Several of southern Africa's largest baobab trees have suddenly and unexpectedly died, and scientists fear climate change is the culprit.
An icon of the African bush, the baobab's swollen trunk and gnarled branches are a familiar sight in the savannahs of southern, east and west Africa. The circumference of a mature tree's trunk can reach 20 metres, and a tree normally lives for about 500 years, though experts estimate some to be as old as 5,000 years.
Research published in the peer-reviewed journal Nature Plants on Monday said: "Nine of the 13 oldest and five or six of the largest baobab trees have died, or at least their oldest parts / stems have collapsed and died, over the past 12 years. The cause of the mortalities is still unclear."
The dead and dying trees were found in Zimbabwe, Namibia, South Africa, Botswana and Zambia. They are all between 1,000 and 2,500 years old.
Adrian Patrut, who organised the survey, added: "It's a strange feeling, because these are trees which may live for 2,000 years or more, and we see that they're dying one after another during our lifetime. It's statistically very unlikely."
Dr Patrut, of Babes-Bolyai University in Romania, told the BBC: "We suspect this is associated with increased temperature and drought. It's shocking and very sad to see them dying."
Thomas Lovejoy, an environmental scientist at George Mason University, told the Washington Post: "I do think climate is a likely culprit, but they don't actually present any evidence of how climate is changing where these ancient trees occur."
The giant trees have long been revered as a way to survive drought. People have used the tree for centuries as a source of food, medicine, shelter and even to make clothes. The ripe fruit pulp, which is naturally dehydrated and ivory coloured, is commonly sucked, chewed or made into a drink when mixed with water or milk.
Sauces for cereal dishes are prepared from the fresh or dried leaves. Edible oil can be extracted from the seeds, which can also be roasted and eaten. The bark provides a strong fibre for rope and cloth. Baskets, bags and mats are also made from it.