Avid mushroom hunters will tell you that fire is essential for finding morels. These fungi, distinguishable for their dark, honeycomblike caps, pop out of the ground by the bushel in spring after a large wildfire.
This ecological knowledge is mostly anecdotal, shared among morel enthusiasts for recreational hunts and commercial harvesting, in what is now a multimillion-dollar, worldwide industry. Yet few scientific studies have actually quantified morels' abundance after a fire.
A paper published Oct. 1 in the journal Forest Ecology and Management is one of only a handful of reports documenting and analyzing the patterns of morel growth following a wildfire. The research was led by the University of Montana, with co-authors from the University of Washington and other institutions.
The part of the mushroom you pick and eat is actually its fruit. Most of the fungus lives underground as a connected, threadlike structure known as mycelium. Certain conditions such as fire prompt some species of morels to fruit, but their affinity for fire and other environmental factors is largely a mystery.
"It's fun being a researcher working on something where there is still so much unknown," said co-author Alina Cansler, a research scientist in the UW's School of Environmental and Forest Sciences. "We now have a working framework of morels' distribution after a fire that can be tested in the future."
Cansler, lead author Andrew Larson, a UW alumnus who is now an associate professor at the University of Montana, and other collaborators, drew from a meticulously mapped, well-studied section of forest in Yosemite National Park for their morel research. The roughly 60-acre plot burned during the 2013 Rim Fire, but for four years prior, these researchers -- along with more than 100 students and professionals volunteering their time -- have mapped every live tree, downed wood slab and shrub patch.
In other words, it was a section of land for which the researchers knew intimately and had scores of data, making it an ideal area to study even after the fire.
"It was really an opportunity we were able to take advantage of," Cansler said. "That's the benefit of having a permanent, long-term research site where you already have information and infrastructure: you can easily add additional studies."
For a week in May 2014, the researchers searched for morels in 1,119 plots within the Yosemite research site. They found the mushrooms did in fact cluster in parts of the forest that had burned completely, where no "fuel" was left on the ground. These are areas where the fire consumes everything along the forest floor, leaving only blackened soil, ash or burnt needles.
Additionally, they found that morels clustered in groups across burned areas, meaning that after finding one mushroom, the likelihood of finding more increased within 10 to 23 feet of the first.
"The mushrooms are very patchily distributed; if you find one, you're much more likely to find another one nearby," said Larson, who completed his bachelor's degree and doctorate at the UW. "Practically, this means if you're picking mushrooms, you really want to focus searching efforts on a local area around where you have already found at least one morel."
This is the first study in Yosemite, and the entire Sierra Nevada, to examine morel abundance after fire. The park has a morel recreational harvest limit of 1 pint a day per person. The researchers believe that limit could potentially quadruple without depleting park morels, given what they now know about the mushroom's abundance in the region. They estimate that burned white fir and sugar pine forests throughout Yosemite -- the type of forest that burned in their study site -- could produce more than one million morels a year in the park.
"The data we have, combined with common sense, says there's not a lot of concern about overharvesting," Larson said. "Mushrooms are a wonderful way to engage the public with its natural resources and the environment. It could be an opportunity for the National Park Service to encourage a different demographic of visitors to value, understand and engage with the natural world."
The researchers expect similar clustering patterns among morels in forests in Washington and Oregon that also see mushrooms pop up after fire disturbances. Cansler, for example, has found fruiting morels in Washington's North Cascades after a fire at nearly 6,000 feet in August -- not a typical time for fruiting, but indicative of their tight relationship with fire.
"We don't know why these species fruit after fire," she said. "There are a number of theories and none have been tested scientifically."
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