Evaluation of Ecological Mitigation Measures in Practice

Land development puts a significant and increasing pressure on biodiversity in the UK due to growing investment in infrastructure and urban developments. In fact, the Government has ambitions to increase housebuilding (300,000 extra homes a year by the middle of the decade) and to continue investing in other infrastructure, such as through Project SPEED, to boost economic growth.

There is existing legislation in place which seeks to manage these pressures on biodiversity. For example, the Conservation of Habitats and Species regulations (2019), and previously the EU Habitats and Wild Birds directives, require that development activities do not have a detrimental impact on the ‘favourable conservation status’ of certain species. Developers are therefore required to include species-based mitigation and compensation measures in developments, such as the construction of artificial nesting sites and translocation of animals, plants and even soils from development sites.

Measures should be applied in line with the ‘mitigation hierarchy’ which gives priority to avoiding development impacts on biodiversity and then mandates that measures should be put in place to reduce, mitigate or compensate for impacts to protected species in decreasing order of preference. Mitigation and compensation measures (reducing the severity of the impacts of development and making up for the loss/damage to biodiversity through offsetting or implementing species-enhancing measures on alternative land) are therefore a vital part of addressing the conflict between development and conservation objectives.

Evidence shortfalls

A recently published research article has concluded that there are major gaps in the scientific evidence necessary to inform decision making in species-based mitigation. The study reviewed the ecological reports, dated from 2011 to 2020, associated with a sample of 50 housing developments. The analysis showed that 446 measures were recommended in total, comprising 65 different mitigation measures, and less than half of the measures identified in the study were supported by scientific evidence, with only 13 assessed as beneficial or likely beneficial.

A further issue raised by the study was that the guidance informing these measures often lacked reference to scientific evidence for effectiveness. It was also often out of date (some was published more than 20 years ago) and the most frequently cited literature in the guidance was based on circular referencing of other guidance documents.

Whilst the lack of evidence does not confirm that mitigation is ineffective, it does raise concerns about the efficacy of current measures to mitigate or compensate for the impact of rapid development, as measures are being applied without a clear understanding of their outcomes.

Reconciling development and conservation objectives

In terms of tackling the issues identified in the study, lead author Bronwen Hunter, a researcher at the University of Sussex, said “We need to address the creation of new evidence for the outcomes of mitigation, as well as ensuring that new evidence is accessible and used by ecological consultants when recommending mitigation measures in practice”.

Furthermore, developers and ecological consultants often generate monitoring data from development projects but do not share this publicly, so it is unavailable to researchers. “Tapping into these data sources would certainly give a much more complete picture of the effectiveness of species mitigation” explained Bronwen.

The research also highlights the need for key policy changes, suggesting that government agencies should regularly update guidance for protected species mitigation and that this should be based on comprehensive evaluation of empirical evidence. It also highlights that improving the design and compliance of post-development monitoring may increase the quality and availability of data that could help inform decision making.

Another researcher on the study, Sophus zu Ermgassen, a researcher at the University of Kent, also explained that a key component of the solution could be slowing the rate of construction and habitat loss initially in order to try to reconcile development and conservation objectives. However, Sophus did acknowledge that this would require some transformative changes to the structure of the English economy. This is something being explored in another paper that Sophus is currently working on, so watch this space.

More widely, the study concludes that in order to meet national biodiversity targets, there should be greater emphasis on impact avoidance in development policies rather than reliance on implementing measures that have not been demonstrated as being effective.

Next steps

Future work associated with the research article will aim to encourage and ensure that the use of robust evidence is properly and fully integrated into mitigation activities as standard practice. Bronwen outlined that to achieve this “Changes could include normalising the use of resources such as the Conservation Evidence synopses to inform mitigation recommendations and the consideration of evidence-use by local planning authorities when reviewing applications”. Hopefully this research will continue to contribute to understanding how best to reconcile development and conservation objectives whilst advocating for evidence-based decision making.

Thank you to Bronwen Hunter and Sophus zu Ermgassen for contributing to this blog. The full research article was published in Ecological Solutions and Evidence and can be accessed here: https://besjournals.onlinelibrary.wiley.com/doi/10.1002/2688-8319.12089