LISBON – Cork and oak trees are losing their leaves and drying up for unknown reasons at an alarming rate, a World Wildlife Fund official warned in a two-day conference held in Portugal.
The problem is killing trees in Portugal, the world's biggest producer of cork, as well as in Mediterranean countries in southern Europe, said Luis Silva, the global conservation group's forest officer for Portugal.

"We don't know yet if it is a disease or if the mortality is caused by climatic factors and this is why the issue is being studied," he told the Lusa news agency at the conference held in the southern town of Evora.
The gathering was organized by the World Wildlife Fund together with the UN Food and Agriculture Organization, the International Association for Mediterranean Forests and Portugal's agriculture ministry.
It is being attended by experts from Portugal, Spain, France, Algeria, Tunisia and the United States.
"This conference aims to boost the scientific discussion of the problems of the abnormal mortality affecting cork and oak plantations," Portugal's agriculture ministry said in a statement.
Portugal produces 160,000 tons of cork per year. Neighboring Spain is the second-biggest producer of cork followed by Algeria, Italy, Morocco, Tunisia and France.