The wily morel is a target of obsession for a large portion of the mushroom-loving world. In the eastern United States, the pitted blond or black mushrooms lure eager hunters into the woods each spring, and a lucky few of them will even bring some back.

What is less well known is that in the western U.S., wildfires can produce morel bonanzas the year following the fire. Although these bumper crops are the stuff of legend, relatively little is known about the the fruiting dynamics of morels within them.

Well, morel hunters, wonder no more. A new study from a team from the University of Montana, the University of Washington, Utah State and Washington State reveals how you should go about searching these crispy windfalls.

But first, for the rest of you who may be reading this, let’s start with something more basic: what exactly is a morel?

Simply put, it’s one of the finest-tasting mushrooms on Earth. With a meaty flavor and texture, they are beloved by meat eaters (steak, morels, and red wine being a classic pairing) and vegetarians alike. Hollow, they are prime targets for stuffing, although just as often they’re breaded or be-corn-flaked and fried, or cooked into delicious sauces or soups. This past spring, I made a cream of morel soup (with mushrooms gathered from my secret patch), and it is in such simple soups that I think the morel flavor is best showcased.

In any case, this may help you understand the passion many people feel for what is admittedly an odd-looking, frustrating mushroom. Its cap is a honeycombed conglomeration of pits in black, grey, or tan. Unlike many other choice edible mushrooms, it is relatively hard to detect, even when you are looking for it. The earthy colors tend to blend in with the forest floor, and that pitted cap bears an irritatingly close resemblance to a pine cone, of which there are demonstrably more in the forest than morels.

Further upping the challenge, morels are notoriously elusive and finicky about popping up where they’re supposed to. They sometimes associate with certain tree species – among others, ash and elm in the east, cottonwoods in the west – but you can search around dozens or hundreds of these trees and not be guaranteed Morel One. In many parts of the country, the supply is sparse, in addition to occurring only once per year for a week or two in mid-spring.

However, there are a few places where they fruit more reliably. In the wake of Dutch Elm Disease, there were a few years where almost everyone near a dying elm tree shared in the bounty. But in most years only a few places like Michigan are so blessed. Boyne City, Michigan, hosts the National Morel Mushroom Festival and a morel hunting championship each year. According to mycologist Bryce Kendrick, the record for this event was set in 1970, when the victor somehow managed to grab over 900 morels in just 90 minutes (that’s 10 morels a minute, or one morel every 6 seconds!)

There is at least one other place that morels are known to fruit abundantly and reliably: in the ashes of fires in the conifer forests of the western U.S. But comparatively little research has been done on the morels found in these fleeting (and blackened) tracts of plenty. With the results of this new study, we know a lot more about how morels grow in these areas and how to go about looking for them, if still not exactly why morels go nuts after their forest burns down.

A(n appropriately black) burn morel emerges in Yosemite National Park the spring following a forest fire. Credit: C. Anna Cansler

Morel hunters refer to the morels that fruit in these flushes as “burn morels”, although the technical term is “phoenicoid”(the same root as phoenix, another creature that sprang from ashes).

Native Americans in California knew about and collected burn morels. They may have even set their own fires to “plant” future crops. Even today, the commercial supply sold in the western United States is composed primarily of burn morels picked in the first year after a fire, so reliable and bounteous is the crop.

Yet other than the timing of their appearance, burn morels remain mysterious. The morels that fruit after fires seem to be different species than those that appear spontaneously and sporadically in unburned forest. Exactly what fire does to trigger their fruiting remains unknown. Many ideas have been proposed, though: loss of food, removal of the burden of needle duff that may physically block morels, soil pH or chemistry changes, sudden release from competition with other organisms, or sudden flushes of mineral nutrients released from burnt trees and needles.

We don't even know exactly what burn morels eat. Some morels seem to be unambiguous decayers, while others that show up repeatedly with favored trees are at least partially mycorrhizal (partners with tree roots, who provide them with sugar), but it is also possible morels can be decayers or mycorrhizae as conditions warrant, or that they swtich food sources in different parts of their life cycle.

Only three previous studies have examined burn morel abundance in the west, in Alaska, British Columbia, and Oregon. But such studies are important because park service and national forest officials have had to guess when setting recreational and commercial collection limits. Knowing exactly how much morel a patch of burnt forest can pump out helps officials base those regulations in science, not guesswork.

The morels in this study fruited in the Yosemite Forest Dynamics Plot, a 25.6 hectare forest research area of old-growth white fir and sugar pine. The area burned on September 1 and 2, 2013, after forest managers set a fire a kilometer from the plot to control the spread of the much larger Rim Fire. That fire had started in the nearby Stanislaus National Forest on August 17 after an illegal campfire burned out of control.

Picking morels is hard work ... but someone's got to do it. Post-fire conditions in Yosemite Forest Dynamics Plot. Burn morels indicated by yellow arrows. Credit: S. Hiebert in Larson et al. 2016

What the scientists learned after picking countless morels (I know, tough job …) over the course of a week in this plot was this: burn morels are a bumper crop, and a nearly inexhaustible resource for recreational hunters. Also, if you find one burn morel, search the surrounding two dozen feet carefully. Burn morels tend strongly to cluster, so finding one is a good clue that it has buddies nearby.

In the 1119 evenly-spaced plots on a rectangular grid sampled in this study, the researchers encountered 595 morel mushrooms in 17.8% of plots. The most they found in a single 3.14 square meter plot was 16. In another valuable finding for recreational hunters, burn morels did not occur in plots where less than 50% of the surface burned, and only occasionally in plots burned between 50% and 99%. The vast majority were on completely crispy soil. Further, morels were much more likely to occur within 7 meters (23 feet) of other morels than would be expected if they were randomly distributed, and even more so within 3 meters(10 feet) of each other.

Why do burn morels fruit in such small patches? The scientists don’t know for sure, but their hypothesis is that burn morels only grow when many variables align. With so many factors needing to be just right, the area over which they hit the morel sweet spot is necessarily quite small. Those factors probably include where the fungus existed in the soil prior to the fire (itself no doubt in some sort of patch), which parts of the fungus survive the fire, which trees existed where prior to the fire, variations in the intensity and behavior of the fire, and variation in soil temperature and moisture after the fire.

They conclude from these findings that the current limits set on recreational picking at Yosemite – one pint per person per day – are probably needlessly low and could be increased to at least four liters per person per day in the first year following a burn without threat of harming the forest. Why? Not only because burn morels are so abundant, but because the majority fruit in a vanishingly brief time, so only those recreational pickers both willing and able to get themselves to the burn in that ephemeral window would even have a chance at a morel bonanza.

That is certainly not the case for commercial collecting, however, because professionals have the time and skill to take many more morels than recreationalists, so they emphasize that current limits on that activity should remain in place.

They further calculated that in an average year, burnt white fir-dominated forests in Yosemite National Park produce over one million morels. What’s more, this is likely an underestimate of morels in the park. The study lasted but a single week, but burn morels can fruit for weeks or even months during the first growing season after a fire (although in this instance, they scientists observed only “incidental” morel finds in the eight weeks after their sampling). Burn morels also occur in non-white fir dominated forests as well as outside burned areas, so the number is still likely an underestimate, they say.

When you extrapolate these findings to the whole of western North America, it becomes clear that the true burn morel bounty in our forests each year must be staggering. Wildfire may be many things, both good and bad. But for burn morels and the people who chase them, there's no question it yields a most welcome Windfall of Unusual Size.

Reference

Larson, Andrew J., C. Alina Cansler, Seth G. Cowdery, Sienna Hiebert, Tucker J. Furniss, Mark E. Swanson, and James A. Lutz. "Post-fire morel (Morchella) mushroom abundance, spatial structure, and harvest sustainability." Forest Ecology and Management 377 (2016): 16-25.