Africa’s baobab tree looks like something from a Dr. Seuss book. When young, the species (Adansonia digitata) is single-stemmed, branchless, and sports fruit that resembles giant sausages. Now, researchers report things get even weirder as the tree grows older. Over its lifetime, its roots send up several more stems in a ring, which eventually fuse to form a cavity “inside” big enough for bars, churches, or prisons for people, and refuges for animals seeking relief from the hot sun. The work also addresses the mystery of why so many of these strange trees are dying.
To conduct the study, researchers combed books, articles, and the internet and asked local Africans in order to locate the biggest baobabs. The team leader is a nuclear chemist who loved giant trees and had developed a way to date ancient trunks without harming them. The scientists considered baobabs a good challenge because others had said wood was difficult to determine the age of. The team dated more than 60 of the trees, revealing that—unlike most other trees—the baobab grows new trunks, instead of branches, which eventually create their giant, hollow interiors.
Some of these trees are more than 2000 years old, the team reports today in Nature Plants. But in 2011 the oldest known specimen—a shrine for rainmakers named Panke that sprouted about 2450 years ago—died and toppled over. And now seven more of the 13 oldest trees, and five of the six biggest trees, have also died, the researchers report.
They suspect climate change—and underground water that’s harder for the roots to reach—may have something to do with the trees’ demise, but also point out that over each one’s life span, it has undergone wetter, drier, colder, and warmer conditions that stress the tree and sometimes kill other plants. Whatever the cause, these mysterious deaths will have a big impact on the southern African landscape, as in addition to shade, the tree’s bark, roots, seeds, and fruit are key food sources for many animals.