Scientists from Oregon State University said the loss of major predators in Northern Hemisphere forest ecosystems has allowed game animal populations to explode, hampering the growth of young trees and reducing biodiversity.
This also contributes to deforestation and results in less carbon sequestration, a potential concern with climate change, they said.
"These issues do not just affect the United States and a few national parks," William Ripple, a professor of forestry and lead author of the study, said in an OSU release.
"The data from Canada, Alaska, the Yukon, Northern Europe and Asia are all showing similar results. There's consistent evidence that large predators help keep populations of large herbivores in check, with positive effects on ecosystem health."
Numbers of mammalian herbivores were six times greater in areas without wolves compared to those in which wolves were present, the researchers said.
"In systems where large predators remain, they appear to have a major role in sustaining the diversity and productivity of native plant communities, thus maintaining healthy ecosystems," study co-author Robert Beschta said.
"When the role of major predators is more fully appreciated, it may allow managers to reconsider some of their assumptions about the management of wildlife."