The baobabs are dying.

No, this isn’t a heart-wrenching sequel to The Little Prince. It’s a report in Nature on a baffling illness striking down some of Africa’s most distinctive trees:

In a study intended to examine why the trees are so long-living, researchers made the unexpected finding that many of the oldest and largest of the trees have died in the past decade or so.

Individual trees — which can contain up to 500 cubic metres of wood — can live for more than 2,000 years. Their wide trunks often have hollow cavities, and their high branches resemble roots sticking up into the air.

Between 2005 and 2017, [Babeş-Bolyai University radiochemist Adrian] Patrut’s team dated more than 60 trees across Africa and its islands — nearly all of the continent’s largest, and potentially longest living, known baobabs. To compare ages of different parts of the trees, the researchers collected samples of wood from the inner cavities and exteriors of the trunks and from deep incisions in the stems, which were then sealed to prevent infection.

Patrut and his colleagues say that their measurements suggest the trees live so long because they periodically produce new stems, similarly to how other trees produce new branches. The team says that over time, these stems fuse into a ring-shaped structure, creating a false cavity in the middle.

But, surprisingly, the scientists also found that most of the oldest and largest baobabs died during the study, often suddenly between measurements. Nine of the 13 oldest, and 5 of the 6 largest, baobabs measured died in the 12-year period — “an event of unprecedented magnitude”, says the study. The researchers found no signs of an epidemic or disease, leading them to suggest that changing climates in southern Africa could be to blame — but they stress that more research is needed to confirm this idea.

In one instance, the researchers observed that in 2010 and 2011, all the stems of Panke, a giant, sacred baobab tree in Zimbabwe, fell over and died. The team estimates that the tree was 2,450 years old, making it the oldest known accurately dated African baobab and angiosperm.