Animating the Carbon Cycle – Oswald SchmitzJune 2021

Please note: This video was one of a number of presentations from the webinar, and in order to allow each video to be watched individually, they all have the same 30 second introduction to provide the required context. If you have already seen this introduction in another video from the webinar, please skip to 0:31.

Read the video transcript:

The subject of the webinar today is animating the carbon cycle. It really explores the very important link between biodiversity and climate. And the goal of this webinar is to launch a new global initiative to launch nature and climate, and set the first global target for restoration and rewilding to address this accelerating climate breakdown.

Our next presenter, Oswald Schmitz. And Oswald is the Oastler professor of population and community ecology at the Yale School of Environment. Oswald is really known as the father of animating the carbon cycle because of his research, his interests, and how species and interactions and ecosystems provide different services. And most recently on climate. His book, the New Rethinking of Science for the Anthropocene, really encapsulate much of his thinking about biodiversity and ecosystems. And it was really heavily inspired by Aldrich Leopold, and it makes ecological science accessible, which I think is so very important. Oswald, thanks for joining us. Please. Okay.

Thank you very much, Vance. I’m going to try and convince everybody today that we should really think about animals as another solution in terms of driving carbon into ecosystems. It’s requiring a change in mindset. So, before I get into the case examples, I just want to give you some background where the troubles are right now in both the scientific community and people’s perception of nature. So one of the classic rules in ecology, for example, is if you were to take all the live biomass available in ecosystems and assign them to different trophic groups, like plants, for example, or herbivores or carnivores, what you would find is that as you go up the trophic chain, the amount of biomass held in the trophic level decreases by orders of magnitude as you move up that trophic chain. This is something classic that you learn when you take an introductory ecology course. And if you were to then do that exercise over the entire planet and then account for the carbon that’s actually contained in all of that biomass, what you would find is that plants by far have the most biomass carbon contained in them.

The next most biomass carbon is actually contained in things that we don’t see. Much of that is the fungi, the bacteria, the protists and viruses and intestinal ecosystems. A lot of these organisms are in the soil. Animals, as you can see, only account for a very, very tiny fraction of all of the carbon held in biomass globally. And if we want to drill down into animals a little more, what you find is most of that carbon is actually held in the tiny things on the planet, arthropods, which tend to be very highly abundant, but they’re not necessarily always the focus of conservation. Wild mammals, those are the kinds of charismatic species that we try to rewild, contain very, very, very tiny amounts of carbon in their biomass.

What this has done is created this reigning view that animals, especially large vertebrates, because they have very low biomass carbon, they’re going to be insignificant in terms of their impact in the global carbon budget. And so when you see the carbon budget constructed, where people are accounting for the pools and the exchanges between the atmosphere and the land and the ocean, what you find is certainly vegetation. Plant biomass is accounted for, but animals are nowhere to be seen in this budget.

The problem with this view, though, is it’s a very static representation of where the carbon is. And certainly animals and plants are stacked in a trophic pyramid, of course, but it ignores the fact that these animals are interdependent with each other in food webs. So, for example, predators consume their herbivore prey. The herbivore prey then consumes grasses. And this also modulates all of the interactions and densities of animals and the biomass that’s in the system. And so, there’s a certain amount of dynamism that’s holding this system together, ergo animating, and ergo animating the carbon cycle. If you’re looking at carbon dynamics now, how do animals do that? Well, they do it simply by walking and trampling.

In compacting soils, they crush vegetation, they eat vegetation. And so the available vegetation becomes less able to take up the atmospheric carbon dioxide into its tissue by trampling. They can also change and warm the soil conditions. And if you warm the soil, microbes become decomposers. They decompose the organic matter that’s on the soil and releases carbon dioxide to the atmosphere. Potentially, animal bodies also decompose and contribute carbon to the soil. And so there are a bunch of ways that animals can modulate these kinds of carbon dynamics. And it happens both in terrestrial and marine and aquatic realms. So if we look at these bow ties, these are all the different places in an ecosystem where animals can modulate the exchange of CO2 between the atmosphere and those bigger pools, like the plant based pool and the carbon based pool in the soil, or the sediment in the ocean.

Here’s a meta-analysis where scientists have actually started to measure the effects of animals by basically excluding them from ecosystems plots and ecosystems, and measuring the carbon uptake strength of the ecosystem relative to cases where animals are present. And what you find is that in certain cases, you might, if you don’t account for animals’ overestimate, that is, you get a reduction because of the animals, you overestimate the carbon budget, or you might actually underestimate the carbon budget. And when you do the calculations, those over or underestimates can be between 50 and 75%. That’s huge. That’s huge potential that we aren’t considering right now. Give you some case examples.

Here’s one success story of recovery of wildebeest and why rewilding is really important to consider. So many of you might know, historically, prior to 1960, there was a rinderpest outbreak in the Serengeti region of Africa because of livestock agriculture that spilled over. The disease spilled over into wildebeest. Basically, the disease reduced the densities of these grazers from their historical level of 1.2 million down to about 300,000 animals. And so the disease actually had a negative effect on the carbon cycle. How has that happened? Because when the animals were low in abundance, there was a whole slew of untapped vegetation. This was fuel. It dried out and burned. And every year, much of the Serengeti burned up because of wildfires. So, the Serengeti was actually historically, a net source of carbon. With the eradication of rinderpest, the wildfire levels went down. Populations rose to now back to their historical levels, about 1.2 million animals. That transformed the ecosystem entirely, where we now have the Serengeti being a net carbon sink. And basically, the disease eradication benefited the grazers. The grazers are eating the vegetation and releasing that carbon as organic matter in their dung, which is then taken up by beetles and other insects to incorporate that in the soil. The reduction in fire has also led to the proliferation of trees that also now take up carbon in the savannah ecosystem.

Another case example is in boreal forest ecosystems, moose tend to be quite damaging on vegetation. Vegetation, obviously, because they’re herbivores. Predators like wolves control the moose abundances. And so wolves have an indirect beneficial effect to the forest by reducing the amount of moose herbivory going on. This is what we call a trophic cascade. And the thing is, though, wolves also have a beneficial effect on soil carbon, because all of the uneaten vegetation eventually senesces, and then the litter falls to the soil surface because it’s a cool surface. There’s not a lot of microbial decomposition going on. And so organic matter builds up in the boreal forest, and that’s a good, huge repository of soil carbon. So, when moose are abundant and wolves aren’t around, you don’t get much soil carbon storage in the ecosystem, and you actually get a lot more released to the atmosphere. When wolves can control moose abundances, you get luxuriant force and a lot of carbon driven into the soil. And if you do, the comparison between what happens when wolves are absent versus when they’re present at their natural densities, you can increase the amount of carbon taken up in that ecosystem by 32%.

Now, here’s a case example of some interesting potential. This is based on a modelling study for a potential success story in the Congo basin area of Africa, central Africa. In the absence of elephants, you get understories of forests that are quite overgrown with understory shrub vegetation. But when elephants are present, they actually thin out the forest. And you might think originally, well, this doesn’t make sense. But it does if you understand how the feeding linkages work. So, with elephants, the elephants clear out the understory, eating all of the understory vegetation. This reduces the competition with the overstory trees. And so the overstory trees are better able to get the nutrients out of the soil, build up their biomass and take up more carbon out of the atmosphere. And they can also grow. The wood density tends to be higher also, which means the carbon density is higher in these trees. So elephants have an indirect beneficial effect to canopy trees.

The modelling suggests that there’s a sweet spot. If you can restore the densities up to this middle level, you could actually increase carbon uptake in the Congo basin by 50% relative to no animal controls. Obviously, if they get too high, then they become damaging again. But what does this mean in terms of the global carbon budget? Well, restoration of wildebeest populations means that now we can take up 0.008 gigatons of carbon annually, which is equivalent to East Africa’s annual carbon emissions from fossil fuel burning. Conserving wolves throughout their north American boreal forest range can add an additional 0.05 to 0.15 gigatons of carbon annually, which is the equivalent of Canada’s annual emissions from fossil fuel burning. And then restoring elephants to the historical Congo basin densities could end up benefiting you by having 1.7 gigatons of carbon taken up annually, which is the equivalent of Russia’s annual emissions from fossil fuel burning.

So here are three animal species that already can contribute to a portfolio of carbon uptake. Now, what about the little creatures, the arthropods? This is some work that we’ve been doing, resolving how food web interactions work here. So we’ve got sit and wait predators and active hunting predators. So different functional types of predators interacting with grasshopper herbivores that eat grassland vegetation. And the research we’ve done, we can show that depending on whether the place is dominated by sitting weight predators or active hunting predators, you get a different canopy along a gradient.

So, if you were to actually look at the soil carbon retention along this gradient, also from highly sit and wait predator dominated communities to highly active hunting predator dominated communities, you can boost soil carbon retention by 2.65 fold. That’s a huge amount. Just for comparison, we learned earlier from Carl’s presentation that people are trying to do amendments to land uses, right, convert forest to pasture, or pasture to secondary forest, or, in the case of the kinds of grasshopper systems, spider systems that I work in, crop to pasture. What people have tried to do is amend land uses to build soil carbon. And in some cases, it’s successful, other cases it might not be. Some of the intermediate levels are about 20% change. You can get up to 60%. We can superimpose the research that I did and look at what kind of benefit you can get by if you rebuild and rewild the food chains in that system. And it turns out that you can get up to 120% increase in soil carbon. Now, percentages are always misleading because they don’t really often represent the full magnitude of effects. So, I plotted the total amount of carbon, actually, that we’re dealing with. And so by rewilding these old fields, even with insects, you can get much more carbon out of the system or into the system than you can just by human interventions and soil amendments alone.

So, hopefully, I’ve convinced you that we need a change in mindset. Climate change is commonly viewed as causing collateral damage to biodiversity. And in the case of animals, they’re viewed as unwitting victims or passengers stuck on a ship that’s headed on an ill-fated voyage. The change in mindset actually sees animal species as important drivers of the climate ships, maybe even captains of the climate ship. And so biodiversity, rewilding and conservation may be an important part of a portfolio to help fix the climate change problem. And so what I would argue, it’s now high time to begin accounting for animals and their effects on regional and global carbon budgets in the carbon cycle analysis. Thank you very much for your time.