Some of the world’s oldest trees are suddenly dying. New research published this week reveals that nine of the 13 oldest baobab trees in the world — some dating back to 2,000 years or more — are dying or have recently died.
Why are these magnificent, ancient trees suddenly perishing? Two words: climate change.
It turns out that rainfall patterns in Africa, where all baobab trees can be found, have completely changed as a result of global warming. Since towering baobab trees require and often store enormous amounts of water, this has put them into a dangerous situation at critical times of their annual cycle. As lead researcher Adrian Patrut told Ed Yong at The Atlantic, “If they don’t have enough rain when they flush their leaves or produce their flowers, they die.”
This isn’t the only climate-related threat to baobabs. Research published in 2013 revealed that global warming will soon make many current baobab habitats unsuitable for many of the big trees, and not just the gigantic elders. Not only that, the research also showed that rapid human development has already restricted where baobab trees can grow, leaving them with nowhere to go once their last-remaining habitats can no longer support them. As a result, at least one of the eight baobab species could be pushed into extinction.
My article on that 2013 research, originally published by Scientific American, follows:
The Ewe people of Togo, Africa, have a proverb: “Wisdom is like a baobab tree; no one individual can embrace it.” The proverb refers to the massive trees of the genus Adansonia that can live thousands of years, reach 100 feet into the sky and achieve trunk diameters of 30 feet or more. One baobab tree in South Africa is so large that a popular pub has been established inside its trunk. Many local cultures consider baobab trees to be sacred. Others use them for their nutritious fruits, edible leaves and beautiful flowers. In addition, old baobabs, like many long-lived trees, often have natural hollows in their trunks, which in their case can store tens of thousands of gallons of water — an important resource not just for the trees themselves but also for the people who live near them.
But the size and cultural value of baobab trees has not necessarily protected them. According to research published in Biological Conservation, two of Madagascar’s endemic baobab tree species will lose much of their available habitat in the next 70 years due to climate change and human development. One species may not survive to the next century. Madagascar is home to seven of the world’s eight baobab species, six of which can be found nowhere else.
The study — by scientists from the French agricultural research center CIRAD and the University of York in England — relied on satellite images and field work to develop population estimates and distribution models for three baobab species: Adansonia grandidieri, A. perrieri and A. suarezensis. All three trees are currently listed as endangered on the IUCN Red List, which has not reassessed any Adansonia species since 1998. The study suggests that two of the species should now be reclassified as critically endangered.
One of those species, A. perrieri, had the lowest current population, according to the study, with just 99 trees observed during 10 years of field study. Based on its adaptation to specific geography and weather conditions, the researchers estimate that climate change will shrink the habitat of this species from about 8,000 square miles today to just over 2,500 square miles in 2080.
The second species, A. suarezensis, had a higher estimated current population of 15,000 trees but a far smaller distribution area of just 460 square miles. Based on climate change models and the species’ adaptation to high levels of precipitation, the researchers estimated that the distribution of this species will shrink to just 6.5 square miles by 2050 and could face potential extinction by 2080.
The one bright spot in their study was A. grandidieri, the largest and most populous baobab species. The researchers counted an estimated one million trees with a distribution of more than 10,000 square miles. According to their climate change models, this isn’t expected to change much by 2050 or 2080, but the team still recommends the species remain classified as endangered.
Unlike other species that may migrate or slowly move to new habitats as the climate shifts, baobab trees in Madagascar will not have that luxury. As the researchers point out, there’s nowhere left for the baobabs to go. Many baobab trees currently reside in “protected area networks” established to preserve Madagascar’s biodiversity, but the areas outside many of these networks have been almost completely converted to agriculture or cattle grazing areas, leaving no room for the trees to expand their distribution. In addition, the large animal species such as elephant birds and giant tortoises, which may have eaten baobab fruit and carried the trees’ seeds several kilometers from where they first fell, have all now gone extinct. With this in mind, the researchers assumed a “zero-colonization hypothesis” when calculating the trees’ distributions in coming decades, meaning they have little to no possibility of spreading to new habitats on their own.
Unfortunately the baobabs may not be alone in this scenario. Researchers warn that baobab trees should be considered a case study and wrote that the existing protected area network system in Madagascar “is not likely to be effective for biodiversity conservation in the future” because they will not always contain the ecological features necessary for the survival of the species that live inside them today. They suggest that the network system will need to be adapted to reflect climate change models and the ecological features that various species will need in the coming decades, but warn that the rest of Madagascar’s ecology must also be reconsidered. As they wrote, “it is only with an integration of ecological, social and economic studies, involving local communities and stakeholders, that we have a hope of restoring [Madagascar’s] ecosystem over the long term.”
