COGNAC, France -- Truffles, one of the most lucrative, prized, secretive yet legal crops in the world, are in trouble. Just what is responsible for this travesty may be impossible to prove, but the experts' list of usual suspects often begins with climate change.
The lumpy, earth-colored fungi prized by chefs and gourmets around the world can fetch $2,000 per pound on the open market. A pound of the rare white truffle (Tuber magnatum) found in the wild in Italy, Slovenia, Croatia, Serbia, Hungary and Romania can fetch $6,000.
The warming climate in Europe is helping one variety, the Burgundy truffle (Tuber uncinatum), to proliferate far beyond what was once thought to be its natural geographic distribution. But supplies of the more market-worthy, more delectable and more sought-after variety, the Perigord or black truffle (Tuber melanosporum), may be in a death spiral.
During the late 19th century, the annual crop in France was about 1,100 tons. Now the numbers range from 13 to 49 tons per year.
Ulf Buentgen, a researcher at the Swiss Federal Research Institute in Birmensdorf near Zurich, analyzed inventories of regional truffle harvests from northeastern Spain, southern France and northern Italy. Buentgen, who prowls likely forest sites in Europe with Lucy, his truffle-hunting dog, says the data show a definite decline.
"There has been an overall increase in temperature in the region since the 1970s, along with a decrease in precipitation," Buentgen said. "Local effects caused by land use changes may contribute, but the only large-scale driver is climate change."
According to Buentgen, the discovery of Burgundy truffles in more than 70 sites in southwest Germany in the last year, as well as in Switzerland, underscores his theory. Buentgen maintains that the expansion in the range of the Burgundy truffle is a direct result of climate change.
Other scientists dispute this finding. Historical evidence shows truffles have been harvested since the 17th century in nations as northerly and far-flung as the United Kingdom, Slovakia, Poland, Austria and Germany.
Claude Murat, a researcher at the French National Institute for Agricultural Research (INRA) lab in Champenoux, near Nancy, believes the numbers for the black truffle yields are suspect, mostly because there is no consistency in the way truffle harvests are reported. France, which probably has the most reliable numbers, is itself unable to keep very good track.
Pigs, dogs, lies and folklore
"All [Italian and Spanish] farmers ever say is 'it was a good year' or 'it was not a good year.' That's the most accurate information we get," Murat said. In the Piedmont area of Italy, where the white truffle is found, the mystery is deliberately and fiercely maintained by local truffle hunters.
"All the sites are kept secret by the people who know about them," said Murat. Competition for these exorbitantly priced truffles is so keen, truffle hunters have been known to poison one another's truffle dogs to prevent them from excavating a lucrative patch.
"White truffles and the guys who hunt them have nothing to do with science or agriculture," Murat said. "They are a different world. These guys are not going to reveal anything. €2,000 to €4,000 [$2,600 to $5,200] a kilogram is a lot of money."
Francis Martin, head of the Lab of Excellence at the Ecogenomics of Interactions Lab at INRA, believes the reported decline in the truffle harvest is probably less due to climate change than to topographical and sociological changes.
"Truffle-growing regions may change because of climate, it's true," Martin said. "There is clearly an impact on production, and it's clear production has decreased in the past 50 years. But many other things have changed as well."
At the beginning of the 20th century, France had 1.09 million acres of open woodland. In the last 100 years, that has been reduced by half. Low-density mixed hardwood forests composed primarily of beech, oak and hazel have given way to high-intensity agriculture, which is much less conducive to propagation of the finicky truffle.
The truffle-hunting tradition was once handed down from father to son, but the depopulation of World War I almost made it a lost art. The image of a truffle-hunting pig handled by a grizzled old farmer wearing a beret -- reinforced every Christmas on French television -- is part of truffle folklore. The pigs have been replaced by trained truffle dogs, which are less likely to either eat the find or bite off the handler's fingers when he tries to take the truffle away.
Martin concedes that more frequent summer droughts have a deleterious effect on fructification -- the ability of the root mycorrhizae to create an actual truffle.
"The fruiting body starts growing in June," Martin said. "It requires summer storms in July, August and September in order to fully form. Summer drought affects the symbiont trees, as well as the fruiting conditions for the truffle itself."
But farmers have discovered the effects of drought can be minimized with irrigation. So, increasingly, they're getting into the business.
What farmers don't want you to know
Orchard-based truffle cultivation started in the 1960s. Eighty percent of truffle production now takes place on plantations. In the last 14 to 20 years, between 1,980 and 2,500 acres of truffle orchards -- trees inoculated with black truffle spores -- have been planted on farms. The numbers are continuing to rise.
Horticulturist Damien Berlureau produces holm oak and hazel seedlings inoculated with truffle spores at a complex of greenhouses outside Bordeaux. His company, Agri-Truffe, is in the business of propagating and inoculating trees and selling them to farmers who grow managed -- often irrigated -- truffle orchards. Berlureau consults with truffle growers and aspiring growers all over the world.
"Truffles are a quest," Berlureau explained. "It's an expensive business. It takes lots of patience -- more than wine." The time an inoculated seedling is planted to the time the first truffle is harvested can take six to eight years.
Unlike other cultivated crops, such as wine, a lot is left up to nature, he said. "The only phase where we exert influence is in inoculation. Once the tree is planted, nature is back. Fructification depends on soil composition, competing fungi and lots of things we can't predict."
Because all farmed truffles originate from naturally occurring sources, there is no discernible difference between wild-grown and cultivated truffles. The distinction is unimportant to both buyers and sellers: The market price fetched by the black truffle is the same, regardless of its origin.
"Since there is no difference, genetically, between wild versus farmed truffles, we can't precisely measure to what degree naturally occurring truffles are in decline," Buentgen said. The problem, he maintains, is that growers are simply not interested.
Buentgen disagrees with Martin and the notion that agricultural and sociological changes are key to the decrease in truffle yield. INRA, he asserts, has at its heart agriculture's and growers' interests, rather than hard science.
"Growers are in business," Buentgen said. "They want to be successful. They don't want anyone to know things aren't working. Local changes don't shift the geographic scope of the entire ecosystem."