Is Climate Change Killing the Baobabs? Nope, even the study authors don’t make the claim!
Guest Essay by Kip Hansen
A recent study into the ages of the oldest of Africa’s iconic baobab trees has spawned a lot of press coverage — very little of it scientifically accurate.
Headlines range all over the intellectual map depending on the general tendency for bias and yellow journalism of the news outlet.
Here are the headlines (with links) and a sample pull-quote from each:
“…the oldest baobabs across Africa have been dying over the past dozen years, and researchers believe it’s a direct result of climate change.”
“The culprit behind their deaths is still unknown, though scientists suspect that changing climate is to blame.”
“They suspect climate change—and underground water that’s harder for the roots to reach—may have something to do with the trees’ demise, but also point out that over each one’s life span, it has undergone wetter, drier, colder, and warmer conditions that stress the tree and sometimes kill other plants.”
“The trees, aged between 1,100 and 2,500 years and some as wide as a bus is long, may have fallen victim to climate change, the team speculated.“
Washinton Post (Chris Mooney)
“Mr. Patrut [the study’s lead author] says the largest trees are the most vulnerable – and he believes that a changing climate is involved, although the study itself says that “further research is necessary to support or refute this supposition.””
“Patrut says more research is needed to understand the cause of the die-off, but he believes the most likely explanation is climate change. “These trees are under pressure by temperature increases and drought,” he says.”
“No one can say if baobabs have died off in this way in centuries past; these trees decay very quickly, and leave few traces behind. “But when around 70 percent of your 1,500 to 2,000-year-old trees died within 12 years, it certainly is not normal,” says Erika Wise from the University of North Carolina, Chapel Hill. “It is difficult to come up with a culprit other than climate change.””
“The trees, aged between 1,100 and 2,500 years and some as wide as a bus is long, may have fallen victim to climate change, the team speculated.”
“It’s still unclear what is driving the baobab deaths. The authors believe that climate change is the culprit.”
“A study published Monday found eight of the 13 oldest trees in Africa have died over the past decade, and the authors suggest climate change may affect the ability of the baobab to survive.”
“… scientists argue the deaths are not a matter of coincidence, but proof of a pattern — a pattern they believe is explained by climate change.”
“Some of Africa’s largest and oldest baobab trees appear to be dying off at an alarming rate, according to a new study. Aged between 1,100 and 2,500 years, researchers suspect climate change as a cause.”
“The researchers found no signs of an epidemic or disease, leading them to suggest that changing climates in southern Africa could be to blame — but they stress that more research is needed to confirm this idea.”
and from 2 years ago:
REUTERS – Intel – July 4, 2016
“Initially the disease attacked damaged trees but it’s spreading to other trees. And the disease is spreading very fast,” warned Lawrence Nyagwande, who heads Environment Africa, a non-governmental organisation in Zimbabwe’s Manicaland province. He said there was little research available on what is causing the disease – suspected to be caused by one or more fungus species – or how to stop it from spreading.“
If you want to read the most even handed report, read the Smithsonian piece, which is a synopsis of some of the others as well as the original study.
WHAT WAS THE STUDY ABOUT?
The original study is titled: The demise of the largest and oldest African baobabs by Adrian Patrut et al. The full study is pay-walled but the DOI is 10.1038/s41477-018-0170-5 and there is a Nature.com article here.
The interesting thing is what the study is actually about. As you may have already guessed, it is not about the cause or causes of the dying baobabs of Africa.
The lead summary paragraph — this is a Brief Communication so it has no formal abstract — starts with this:
“The African baobab is the biggest and longest-living angiosperm tree. By using radiocarbon dating we identified the stable architectures that enable baobabs to reach large sizes and great ages.”
It is a study that attempts to establish the true ages of what are considered to be the oldest baobabs using radiocarbon dating. Dating baobabs is tricky, and controversial, because of their unusual growth pattern (not everyone agrees with their dating methods (see some of the stories linked):
“…big African baobabs are always multistemmed. The majority of baobabs start growing as single-stemmed trees. Over time, single-stemmed individuals become multistemmed, owing to the baobabs’ ability to periodically produce new stems, in much the same way other tree species produce branches. With this special ability, baobabs develop architectures of increasing complexity over time.”
The summary paragraph then gives us this report:
“We report that 9 of the 13 oldest and 5 of the 6 largest individuals have died, or at least their oldest parts/ stems have collapsed and died, over the past 12 years; the cause of the mortalities is still unclear.”
The authors report their findings on the ages of the 12 oldest baobabs, following the study design and methods appended to the study (if one has access or obtains the full study in pdf form via its DOI) which range from 850 to over 2,500 years.
After detailing their findings on ages of the trees and which ones have collapsed and/or died over the last decade, the authors offer us this:
“The deaths of the majority of the oldest and largest African baobabs over the past 12 years is an event of an unprecedented magnitude. These deaths were not caused by an epidemic and there has also been a rapid increase in the apparently natural deaths of many other mature baobabs. 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. However, further research is necessary to support or refute this supposition.”
All the hub-bub over “killer climate change” results from the stated “suspicion” of the authors. It is not true that “further research is necessary to support or refute this supposition”. There has not been any research about baobabs and local climate, baobabs and local temperatures, baobabs and local rainfall or local drought. None at all. Certainly not in this study — though there is sociological research showing that local peoples depend on the baobabs to provide food during the historically frequent droughts experienced in these areas, which implies that baobabs are drought survivors.
The article in Nature.com is a bit more skeptical than the study authors on the climate claim:
“Local experts welcomed the technique for dating baobabs, but some were sceptical of the team’s findings about the die-off. Michael Wingfield, a plant pathologist at the University of Pretoria in South Africa, says that the team’s sample was small and did not provide evidence that baobabs are not afflicted by an epidemic. “We know very little about baobab health,” Wingfield says. “There is much more to this picture than purely the fact that the oldest trees are dying.”
Sarah Venter, a baobab specialist at the University of Witwatersrand in Johannesburg, South Africa, says that her team’s ongoing research shows that baobabs may not be as drought resistant as previously thought — and this could be the cause of the deaths. But lower tolerance for drought would affect all the trees, not just the largest and oldest ones, she says.”
“Baobabs, especially old ones, can be more vulnerable to drought than their grizzled appearance might suggest, says David Baum, an ecologist at the University of Wisconsin-Madison. But more evidence is needed, he says, to strengthen the link between climate change and the baobab deaths.
Other factors, including human interference with individual trees (installing a cocktail bar, for example), could also be responsible.
In any case, Baum said in an email, “it is very likely that human actions, whether by changing the local landscape or altering global climate, have contributed to the death of so many large baobabs.”
These older baobabs, with cavities in the center or a ring of trunk(s) have been used for everything from jails to cocktail lounges. Their very notoriety has brought an unending stream of tourists to many of them — and the use of them for folk rites and as bars, stores, jails and restaurants — to the result that thousands of people visit these trees and walk around on the soil above their root zone. This fact alone could account for the demise of the oldest, most famous baobabs — see this paper “Soil Compaction & Trees: Causes, Symptoms & Effects” by Dr. Kim D. Coder (University of Georgia July 2000). Many arboretums, National Parks, local parks featuring famous trees have found that the celebrity of a tree can bring about its demise. Foot traffic leads to compaction of soils and “crusting”:
[from the paper linked just above}
Crusting…..a damaged top surface layer of the soil or a top seal on a soil column. Crusting is the dislocation and packing of fine particles and organic matter on the soil surface. In addition, natural products and pollutants can be associated with the surface making a hydrophobic surface, and preventing water and oxygen infiltration. Primary causes of crusting is the impact of rain drops on open soil surfaces, irrigation impacts, and animal and pedestrian traffic. Small local impacts on the soil surface help facilitate crusting.
For those interested, this piece in the Chicago Tribune is a little less scientifically dense on the topic of soil compaction and its effects on trees.
It is a shame that these ancient venerable trees did not receive the protection from their local or national governments that they deserved — a little care, reasonable regulations restricting inappropriate commercial use, forbidding bark stripping and other intentional damage and requiring biota-friendly tourism would perhaps have saved these trees that had struggled and survived for so long.
For the authors of this study, and the echo-chamber MSM (mostly, not all) to blame a cause over which we have no control (at least infinitely little control), a cause for which there no evidence whatever was sought or found, is a scientific and journalistic failure. My congratulations to those journalists that did not fall into the trap set for them by the journal Nature Plants, a trap set by allowing the authors to report a cause not investigated.
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