Of those nine, four were believed to be the largest African baobab trees in existence.
Something obviously is going on in nearly selectively affecting the largest and oldest, Thomas Lovejoy, an environmental scientist and Amazon rain forest expert at George Mason University, wrote in an email comment on the study. But his finding about the deaths came as no surprise: Anecdotal evidence of a die-off was already spreading in the baobab research community.
"The deaths of the majority of the oldest and largest African baobabs over the past 12 years is an event of an unprecedented magnitude", the study authors said. The work also addresses the mystery of why so many of these unusual trees are dying.
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.
A baobab tree is surrounded by reeds and stagnant water in an area outside the "Avenue of the Baobabs", a famous natural reserve in western Madagascar, near Morondava, in 2011.
Researchers taking a survey of some of the world's oldest and funkiest trees have bad news to report: Africa's legendary baobobs are dying. The Sunland baobab in South Africa's Limpopo Province, which is so large it houses a cocktail bar, suddenly began splitting apart in 2016 and may not last much longer.
However the report says researchers have not linked disease or some other similar phenomena to the baobab's decline.
The oldest tree to suffer the collapse of all its stems was the Panke tree in Zimbabwe‚ estimated to have existed for 2‚500 years.
"It is very surprising to visit monumental baobabs, with ages greater than a thousand to two thousand years, which seem to be in a good state of health, and to find them after several years fallen to the ground and dead", Adrian Patrut, a researcher at Babes-Bolyai University, told National Geographic.
Is Climate Change To Blame?
"We suspect this is associated with increased temperature and drought", Dr Patrut told BBC News. They have been surveying the trees since 2005 and have developed a theory of how they grow, while also documenting the losses. Dry conditions and increasing temperatures might have something to do with the sudden deaths, but the scientists say that more research is needed to know for sure.
The southern African countries where the trees died are warming faster than the global average.
But Baum does not contest that large baobabs are dying - something he calls heartbreaking.. "They have seen more history than we can imagine".
According to a report in the journal Nature Plants, no one has been able to figure out the reason behind the falling of these enormous trees, but scientists suspect climate change to be the culprit.