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The IUCN Red List threat assessments for priority tree species

Completing threat assessments for key tree groups to prioritize species for conservation and enable policymakers and conservation practitioners to protect threatened trees. 

The IUCN Red List threat assessments for priority tree species


The collection of biological, ecological, and demographic information on threatened species is vital for planning effective conservation action. Our goal is to add all trees to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The IUCN Red List is the world’s most widely recognized objective system for assessing the extinction risk of plant and animal species based on past, present, and projected future threats. The Morton Arboretum’s Global Tree Conservation Program is an active partner in the Global Tree Assessment, which aims to assess the threat level of all of the world’s tree species by the year 2020.

Oaks: the genus Quercus
We are assessing all of the world's roughly 450 oak species (genus Quercus) to the IUCN Red List. In 2017 we completed assessments for all 91 native species of US oaks. In September, 2017 we published The Red List of US Oaks report, which details for the first time the distributions, population trends, and threats facing all 91 native oak species in the U.S. using the IUCN Red List assessment methodology, including updated versions of previously published assessments. Sixteen species of oaks, all in the southern and western US, are now classified as Critically Endangered, Endangered, or Vulnerable on the IUCN Red List, with another four species deemed Near Threatened. This report serves as a baseline for our current understanding of the state of the country’s oak trees and an authoritative guide for future conservation action. The individual species assessments for US oaks can be viewed on the IUCN Red List website here. This project has also supported the completion of assessments for European oaks in conjunction with BGCI. We are now focusing on assessing the rest of the oaks of the Americas (~180 species) and the oaks of Asia.

Ashes: the genus Fraxinus
In 2017, we completed assessments for the eastern US species of ash (genus Fraxinus) and in 2018, in partnership with BGCI, we published The Red List of Fraxinus. One of the accomplishments of this project has been the assessment of six North American ash species. Ash trees are a key component of North American forests. They provide habitat and food for birds, squirrels, and insects, and support important pollinator species such as butterflies and moths. Five of six prominent ash tree species in North America (Fraxinus americana, F. pennsylvanica, F. nigra, F. quadrangulata, and F. profunda) entered The IUCN Red List as Critically Endangered, with the sixth species (F. caroliniana) assessed as Endangered. These ash species are being decimated by the invasive emerald ash borer (EAB) beetle, Agrilus planipennis, which likely arrived in infested shipping pallets in Detroit in the late 1990’s and has since spread to over 30 US states and Canada. Three of the six ash species – Green ash (F. pennsylvanica), White ash (F. americana), and Black ash (F. nigra) are the most dominant ash species in North America and together comprise nearly nine billion trees in the forested lands of the contiguous United States. The individual species assessments can be viewed on the IUCN Red List website here.

Red List of US Trees
Currently, the tree flora of North America is poorly represented in the IUCN Red List, only 30% of native trees north of Mexico have been assessed on the Red List. In partnership with NatureServe and Botanic Gardens Conservation International-US, The Morton Arboretum is working to create a definitive list of the native tree species of continental North America (north of Mexico) and complete threat assessments for all of the tree species that have not been evaluated for the Red List. Despite having a thoroughly well studied native flora, the U.S. and Canada do not have a single, centralized database of native tree species. Several floras and checklists exist for the region, but they have varying degrees of agreement over taxonomic concepts and which taxa are considered trees. The checklist of tree species and the completed threat assessments will provide the critical knowledge needed to inform and coordinate tree conservation actions across an entire continent.

Funding Sources

Botanic Gardens Conservation International-US
United States Botanic Garden

Project Status