Mysterious deaths are striking the largest and oldest African baobab trees, reports a paper published online this week in Nature Plants.

Baobabs - also known as ‘dead-rat’ trees, after the shape of their fruit - are among the most distinctive plants in the world, with stout, massive, branchless trunks that can look like pillars. African baobabs can live for hundreds, if not thousands, of years and can contain hundreds of square meters of wood - and some have massive hollow centers.

Adrian Patrut and colleagues analysed over 60 of the largest and potentially oldest baobab trees in Africa to understand how the baobabs’ biology and structure allows the trees to get so big. The authors used radiocarbon dating to age samples taken from different parts of each tree’s trunk.

Unexpectedly, they found that eight of the 13 oldest, and five of the six largest baobabs have either completely died or had their oldest parts collapse since 2005. Baobab trees have a ring-shaped structure composed of multiple stems and trunks, often of different ages, that can fuse together to form a closed circle, or remain open. False cavities like these are exclusive to baobab trees.

In the case of the oldest trees in this study, such ring-shaped structures are composed of stems that have each existed for hundreds of years, but in some cases all the stems have died suddenly. The authors suggest that climate change may be affecting the ability of the baobab to survive in its habitat, although data do not yet exist to support this conclusion.