Africa's ancient baobab trees that have survived thousands of years are now rapidly dying due to climate change

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'It is definitely shocking and dramatic to experience during our lifetime the demise of so many trees with millennial ages,' said the study's co-author Adrian Patrut of the Babes-Bolyai University in Romania.

Among the nine were four of the largest African baobabs.

While the cause of the die-off remains unclear, the researchers 'suspect that the demise of monumental baobabs may be associated at least in part with significant modifications of climate conditions that affect southern Africa in particular.'

Further research is needed, said the team from Romania, South Africa and the United States, 'to support or refute this supposition.'

Between 2005 and 2017, the researchers probed and dated 'practically all known very large and potentially old' African baobabs - more than 60 individuals in all.

Collating data on girth, height, wood volume, and age, they noted the 'unexpected and intriguing fact' that most of the very oldest and biggest trees died during the study period.

All were in southern Africa - Zimbabwe, Namibia, South Africa, Botswana, and Zambia.

The baobab is the biggest and longest-living flowering tree, according to the research team. It is found naturally in Africa's savannah region, and outside the continent in tropical areas to which it was introduced.

It is a strange-looking plant, with branches resembling gnarled roots reaching for the sky, giving it an upside-down look.