猴面包树的神秘死亡事件| Nature Podcast

本周开始，我们会在每周日推送 Nature Podcast 。欢迎收听本周由Ellie Mackay 和 Benjamin Thompson 带来的一周科学故事，本期播客片段讨论猴面包树的神秘死亡事件。欢迎前往iTunes或你喜欢的其他播客..下载完整版，随时随地收听一周科研新鲜事。

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[Witness and family singing a traditional song about the baobab]

Interviewee: Witness Konzanayi

Growing up we would name the baobab trees after, you know, maybe after their shape. If it is too ugly, say ‘this ugly one’, if it produces a fruit or sweet foods, we’ll say this one is ‘sweet mama’.

Interviewee: Chris Surridge

The baobab is a completely unique tree in lots of respects, those sort of massive trees that are just about as wide as they are tall. It’s probably the oldest lived, it’s certainly the largest of the angiosperms, these flowering plants.

Interviewee: Witness Konzanayi

It is a tree that every child will identify with.

Interviewer: Noah Baker

If you picture an African savannah, more likely than not you’ll picture a baobab tree. A solemn giant, somehow bulbous and spindly at the same time, often described as growing upside-down. Now, new research investigating the age of baobabs has shown that many of the largest and oldest trees in the world are dead or dying, and scientists don’t know why.

Interviewee: Witness Konzanayi

Once upon a time, a long time ago, the Creator invited all animals to his office so that he could give them trees, you know seedlings for planting.

Interviewer: Noah Baker

That’s Witness Konzanayi from the University of Cape Town in SouthAfrica. He’s just finished his PhD on the governance of the baobab.

Interviewee: Witness Konzanayi

And the hyena of all animals was very lazy and he went to the Creatorvery late, and when he got there the only seedling that was left was that of abaobab tree. And he didn’t impress the hyena, so in anger the hyena took the seedling, threw it far away. That’s what happened, that’s how the baobab ended up with such an ugly shape.

Interviewer: Noah Baker

There are countless folktales like this one, each surrounding thebaobab, many explaining its bizarre shape. Here’s Chris Surridge, the editorof Nature Plants with the scientific version.

Interviewee: Chris Surridge

Normally, trees grow, they have a trunk, and they pretty much have one trunk and they split off further up into branches. Now baobabs are a bit weird in that they through their life can produce additional trunks that come up out of the ground. You sometimes see suckers come out of things like blackberries, but trees do not do this. But the baobab does, it throws up these extra trunks, a ring of stems which then fuse together to form this empty centre. They become sort of circular but with a gap in the middle.

Interviewer: Noah Baker

This is the leading theory for how baobabs have ended up so fat, and also explains why, more often than not, they have huge cavities inside. This bizarre architecture leads to problems if scientists want to find out how old a tree is.

Interviewee: Chris Surridge

Normally, when you try and date a tree you have to chop it down and count the rings into the centre, or you put a bore in and you can do that and check these. But there’s no centre to a baobab tree.

Interviewer: Noah Baker

So, when researchers decided to measure the age of the largest baobabs known across the African continent, they had to turn to another method. Here’s Adrian Patrut from the University of Babeş-Bolyai in Romania.

Interviewee: Adrian Patrut

The only possibility to date a baobab is actually to radiocarbon date samples collected from each stem.

Interviewer: Noah Baker

Radio carbon dating is not uncommon when dealing with very old trees. In fact, trees are often used to calibrate carbon dating methods – because counting tree rings is such a reliable way of measuring age, it can be used asa solid point of comparison. Adrian Patrut’s team started surveying trees in 2005, and some of those they surveyed were truly ancient.

Interviewee: Adrian Patrut

The oldest trees were around 2,000 years old, and we found a specimen in Zimbabwe, the so-called Panke baobab, and we collected samples which were up to 2,450 years old.

Interviewer: Noah Baker

These are trees which sprouted before Aristotle even proposed the division of the sciences. Trees which were already centuries old when Julius Caesar took the throne in Rome.

Interviewee: Chris Surridge

This is just an incredible age. Trees are happy to grow for hundreds of years, but getting up to these sorts of millennial ages is something that the flowering plants and flowering trees just don’t do.

Interviewer: Noah Baker

It’s worth noting here that there are non-flowering trees which are even older. Now, when a baobab gets really large or old, it can take on a particular significance. Here’s Witness again.

Interviewee: Witness Konzanayi

To an African person who identifies with these trees, once a tree becomes this big, it becomes sacred. They become more venues for spirits of the land.

Interviewer: Noah Baker

This significance adds even more weight to another discovery that Patrut and his team made.

Interviewee: Adrian Patrut

It was very unexpected to find that many old and large trees die in avery short timespan.

Interviewer: Noah Baker

Specifically, they found that 9 of the 13 oldest trees measured, and 5 of the 6 largest trees, have all died in the last 12 years. Now, these trees are all spread across Africa, sometimes thousands of miles apart. There was nosign of disease and the revered trees are usually very well cared for – they all even had names. It therefore seems too much of a coincidence that all of these deaths could happen by chance so suddenly. In fact, Patrut claims that it’s impossible.

Interviewee: Adrian Patrut

Scientifically it is impossible for trees which have an age limit of over 2,000 years to die in such a large number over a such short timespan.

Interviewer: Noah Baker

It begs the question then – what’s causing the deaths of these Baobabs?

Interviewee: Chris Surridge

The obvious conclusion is that it’s something environmental, something to do with changes in climate. But again, that’s very difficult to nail down because over 2,000 years these trees have seen a great deal of climate. I mean, they’ve lived through the Little Ice Ages that happened in about the 1400s,1500s, so they’ve seen much colder temperatures than now. They’ve seen droughts, they’ve seen practically floods, and yet they have carried through that. It is true that as far as we can tell, the temperature in these areas is warmer now than it has often been in the past, and it is also quite dry at the moment so maybe this is going on. But we really don’t know what it is that is killing these trees, if indeed this is an unusual amount of deaths.

Interviewer: Noah Baker

It’s an interesting scientific mystery. As an academic who works with the baobab, Witness too was intrigued, but for him speaking as a Zimbabwean, the findings also represented something else.

Interviewee: Witness Konzanayi

To ecologists it is just the dying of trees, but to an African person the death of such big trees means the death of culture, it means the death of identity, it means the death of spirituality.

[Witness and family singing a traditional song about the baobab]

Interviewee: Witness Konzanayi

Increasingly I think people are getting to know about climate change,even in the modest areas, in fact you don’t need to be told – you live it because you see your leaves are drying, we experience floods every year. But what I’m not sure of is if people are able to relate the deaths of these trees to climate change. If the big trees are dying I think what we need to do is to quickly establish what the cause is, because for some communities, the baobab tree defines who they are.

[Witness and family singing a traditional song about the baobab]

Host: Benjamin Thompson

That was Witness Konzanayi from the University of Cape Town, Adrian Patrut from University of Babeş-Bolyai, and Chris Surridge, the editor-in-chief of Nature Plants, where Adrian’s study was published. Thanks in particular to Witness and his wife and children for performing the song about the baobab, or ‘Muuyu’ in their mother tongue.ⓝ

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