3.4.1. Equivalence assessment methods

The design of compensation measures must include three steps:

1. Assess the ecological baseline of the impacted site before the project commences. This baseline will serve as a reference for the calculation of equivalence through the mitigation hierarchy implementation. In some cases, degraded areas, for example, the selected baseline can be the desired ecological condition of the site rather than the current condition.
2. Assess the impact associated with the project, following two different steps:
   • Select the target species and habitats, currencies, and metrics to be used in the impact assessment.
   • Assess the expected loss of biodiversity due to the project development.
3. Determine the expected gains generated by the compensation measure. These must be evaluated with the same indicators as those used to measure impacts of the project and gains provided by avoidance and reduction measures.

The principles associated with compensation in the context of a NNL objective state that the gains generated by offset measures must be at least equivalent to the loss incurred by the impacts (Figure 3.1.1). This equivalence is evaluated taking account of both the ecological baselines of the impacted and restored sites, including their functional dynamics, and the equivalence between biodiversity loss at the impacted site and gains of biodiversity at the compensation site. The design of offset measure relies therefore on this assessment.

Numerous methods have been proposed to assess this ecological equivalence, but no standard method has been designed at the EU scale (Table 3.1). The operator responsible for the design and the implementation of offset measures is thus free to apply any method consistent with the relevant country regulations and the regulator’s opinion. Two approaches are applied in the design of offset measures, either by relying on qualitative assessment and ratios or by focusing on quantitative equivalence assessment. Qualitative assessment and ratios methods do not permit clear objectivity in the offset design and do not assess equivalence in detail. These approaches rely on general considerations set by the regulator’s opinion on how each habitat or species should be offset (in terms of surface ratio, proximity, and type of actions engaged). A quantitative equivalence assessment approach focuses on the evaluation of equivalence between sites, comparing impacted sites with the site proposed for compensation. This comparison relies on a predefined list of criteria to explore different components of biodiversity at both sites. Once the scoring is set for both the impacted site and the offset site, a calculation is applied to evaluate the equivalence.

Multiple methods exist across the world to assess equivalence and, more broadly, to design compensation measures. These methods have been developed in various regulatory contexts but can be implemented within the European regulatory framework. There are many challenges for offset implementation. These challenges must be considered when a methodology is implemented for equivalence assessment of offset measure design and include: operationality, timeframe, geographical scale, currency, and uncertainty, as outlined below:

• Operationality is defined by how closely the offset measure design is aligned with relevant regulations, the operating cost of assessment implementation, and the acceptability of the methods, including their transparency and scientific robustness.
• Timeframe analysis involves considering ecological dynamics as well as the delay between the impact, the implementation of the measure, and their effects over time. Tackling this challenge requires careful consideration of the methodology used to project the assessment into the future.
• Geographical scale refers to the scope of the assessment from its site scale to a broader, large spatial scale that allows the operator to assess the demographic dynamics of the species considered as well as ecological connectivity between sites.
• Currency describes the biodiversity component targeted by an evaluation and therefore considered in the design of measures. It defines what is evaluated in the assessment and what is compared to the equivalence of gains. The currency is determined by the variety of criteria upon which the assessment is set.
• Uncertainty factors in how a method handles unknown or unanticipated circumstances, both within the assessment and when measuring success.

Table 3.1 – Examples of methods developed or adapted in the EU to design mitigation measures (Adapted from Boileau et al. 2022).