Truffle farmers have never had to worry about demand. It is the supply side that is worrying, with global warming an ever more present threats to their success. \"You don\'t market the truffle, you manage its scarcity,\" said Jean-Charles Savignac, president of the French Truffle Growers Federation (FFT). The 2010-11 season\'s output was a meagre 25 tonnes, a severe shortfall blamed on a lack of water, which is vital for the Tuber melanosporum, the scientific name for the black truffle cherished by gourmets. \"If we had supplied 100 times more, it would all be sold,\" Savignac said, recalling annual harvests of 200 to 300 tonnes in the 1960s, \"sold without the slightest difficulty.\" He said a century ago output reached a \"somewhat mythical 1,000 tonnes,\" and still found takers despite a smaller world population and far more difficult delivery means. Explanations for the ever-shrinking supply begin with the rural exodus that emptied the French countryside after World War II. The truffle\'s natural habitat was affected as farmland gave way to natural reforestation or bush, according to truffle expert Pierre Sourzat, who added that \"sometimes very effective competitors\" -- other fungi that colonise tree roots -- encroached on its territory. Weather variations are no help. \"The truffle, which is very sensitive to water, is something of a marker of climatic changes,\" Savignac said. In the summer of 2003, when a devastating heatwave gripped France, \"three quarters of natural truffles vanished,\" Sourzat said. \"In the plantations, two-thirds to three-quarters of the trees stopped producing the following years. Other mushrooms that are more adapted to drought beat out the truffle.\" The FFT held a seminar in 2008 on the future of the sector in the face of global warming. \"We didn\'t realise it right away, but the diminishing production is certainly affected by this phenomenon,\" Savignac said. But the truffle sector is fighting back. \"Every year, we plant 300,000 to 400,000 trees in France, or around 1,000 more hectares (2,500 acres)\" dedicated to the truffle, Savignac said. With such a larger park to rely on, \"in the worst years we can reach an output of around 20 tonnes instead of the 10 tonnes we would get if nothing were done,\" he said. The sector also benefits from regional government subsidies, for example to fund experiments on improving production techniques. In the Midi-Pyrenees region, subsidies help truffle growers plant around 100 hectares each year of pubescent oaks, green oaks or hazelnut trees whose roots are impregnated with truffle spores, said Guy Delher, head of the regional federation of truffle growers. However, it takes a good decade for the plantations to begin producing in significant quantities. In Lalbenque, the town of some 1,600 souls where the main truffle wholesaler of southwestern France is located, it took only a few minutes for buyers to snap up some 60 kilogrammes (130 pounds) on offer by the truffle farmers, most of them landowners for whom the black diamond is a source of extra income. Lalbenque conducts the first sale of the season, and the precious tuber went for between 400 and 600 euros per kilo wholesale, or 1,000 euros ($1,320) per kilo retail. The region\'s truffle growers hope this season will be better than last year\'s, when only 500 kilos of the coveted Causses du Quercy truffles -- which connoisseurs say has an \"initial nose of strawberry jam\" -- were produced.