Johannesburg — A MYSTERIOUS fungus attacking and killing Southern Africa's mighty baobab trees has got local scientists scratching their heads.

The fungus turns the bark black and leads to the tree - which is made up mostly of water - dissolving into a heap of fibre.

But local tree experts are unsure whether the fungus is the cause of a disease or whether the trees are dying naturally.

"We're incredibly complacent as humans and we take things like trees for granted," said Professor Mike Wingfield, Mondi professor of forest protection at the University of Pretoria. "Unfortunately we don't see the change in trees because it's such a gradual process."

The death of Zimbabwean baobabs over the past 15 years had been attributed to drought and the natural death of old trees, but Wingfield and Dr Jolanda Roux, from the Forestry and Agricultural Biotechnology Institute, decided to investigate in 2002.

Humans accidentally introduce tree diseases from other continents all the time, said Wingfield, and it was possible that a disease from Madagascar was the cause of the problem.

Roux, a microbiologist who specialises in tree diseases, said a survey of baobabs in the Mussina Nature Reserve, near the Zimbabwean border, did not provide any conclusive results.

Experiments on 40 baby baobabs at the institute have also not yielded any clues.

Roux said that "information from nature reserves and members of the public who have baobabs on their farms" was needed.

"In my opinion, it's a natural process," said Johan Hurter, a botanist at the Lowveld National Botanical Garden in Nelspruit. "It happens mainly with trees that are growing where they shouldn't be."

Hurter believes that natural tree diseases could be attacking the baobabs that are already under stress because they are growing in areas that are too wet or on former grassland.

Rudolf Erasmus, manager of the Mussina Nature Reserve, said it was believed that some baobabs lived for up to 2 000 years - and it was possible they were dying from a natural process that happens every 500 years. He added that it was vital for the problem to be studied as baobabs supported whole ecosystems.

- GILL MOODIE