News Published: 16 October 2026

Over the last 11 years, the Global Tree Assessment (GTA), generously funded by Fondation Franklinia, has been working to comprehensive list of the world’s tree species and assess their extinction risk. As of 2024, trees became a comprehensively assessed group on the IUCN Red List, and an assessment for all 58,000 species is in sight. However, as time passes, the status of a species’ population, distribution, threats, and the conservation measures in place can change. The IUCN Red List therefore recommends that assessments be updated every 5-10 years. A large part of the GTA effort is now focused on reassessing these tree species, to keep their information up to date.

There are some key differences with reassessing a species compared to the first assessment, such as checking for taxonomic changes, and adding in the reason for change if the category changes. The GTA and Global Tree Specialist Group (GTSG) have already created IUCN Red List Reassessment Guidelines for trees, and within the last year some key groups have been reassessed.

In 2025, 42 species of Sorbus, the UK’s most threatened trees, were reassessed. There have also been reassessments for many species which hadn’t been evaluated since 2018. These reassessments now include information from old 1998 assessments, which were under names now considered synonyms, updating taxonomy and distribution data. These species include Terminalia triflora, Timonius flavescens, and Macrocnemum roseum, which will be published on the IUCN Red List in the 2026-2 update. Plant taxonomy is ever changing, so keeping the IUCN Red List up to date with information from new revisions is important.

A tropical tree genus from the Annonaceae family, Guatteria, has also been reassessed. Using a new expert-curated Annonaceae dataset led to multiple previously Data Deficient species being reassessed in another category, providing new information for conservation efforts. This dataset also provided more accurate distribution data for threatened species, such as Guatteria jefensis (Endangered). New data from the GTA team collaborating with the Flora Uruguay project has also allowed Least Concern South American species to have their distributions updated regarding their presence in Uruguay, allowing any national conservation efforts to be streamlined.

Some reassessments on the horizon include key tree species found across the Indomalaya biogeographic realm. Recent surveys have been completed by GTA partners in the riparian forests on the Mekong floodplain in Cambodia. This data will be integrated into the reassessments and will provide a high-resolution distribution for this area which is severely threatened by energy production and agriculture.

Without reassessments, the IUCN Red List becomes a static resource that doesn’t evolve as biodiversity data improves and would no longer catalyse conservation as it aims to. Reassessments are a priority for the GTA, and they will continue working with their partner network and the GTSG to keep trees as comprehensively assessed.