Mysterious Deaths Of Ancient Baobabs

h/t Various!

From the BBC, the strange news about baobab trees:

A tree regarded as the icon of the African savannah is dying in mysterious circumstances.

International scientists have discovered that most of the oldest and largest African baobab trees have died over the past 12 years.

They suspect the demise may be linked to climate change, although they have no direct evidence of this.

The tree can grow to an enormous size, and may live hundreds if not thousands of years.

The researchers, from universities in South Africa, Romania and the US, say the loss of the trees is "an event of an unprecedented magnitude".

Revealing the findings in the journal Nature Plants, they say the deaths were not caused by an epidemic.

"We 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," said the team, led by Dr Adrian Patrut of Babes-Bolyai University in Romania. "However, further research is necessary to support or refute this supposition."

‘Shocking and very sad’

The researchers have been visiting ancient trees across southern Africa since 2005, using radio carbon dating to investigate their structure and age.

Unexpectedly, they found that eight of the 13 oldest and five of the six largest baobabs had either completely died or had their oldest parts collapse.

Baobab trees have many stems and trunks, often of different ages. In some cases all the stems died suddenly.

"We suspect this is associated with increased temperature and drought," Dr Patrut told BBC News. "It’s shocking and very sad to see them dying."

The trees that have died or are dying are found in Zimbabwe, Namibia, South Africa, Botswana and Zambia. They are all between 1,000 and more than 2,500 years old.

Also known as "dead-rat" trees, after the shape of their fruit, baobab trees have stout, branchless trunks.

They store large quantities of water inside their trunks to endure the harsh conditions of the arid areas in which they live.

The trees also support wildlife; they are important nesting sites for birds.

https://www.bbc.co.uk/news/science-environment-44418849

My first reaction was that these trees, all more than 1000 years old, must have lived through many changes of climate, particularly during warmer periods than now. Why should today’s climate be a particular problem?

Unsurprisingly these days, the authors were quick to point the finger at climate change. However, the fact that they could not actually find any evidence for this totally destroys their argument. After all, it should not have been very difficult to track down the temperature and rainfall data in the regions affected, and carry out a proper statistical analysis.

Given their failure to provide evidence, their claim should never have been put forward. That is not how science is supposed to work.

But there are some clues that their claim is insubstantial.

Firstly, look at the areas where they have found dying trees:

Zimbabwe, Namibia, South Africa, Botswana and Zambia.

There are actually big differences in climate between these countries. The idea, for instance, that it is now too hot for baobabs in South Africa is a nonsense, as they have been growing in hotter climates further north.

Similarly, there are large variations in rainfall between these different areas.

Indeed, baobabs have a much greater range in Africa, beyond southern Africa, for instance extending to Somalia and the Sudan, as Wickens and Lowe’s comprehensive book on baobabs shows:

https://www.amazon.co.uk/Baobabs-Pachycauls-Africa-Madagascar-Australia/dp/9048176395#reader_9048176395

A relatively minor shift in temperature, or a couple of years of drought surely cannot explain the trees’ demise, when they already manage to grow in much more extreme climates across the continent.

It is a great pity that the authors did not spend time attempting to get to the real reasons, rather than conveniently blaming climate change.

There is after all quite a lot that we do know about baobabs. The Feedipedia website tells us that:

Distribution

The origin of the baobab is still debated. They may have originated from the savannas and savanna woodlands of Sub-Saharan Africa, or they may have occured first in Madagascar (which has six endemic Adansonia species), from where they would have spread to continental Africa and Australia (Wickens et al., 2008; Watson, 2007). The baobab was introduced in many tropical and subtropical regions: central African countries, many Asian countries (e.g. India, Sri Lanka, Indonesia and the Philippines), the Middle East and the West Indies. The African baobab is found from sea level up to 1500 m in regions with a dry season lasting about 4-10 months split into 1 or 2 periods. Baobabs often grow close to villages (Orwa et al., 2009; ICUC, 2002; Bosch et al., 2004; Ecocrop, 2011).

Optimal growth conditions are average day temperatures ranging from 19°C to 35°C, annual rainfall between 300 and 500 mm, and fertile, slightly acidic, sandy topsoil overlaying loamy subsoil. However, the African baobab may withstand much lower and more irregular rainfall conditions (90-1500 mm) and grow on poorly drained soils with a heavy texture, though not on deep sands probably due to the lack of anchorage (Orwa et al., 2009; Bosch et al., 2004). It cannot withstand seasonal flooding, waterlogging or severe frost, which may kill even mature trees (Ecocrop, 2011; Bosch et al., 2004).

https://www.feedipedia.org/node/525

In other words, they can flourish in quite a wide range of climate conditions, and can survive periods of severe drought.

Indeed, if we look at the Nature paper’s supplementary information, it gives a list of the trees recorded (blue being “dead/dying”):

https://www.nature.com/articles/s41477-018-0170-5#Sec13

As we can see, they are widely distributed across southern Africa, and across varying rainfall regimes, from Limpopo with 388mm a year, to Zambia with 817mm.

The other significant thing which Feedipedia tells us is that baobabs are an important source of food:

The African baobab (Adansonia digitata L.) is one of the eight species of baobab (Adansonia) and the only one native to mainland Africa. Like other baobabs, the African baobab is a massive deciduous fruit tree, up to 20-30 m high, with a lifespan of several hundred years. Its swollen and often hollow trunk looks like a huge bottle and can be as broad as 3-7 m in diameter. It bears short, stout and tortuous branches and has a thin canopy. Baobab is strongly anchored in the soil by an extensive and strong root system that grows 2 m deep, and whose diameter may be higher than the tree height. The leaves are simple or digitally compound, dark-green on top, and borne at the end of a 16 cm-long petiole. The leaflets are between 5-15 cm long and 1.5-7 cm broad. The baobab shed its leaves during the early dry season and new leaves appear after flowering. The pentamerous flowers are white, large (20 cm in diameter and 25 cm long), and hang from stalks on pedicels up to 90 cm long. The fruit is a voluminous (35 cm long and 17 cm in diameter) ovoid capsule with a hard woody envelope containing a pulp and black seeds. Once ripe, the fruit envelope becomes brittle and the pulp takes on a chalky consistency. The tree starts producing fruits 8-10 years after planting but consistent production only occurs after 30 years (Ecocrop, 2011; FAO, 2011; Orwa et al., 2009; Bosch et al., 2004; Jansen et al., 1991).

The baobab is mainly used for food. The fruits, flowers, leaves, shoots, roots of seedlings and even the tree roots are edible. The leaves can be used either fresh, as a cooked vegetable, or dried and powdered as a functional ingredient (thickener) of soups and sauces. The flowers, shoots and roots of seedlings are eaten (Bosch et al., 2004). The fruits, called monkey-bread, contain a white, mealy, acidic tasting nutritious flesh that can be eaten as a sweet, used to make refreshing drinks and ice-creams, or used to adulterate and curdle milk. The seeds yield an edible and pleasant tasting oil, and oil extraction results in an oil meal. The bark is used for fibre or as firewood. The roots, that are boiled and eaten in times of famine, contain tannins that provide a useful red dye (Orwa et al., 2009). In the Sahel, black bark and red bark baobabs are preferred for their fruits, while dark leaf types are mainly used as a leaf vegetable and grey bark types are used for fibre (Bosch et al., 2004). Burning baobab fruit pulp produces an acrid smoke used to deter insects troublesome to livestock (Orwa et al., 2009).

Baobab trees provide fodder for animals: young leaves, fruits, seeds and the oil meal are consumed by livestock (Bosch et al., 2004). During drought, donkeys and game animals chew the bark and the fibrous wood for sap. Livestock and game often destroy young trees. Elephants can badly damage baobabs when they rub themselves against the trunk (FAO, 2011; Orwa et al., 2009).

Surely the first consideration for the authors should have been the impact on trees from humans. Have they been overharvested? Or damaged in some way?

Then there is the impact of tourism. There is a website for the Sunland Baobab in Limpopo, which contained this prescient tale:

It was at one time believed that Baobabs were in danger of becoming extinct. This was before botanists realised that the small trees do not resemble the mature trees at all. Fortunately the Baobab is not threatened. But the large trees are not immune to man’s intrusion. A famous tree, the Nomsiang Baobab, named after the farm in which it stood, was close to the highway and thousands of visitors trampled the ground so hard that it became impervious to rainwater and the magnificent tree died.

http://www.bigbaobab.co.za/baobab_facts

It is a sad fact that the most ancient of these trees are huge tourist attractions. Thousands come to look, and many will climb them, maybe even taking home souvenirs. There is also the question of vehicles approaching too close. Just how much damage does all of this do?

I said prescient, because the Sunland baobab itself toppled over last year. With the best of intentions, the owners had decided to develop their farm in the 1990s:

The Sunland ‘Big Baobab’ is in Modjadjiskloof in Limpopo Province, South Africa and is famous internationally for being the widest of its species in the world. Africa is symbolised by these magnificent trees. The Sunland Big Baobab is carbon dated to be well over 1 700 years old and has even made the front page of the Wall Street Journal!
When baobabs become a thousand years old, they begin to hollow inside. In the Big Baobab this has resulted in wonderful caverns and caves, where the world famous Baobab Tree Bar now amazes visitors.

The Big Baobab is on the mango farm Sunland, where day visitors are welcome. Sunland can also accommodate 20 overnight visitors in 5 chalets. We also offer quadbiking on our own quads or you can bring your own. There are hikes, waterfalls in the surrounding area and mountain biking trails, while the tree itself hosts a variety of activities. The Big Baobab has hosted many weddings over the years an there is now a honeymoon suite in a tree house for a wedding with a difference!

Sunland Farm is an ideal base for exploring the surrounding area – the Modjadjiskloof Cycad Forest, the Magoebaskloof hills and forest, the verdant area of Tzaneen and more.

Doug and Heather van Heerden bought the farm in 1989 and cleared half, planting mangoes and Palm trees. The Big Baobab is important both historically and ecologically and is home to many animals and birds, as well as providing food for many others. The van Heerdens fiercely protect the tree and the surroundings – woe betide anyone who doesn’t share their views!

http://www.bigbaobab.co.za/home

They hold weddings around the tree:

Let kids climb all over it:

And have even built a bar inside the trunk:

In 1993 the van Heerdens cleared out the hollow centre of the tree, removing masses of compost build up, to uncover the floor about a meter below ground level. In the process they found evidence of both Bushmen and Voortrekkers, attesting to the historical importance of the tree.

They squared off a natural vent in the trunk to make a door and installed a railway sleeper pub inside the trunk, complete with draft beer, seats and a music system. One party had 60 people inside the tree bar!. A wine cellar was installed in a second hollow, with a constant temperature of 22° C, ventilated by natural vents.