Protect native species, eliminate invasive trees and plant more that belong here. Those are three tips that conservationists would like to see followed to halt the decline or even extinction of tree species across the globe. Malin Rivers is head of conservation prioritization at the Botanic Gardens Conservation International, which runs the Global Tree Assessment project and produced a paper warning about the risk of massive tree extinction. In Quebec, Rivers and her team assessed 78 species of trees and found that four of them are at risk: White ash; Eastern hemlock; Butternut; and American elm. …Invasive trees are common in Quebec as well. The Norway Maple, for example, was introduced to North America in the 1700s. Tree Canada says the Norway Maple can prevent native tree seedlings (sugar maple and red oak) from establishing, and its leaves release toxins that affect soil fungi and microbes.