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IUCN Red List of Fraxinus Released; Offers Comprehensive Look at Conservation Status of World’s Ash Trees

Cover photo of ash report featuring a shot of an ash tree's canopy
February 7, 2018

The Morton Arboretum, in collaboration with Botanic Gardens Conservation International (BGCI) and the International Union for Conservation of Nature (IUCN) Global Tree Specialist Group, today unveiled The Red List of Fraxinus, the first-ever comprehensive look at the conservation status of the world’s ash trees. Researchers at The Morton Arboretum helped to assess 53 species of ash for the report, including 11 species threatened with extinction in the wild.

Ash (Fraxinus) are known for their horticultural significance and the ecosystem benefits they provide in temperate woodlands around the world, but these iconic trees face many challenges. While the report reveals that the majority of the world’s ash species (79 percent) are not yet threatened with extinction in the wild, 11 ash species are now at high risk of being lost. Of that group, Arboretum researchers found that five of six of the United States’ most prominent ash species are now listed as Critically Endangered—only one step away from extinction—due to devastation from the invasive emerald ash borer (EAB) beetle.

Originally from Asia, EAB has devastated previously abundant and dominant ash tree populations such as those of Fraxinus americana and F. nigra. Since its arrival in the US in the late 1990s on infested shipping pallets, EAB has decimated more than 100 million ash trees in 31 states. The spread of the pest shows no sign of stopping, with the potential to decimate more than 8 billion ash trees as it makes its way across the country, eliminating the important ecosystem benefits these trees provide. There is currently no treatment or remediation available for trees in the wild.

Historically, ash trees were once a very popular horticultural species, planted by millions along streets and in gardens. But today, a look at the Chicago region reveals that one of every five street trees is expected to be lost to EAB—dramatically altering the region’s landscape. The Morton Arboretum is currently undertaking research to understand the spread and impact of the emerald ash borer beetle. 

The Red List, formally the IUCN Red List of Threatened Species™, is widely recognized as the most comprehensive, objective global approach for evaluating the conservation status of plant and animal species.