By A Correspondent- Big Tree in Victoria Falls, one of the world’s best-known trees and one of the oldest, has had its age determined by a more accurate chemical analysis method known as carbon dating.
The Big Tree is a colossal structure, soaring over 26 metres in the air, around 24 metres in circumference, with bulky branches, many stems that make up its trunk, and a wide, gaping hole at its core.
Its proximity to the falls, a major tourist destination, means that millions of visitors see it in a normal year, making it a sensation in its own right.
Some equally or more impressive trees were lost under the flooding further downstream that occurred after the construction of the Kariba Dam in 1956. Unlike the animals rescued and saved by ‘Operation Noah’ during the flooding the trees had to stay where they were, many were bulldozed so they would not become underwater hazards.
African baobabs—including the Big Tree—can live more than a thousand years and the previous estimates said the Big Tree was between 1 200 and 2 000 years old, although others put it at 2 500 years. But how old is this tree on which even Scottish treasure hunter David Livingstone inscribed his name in 1855?
To answer that question, a team of three scientists led by Adrian Partrut recently arrived at Victoria Falls and immediately rented a car to see the Big Tree in person.
The sight did not disappoint, Patrut says. “It was as if we had entered straight into a museum, into a well-known painting of a master, but we operated as scientists,” according to the nuclear chemist at Babes-Bolyai University in Romania. “I circled the baobab and admired it from all possible angles.”
Patrut, who has been studying ancient trees for decades, and his team made the pilgrimage to study the growth, age, and architecture of the tree. Dating ancient trees often involves counting “growth rings” that appear seasonally, a tried and true method that unfortunately doesn’t work well for baobabs.
These often massive trees have only very faint growth rings, and many have large cavities in their trunk and stems that confound attempts to date them. Until recently, most of evaluations of African baobab trees have been “guesstimates,” he says.
But over the past decade, Patrut has been refining a more precise method for estimating the age of baobab trees: radiocarbon dating. Patrut has used it on trees across the continent: South Africa, Mozambique, Namibia. For the Big Tree, his team found that its multiple stems have different ages, with its oldest one dating back to about 870AD.
The African baobab tree is different from the Australian one, for example, and is composed of several stems knitted together at the base to form a ring shape. Each stem may have started growing at a different time, so they each merit separate study.
To do this, the team inserted a T-shaped tool called an “increment borer” into different areas of the stems of the baobab. The tool extracts tiny wood samples at different depths, which the team then treated and sent to a lab for dating. The results show that the nine stems (including a “false” stem that emerged out of an adjacent one) can be lumped into three distinct generations.
There was the oldest one, at about 1,100 to 1,200 years old, a group that are around 600 to 700 years old, and another generation that dates to between 200 and 250 years ago. The team also found that the oldest stems haven’t grown further for more than a century.
The Big Tree is something of an outlier. While there are more than 100 million African baobabs in the world, fewer than 100 are thought to be 1,000 years or more old, says Patrut. All of them have inevitably endured countless threats, both acute and chronic.
The Big Tree is no exception: In the 1960s, it survived a violent storm that virtually destroyed the upper part of its canopy. As climate change continues, African baobabs, especially older ones that rely on heavy rainfalls, could face scorching heat and prolonged drought can push them to their limits.
Scientists (including Adrian Patrut, visible at lower left) had to sample all of the Big Tree’s stems to determine its age. ROXANA PATRUT
“[These are] very old trees that have survived for centuries, withstanding various abiotic and biotic factors including but not limited to extreme weather events,” says Patrut.
The Big Tree is large and old, but more than that, he says, it is resilient and adaptive—traits that are ever-more-critical in the face of an uncertain future.
The BaTonga elders believe a ‘curse’ started on their land when David Livingstone carved his name on the giant tree in 1855 and the ‘curse’ is spreading to other baobabs in the form of the disease.
They believe great ancestral spirits of the Zambezi River dwelt on the tree and when Livingstone etched his name on it, they became very angry and were never appeased therefore causing the sooty disease now threatening the survival of other baobabs in Zimbabwe.
Communities that directly benefit from the grotesque trees in Binga and Hwange are already counting the cost, as they can no longer benefit from the bark, which they traditionally used for making mats and other pieces of craft.
While the robustness and extreme longevity of these trees imply that they are generally healthy, research carried out recently by the Forestry Commission and Environment Africa’s Tree Africa has revealed that the trees are under threat from the sooty baobab disease.