It's white truffle season, and Ivana Karlic Ban and her two dogs cruise the autumn-coloured forests of Croatia's northwestern Istria region in hunt of one of the world's most expensive delicacies.

The white truffle, an underground fungus that only grows from September to December in symbiosis with some trees, can be found solely in Italy and Croatia.

Sometimes the delicacy is buried a meter (3.2 feet) beneath the ground, but Karlic Ban's Lagotto Romagnolo-breed dogs detect it due to the fungus' specific, intensive scent.

"The white truffle is very rare, its price can reach €6,000 to €7,000 ($7,000 to $8,000) per kilogram," Karlic Ban said. She added that the fungus sought by gourmets cannot be cultivated. However, black truffles grow throughout the year, can be cultivated and as a result are much cheaper.

Born into a family of passionate truffle hunters, Karlic Ban and her brother are the third generation of fungus lovers. They own a shop selling their truffle-based products in the village of Paladini, close to the northern Istrian town of Buzet. Istria is the region of Croatia bordering Italy.

"We have a wide range of products," she said. "We also have some world original products, such as the first chocolate with truffles and sweet treats for dogs with truffles."

But Karlic Ban says the number of white truffles has shrunk since the time her grandfather hunted for them 50 years ago because climate change and deforestation have had a negative impact on the natural habitat in which the fungus grows.

"Too harsh droughts prevent the fungus from growing while too hard rains make it soft and rotten," Karlic Ban said. "Their numbers have definitely gone down so the prices for them have gone up."