Losing large plant-eating mammals can have a dramatic and long-term impact on ecosystems, a study has found.

Scientists looked into the past to learn lessons about what might happen if nothing is done to save threatened and vulnerable species such as elephants, rhino and buffalo.

They discovered that extinctions of mammoths, mastodons, wild horses and other large animals drastically altered the landscapes they formerly lived in, as well as species diversity.

Many types of “megafauna” vanished from the Americas after the arrival of humans some 15,000 years ago.

Mammoths, mastodons, horses, elk and moose all disappeared from North America along with carnivores such as the sabre toothed cat and dire wolf.

In South America, llamas, vicuna camels, panthers, giant sloths and mastodon relatives called gomphotheres went the same way.

Experts believe a combination of hunting by humans and climate change was to blame.

Vegetation changes linked to the extinctions in three areas of north America led to denser forests and an increase in the frequency of fires, as well as fewer species of small mammals, the scientists found.

Elizabeth Hadly, from Stanford University in the US, said: “The take-home message from western North America is that grazing and browsing by extinct megafauna such as proboscideans favoured open-habitat mosaics.

“When these ecosystem engineers became extinct at the end of the Pleistocene, denser deciduous forests established. The loss of the mosaic Pleistocene habitats in western North America led to a decrease in the diversity of small mammals.”

Large browsers such as mammoths and elephants eat small trees and shrubs and also trample and churn the soil, said the researchers writing in the journal Proceedings of the National Academy of Sciences.

Other large herbivores such as bison and moose kept shrubs in check and altered soil structure and nutrients.

Co-author Charles Marshall, director of the University of California Museum of Palaeontology, said: “You see the impact of defaunation today in Africa, where the removal of elephant populations has led to these shrubby, scraggly acacias filling the savanna landscape.

“Africa today, with its elephant populations, seems to fit the model of North America with its mammoths and mastodons.”