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Applying Metric 3.0 to intertidal habitats

Our White Paper tests the updated intertidal metric for assessing biodiversity net gain requirements when coastal developments adversely affect shoreline habitat.

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White Paper: Marine Net Gain - Applying Metric 3.0 to intertidal habitats

Following the publication of Biodiversity Net Gain Metric 3.0, our White Paper tests the updated intertidal metric for assessing the biodiversity net gain requirements when coastal developments adversely affect shoreline habitat.

Natural England recently published Biodiversity Net Gain Metric version 3.0. This includes an updated version of an intertidal metric for assessing the biodiversity net gain requirements when coastal developments adversely affect shoreline habitat.

ABPmer has tested Intertidal Metric 3.0, to understand how it is likely to work using a hypothetical case study. Our latest White Paper shares the outcome and compares the findings with the previous Intertidal Metric 2.0.

The analysis indicates that, where a development results in the loss of intertidal mudflat and saltmarsh habitat, the metric will require the creation of replacement habitat in a ratio of 9.75:1 for mudflat and 15:1 for saltmarsh to deliver the requisite 10% net gain in normal situations. This compares with ratios of 2.4:1 for mudflat and 12.75:1 for saltmarsh under Intertidal Metric 2.0.

The UK has substantial experience with delivering compensatory measures, under the Birds & Habitats Directives (now enforced through the Conservation of Habitats and Species (Amendment) (EU Exit) Regulations 2019), to address losses of intertidal mudflat and saltmarsh habitat within Special Protection Areas or Special Areas of Conservation. This experience, gained over nearly three decades, indicates that typical ratios of around 2:1 (gain:loss) are requested and accepted by regulators and advisors. These ratios are deemed sufficient to ensure the coherence of the Marine Protected Area (MPA) network is protected and any uncertainties about restoration effectiveness are addressed. On this basis, one might expect a 10% net gain to perhaps require a ratio of 2.2:1 (The ratios required by Intertidal Metric 3.0 therefore appear to be disproportionately large).

The reasons for such large multipliers reflect the conservatism that has been built into the components of Intertidal Metric 3.0 which when multiplied up generates an overly conservative output. In particular, the metric fails to recognise the very significant structural and functional benefits that newly created intertidal habitats provide. These benefits are ignored until NE judges that full function is achieved. These weaknesses were identified in earlier versions of the Intertidal Metric 3.0 but have not been addressed.

Trading rules under Metric 3.0 state that intertidal net gain which occurs on terrestrial habitat, in the form of managed realignment, cannot occur on terrestrial habitats which are classified as high distinctiveness or higher (unless additional compensation is provided). Realigning over sites containing ‘medium’ distinctiveness habitats would trigger additional net gain requirements (though the tool which is currently available does not facilitate testing of the managed realignment trading changes which have been made in Metric 3.0). Both of these changes are likely to increase the complexity and cost of managed realignment projects. An analysis for the Solent Region indicates that approximately 85% of potential realignment sites would be affected in this way. This is likely to limit options for viable managed realignment projects in the future.

Where developers need to deliver compensatory measures for damage to intertidal habitats inside MPAs then net gain policy currently also requires delivery of net gain for any terrestrial losses associated with those compensatory measures. This will potentially create a snowball effect and lead to very substantial habitat intervention projects to meet the requirements of both the Habitats Regulations and the proposed net gain policy under the Environment Bill. Given the scale of measures required to achieve net gain and the potentially limited opportunities to deliver them under Metric 3.0, there is a serious risk that development in the intertidal zone will become highly constrained. Significant revision and rethinking of Intertidal Metric 3.0 is likely to be required to create a workable process that can support sustainable development in intertidal areas.

To learn more, download the White Paper at

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