584 R. J. Fensham
FIG. 2 Schematic representation of species decline for salmon gum and poplar box and the thresholds for threatened as Vulnerable and not threatened according to the Red List subcriterion A2. Species are categorized as Vulnerable when decline is .30% over the previous three generations (210 years, as indicated by grey lines; Fensham et al., 2020). The decline rate for both species until 2020 is represented by the estimated value of 36.4% (Fensham et al., 2020). Assuming a constant rate of decline from 1810, both species qualified for listing as threatened in 1971. Hypothetical future scenarios are presented in which salmon gum has no decline after 2020 until it is disqualified for categorization as threatened in 2073, followed by a low rate of decline. Poplar box continues to decline after 2020 albeit at a lower rate than previously and is thus disqualified as a threatened species in 2130. Supposing poplar box undergoes a rapid future decline it would requalify as a threatened species in 2440. The dashed line indicates the trajectory to extinction based on the historical trend. Both species occur in protected areas and these are indicated as 10% of the habitat for the populations. To demonstrate the clear distinction between decline (assessed under subcriterion A2) and rarity or range restriction utilized by other criteria, the situations where criteria B, C and D would likely become relevant are indicated.
rate (amount per generation expressed as a positive num- ber) after the reference year, GRY is the reference year that the decline rate changed from R1 to R2 (in generations from time = 0), and A0 is the initial abundance (at time = 0 generations). The rate R2 must be #0.1(A0–R1 ×GRY)or disqualification as a threatened species does not occur. This formula assumes linear past and future rates of decline. IUCN Red List Guidelines (IUCN Standards and Petitions Committee, 2019, Section 2.2.1) require that a species can only be moved from a higher to a lower category of threat if and when none of the criteria of the higher category has been met for 5 years or more. When applied to the taxa assessed as threatened under
subcriterionA2 by Fenshamet al. (2020), 56 of the 134 species would be disqualified as threatened species under the same criterion within one generation (70 years), although four of them qualify under other criteria (Table 1). However, if deforestation continues, disqualification of threatened spe- cies would be less frequent and new species would qualify for listing as threatened under subcriterion A2.
Discussion
There is a common misunderstanding that criterion A requires population monitoring datasets to assess decline
(Le Breton et al., 2019). Deforestation is a common cause of population decline and can be interpreted by quantifying change from forest to intensive land use relative to the gen- eration length of a species even when land-use mapping is unavailable (Fensham et al., 2020). However, because pop- ulation decline under criterion A relates to time (i.e. three generation lengths), species that currently qualify can be disqualified in the future if decline stabilizes. In Europe, for example, where most deforestation occurred in the dis- tant past, subcriterionA2 does not apply for long-lived trees. In Australia and other places where deforestation is more recent or ongoing, subcriterion A2 has probably been over- looked (Le Breton et al., 2019), particularly for long-lived organisms such as trees. The scenarios of decline presented here for widespread eucalypts occurring on productive soils provide examples of how the status of long-lived species can vary between qualification and disqualification for the IUCN Red List threshold of 30% decline under subcriterion
A2.Many of the eucalypt species proposed for listing as threat- ened under subcriterion A2 will be disqualified within the length of a single generation (Table 1)ifthe causeofdecline, in this case deforestation, is arrested. By corollary, if deforesta- tion is ongoing many common and widespread species can and should be categorized under subcriterion A2 and will continue to qualify until the cause of decline is arrested.
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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