June 11 (UPI) -- Old trees eventually die. In isolation, a tree's death isn't necessarily unusual. But in Africa, a worrying pattern has emerged.
Over the last 12 years, the continent has lost several of its oldest and largest specimens of the African baobab, the most common species in the baobab genus, which is characterized by the trees' short stature, thick trunks and impressive longevity.
A team of researchers led by scientists from Babes-Bolyai University in Romania has been regularly visiting Africa's oldest baobab specimens, measuring their dimensions and observing their health, one by one, since 2005. During the last 12 years, the researchers witnessed the death or partial death, the loss of the oldest stem or stems, of 8 of the 13 oldest and five of the six largest specimens.
In a new study, published Monday in the journal Nature Plants, scientists argue the deaths are not a matter of coincidence, but proof of a pattern -- a pattern they believe is explained by climate change.
"It is very surprising to visit monumental baobabs, with ages greater than a thousand to two thousand years, which seem to be in a good state of health, and to find them after several years fallen to the ground and dead," Adrian Patrut, a researcher at Babes-Bolyai University, told National Geographic. "Statistically, it is practically impossible that such a high number of large old baobabs die in such a short time frame due to natural causes."
Baobab trees commonly form multiple stems, and though the walls of these stems, or trunks, can hold large amounts of water, many of the stems are hollow. Throughout history, humans have converted these hollow trunks into shops, houses, chapels and even bars. For 20 years, visitors were able to enjoy a pint inside the Sunland baobab, located in South Africa's Limpopo province. But in 2016, its stems began to crack and collapse, one by one.
Baobab trees also offer shelter for wildlife. Many bird species use the trees' broad canopy for nesting, while many small mammals climb it to avoid predators.
All of the dead or dying baobabs detailed in the latest study are located in Zimbabwe, Namibia, South Africa, Botswana and Zambia, and all are between 1,000 and more than 2,500 years old.
Temperatures have been rising in Africa over the last several decades, and many climate models suggest the continent is the most vulnerable to climate change. Several have studies showing Africa is likely to host longer and more frequent heat waves and droughts as the planet continues to warm.
The latest survey of ancient baobabs suggests climate change may already be affecting the continent's vegetation.
"We suspect this is associated with increased temperature and drought," Patrut told BBC News. "It's shocking and very sad to see them dying."