Photo: Jesse Miller

As photos of charred forest remains emerge from California’s latest round of explosive wildfires, it’s becoming clear that a worsening wildfire season will have ecological consequences. And not just for the trees: Understory plants and fungi, and the food webs that depend on them, are also feeling the burn.

A new study published in Global Change Biology is among the first to demonstrate this, showing how larger, hotter fires in the Sierra Nevada are causing lichen, a key component of forest food webs, to take a hit.

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The researchers looked at 104 conifer forest plots that had burned four to 16 years prior in five large fires. They found that while low-intensity burns had little or no effect on bark-dwelling lichen, diversity and abundance declined as fire severity increased. On the plots that burned most intensively, lichen were severely reduced, and had made little recovery even after 15 years.

Lead study author Jesse Miller, an ecologist at the University of California, Davis called the change “pretty dramatic.”

“It’s not really surprising that lichens burn up,” he told Earther. “What is surprising is we’re not seeing them recolonize.”

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Photo: Jesse Miller

The researchers ran their data through models to see which environmental factors could help explain patterns of lichen diversity. They found that diversity was strongly tied to tree canopy cover, which makes sense seeing as lichen prefer cooler, wetter understory environments. Unfortunately, canopy cover is often gone for years after hot, intense fires torch treetops.

But why fuss over the fact that some rubbery bark garnish is struggling to survive more intense wildfires? The answer is that in a forest, everything’s connected.

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Lichens are an important food source for flying squirrels and a source of nesting material for some mammals, birds, and insects. Losing them could ripple up the food chain. They’re also nitrogen fixers, providing up to half of this critical plant nutrient in some forest ecosystems.

Merritt Turetsky, a fire and forest ecologist at the University of Guelph who wasn’t involved with the study, told Earther the new research “echoes what we also have found using separate methods and data in northwestern Canada.”

There, lichen are a critical food source for economically and culturally-important caribou, suggesting the impact of their loss could ripple into human societies, too.

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More research is needed to suss out whether lichen will return to the most intensively burned parts of forests over longer periods, or whether some species will be better suited to the fiery future. But Miller suspects lichen won’t make a full rebound in severely burned forests until the canopy regenerates, “and that’s not happening fast.”

And a hotter and drier climate could make that recovery even harder.

“It’s kind of a grim picture,” Miller said.

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