All was not right in the shady oak groves of northeastern Spain.
The fragrant, beloved truffles that farmers could usually find nestled deep in the roots of the trees were getting harder to find, the farmers reported to Ulf Büntgen, a scientist from the University of Cambridge. Maybe the local trees weren’t healthy, they said, or maybe something was changing in the local habitat.
Büntgen talked to farmers in Italy. Then he talked to others in France. Across the western Mediterranean he heard the same story: Something wasn’t right with the elusive, wildly valuable fungi that many small farmers relied upon for a major part of their annual income.
Büntgen is a climate scientist, and so as he kept hearing these stories from across such a broad region, he thought: Maybe there’s a climate pattern that’s driving all of this. And maybe climate change is exacerbating the problems.
It took several years to pin down the specifics, but now, he and a team have found that link. Truffle production, they report in a study in July’s Environmental Research Letters, is highly sensitive to how much rain falls the summer before harvest.
And in the western Mediterranean, summer rain patterns have changed over the past 40 years, with summer droughts deepening and temperatures climbing. The result has been growing stress on the delicately balanced natural system that the truffles need to survive.
“If you see the patterns this synchronous across such a large domain, the driver—it’s usually climate,” Büntgen says.
Truffle loves oak
Truffles are worth big money: The global market is expected to grow to over $6 billion within about ten years.
That’s in part because they are notoriously finicky fungi. Some varieties, like the extra-precious white truffle, can’t be cultivated at all. They’re found only in a few old, intact remnant oak forests across Europe, and they generally sell for well over $1000 per pound today (and sometimes for much more).
Other types, like the more common black Perigord truffle, can be cultivated, though imperfectly.
The fungi grow underground, usually nestled in the deep, fine network of tiny rootlets of oak trees, in a special kind of symbiosis. The truffles take little sips of sugar and water out of their host tree’s roots, and in return feed soil nutrients back into the tree—or so the theory goes. The exact details of the partnership are still something of a black box, because scientists have no way to study the underground interactions. As soon as they dig up a truffle to study it, its habitat is destroyed, so ongoing analysis is impossible.
Since the 1800s farmers in Spain, Italy, and southern France have cultivated stands of truffle-friendly trees and cared for the groves in ways they think encourage the growth of the fungus. But as agricultural practices intensified across the continent, the old oak forests were often destroyed—leading to the loss of the associated truffles.
In response, in the 1950s growers, scientists, and communities started figuring out how to cultivate the precious fungi, developing semi-structured “plantations” of oaks that could support truffle growth. Today, about 100,000 acres of truffle plantations dot Spain, France, and Italy and provide about 80 percent of all the truffles on the legal market.
Many growers installed irrigation systems to keep the trees healthy through hot, dry southern European summers. Others experimented with encouraging rich biodiversity in their truffle woods, or testing different inoculation techniques, or more. But even with all the tools and strategies, the annual harvest is uncertain. One of the potential stresses, scientists and some truffle famers think, is a changing climate.
“Absolutely, [the growers] are aware of climate impacts,” says Yildiz Aumeeruddy-Thomas, a cultural anthropologist at the French National Center for Scientific Research who has worked with truffle-growing communities across Europe. “These growers are very close observers of complex interactions between weather and the environment for the truffles.”
Climate change comes for the truffles
For these careful observers of the truffle system, there was an ideal set of conditions: good spring rains. Hot summers with a smattering of rain events. Mild winters. Some years were good, and the truffles were abundant.
But other years were bad. Especially bad were the years with long, hot, dry summers. And when Büngen and his colleagues started digging in to the 49 years of data at their disposal, they saw that intense summer conditions got more and more common in parts of southern Europe between 1970 and the early 2000s—and matched up with years where the truffle harvest was particularly low.
It wasn’t exactly temperature that was driving the pattern, they found, but the amount of rain that fell during the summer before the annual winter harvest. Heat seemed to exacerbate the situation, since higher temperatures enhance the drought stress experienced by trees everywhere. But from the 1990s onward, it was the rain that seemed to matter the most.
Surprisingly, that pattern held even for the plantations that irrigated their trees, suggesting that the precious, expensive water the growers doused their oaks with was going to waste.
Climate scientists predict that droughts will intensify further as the planet heats up. That’s likely to push black truffles past their limits of survival in Europe, says Paul Thomas, a fungi-focused scientist at the University of Stirling in the U.K.
“By 2071, many climate zones where black truffles are found today will be unsuitable because of climate change,” he says. “And we won’t necessarily be able to irrigate because the water will likely be more scarce.”
“It’s a very difficult future for the truffles,” he says.