Improving averted loss estimates 401 Many socio-political factors influence offset policies,
design and implementation. Ratios are particularly prone to these influences in that politically acceptable multipliers are likely to be smaller than ecologically necessary (Bull et al., 2017). This results in decisions around multipliers resting on reasonable effort, rather than levels required to achieve no net loss (e.g. Carver&Sullivan, 2017). In the con- text of averted loss offsets, this preference for acceptable levels of effort can translate into a willingness to accept un- realistic assumptions about future loss that support a smal- ler offset effort. Thus, methods such as the one proposed here, which employ more realistic assumptions about future loss, are necessary to counter the tendency to favour smaller offset requirements.
Limitations of relying on protection actions to achieve biodiversity gains
The use of protection actions to generate biodiversity gains as an offset for development impacts is common practice in some regions. Changing land tenure, in many places, may be perceived to be relatively straightforward, inexpensive, and quick compared to the complexities, uncertainties, expense and long timeframes associated with maintenance or en- hancement activities. In addition, protection offsets such as land acquisition compared favourably to other offset types in terms of environmental outcomes in Western Australia (May et al., 2016). However, the amount of gain that can be credited to the offset action can only be calcu- lated if likelihood of loss in absence of protection has also been estimated. The protection of 100 ha only equates to 100 ha offset gain if the land would otherwise have been cleared immediately. Although the action of protecting the site can carry greater certainty, and greater ease of implementation monitoring (e.g. land protected or not protected), the outcome remains uncertain because the counterfactual is uncertain. This illustrates the critical dif- ference between an action occurring (e.g. Was the land pro- cured? Were the trees planted?) and whether the chosen offset action is likely to generate the amount of gain antici- pated (e.g. Was the estimated future loss averted?; Ferraro, 2009;Maron et al., 2013; Gibbons et al., 2016). Whereas the former is straightforward to measure, the latter can only ever be estimated, such as by examining trends in the sur- rounding landscape and extrapolating these trends to the site in question. Furthermore, protection actions aimed at averting loss
of area are often perceived to secure existing biodiversity values immediately (from the point at which the area is protected), apparently avoiding uncertainties associated with time lags between losses occurring and gains being generated. Thus, if there is a tangible threat to the persis- tence of that biodiversity into the future, averting loss can be seen as a more socially acceptable offset option than
restoration offsets, where there is greater uncertainty that the anticipated gains will be achieved. However, immediate biodiversity gains are only generated where the likelihood of loss is high and expected loss is imminent. Typically, the likelihood that a site might be lost accrues gradually, and so the gains secured by a protection offset will also gradually accrue over time (Sonter et al., 2017). Prediction becomes progressively more difficult as the time horizon increases (e.g. 10 vs 50 years). Thus, defining a time horizon is import- ant and needs to be both realistic in terms of capturing fu- ture likelihood of loss, yet relevant to policy timeframes, and meaningful for monitoring ecological change in response to offset actions. The method proposed here does not explicitly attempt to
account for non-compliance with protection agreements or the likelihood of illegal activities occurring within the offset site, and also assumes that offset sites would be protected in perpetuity (i.e. protection status would not be downgraded or removed in the future). If the likelihood of illegal damage at a potential offset site was considered too high even with the protection that could be afforded, then alternative offset sites should be sought. It should be noted, however, that the lack of permanence for offset sites as a result of expected non-compliance or protected area downgrading, downsiz- ing and degazettement events (Golden Kroner et al., 2019) further reduces the expected biodiversity gain delivered by averted loss offsets. Although we focus on likelihood of complete loss of a
proposed offset site, the same logic can be applied to other situations (such as future loss of condition) by substituting protection actions for alternative actions targeted to prevent further habitat degradation. This will pose the same prac- tical challengesmentioned here (determining the appropri- ate scale at which to calculate past loss and the inherent difficulties in predicting the future). However, biodiversity condition data are often lacking and trends in change of condition are often difficult to determine. This can be re- solved to some degree by predictive modelling, or informed by structured expert judgement (Hemming et al., 2018).
Using recent background rates of loss to inform future estimates
In many situations, relying on past background rates of loss (e.g. the previous 10 years) can be a plausible predictor of future rates of loss, or at least a good starting point. This method introduces consistency and transparency, and is less open to misuse than unguided site-by-site estimates. However, it may not always be reasonable to use past rates of loss to inform future likelihoods of loss, such as when fluctuating commodity prices or economic shocks have driven land-use change at a faster rate than experienced in the recent past. Reliably predicting such future events is extremely difficult and therefore past rates are often a
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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