GENEVA (AP) — An international conservation group is warning that more than half of the trees in Europe that exist nowhere else in the world are threatened with extinction.

The International Union for the Conservation of Nature says in their latest assessment of Europe's biodiversity that 58% of the 454 trees species native to the continent are threatened, and 15% are "critically endangered" — one step away from extinction.

IUCN, a 71-year-old organization perhaps best known for its "Red List" classification of threatened species, said that "invasive and problematic" species are the top threat to European trees. It cited urban development and "unsustainable logging" as other factors.

IUCN Europe director Luc Bas said "human-led activities" were resulting in population declines of important tree species. More than 150 experts contributed to the project.