Do Current Habitat Scoring Metrics Appropriately Reflect Insect Diversity?

Both infrastructural development and cessation of biodiversity loss are UN Sustainable Development Goals (United Nations, 2015), presenting a potential conflict, given that much of the world's biodiversity is threatened by the continued development and expansion of human infrastructure (Maxwell et al., 2016) To mitigate this conflict, there is a need to shift toward more sustainable infrastructure development (Spaiser et al., 2017); for example by integrating biodiversity conservation into infrastructure via the "global mitigation hierarchy", which seeks to minimise harm to biodiversity, and offset unavoidable harms and losses to biodiversity (Arlidge et al., 2018). An example of use of this hierarchy comes from the UK government's new "Environment Act 2021" which creates a legal requirement for a biodiversity net gain (BNG) of at least 10% in the planning system, a target which goes beyond just offsetting losses (Environment Act, 2021). To implement this, a metric is used to convert habitats into 'biodiversity value units' pre-development, and then estimate the change in value units post-development (Natural England, 2021). In order to achieve the 10% net gain, developers must act to minimise harm to the habitat, take steps to enhance the habitat, and if necessary carry out off-site habitat enhancements or creation (Natural England, 2021). Projects can then be approved on the basis that the developer's evidence that the 10% net gain is achievable.

There is concern that current vegetation-based methods for scoring biodiversity value may not provide general and appropriate proxies for site-level biodiversity (Willis, 2021; zu Ermgassen et al., 2021). Insects and their requirements are absent from current biodiversity calculators, despite their value as ecological indicators for biodiversity more widely (Thomas, 2005; Maleque, Maeto and Ishii, 2009) and their contribution to important ecosystem functions including pollination, decomposition, and carbon cycling (Klatt et al., 2014; Metcalfe et al., 2014; Seibold et al., 2021). For example, the new DEFRA/Natural England Biodiversity Metric 3.0 (an Excel-based biodiversity calculator) has been criticised for its assignment of low values to plants such as bramble and ragwort which are key resources for many insect species (Weston, 2021). To address this concern, I will investigate the relationship between insect biodiversity of different habitat types and metrics, including the Biodiversity Metric 3.0, as well as other available metrics, such as the Pantheon Species Quality indices (Webb et al., 2018).