Scientists describe an 'event of an unprecedented magnitude' among Africa's oldest and largest baobab trees.
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By Christopher Mooney, The Washington Post
The baobab tree, sometimes called the “Tree of Life,” has an unforgettable appearance. Found in savanna regions of Africa, Madagascar and Australia, the trees form a very thick and wide trunk and mainly branch high above the ground. They can grow to be thousands of years old, and develop hollows inside so large that one massive baobab in South Africa had a bar inside it.
But that tree, the more than 1,000-year-old Sunland baobab, apparently the biggest of these trees in Africa, “toppled over” last year. Another famous baobab, the Chapman tree in Botswana, collapsed in 2016.
Something similar, a new scientific study suggests, is happening to the oldest and largest baobabs across the world in “an event of an unprecedented magnitude.”
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The research, by Adrian Patrut of Babes-Bolyai University in Romania and an international group of colleagues, finds that in the past 12 years, “9 of the 13 oldest and 5 of the 6 largest individuals have died, or at least their oldest parts/stems have collapsed and died.”
That’s a tragic loss, considering the history and culture attached to these trees — which are also a key food source for people. The baobab “is famous because it is the biggest angiosperm, and it is the most iconic tree of Africa,” Patrut said.
Patrut’s co-authors hail from institutions in South Africa and the United States, and the work was published in Nature Plants on Monday. They have been surveying the trees since 2005 and have developed a theory of how they grow, while also documenting the losses.
The contention is that the largest baobabs weave together multiple tree stems around a small “false cavity,” and this is what gives them their unique structure. These stems also can grow together. This leads to a strange feature in which, moving outward from the cavity center, the wood can get older for a time, rather than younger, as might normally be expected.
“This a unique characteristic of the African baobab and all the baobab trees,” said Patrut, who has dated different parts of the trees using radiocarbon-dating methods.
However, another expert on the trees was not fully convinced by this theory of how they grow.
“Pretty much every baobab tree in Southern Africa is covered in the healed scars of past elephant attacks, which speaks to the trees’ amazing repair ability,” said David Baum, a University of Wisconsin at Madison botanist who is familiar with the new study and contributed to a Biodiversity International publication cataloguing the trees’ attributes, in an email. “When a tree is damaged to form a hollow, bark can grow into the cavity and eventually start making new wood to fill in the hole. Such repair growth would lead to an inverted age sequence where wood initially gets older as you move towards the outside of the tree from the hollow.”
But Baum does not contest that large baobabs are dying — something he calls “heartbreaking.”
“Each of these trees was unique and special,” he wrote. “They have seen more history than we can imagine.”
Patrut says the largest trees are the most vulnerable — and he believes that a changing climate is involved, although the study itself says that “further research is necessary to support or refute this supposition.”
“The largest trees, they need more water and nutrients than the smaller trees, and they are most affected by temperature increase and drought,” Patrut said.
“Something obviously is going on in almost selectively affecting the largest and oldest,” Thomas Lovejoy, an environmental scientist and Amazon rainforest expert at George Mason University, wrote in an email comment on the study.
“(They do refer to other baobab mortality but don’t have real data on it),” Lovejoy continued. “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.”
In Zimbabwe, baobab deaths are reportedly being accompanied by what appears to be some type of fungus that turns the trees black before they die.
But Patrut’s study, which surveys baobabs much more widely, contends that for the oldest trees in particular, the deaths “were not caused by an epidemic.”
The deaths are “an important modification in the ecosystem and the integrity of the biodiversity,” Patrut said.
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