Mariska te Beest on why grasslands are essential to the climate discussion

Although grasslands are often assumed to be degraded ecosystems of little importance, in many areas they are ancient and brimming with diverse forms of life. So why are they largely forgotten, and why is it essential that they’re given the same attention as forests? 

Mariska te Beest is an assistant professor at the Copernicus Institute of Sustainable Development at Utrecht University, where she focuses on plant communities, global change and the ongoing biodiversity crisis. In this interview she explains how our poor understanding of grassland processes means that many proposed solutions to climate change don’t consider their potentially devastating impacts on grassland ecosystems, and details what this will mean for the planet’s capacity to adapt to a changing climate.

Photo: Charlotte Ballard

Most of your work is on grasslands and savannas in Africa. Why are they important in how we understand and research climate change? 

If I tell you to think about an ecosystem that plays an important role in regulating climate, grasslands won’t be the first to come to mind. You’ll probably think about forests, and maybe how we should be planting trees to combat climate change. This has been in the news a lot recently. But grasslands also play an important role, and for a number of reasons are largely left out of the discussion.

In my work I try to understand how grasslands influence and are influenced by the climate to better understand the impacts of biodiversity loss or changes in land use like tree planting, and especially under a changing climate.

And is this why you are strongly advocating more international research focus grasslands?

Grassland-savanna-forest mosaics in Hluhluwe-iMfolozi Park, South Africa. Photo: Mariska te Beest

Yes. There are two main reasons. Firstly, it’s widely understood that diverse ecosystems are able to take in and store more carbon dioxide from the atmosphere. Think about the importance of tropical rainforests for storing carbon. The natural grasslands of Africa are also very old ecosystems that are extremely diverse, and can be compared to tropical rainforests in their antiquity and diversity. Yet, they are often not recognised as such.

The problem is that it is difficult to distinguish natural ancient systems from less diverse secondary systems without performing field surveys. Most of our current knowledge on grassland-climate interactions is derived from secondary grasslands, or even agricultural grasslands. This means that the sequestration potential assigned to grasslands  - the ability of grasses to take in and store carbon dioxide from the atmosphere - is much lower than it probably is.

And what’s the other reason?

The influence of the so-called albedo effect - the amount of radiation reflected from the land’s surface. Working on grass-shrub transitions in the northern tundra, I found that due to differences in colour and vegetation height, grass is better at reflecting the sun’s radiation than shrubs. In other words, in the tundra at least, grass has a greater cooling effect on the earth - which is important when thinking about climate change.

Afromontane grasslands in the Drakensberg Mountains, South Africa. Photo: Mariska te Beest

We know this effect is less important in tropical systems due to evaporative cooling and cloud cover. But what about mid-latitude grassland systems south of the equator? The literature says very little, which makes it look like the albedo effect plays no role in this region. I see it from the other side - for every ten forest scientists there is one grassland scientist. We just don’t understand grasslands!

For every ten forest scientists there is one grassland scientist. We just don’t understand grasslands!

What are the consequences of not understanding grasslands?

Many grassland processes are poorly represented in climate models, and subsequently many proposed solutions to climate change don’t consider the potentially devastating harm they will do to grasslands.

A good example of this is the highly publicised push to plant billions of trees to mitigate climate change, with African savannas and grasslands flagged as ideal locations due to their climatic suitability. Afforestation is often pushed through with non-native species like pines and eucalyptus. This will decrease biodiversity, reduce the capacity to adapt to climate change and reduce the long-term sequestration potential of the land. And if what’s happening in the tundra is any indicator, there may also be a warming effect via albedo.

Losing large herbivores could see cascading effects on the climate.

So what kinds of research have you been doing on grasslands? 

One of the things I’ve looked at is how herbivores - animals that eat plants - change the vegetation and how this influences the climate, as was published in a recent review. This is one reason why it is extremely important to conserve the often endangered herbivores found in Sub-Saharan Africa! They are part of a complex and delicate ecosystem. If we lose them we could see cascading effects on the climate.

Passive warming chambers set-up in the long-term Brotherton fire experiment at Cathedral Peak, South Africa. Photo: Mariska te Beest

At the moment you have some novel experiments going on in South Africa. Can you tell us about them?

Within a long-term ecological research site in the Drakensberg Mountains I am among the first researchers in Africa to set up passive warming chambers that simulate climate change. I am studying the interactive effect of increasing temperatures and fire on grasslands. 

Fires in these grasslands are naturally occuring, but increasing temperature will change the frequency and intensity of fire, which of course influences which species can grow there. As I just mentioned, different types of vegetation have different potentials for storing carbon and reflecting radiation, but in ways we still poorly understand. I’m trying to understand how the changes to fire behaviour and vegetation composition that we will see under climate change will end up further changing the climate.

Further reading

Cromsigt, J. P., te Beest, M., Kerley, G. I., Landman, M., le Roux, E., & Smith, F. A. (2018). Trophic rewilding as a climate change mitigation strategy? Philosophical Transactions of the Royal Society B: Biological Sciences, 373(1761), 20170440.

te Beest M., Sitters J., Ménard C. B., & Olofsson J. (2016). Reindeer grazing reduces shrub abundance and increases summer albedo in Arctic tundra. Environmental Research Letters, 11(12), 125013.