Forum
Red List assessment of widespread and long-lived species
RODERIC K J. F ENS HAM
Abstract The use of criterionAof the IUCN Red List to cat- egorize species as threatened that have undergone recent decline can lead to the listing of relatively common and widespread species. Loss of habitat through deforestation is a common cause of decline throughout much of the world but is often not incorporated into assessments be- cause of uncertainty about the magnitude of change. A re- cent assessment of eucalypt species in Australia subject to deforestation provides a method for assessment under cri- terion A and has implications for listing of long-lived, wide- spread species affected by deforestation. Scenarios for two widespread eucalypt species subject to extensive deforesta- tion are used to demonstrate how the threat status of a species may be recategorized in a lower threat category as declines resulting from a threatening process are mitigated. I argue that criterion A indicates an appropriate assessment of extinction risk and I provide a simple function based on predicted diminishment of the population decline to iden- tify when a species could be disqualified from a threat cat- egory under subcriterion A2 (past decline).
Keywords Australia, deforestation, eucalypts, habitat loss, Red List, threatened species
Introduction
to assess a trajectory of population decline regardless of population size or geographical extent. It has been argued that this criterion is justified by the numerous examples of common species becoming extinct (Butchart et al., 2010; Lindenmayer et al., 2011), but is not readily applied because of a perceived difficulty in generating unbiased estimates of decline (Mace et al., 2008; Le Breton et al., 2019). Habitat loss is a common measure of decline and with adequate data on timing and extent can be used to estimate
T RODERICK J. FENSHAM* (Corresponding author,
orcid.org/0000-0003-3658-
5867) Department of Science, Information Technology and Innovation, Queensland Herbarium, Brisbane Botanic Gardens, Mt Coot-tha Road, Toowong, Queensland, 4066, Australia. E-mail
rod.fensham@qld.gov.au
*Also at: School of Biological Sciences, University of Queensland, St Lucia, Australia
Received 25 March 2020. Revision requested 1 June 2020. Accepted 12 November 2020. First published online 19 August 2021.
he IUCN Red List procedures for identifying the threat status of species include criterion A, which is designed
population decline under criterion A. This process is gener- ally not applicable to criterion A1, which assesses reversible decline, but may be relevant under the other criteria that as- sess irreversible decline in the past (A2), future (A3) or both the past and future (A4). These criteria identify threatened species based on ‘population reduction observed, estimated, inferred, or suspected in the past [and/or future] where the causes of reduction may not have ceased or may not be understood or may not be reversible’ (Annex 4, IUCN, 2012). SubcriteriaA2,A3 andA4 require population declines of 30–50%over a three-generation period (for species with a generation length .3 years) to be categorized as Vulnerable, 50–80% to be categorized as Endangered and .80%tobe categorized as Critically Endangered. The criteria can result in relatively common, long-lived species qualifying as threat- ened, and this apparently perverse outcome has not been lost on the architects of the IUCN Red List procedure; ‘on the basis of decline rates only and with no threshold popu- lation sizes, criterion A has the potential to force the inclu- sion of some extremely abundant populations into lists of threatened species. Criterion A has therefore been contro- versial, especially for widespread species with historical de- clines that are believed to have stabilized’ (Mace et al., 2008, p. 1,437; IUCN Standards and Petitions Committee, 2019, Section 5.4). Subcriteria A3 and A4 are particularly contro- versial because they require estimates of future decline, with obvious difficulties of determination. A recent continental assessment of eucalypts resulted
in 134 of the 822 Australian eucalypt species (species of Angophora, Corymbia and Eucalyptus) being categorized as threatened under subcriterion A2 (Fensham et al., 2020). The eucalypts eligible under this criterion have undergone population declines as a result of deforestation for cropping, pasture and urbanization. Consistent with the IUCN Guidelines (IUCN Standards and Petitions Committee, 2019), these land-use conversions are ‘under- stood’, have ‘ceased’ in some areas, but are not ‘reversible’, especially over large areas, such as cities and core food producing regions. Population declines as a result of these land-use changes were assumed to have commenced with the broadscale expansion of agriculture and pastoralism in Australia from 1810, coinciding with three generations (c. 210 years) of these long-lived trees. Because eucalypts are the dominant tree in many Australian ecosystems, de- forestation was considered a proxy for a ‘decline in habitat quality’ under subcriterion A2b after the application of
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Oryx, 2022, 56(4), 581–586 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605320001325
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