African baobab trees are truly one of the wonders of the natural world. Native to Sub-Saharan Africa, the strange trees look like they were drawn by Dr. Seuss, with wide, fat, trunks capped by sparse branches covered in green leaves. The trunks are often completely hollow, sometimes big enough to provide homes, shops and meeting spaces for local villagers. Even more impressive, the trees can live up to 2,500 years — perhaps longer. But we may not be able to figure out just how long: Ed Yong at The Atlantic reports that the oldest baobabs across Africa have been dying over the past dozen years, and researchers believe it’s a direct result of climate change.
The study in the journal Nature Plants is the result of a survey conducted by co-author Adrian Patrut of Romania’s Babes-Bolyai University. Nadia Drake at National Geographic reports that Patrut began studying baobabs in 2000, mainly focusing on Adansonia digitata, a very large species of baobab found primarily in southern Africa. Over 15 years, Patrut identified about 60 of the largest and oldest baobabs. Because they don’t put down a growth ring every year like other trees, he collected samples from the trees, using radio-carbon dating to determine their age, finding that many of them were over 2,000 years old, though some researchers think his dating techniques might be conservative, shaving 1,000 years off their age.
But something strange happened during the course of his research. In the last dozen years, four of the largest 13 trees studied have died, suddenly rotting and splitting apart. Another five have lost their oldest stems and are on the way to dying completely. The fallen include Homasi, also known as Grootboom, a giant tree in Namibia. The Sunland baobab in South Africa’s Limpopo Province, which is so large it houses a cocktail bar, suddenly began splitting apart in 2016 and may not last much longer.
“Such a disastrous decline is very unexpected,” Patrut tells Tim McDonnell at NPR. “It's a strange feeling, because these are trees which may live for 2,000 years or more, and we see that they're dying one after another during our lifetime. It’s statistically very unlikely.”
Which means there must be a cause for the die-off. In recent years, a mysterious fungal disease has been hitting baobabs trees in certain parts of the continent. But Patrut tells Drake that he doesn’t think the fungus is taking out these ancient trees since they have shown no sign of disease. Instead, the researchers believe climate-change-fueled drought has weakened the trees.
Temperature increases and reduced rainfall have been recorded across southern Africa in the last decade. Baobabs are particularly reliant on the annual rainy season and need to sip up about 70 to 80 percent of their volume in water to stay upright. If there isn’t enough water in their system when they produce their leaves, flowers and fruit, the tree will die quickly and collapse. That seems to have been the fate of Botswana’s Chapman baobab. In 2015, the rainy season, which normally starts in September, was delayed until February 2016. But the tree collapsed in January, a month before the rains came.
It’s possible that the deaths are part of a natural cycle, though it’s hard to say because baobabs decay rapidly and don’t leave behind any evidence of previous die-offs. But Erika Wise of the University of North Carolina, Chapel Hill, and head of the Climate & Tree Ring Environmental Science research group tells Yong it’s unlikely to be a natural cycle. “[W]hen around 70 percent of your 1,500 to 2,000-year-old trees died within 12 years, it certainly is not normal,” she says. “It is difficult to come up with a culprit other than climate change.”
Southern Africa is warming faster than the global average and is expected to warm more quickly than other parts of the continent, adding even more stress to mature baobabs. Wise points out that baobabs are not the only trees suffering, and that drought and temperature changes are making trees and forests vulnerable to problems around the world. The American West has seen huge die-offs of forests from insect infestations in recent years, she says. “The die-off has other immediate causes, like insects, but a 500-year-old tree has experienced a lot of insect outbreaks and lived through them. Something is pushing them over the brink this time around.”
However, not everyone is convinced climate change is to blame for the baobab deaths. Michael Wingfield, a plant pathologist at the University of Pretoria, tells Sarah Wild at Nature that the sample size is very small and the study does not fully rule out a disease afflicting older trees. And baobab specialist Sarah Venter of the University of Witwatersrand says if drought was the problem, it would affect all baobabs, not just the largest and oldest. Whatever the case, it's sad to see these trees go — especially the ones that were serving cocktails.