Evidence shortfalls in the recommendations and guidance underpinning ecological mitigation for infrastructure developments

1. In the UK and European Union, legal protection of species from the
impacts of infrastructure development depends upon a number of ecological
mitigation and compensation (EMC) measures to moderate the conflict
between development and conservation. However, the scientific evidence
supporting their effectiveness has not yet been comprehensively assessed.
2. This study compiled the measures used in practice, identified and
explored the guidance that informed them and, using the
Conservation Evidence database, evaluated the empirical evidence for their
effectiveness. 3. In a sample of 50 UK housing applications, we identified
the recommendation of 446 measures in total, comprising 65 different
mitigation measures relating to eight taxa. Although most (56%) measures
were justified by citing published guidance, exploration of the literature
underpinning this guidance revealed that empirical evaluations of EMC
measure effectiveness accounted for less than 10% of referenced texts.
Citation network analysis also identified circular referencing across bat,
amphibian and reptile EMC guidance. Comparison with Conservation Evidence
synopses showed that over half of measures recommended in ecological
reports had not been empirically evaluated, with only 13 measures assessed
as beneficial. 4. As such, most EMC measures recommended in practice are
not evidence-based. The limited reference to empirical evidence in
published guidance, as well as the circular referencing, suggests
potential ‘evidence complacency’, in which evidence is not sought to
inform recommendations. In addition, limited evidence availability
indicates a thematic gap between conservation research and mitigation
practice. More broadly, absence of evidence on the effectiveness of EMC
measures calls into question the ability of current practice to compensate
for the impact of development on protected species, thus highlighting the
need to strengthen requirements for impact avoidance. Given the recent
political drive to invest in infrastructure expansion, high-quality,
context-specific evidence is urgently needed to inform decision-making in
infrastructure development.