Facing threats from invasive pests, climate change and habitat loss, up to 135 tree species—about one-sixth of those found in the continental U.S.—could be lost forever. Only eight of them currently enjoy federal protection. In a study published in the journal Plants People Planet that focused on 881 tree species native to the continental United States, researchers evaluated how endangered each tree is according to criteria developed by NatureServe and the International Union for Conservation of Nature. Murphy Westwood, vice president of science and conservation at the Morton Arboretum, in Lisle, Illinois, and lead author of the study, says, “That’s a lot of species.”

Noah Greenwald, endangered species director for the Tucson-based Center for Biological Diversity, notes that trees play foundational roles in ecosystems. When they die out, whole swaths of biodiversity can perish along with them, as well as the ecosystem services that humans depend on. He says, “Trees and forests are really the bench that we all rest on.”

Leigh Greenwood, a forest specialist at the Nature Conservancy, believes that preventing new tree killers from reaching the U.S. is critical, saying, “This paper is very much a call to action to bolster the prevention strategies that we have against the entry of new forest pests and pathogens.”