The oldest African baobabs (between 1,100 and 2,500 years old) are dying abruptly, according to a new survey of the species published on Monday in the scientific journal Nature Plants.
The numbers are grim: 8 of the 13 oldest and 5 of the 6 largest trees on record have died or experienced deterioration over the past 12 years.
The culprit is still unknown—and at large.
"Baobabs are peculiar trees, with unique architectures, remarkable regeneration properties and high cultural and historic value," says lead author Adrian Patrut, a chemist at Babes-Bolyai University in Romania, Popsci.com reported.
"They're the oldest and largest angiosperms. The impact of their loss would have profound consequences on many levels."
Between 2005 and 2017, the research team identified and dated more than 60 of the oldest and largest known individual baobab trees throughout southern Africa, initially in a quest to understand how and why they grow so big. The team probed each tree and assessed girth, height, volume, age and relative health. That is when they noticed the oldest were dying off surprisingly quickly during the survey's run, sans any sign of disease.
Prime Suspect
The biggest suspect, of course, is climate change.
"Paleoclimate evidence suggests that baobabs are adapted to wetter, drier and colder conditions, but possibly not to hotter conditions," says Patrut. Large trees need more water, and when that water is not available, the wood gets weaker, especially in larger and older specimens.
"We suspect that an unprecedented combination of temperature increase and extreme drought stress were responsible for these demises."
And in other cases climate change may have induced extreme weather events. For instance, Botswana's Chapman's Baobab, which died in 2016, flushed leaves and produced flowers well before the rainy season started.
"Having depleted its water resources, it was no longer able to stay erect, and collapsed," he says. However, he is quick to note that there is still not enough proof to indict climate change outright.
"Since there are relatively few millennial baobabs throughout southern Africa," he says, "it is impossible to make a statistical analysis. Also there aren't any climate records in some areas where the demises were recorded."
Ghislain Vieilledent, who has previously studied tropical forest loss and baobab mortality on Madagascar, thinks the new findings show "concretely that something abnormal is happening regarding baobab tree mortality. Using an emblematic species, it alerts once again on the potential negative effects of climate change on tree species and forests in general. Other types of disturbances, like insect attacks, fires or storms are less likely in this case."
Not on Extinction Path
"Nonetheless", he emphasizes, "it does not mean that the African baobab is threatened with extinction. Mature but younger and more vigorous individuals of the same species might not be as vulnerable to climate change as old individuals."
More research is needed to properly figure out how grave the situation is and what conservationists ought to do, but if climate change really is to blame, the clock is ticking fast.
