Windhoek — Namibia's oldest and largest trees, the baobabs, some of which have lived for 1,700 years, have begun dying in the last 13 years, leaving scientists stunted.
Scientists who have been researching the African baobabs reported in Nature Plants that the trees, aged between 1,100 and 2,500 years, some with the width of a small Katutura house, might have fallen victim to climate change in the last 13.
The scientists have been monitoring over 60 baobab trees in South Africa, Namibia, Zimbabwe, Mozambique and Zambia since 2005. They found that eight of the 13 oldest African baobab specimens and five of the six largest trees have died or at least their largest or oldest stems have collapsed and died.
Of the over 60 trees researchers found the 13 oldest trees and six with the largest trunks. The majority of the oldest and largest baobab trees were found in Southern Africa.
In the period between 2005 and 2017, the researchers found that five trees died in South Africa, four trees died in Namibia, three died in Zimbabwe and one tree each died in Botswana, Mozambique and Zambia.
In Namibia one of the baobabs that died had the largest circumference of all 60 baobab trees found in Africa. At 30.2 metres the tree, named Holboom, also had one of the tallest heights and is dated to be about 1,700 years old.
Researchers from Romania, South Africa and the United States said the Holboom, which is located in Tsumkwe's Nyae Nyae Conservancy, started its decline in 2012 when the entire left stem collapsed and the cavity walls broke off. Besides Tsumkwe the scientists have also been monitoring the baobab trees in Okahao, Anamulenge and Onesi in Omusati Region.
The oldest tree by far, of which all the stems collapsed in 2010/11, is the Panke tree in Zimbabwe, estimated to have existed for 2,500 years.
"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," says study co-author Adrian Patrut of Romania's Babes-Bolyai University.
"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," they said.
"It is definitely shocking and dramatic to experience during our lifetime the demise of so many trees with millennial ages," said Patrut.
While the cause of the die-off remains unclear, the researchers "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". They are saying further research is needed "to support or refute this supposition".
The baobab is the biggest and longest-living flowering tree, according to the research team. It is found naturally in Africa's savannah region and outside the continent in tropical areas to which it was introduced. It is a strange-looking plant, with branches resembling gnarled roots reaching for the sky, giving it an upside-down look.
The tree serves as a massive store of water, and bears fruit that feeds animals and humans. Its leaves are boiled and eaten as an accompaniment similar to spinach, or used to make traditional medicines, while the bark is pounded and woven into rope, baskets, cloth and waterproof hats.
The purpose of the study was to learn how the trees become so enormous. The researchers used radiocarbon dating to analyse samples taken from different parts of each tree's trunk.