582 R. J. Fensham
conservative assumptions about the extent of habitat within the geographical range of a species (Fensham et al., 2020). Examples of the conservative assumptions were that species occurring in productive habitat (on fertile soils)were not as- sumed to have been preferentially cleared and no attempt was made to assess decline for species with a preference for unproductive habitat (e.g. rocky landscapes). For many countries, including Australia, land-use mapping is not ad- equate to represent deforestation as ‘an index of abundance appropriate to the taxon’. This is because land-use change often results in partial deforestation or the removal of a for- est canopy and does not necessarily result in population de- cline as young trees may persist despite clearing. However, amethod assessing intensive deforestation by interpretation of random points over satellite imagery using a ,5% tree cover cut-off for deforestation (Fig. 1) essentially represents decline as both ‘decline in habitat quality’ and ‘an index of abundance appropriate to the taxon’. Deforestation was not equated to a decline in extent of occurrence (EOO) or area of occupancy (AOO) because population fragments gener- ally persist as paddock trees, along roadsides and in numer- ous small nature reserves and other tenures. Species with restricted or diminished AOO and EOO become eligible under criterion B which is the criterion most commonly applied to determine threat status (Brummitt et al., 2015;Le Breton et al., 2019). Formost of the eucalypt species assessed as Threatened under subcriterion A2, their large AOO and EOO determined that they only rarely also qualified under criterion B (Fensham et al., 2020). All Australian state jurisdictions address native vegeta-
tion clearance in legislation, and clearing for agriculture has slowed substantially as a result (Evans, 2016). How- ever, clearing has not ceased altogether, and the signifi- cance of loopholes and enforcement of the laws is subject to political will (Maron et al., 2015). The threat status of euca- lypt species and many other Australian species is condition- al on the cessation of habitat clearance and the efficacy of the laws that regulate this management practice. Of the 134 eucalypt taxa assessed as threatened under subcriterion A2, the majority are widespread and common species that occur in arable parts of the landscape. Most of these species are not currently categorized as threatened under Australian federal and state legislations. Alongside the new recommendations for listing, 33 of the existing threatened species no longer meet the criteria to qualify as threatened, because of an absence of tangible threats (amongst other criteria; Fensham et al., 2020). Thus the previous list of 89 eucalypt species categorized as threatened under Australian legislation is substantially different from the 192 species (including 58 qualifying under subcriteria other than A2) categorized as threatened by the recent ana- lysis (Fensham et al., 2020). This apparently radical proposal to list common species exhibiting declines as threatened and lower the threat status of rare species that are not declining
met with considerable consternation in the workshop held for the eucalypt listing project in Brisbane on 30 November 2018 and generated debate about the application of criterion A. In Australia, listing has considerable gravity because threatened species are protected by both state and federal laws and there is a clear distinction in terms of protec- tion between species qualifying as Near Threatened and Vulnerable under Red List criteria. In general, the listing of a species under Australian law ensures that actions that have a significant impact on a population of a listed threat- ened species triggers assessment and may prohibit or require modification of the action (Commonwealth of Australia, 2013). Here I explore issues associated with subcriterion A2 by examining contrasting future hypothetical decline scenarios of two eucalypt species, both of which are wide- spread and qualify as Vulnerable based on the magnitude of historical population decline. I provide a simple function to determine the time in the future when the threat status of a threatened species will no longer apply as a result of changing magnitude of decline.
Future scenarios under criterion A
Salmon gum Eucalyptus salmonophloia and poplar box Eucalyptus populnea are dominant woodland trees that are extremely widespread and thus the signature species for vast landscapes in western and eastern Australia, respectively (Fig. 1). Both species have undergone estimated population declines of 36% in three generations (Fensham et al., 2020). Assuming a constant rate of habitat decline since 1810,and stable populations for the decades before European settle- ment, both species qualified for listing as threatened with a Vulnerable status in 1971 (Fig. 2).The logic of listing both spe- cies as threatened is apparent as the continuation of previous rates of declinewould render both species extinctwithin eight generations, in 2370 (Fig. 2). However, assuming 10%of the population is secured in conservation reserves, extinction may be prevented in the absence of other threatening pro- cesses. For locally abundant and widespread species such as salmon gum and poplar box, 10% of the original population represent populations at least in the order ofmillions of indi- viduals. Criteria B, C and D, which include provisions for rar- ity, are unlikely to be relevant until much greater population decline has occurred for these species (Fig 2). Salmon gum occurs over a large geographical range
(287,718 km2) in south-western Western Australia (Fig. 1). In the eastern part of the species’ range, salmon gum wood- lands are largely intact as a result of legislative protection and a relatively arid climate that limits cropping activity. These woodlands are typically lightly grazed because of scarce surface and groundwater, with landscape-scale natural disturbances driving population dynamics and regeneration (Yates et al., 1994b;Gosper et al., 2018). Vegetation clearance is regulated in Western Australia by the Environmental
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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