Large herbivores can keep invasive plants at bay in India: Study

Large herbivores can protect local nature by eating and trampling on biodiversity-threatening invasive plant species, according to a study conducted in India.

The researchers from the Wildlife Institute of India in Uttarakhand and Aarhus University in Denmark found that native plants have evolved in such a way that they can withstand brutal treatment from species of herbivores they have co-existed with for millennia, while invasive plants usually cannot.

The study, published in the journal Nature Ecology & Evolution, shows great potential for using large herbivores as a natural weapon to prevent invasive plants from out-competing native species.

Ninad Avinash Mungi, a postdoc at Aarhus University and the study's lead author, stresses that the size of grazing animals is not decisive in the fight against invasive species.

"You can easily use a mixture of large, medium and small herbivores. Deer, buffalo, cattle and horses work well together in rewilding projects, and together they can also target different invasive plant species. This also makes efforts more flexible and resilient," Mungi said.

The researchers gathered their data from the world's largest wildlife survey using camera traps, which takes place every four years, as well as India's extensive monitoring programme for plants. They noted that the results are also relevant for areas that do not have herbivores quite as large as those in India.

The study is based on what the researchers call mega-herbivores, i.e. animals weighing more than one tonne. In India, these are elephants, rhinos, wild water buffalo and Indian bison -- the largest and heaviest bovine in the world.

The team demonstrated a positive correlation between the number of mega-herbivores and the balance between native and invasive plant species: Where there are many mega-herbivores, there are also many native plants and fewer invasive plants.

In places where invasive species predominate, there are few or no mega-herbivores, except in some areas in India where invasive plant growth has become so tall and dense that mega-herbivores cannot get to it.

The UN has designated invasive species as one of the five most important threats to global biodiversity.

Invasive species are animals, plants and fungi that are introduced to areas to which they could not spread themselves, and that also harm native biodiversity.

These biological invasions also impose enormous costs on society, and more than USD 120 billion has been spent world-wide over the last 50 years on combating and controlling them, without any great success, the researchers said.

"It'd be a really good idea to carry out a large-scale European biodiversity survey like the one in India, which holds the Guinness World Record," Mungi added.