Baobab reforestation in Loaga village, Burkina Faso. CIFOR/Ollivier Girard

Ancient baobab trees in Africa under threat due to erratic climate, scientists theorize

Extreme drought stress

BONN, Germany (Landscape News) — When Adrian Patrut and an international team of scientists set out to study baobab trees (Adansonia digitata) in 2005, they did not expect to see so many of the oldest and largest specimens suddenly die over the following years.

A unique looking angiosperm that is actually one of the world’s largest flowering plants, the baobab is iconic throughout the African continent.

Ceremonies and village meetings take place beneath their branches, their fruit is a source of food for both humans and wildlife, and the bark can be harvested for medicinal uses.

The baobab’s unique structure – a hollow centre formed when newly generated stems fuse together in open or closed circles – have seen some of the largest specimens used as shops, bus stops and, in one case, a bar.

While they are known to live for centuries, their structure and faint growth rings make accurately dating their age almost impossible. Patrut, a chemist at Babes-Bolyai University in Romania and lead author of the study, “decided that the best method to do that was to take samples from live trees and carbon date them,” said team member Roxana Patrut, a doctoral student in biology at the same university.

The researchers measured and dated more than 60 trees, some as old as 2,500 years, in the southern regions of Africa and in Madagascar. By last year, however, they discovered that 14 trees had collapsed, according to a paper recently published in Nature Plants.

“The deaths of the majority of the oldest and largest African baobabs over the past 12 years is an event of an unprecedented magnitude,” the paper states. “These deaths were not caused by an epidemic and there has also been a rapid increase in the apparently natural deaths of many other mature baobabs. We suspect that the demise of monumental baobabs may be associated at least in part with significant modifications of climate conditions that affect southern Africa in particular. However, further research is necessary to support or refute this supposition.”

For Roxana Patrut, a number of facts nonetheless support the climate change theory.

“Because they were spread throughout Southern Africa, an area which is very vulnerable to climate change, it is one of the fastest warming areas of the planet,” she said. “Part of the team I am working with also did a climate reconstruction using baobab trees in certain areas and climatic records. It showed that baobabs survived wetter periods, colder periods and dryer periods. So we think it’s a combination of increased temperature with extreme drought stress that produced these demises. The large trees need a lot of water, proportionate to their volume, are already weakened by age, and are the most likely to collapse.”

The famous Chapman Baobab in Botswana — estimated to be 1,000 years old — on which English explorer David Livingstone (1813-1873) once carved his initials, is a case in point. “All six stems collapsed in January 2016,” she said, “because the rainy season started several months late. So the tree had already flushed leaves and produced flowers. Its water resources were depleted and it just collapsed.”

The water content of the Chapman Baobab was found to be just 40 percent, half of the normal percentage in healthy trees.

“So it’s also extreme climate episodes,” she said, “not just climate change in general.”

Ms. Patrut said that the attention their study has brought to the plight of Africa’s baobabs “was a pleasant surprise.” Some mitigation, such as watering the trees during drought, leaving bark intact, and protecting them from elephants, would help them survive.

But the real message of their paper, she said, is that “climate change is real and we should act on it. I hope that people will also acknowledge these extraordinary trees, and realize that there are so many beautiful things on this planet that we are unfortunately destroying, and that we should try to protect them by doing our part.”

Find out about restoration initiatives throughout Africa at the Global Landscapes Forum GLF Nairobi summit, August 29-30, 2018Click here



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