More than a third of the world’s tree species are threatened with extinction, according to the first comprehensive assessment of trees by the world’s leading scientific authority on the status of species.

The findings, announced on Monday by the International Union for Conservation of Nature Red List, are especially sobering given the amount of life that trees sustain. Countless species of other plants, animals and fungi rely on forest ecosystems. Trees are also fundamental to regulating water, nutrients and planet-warming carbon.

“Trees are essential to support life on Earth through their vital role in ecosystems, and millions of people depend on them for their lives and livelihoods,” Grethel Aguilar, director general of the International Union for Conservation of Nature, said in a statement.

The tree assessment is considered comprehensive because it includes more than 80 percent of known tree species. In all, 38 percent were found to be at risk of extinction. More than a thousand experts from around the world contributed.