Baobabs get through the savanna by acting as living water tanks. Their swollen trunks soak up water in the rainy season and release it slowly through the long dry months.1Cambridge University Press. The Growth Stop Phenomenon Of Baobabs (Adansonia Spp.) Identified By Radiocarbon Dating Much of that trunk is not hard timber at all but soft, living, water-filled tissue, closer to a giant succulent than a typical tree. A tree built around a full tank has to refill it every rainy season, and that dependence shapes nearly everything else about how it lives.
How the Trunk Stores Water
Baobab wood can be up to 79% water by weight.2PubMed. A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansonia spp.; Bombacaceae) That is possible because most of it, between 69% and 88%, is soft living storage tissue rather than hard woody fibre.3PubMed. A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansonia spp.; Bombacaceae) Living cells reach more than 35 cm into the trunk from the bark, far deeper than in most trees.4PubMed. A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansonia spp.; Bombacaceae) When dry, the wood is extremely light, roughly a tenth to a fifth the density of water.5PubMed. A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansonia spp.; Bombacaceae)
When the tree is in leaf, daily trunk shrinkage suggests it can use around 400 litres of stored water in a single day.6Cambridge University Press. The Growth Stop Phenomenon Of Baobabs (Adansonia Spp.) Identified By Radiocarbon Dating7Biotropica. Some Measurements on the Water Relations of Baobab Trees Over a dry spell, a trunk can lose up to 1,500 litres,8Biotropica. Some Measurements on the Water Relations of Baobab Trees close to the volume of a small garden water tank.
Shallow Roots That Catch Rare Rain
Baobab roots are fairly shallow, reaching down only about 1.8 metres.9Biotropica. Some Measurements on the Water Relations of Baobab Trees Most other trees store far less water and rely more on deeper roots to reach moisture. But they spread sideways farther than the tree is tall.10Biotropica. Some Measurements on the Water Relations of Baobab Trees Savanna rain often comes as a few heavy downpours, and a wide, shallow net catches that water quickly.11Biotropica. Some Measurements on the Water Relations of Baobab Trees The roots grab water in short bursts, and the trunk banks it for months.
Dropping Leaves and Closing Pores to Save Water
When water runs short, baobabs drop their leaves, and with fewer leaves far less water escapes into the air.12PubMed Central. Leaf phenology of thirteen African origins of baobab (Adansonia digitata (L.)) as influenced by daylength and water availability Some water still evaporates through the surface of the trunk itself, which slowly loses firmness.13PubMed Central. Leaf phenology of thirteen African origins of baobab (Adansonia digitata (L.)) as influenced by daylength and water availability
Leaves lose water through tiny pores, which open to take in air for growth. In baobab seedlings under drought, pore opening drops by about 85%, and then the plants shed many leaves.14South African Journal of Botany. Sap flow and water use in African baobab (Adansonia digitata L.) seedlings in response to drought stress Adult baobabs in the rainy season open their leaf pores in the morning but close them quickly as the day heats up.15PubMed. Water relations of baobab trees (Adansonia spp. L.) during the rainy season: does stem water buffer daily water deficits? The reason is that their branch water pipes are fairly easily damaged by air bubbles if the tree dries too much, and tight control keeps that damage in check.16PubMed. Water relations of baobab trees (Adansonia spp. L.) during the rainy season: does stem water buffer daily water deficits?
Many baobabs grow new leaves near the end of the dry season, before the rains begin.17PubMed. Baobab trees (Adansonia) in Madagascar use stored water to flush new leaves but not to support stomatal opening before the rainy season Almost no water is coming up from the roots at that time, so the new leaves are built almost entirely from trunk water.18PubMed. Baobab trees (Adansonia) in Madagascar use stored water to flush new leaves but not to support stomatal opening before the rainy season Trunk water can drop by up to 12% during this leaf flush.19PubMed. Baobab trees (Adansonia) in Madagascar use stored water to flush new leaves but not to support stomatal opening before the rainy season Even so, the tree keeps its leaf pores mostly closed until the rains arrive.20PubMed. Baobab trees (Adansonia) in Madagascar use stored water to flush new leaves but not to support stomatal opening before the rainy season
Over a savanna year, this gives the tree a clear rhythm. For much of the dry season it stands bare, which earns it the “upside-down tree” nickname because its branches look like roots. Fresh leaves appear shortly before the rains, paid for with banked water. In the wet season it is fully leafy and refills its trunk. As drought returns, the leaves drop again.
Surviving Fire and Elephants
Baobab bark resists fire, and the fibrous wood can regenerate even after serious damage.21Wilderness. Guardians of the giants: Preserving baobabs in the Okavango Delta The ability to resprout and regrow bark evolved in fire-prone, disturbed landscapes and helps the trees recover.22Frontiers in Forests and Global Change. Baobabs at the edge: 90-year dynamics of climate variability, growth, resilience, and evolutionary legacy effects
Soft, watery wood is both a weakness and a strength. It is easy for elephants to tusk and chew, but the same living tissue can heal and grow new bark, which most hard-wooded trees cannot do after losing that much.
Elephants and other animals eat the spongy bark for its moisture when water is scarce.23San Diego Zoo Wildlife Alliance. Baobab In one Zimbabwe park, close to 3 in 10 monitored baobabs near a river died over four years of elephant damage.24African Journal of Ecology. Baobab damage in Mana Pools National Park, Zimbabwe Only smaller trees, under about 7.5 metres around the trunk, could resprout after being knocked over.25African Journal of Ecology. Baobab damage in Mana Pools National Park, Zimbabwe Regrowth protects young trees well, but large old trees can be lost where elephants crowd around scarce water.26African Journal of Ecology. Baobab damage in Mana Pools National Park, Zimbabwe
Drought makes this worse. When rivers and pools dry, the baobab’s wet bark becomes a water source, and elephants concentrate on trees near the remaining water. Trees already short of water have less to spend on repair.
Why the Trunk Can’t Run Dry
Baobabs are built with no more safety margin against bending than other trees.27PubMed. A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansonia spp.; Bombacaceae) But their wood becomes less stiff as its water content drops.28PubMed. A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansonia spp.; Bombacaceae) Drawing too much water out of the trunk could therefore affect how well the tree holds itself up.29PubMed. A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansonia spp.; Bombacaceae)
Water works as part of the tree’s skeleton. A firm, well-watered stalk stands upright while a wilted one flops, because water pressure helps keep the tissue rigid. The leafless trunk losing firmness in drought is this effect in action.
Hollow Trunks and Great Age
In some large African baobabs, the wood gets older the deeper you go into the wall of an inner cavity.30PubMed Central. African Baobabs with False Inner Cavities: The Radiocarbon Investigation of the Lebombo Eco Trail Baobab In those trees, the cavity isn’t rot but a natural gap between several stems that grew together in a ring.31PubMed Central. African Baobabs with False Inner Cavities: The Radiocarbon Investigation of the Lebombo Eco Trail Baobab What looks like one enormous trunk can be a cluster of fused trunks.
The oldest dated baobabs were around 2,000 years old.32Nature. Africa’s iconic baobab trees are dying, and scientists don’t know why Samples from the Panke baobab in Zimbabwe dated to as much as 2,450 years.33Nature. Africa’s iconic baobab trees are dying, and scientists don’t know why Yet 9 of the 13 oldest and 5 of the 6 largest measured trees died within about 12 years.34Nature. Africa’s iconic baobab trees are dying, and scientists don’t know why The cause of those deaths has not been confirmed.35Nature. Africa’s iconic baobab trees are dying, and scientists don’t know why
Flowers That Bloom at Night
The African baobab has hanging white flowers that open at night with a musky scent, traits typical of bat-pollinated plants.36Biotropica. Evidence for hawkmoth pollination in the chiropterophilous African baobab (Adansonia digitata) Hawkmoths have been found pollinating it too.37Biotropica. Evidence for hawkmoth pollination in the chiropterophilous African baobab (Adansonia digitata) In Madagascar, two baobab species are pollinated by fruit bats and lemurs, while most others rely on hawkmoths.38Annals of the Missouri Botanical Garden. The Comparative Pollination and Floral Biology of Baobabs (Adansonia- Bombacaceae) In Africa, galagos, or bushbabies, and fruit bats drink baobab nectar.39San Diego Zoo Wildlife Alliance. Baobab
How Baobabs Spread Across Continents
The best-supported explanation is that baobabs arose in Madagascar.40PubMed Central. The rise of baobab trees in Madagascar The Australian baobab most likely descends from a single crossing from Madagascar.41PubMed Central. The rise of baobab trees in Madagascar That crossing happened long after the old supercontinent broke apart, so seeds had to travel over the sea.42PubMed. Biogeography and floral evolution of baobabs (Adansonia, Bombacaceae) as inferred from multiple data sets An ancestor that reached Africa doubled its chromosome sets in West Africa, producing the African baobab.43PubMed Central. Chromosome-level baobab genome illuminates its evolutionary trajectory and environmental adaptation That doubling likely gave advantages that helped it spread east and south across the continent.44PubMed Central. Chromosome-level baobab genome illuminates its evolutionary trajectory and environmental adaptation
A Tree That Supports a Whole Habitat
A mature baobab supports birds, reptiles, insects and mammals with food, water and shelter.45San Diego Zoo Wildlife Alliance. Baobab Monkeys and warthogs eat the fruit, and weaver birds build nests in the huge branches.46San Diego Zoo Wildlife Alliance. Baobab Baobabs also help keep soil moist, recycle nutrients and prevent erosion.47San Diego Zoo Wildlife Alliance. Baobab Losing one large tree can remove a hub that many species use.
People use baobabs too. In very dry areas, they cut hollows into the trees to collect rainwater.48Baobab Foundation. water in baobab trees This practice may be the origin of the belief that baobabs offer drinking water to passers-by.49Baobab Foundation. water in baobab trees
Black marks on the bark are usually not a threat. Black mould on baobab branches in southern Africa comes from several fungi.50Springer Link / Antonie Van Leeuwenhoek. Fungi associated with black mould on baobab trees in southern Africa It can kill small twigs on badly affected branches, but it has not been found to kill trees.51Springer Link / Antonie Van Leeuwenhoek. Fungi associated with black mould on baobab trees in southern Africa