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IUCN Red List Threat Assessments for Priority Tree Species

Determining the threat of extinction for tree species globally.

IUCN Red List Threat Assessments for Priority Tree Species


The IUCN Red List

In a rapidly changing world, it is crucial for conservationists, policy makers, and communities to have accurate, up-to-date information on the threats that face global plant diversity, since all life depends on plants. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is the globally recognized and standardized system for assessing the extinction risk of the world’s plant, animal, and fungal species. Since 2015, The Morton Arboretum has worked in partnership with IUCN, the IUCN SSC Global Tree Specialist Group, and Botanic Gardens Conservation International (BGCI) to assess, review, contribute to, and facilitate IUCN Red List threat assessments for priority tree species globally. 



  • Improve knowledge about threats that trees currently face globally;
  • Prioritize species for scientifically informed conservation action and policy;
  • Build capacity for conservation in biodiversity-rich regions around the world;
  • Strengthen the global network of conservation practitioners working to save trees from extinction.


The Process

Research: Gather scientific literature on target tree species, consult with experts, determine the most serious threats.

Assess: Use this information to assess the species for threat status based on the categories and criteria set by the IUCN.

Review: Invite an expert on the species to review the assessment for accuracy.

Submit: Submit assessment to IUCN for approval.

Publish: The IUCN publishes all approved assessments on their website.


Our Projects

  • Oaks: the genus Quercus In 2020, The Morton Arboretum completed Red List assessments for all of the world’s estimated 430 oak species (genus Quercus), in partnership with Botanic Gardens Conservation International (BGCI), the IUCN SSC Global Tree Specialist Group, and dozens of oak experts in Asia, Central America, Europe, and Mexico. A detailed report that synthesizes the global patterns of oak diversity and threatsand provides recommendations for conservationcan be read here: The Red List of Oaks (2020). For a more detailed analysis of the 91 native species of US oaks, see our 2017 publication: The Red List of US Oaks. The Red List threat assessments for every oak species can be found here. 
  • Native trees of the United States Working in partnership with NatureServe and Botanic Gardens Conservation International-US, The Morton Arboretum is compiling the first comprehensive list of the nearly 850 native tree species of the continental United States and is completing threat assessments for all of the tree species (about 400) that have not been evaluated for the Red List. 
  • The Fagaceae family The Fagaceae family includes around 1,000 species of globally important trees, such as the oaks (genus Quercus), beeches (genus Fagus), and chestnuts (genus Castanea). The Morton Arboretum is collaborating with Joeri S. Strijk (Alliance for Conservation Tree Genomics) to complete Red List assessments for all Fagaceae species of the world. Because Asia hosts the largest number of Fagaceae species, partners in this region are critical to the success of this project, ensuring that the species in most urgent need of conservation are identified. 
  • Ashes: the genus Fraxinus In 2017, The Morton Arboretum, IUCN SSC Global Tree Specialist Group, and Jeanne Romero-Severson (University of Notre Dame) completed assessments for the eastern US species of ash (genus Fraxinus). The team determined that, faced with the devastating impacts of the rapidly spreading invasive beetle, emerald ash borer (EAB), five species of native ash are critically endangered. In 2018, The Red List of Fraxinus was published, summarizing global patterns of diversity and threat for ashes. The United States has the highest concentration of threatened ash species.  


PDF iconThe Red List of Oaks (2020)

PDF iconThe Red List of Fraxinus (2018)

PDF iconThe Red List of US Oaks (2017)

    Funding sources

    Botanic Gardens Conservation International–US
    United States Botanic Garden

    USDA Forest Service


    Project status