elephant herd grazing in the grass

The tale of the elephant

There are many reasons for scientific research, from product development to saving the planet; all are justifiable to a degree, but sometimes the objectives get a little out of whack and affect the science. Here is an elephant example.

Scientists are humans with all the failings that affect everyone else.

I know we are trained to be objective and apply rigour in our work. We are supported by the scientific method designed to keep much of the normative instincts at bay, and we must see our results critiqued by our peers, who are not always as knowledgeable as they might be.

Often this is not enough to keep opinions and prejudices out of the process.

Recently I came across a potent example of how desires can get the better of the deliberate.


Saving wild elephants

Elephant populations in Africa are in trouble. They have been for over a century. It has already caused some bizarre controversy over numbers and a misunderstanding of the basic logic, not enough animal biomass to go around.

Saving wild elephants is high on the conservation agenda. As it should be. 

There is no need to justify why because it is evident, although the how takes a lot of thought and delicate negotiation. But this does not stop conservationists from finding new reasons why elephants should be saved, including the idea that megaherbivores fulfil multiple ecological functions that cannot be replaced by smaller herbivores or livestock.

Researchers move in to prove the point with an observational study to see if elephant numbers influence the carbon balance of the savanna. Not surprisingly, a shift from low to high elephant numbers reduced the amount of tree biomass and that of carbon stored therein by 6.4 tC ha−1. This is precisely what to expect from foraging by a large herbivore fond of leaves and twigs. 

However, the researchers also found that in the soil, carbon stocks increased with higher elephant densities by 4.7 tC ha−1, almost offsetting woody carbon losses.

Here is what that looks like in a neat graphic.

graphic showing where the carbon exists in savanna habitat with different levels of elephant activity

Source: Sandhage-Hofmann, A., Linstädter, A., Kindermann, L., Angombe, S., & Amelung, W. (2021). Conservation with elevated elephant densities sequesters carbon in soils despite losses of woody biomass. Global Change Biology, 27(19), 4601-4614.

The extra soil carbon was mainly in the topsoil. 

Anyone who has taken a walk in elephant country has seen the dead wood and dung lying around—an adult African elephant defecates 20–30 times a day, releasing up to 100 boluses of 1–2 kg day-1, summing up to 150 kg fresh dung or 30 kg dry weight dung day−1. This is a significant input often incorporated into the topsoil by dung beetles and termites. 

More open habitats might also encourage C4 grasses adapted to warm or hot seasonal conditions under moist or dry environments. The researchers detected changes in wood-derived C increased in the inner canopy and bare soil habitats with rising levels of elephant densities. In contrast, the woody vegetation patches already had elevated levels of wood-derived C.

The conclusion from this soil carbon accumulation was that tree toppling and broken parts of trees do not necessarily lead to net carbon losses from the savanna ecosystem because much of this C was transferred into the soil.

elephant mother and calf in mopane woodland, Botswana
Source : Alloporus 

Elephants and the trees they knock over on the Okavango delta, Botswana.


Pinning the tail on the elephant

Comparisons of a ‘shift to high elephant numbers’ was not constrained in time. There was no evidence to determine if the shift was recent, repeated regularly over time, or the shift’s duration. All these parameters must be in sync with the soil carbon dynamics to attribute any elephant effect. And we know that nutrient-poor soils in predominantly dry environments with pulsed rainfall have short and long-cycle carbon changes.

So there are doubts about these conclusions given the design of the research.

Let’s ignore the design limitations in this research and see what the authors thought about the results with this quote

Our results should be of major interest for future biodiversity conservation measures including (trophic) rewilding…  Aboveground carbon removal by wild herbivores presents a trade-off between climate mitigation through increased carbon storage and addressing the biodiversity crisis through rewilding. But, as current data show, restoring elephant densities does not necessarily lead to a pronounced negative carbon footprint. A major fraction of woody biomass C is merely redistributed into soil during decomposition. Including soil into ecosystem assessment could therefore help to better align climate mitigation measures with those of biodiversity conservation, thereby linking two large scientific directions with the aim of potentially reducing joint coordination efforts for reaching the sustainable development goals.

Sandhage-Hofmann, A., Linstädter, A., Kindermann, L., Angombe, S., & Amelung, W. (2021). Conservation with elevated elephant densities sequesters carbon in soils despite losses of woody biomass. Global Change Biology, 27(19), 4601-4614.

What sustainably FED suggests

Back in the mid-1980s, I was privileged to spend two years working at the University of Zimbabwe. It was a wild time, a few years from independence and before the economy tanked.

Early on in the adventure, I took a trip to the Zambezi valley, and with the sun sinking below the mopane trees, I was standing on the sandy soil close enough to a female elephant to hear her massive molars masticate the dry grass. 

Elephants are majestic when you stand with them. 

It was an unforgettable experience; even now, I can smell the pungent savanna and feel its majesty. The elephant just kept on eating, unperturbed.

Just a moment showed me that elephants are vegetation hoovers and consummate habitat modifiers, but they have always been. They are as much the savanna as the mopane trees and the thorny acacias.

They have little to do with carbon emissions and everything to do with millions of years of coevolution.

Instead of accepting it as it is, researchers are prompted to do science on natural systems because humans have stuffed everything up, and there might be a publication with ‘sequesters carbon’ in the title.

It would be better if we were more objective than this.


Science source

Sandhage-Hofmann, A., Linstädter, A., Kindermann, L., Angombe, S., & Amelung, W. (2021). Conservation with elevated elephant densities sequesters carbon in soils despite losses of woody biomass. Global Change Biology, 27(19), 4601-4614.


Hero image from photo by elCarito on Unsplash

Mark

Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

Add comment

Subscribe to our explainer series

* indicates required

Most discussed