400 F. J. F. Maseyk et al.


FIG. 4 Mean annual rate of forest loss during 2005–2014 within each local government area across Australia (adapted from Maseyk et al., 2017). These rates calculated from past deforestation rates are considerably lower than declines assumed in offset approaches in Australia (Maron et al., 2015).


assumptions regarding likelihood of loss at a proposed offset site need to be supported with site-specific, credible, and robust evidence that is documented and made publicly available. In particular, if it has been determined that the likelihood of loss for a proposed offset site is greater than the background rate of loss, the evidence needs to demon- strate the likelihood of the proposed offset site being lost, and not just state that loss may occur (e.g. under current planning legislation and policy), or that it is known to occur at other sites.


Discussion


Biodiversity conservation requires the long-term mainte- nance and enhancement of both habitat extent and quality and this necessitates a combination of actions that avert loss of area, increase quality of existing biodiversity and re- instate lost biodiversity. The greatest offset gains will be se- cured by averting loss in circumstances where future threat is high, and defensibly estimated, and by increasing quality of existing biodiversity through both protection and man- agement of habitat in accordance with clearly stated objec- tives for offset policies and conservation outcomes. It must also be acknowledged that obtaining no net loss outcomes by averting loss is relative to a baseline of decline (Maron et al., 2018), and real conservation gains can only be


achieved through policies that are targeted at protection and restoration (Arlidge et al., 2018). Here we propose a transparent, robust, and consistent


method to improve estimation of likelihood of future loss of biodiversity at a site, which in turn will improve the ac- curacy of the estimated amount of biodiversity gain gener- ated by an averted loss offset. For simplicity we focus only on averting loss of area and only one offset action, protec- tion of the site. However, the basic logic presented here is also applicable to evaluating biodiversity gain by averting loss of condition. In particular, the emphasis on explicitly separating estimations for offset and counterfactual scen- arios and differentiating between type I and type II impacts is universally relevant. We also show that observed background rates of loss in


forest extent inAustralia during 2005–2014 are substantial- ly lower than rates being used to estimate future likelihood of loss (Maseyk et al., 2017), or assumed within Australian biodiversity offset policies (Maron et al., 2015). It has been suggested that no net loss offsets based purely on averted loss are only likely to be acceptable to industry at ratios below 10:1 (Gibbons et al., 2016), which would equate to a counterfactual annual rate of biodiversity loss$6%. As the highest mean annual rate of loss we recorded within a local government area was,1%, this underscores the very limited scope for no net loss to be achieved using only averted loss offsets.


Oryx, 2021, 55(3), 393–403 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605319000528


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