The baobab tree (Adansonia) is one of the longest-lived flowering plants on Earth. Its iconic appearance, with a massive trunk and sparse branches that resemble roots, has earned it the nickname “upside-down tree.” Its capacity for survival in arid environments has also led to its designation as the “Tree of Life.” The baobab’s reputation for great age is well-deserved, with some individuals surviving for millennia in the savannas of Africa, Madagascar, and Australia. The sheer size and longevity of these pachycaul trees place them among the most impressive botanical specimens in the world.
Determining Maximum Age
Dating a baobab tree poses a significant challenge because traditional methods used for other trees are not effective. The process of counting annual growth rings, called dendrochronology, is unreliable for baobabs because their soft, fibrous wood does not form clear, consistent rings. Furthermore, the growth rate of a baobab can fluctuate dramatically depending on the availability of water, meaning that trunk girth is a poor indicator of age.
The most accurate method for determining the age of these trees is Accelerator Mass Spectrometry (AMS) radiocarbon dating. This technique involves taking wood samples from different parts of the trunk structure and analyzing the remaining carbon-14 isotopes to establish an accurate calendar age.
Radiocarbon dating has confirmed that African baobabs (Adansonia digitata) are capable of ages exceeding 1,000 years. For instance, the Panke baobab in Zimbabwe was estimated to be around 2,450 years old when it died in 2011, making it the oldest angiosperm ever documented. Other dated examples have reached ages of approximately 2,000 years, such as the Dorslandboom in Namibia and the Glencoe baobab in South Africa. The AMS dating process has also revealed that baobabs often consist of multiple stems of different ages that have fused over time, creating a complex, multi-generational structure that contributes to their longevity.
Unique Adaptations for Survival
The longevity of the baobab is directly linked to its biological structure, which allows it to thrive in arid climates. The massive, barrel-like trunk is a specialized pachycaul structure designed primarily for water storage. Baobabs can store vast amounts of water within their spongy wood, with some large individuals estimated to hold up to 120,000 liters.
This stored water is crucial for surviving prolonged dry seasons, enabling the tree to shed its leaves and enter a dormant state until the rains return. The wood contains a high proportion of parenchyma cells, responsible for water and nutrient storage, sometimes accounting for up to 88% of the trunk’s volume. This high water content results in the baobab’s characteristic soft, fibrous trunk instead of hard wood.
A factor in the baobab’s ability to live for millennia is its method of regeneration and growth. As the tree ages, the center of its trunk often rots away, creating the large, hollow “false cavities” for which baobabs are famous. This hollowing does not kill the tree, as the living tissues are located just beneath the bark. New stems often sprout and fuse with the existing trunk over time, creating a ring-shaped or cluster structure that is continually self-renewing.
The baobab also employs physiological controls, such as regulating stomatal conductance, to minimize water loss during drought. This ability to limit transpiration, along with the capacity to quickly allocate biomass to the root system in the seedling phase, contributes to its resilience. These specialized mechanisms allow the tree to maintain a high pressure of leaf water, which prevents the failure of its water transport system, known as xylem cavitation.
Current Threats to Ancient Baobabs
Despite their millennial lifespans and impressive adaptations, the oldest and largest baobab trees are now facing threats. In the past two decades, a sudden and significant die-off of the most ancient specimens has been documented across Southern Africa. Researchers found that nine of the 13 oldest baobabs, those aged between 1,100 and 2,500 years, had either died completely or had their oldest parts collapse.
This mass mortality event is primarily linked to the effects of climate change, specifically increased temperatures and prolonged drought conditions. The ancient trees, which rely heavily on their stored water, are being overwhelmed by the severity and duration of modern dry periods. Extreme drought episodes deplete the water reserves in the trunk faster than the tree can replenish them, leading to the collapse of the weakened structure.
While other factors like human impact and elephant damage contribute to mortality, the die-off of the oldest trees is strongly suspected to be a consequence of climatic stressors. The oldest and largest baobabs are disproportionately affected because they require more water to sustain their massive volume. This recent decline raises concerns about the future longevity of a species that has survived for thousands of years.