Study shows large herbivores keep invasive plants at bay

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The elephant makes its way to the golden-crowned beard (Verbesina encelioides), which originates from North America and is widespread in India, where it is a nuisance to arable farmers. The plant is also invaded in Denmark. Credit: Suryoday Singh Man

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The elephant makes its way to the golden-crowned beard (Verbesina encelioides), which originates from North America and is widespread in India, where it is a nuisance to arable farmers. The plant is also invaded in Denmark. Credit: Suryoday Singh Man

Large herbivores can protect local nature by eating and trampling invasive plant species that threaten biodiversity.

Where, you might object, is the logic in that, since the big animals eat and trample the native plants as well?

But this is not the case. Native plants have evolved so that they can withstand harsh treatment from the herbivorous species that have coexisted with them for thousands of years, whereas invasive plants usually cannot.

This is the conclusion of a new study conducted by Aarhus University and the Wildlife Institute of India, which has just been published in the scientific journal, ecology of nature and evolution. The study shows great potential for using large herbivores as a natural weapon to prevent invasive plants from competing with native species.

At least it worked in India, where the researchers collected their data. More specifically from the world’s largest wildlife survey using camera traps, which is conducted every four years, as well as India’s extensive vegetation monitoring programme.

However, the researchers point out that the findings also apply to regions without large herbivores such as those in India. More on this later.

huge herbivores

The study relies on what the researchers call megaherbivores, meaning animals weighing more than one ton. In India, these are elephants, rhinos, wild water buffaloes and Indian bison (the largest and heaviest cow in the world).


A herd of Indian gaur or bison “caught” by the camera trap. The gaur is the largest living bovine species in the world, and can weigh more than a ton. Source: AITE 2018, NTCA-WII, India

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A herd of Indian gaur or bison “caught” by the camera trap. The gaur is the largest living bovine species in the world, and can weigh more than a ton. Source: AITE 2018, NTCA-WII, India

The study demonstrates a positive relationship between the number of megaherbivores and the balance between native and invasive plant species: where there are many megaherbivores, there are also many native plants and fewer invasive plants.

vice versa. Where invasive species predominate, there are few or no large herbivores.

Except in some areas in India where the growth of invasive plants has become too tall and dense for the huge herbivores to reach.

Because the United Nations has ranked invasive species as one of the top five threats to global biodiversity.

Invasive species are animals, plants and fungi that are introduced to areas where they cannot spread, which also damages local biodiversity.

These biological invasions also impose huge costs on society, as more than US$120 billion has been spent worldwide over the past 50 years to combat and control them. without any great success.

Because their large size means they have to eat a lot. They are used to eating many different types of plants, even ones with less nutritional value, simply because they cannot be selective. Therefore, they are more likely to include unfamiliar plants in their diet.

The research team could have included smaller species of herbivores in the study, but their roles in local ecosystems are more complex. They are also on the list of tigers and leopards. Elephants etc. are not.


Horse and water buffalo at the Wildlife Restoration Project at Geddingcaste Moss near Aarhus, Denmark. Credit: Peter F. Gamelby, Aarhus University

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Horse and water buffalo at the Wildlife Restoration Project at Geddingcaste Moss near Aarhus, Denmark. Credit: Peter F. Gamelby, Aarhus University

Big is good, but not critical

Thus, we return to how the study is applied in countries that do not have elephants, rhinos, and so on.

You don’t need large herbivores to keep invasive plant species at bay—smaller and medium-sized species can have similar effects.

“Although some cattle released in reintroduction projects in Europe can grow to more than a ton, animals weighing less than a ton can have similar effects. And in Hungary, water buffalo has been shown to expel golden sticks. Giant invasive, a species that is also a problem in Denmark, says Professor Jens Christian Svenning of Aarhus University. Scottish Highland cows are also used in Denmark to maintain rosehip bushes, an Asian species often considered problematic in Danish nature.”

The lead author of the study, Nenad Avinash Monje, a postdoctoral researcher at Aarhus University, stresses that the size of grazing animals is not crucial to combating invasive species.

“You can easily use a mix of large, medium, and small herbivores. Deer, buffalo, cattle, and horses work well together in re-wildlife projects, and can also target different invasive plant species. This also makes efforts more agile and flexible.” He says.

“It would be a really good idea to do a large-scale European biodiversity survey like the one done in India, which entered the Guinness Book of Records. Europe has more money to invest in and restore nature.”

more information:
Nenad Avinash Monji et al., Large herbivores provide vital resistance against the dominance of alien plants, ecology of nature and evolution (2023). doi: 10.1038/s41559-023-02181-y

Journal information:
ecology of nature and evolution

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