River Red Gum © Mayu Kataoka

Assessments completed for the world’s third largest tree genus

Posted on by Megan Barstow


Australian eucalypts include an astounding 822 species across three Genera (Eucalytpus, Corymbia and Angophora). This includes 723 species of Eucalytpus spp., the third largest tree genus in the world! In a recent collaboration between The National Environmental Science Program (NESP) Threatened Species Recovery Hub, The Australian Government and Botanic Gardens Australia and New Zealand the conservation status of all these species has been assessed and published on the IUCN Red List of Threatened Species. The results have also been published in the journal, Biological Conservation.

A nationally important group in trouble

Eucalypts define the entire Australian continental landscape and are culturally significant to its First Nations People. They occupy almost every habitat type in Australia and are often keystone species, supporting a huge wealth of biological diversity. However, 23% of eucalypt trees (193 species) have now been identified as threatened.

The major cause of decline in eucalypt populations has been the past conversion of habitat to crop and pasture land. In Western Australia, high species diversity and land use conversion to intensive agriculture overlap so that 54% of all threatened eucalypts are found there. The ‘wheat cropping’ region of the Wimmera district, straddling the Victoria-South Australia state border, also has many threatened species.

Eucalyptus pauciflora ssp. niphopila tree. Credit: Courtney Whitton/Australian Native Plant Enthusiasts

Eucalyptus pauciflora subspecies niphopila tree. Credit: Courtney Whitton/Australian Native Plant Enthusiasts

Interestingly, no species were identified as threatened in northern Australia where, despite high species diversity, there is less exposure to threats. The analysis also identified that wood harvesting was not a major threat to the group nor was too-frequent fires, due to the adaption of eucalypts to post-fire recovery.

The latest IUCN Red List assessments

Of the 193 species that are threatened, 16 are Critically Endangered, 58 species are Endangered and 119 species are Vulnerable. Data Deficient was assigned to 36 species due to taxonomic and geographic uncertainty. The remaining species were assessed as Least Concern, including all species of Corymbia and Angophora, which are often widespread and occur in unproductive landscapes.

The majority of these assessments (134) were based on past and irreversible population declines of at least 30% (criterion A2). These analysed how the Australian landscape has changed since European colonisation 210 years ago. This emphasized the importance of large historical declines and deforestation on the widespread and abundant species, which conservation policy and prioritisation often overlook in favour of ‘rare’ species or those with small geographic ranges.

An additional 22 species were considered threatened due to narrow geographic range (Criterion B) and 53 were assessed as threatened based on small population size (Criterion C and D).

The numberous stamens of a Eucalypt flower. Credit: Rose Mallee/ecologyweb (CC BY-NC-ND 2.0)

The numberous stamens of a Eucalypt flower. Credit: Rose Mallee/ecologyweb (CC BY-NC-ND 2.0)

This systematic assessment has identified an additional 147 Eucalypt species that need protection under Australian environmental law, which currently has 89. It also recommended to be downgraded to Near Threatened or Least Concern 32 of the already protected species.

This work contributes to the Global Tree Assessment, an initiative to have conservation assessments for all the world’s trees by the end of 2020. The full article in Biological Conservation can be found here and a summary of the results can be found here.

Written by Megan Barstow

Megan is the Red List Conservation Assistant at Botanic Gardens Conservation International (BGCI), working on the Global Trees Campaign contributing to IUCN Red Lists and communications. Previously she was involved with Global Trees Campaign as an intern working to complete GlobalTreeSearch.

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