Extinctions of large animals — a fate that could soon befall elephants and rhinoceros — have a cascade effect on local ecosystems, including Northern California, where many smaller animals and plants died off after mammoths were wiped out, a team of scientists has discovered.

The size of elephants, wildebeest and other big plant-eaters not only makes them impressive and fascinating, but vital to the many species, including flora and fauna, that live with and depend on them, according to a joint report by UC Berkeley, Stanford University, California State University Sacramento and the University of Chile.

“Ecological studies have shown that if you pull out a top predator or a key herbivore today, you get dramatic change in the ecosystem,” said Anthony Barnosky, a UC Berkeley professor of integrative biology and the study leader. “Our study makes it clear that in the past, such changes have lasted for thousands of years. These extinctions really do permanently change the dynamics. You can’t go back.”

The study, which was released Monday and is to be published in the journal Proceedings of the National Academy of Sciences, looked at past extinctions in North and South America since humans arrived about 15,000 years ago.

The scientists found that the number and diversity of small animals and vegetation decreased all along the Pacific Northwest, as well as the western and northeastern United States, after mammoth and mastodon extinctions. In Alaska and the Yukon, what was once a mix of forest and grassland became mostly tundra after the loss of mammoths, native horses and other large animals, according to the study.