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.

Island biodiversity is particularly vulnerable, in part because those species often have small populations that exist nowhere else, and island trees accounted for the highest proportion of trees threatened with extinction. In Madagascar, for example, numerous species of rosewoods and ebonies are threatened. In Borneo, 99 species in the family of trees called Dipterocarpaceae are imperiled. In Cuba, fewer than 75 mature individuals of the red-flowered Harpalyce macrocarpa, known in Spanish as maiden’s blood, remain.

Around the world, the biggest threats to trees are agriculture and logging, followed by urbanization, said Emily Beech, head of conservation prioritization at Botanic Gardens Conservation International, a nonprofit group that led the research now included in the Red List…