Review
Under the radar: mitigating enigmatic ecological impacts

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Highlights

  • There are ecological impacts that are overlooked by standard impact evaluations.

  • These ‘enigmatic’ impacts can be cumulative, offsite, cryptic, or secondary.

  • Enigmatic impacts can act synergistically and are hard to detect and mitigate.

  • Potential solutions include strategic assessments and insurance schemes.

Identifying the deleterious ecological effects of developments, such as roads, mining, and urban expansion, is essential for informing development decisions and identifying appropriate mitigation actions. However, there are many types of ecological impacts that slip ‘under the radar’ of conventional impact evaluations and undermine the potential for successful impact mitigation (including offsets). These ‘enigmatic’ impacts include those that are small but act cumulatively; those outside of the area directly considered in the evaluation; those not detectable with the methods, paradigms, or spatiotemporal scales used to detect them; those facilitated, but not directly caused, by development; and synergistic impact interactions. Here, we propose a framework for conceptualising enigmatic impacts and discuss ways to address them.

Section snippets

The problem of enigmatic ecological impacts

There is increasing recognition of the need to find ways to reduce the environmental impact of human development (e.g., 1, 2, 3, 4, 5). This has led to a proliferation of approaches to evaluate, manage, mitigate, and offset the ecological impacts of developments. Evaluations of ecological impact, such as environmental impact assessments, biodiversity offset calculations, and conservation or land-use plans, are generally intended to account for the full range of foreseeable ecological impacts of

Four categories of enigmatic impact

Our framework identifies four categories of impact that are often overlooked or inadequately addressed in impact evaluations: (i) cumulative; (ii) offsite; (iii) cryptic; and (iv) secondary impacts. Interactions between multiple impacts may also be overlooked. These categories, named after the reasons for which the impacts are excluded from impact evaluations, act as a checklist for scoping the various ‘enigmatic’ impacts that could result from a development or series of developments. As such,

Impact synergies

For every pair of impacts, there are possible synergies that exacerbate environmental damage. The combined effect of the two impacts could be greater than their sum, or one phenomenon might facilitate another. For example, the synergistic effects of multiple species extinctions on ecosystem function are often greater than the additive effect of each extinction, were it to occur in isolation; also, forest fragmentation can facilitate fires 44, 46. It is difficult to predict interactions between

Challenges and opportunities

Evaluating impacts is the first step to mitigating them. Some impacts are overlooked because they are difficult to detect, quantify, and attribute. In other cases, ignoring them may simply be convenient or politically expedient from a development perspective (e.g., 12, 49).

The difficulty of accounting for enigmatic impacts is not the only hurdle to achieving credible impact evaluations. The effectiveness of many impact evaluations can be undermined by a suite of political and economic

Concluding remarks

Accounting for and mitigating the full breadth of enigmatic impacts resulting from developments is ambitious but important for preventing the continued degradation of ecosystems and the biodiversity, ecological processes, and services that they support. While this may be difficult to achieve comprehensively, significant advances can be made by improving existing mechanisms and developing new ones, to account for the cumulative, offsite, cryptic, and secondary impacts of developments and their

Acknowledgements

We thank B. Laurance, H. Murphy, M. Maron and an anonymous reviewer for constructive comments on previous versions of this manuscript. We gratefully acknowledge support from the Gledden Postgraduate Scholarship, The Wilderness Society, the Australian Research Council Centre of Excellence for Environmental Decisions, the National Environmental Research Program's Environmental Decisions Hub and the Great Western Woodlands Supersite, part of Australia's Terrestrial Ecosystem Research Network.

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