity to the forest structure.

But the unprecedented patchwork of high-severity fires of 2020-21 altered the forest composition in ways that may have a lasting effect on many species.

Where do salamanders go during a fire … and more importantly, after?

Researchers are studying how high-severity fires affect wildlife, but it will take time for the long-term impacts to become clear. Previous studies about long-toed salamanders have shown that the species may decline years after a fire.

For example, for a 2012 article in Conservation Biology co-authored by Blake Hossack, research zoologist for the U.S. Geological Survey at the Northern Rocky Mountain Science Center, researchers conducted long-term amphibian monitoring for three species, including the long-toed salamander, in Glacier National Park. They studied how animals responded to six wildfires of different sizes and severity levels that took place between 1988 and 2003. For the first six years after the fires burned, they found that the long-toed salamanders continued to live in the same areas. But seven to 21 years after the fire was another story: They found the population decreased by 25% or more in areas where more than 50% of the forest had burned in areas within 500 meters of wetlands.

In other words, salamander populations declined in some areas as time went on. Why?

Salamanders live in a variety of habitats, such as forests, woodlands, and sagebrush. But they reproduce in bodies of water like springs, ponds, slow streams, small lakes, and marshlands. In larval form, they can take cover under objects or plants in the water. Otherwise, salamanders spend much of their lives below ground — a trait that can help keep them alive during a fire.

“The long-toed salamander, that genus is Ambystoma, those are considered the mole salamanders,” Hossack says. “They’re called that because they spend most of their lives underground like moles — especially during hot dry seasons when fires burn.” So fires don’t cause a lot of direct mortality for adult salamanders because they’re generally underground anyway.

But a major fire can change the habitat in ways that make it less hospitable for salamanders over time. Fires can cause habitat changes like removing understory vegetation and logs, which help shelter salamanders as they make their way to wetlands to breed. Without that protection, they are more exposed to the elements, facing potential threats from drying out, overheating, or even being eaten by predators. Fires can also trigger hydrological changes to wetlands and other watery areas where salamanders reproduce. Hossack says this can lead to changes in recruitment, which is how a population grows through reproduction, immigration, or individuals maturing.

“The general thought is there’s not a lot of direct mortality on the adults, but if you’re getting reduced recruitments, fewer to larvae, fewer to juveniles … then eventually as those adults die off they’re not getting replaced,” Hossack says. “It can take a while to see the signatures of those events.”

An uncertain future for fire country — and the animals living there

The long-term impacts of the 2020 and 2021 California wildfires remain to be seen. While the authors suggest that a variety of management strategies may help in the future, they emphasize the importance of learning more about these megafires because past studies may not hold the clues they need.

“One of the motivations for future research is these fires in 2020 and 2021 were so off-the-charts in terms of how they burned that we just don’t even know what to think,” Jones says. “The past studies that might provide some context for how species might respond, they might not really apply here because the fires are so different than what we’ve ever seen in terms of the amount that burned at high severity. Can we predict based on past studies? I don’t really know if we can.”

So researchers hope as they learn more about high-severity fire, they can better understand how it affects a wide variety of wildlife species, including salamanders, as well as ecosystems as a whole.

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