BN Genius or Biodiversity Net Pain: Statutory Metric, Friend or Foe? Tom Docker 26 June 2024

BN Genius or Biodiversity Net Pain: Statutory Metric, Friend or Foe?

Welcome to our ‘BN Genius or Biodiversity Net Pain’ series, in which our managing director, Tom Docker, reflects on key areas of discussion arising from the rollout of statutory Biodiversity Net Gain (BNG) in February 2024. In this first post, Tom explores whether the Statutory Metric is a friend or foe. 

The Department for Environment, Food and Rural Affairs’ (Defra) biodiversity metric has gone through several iterations over the past decade, culminating in the current “Statutory Metric” that forms the basis of demonstrating net gain for planning projects. Each version of the metric has had its champions and detractors within the sector, with concerns focused in two main areas:

  1. the concept of using a simple metric to attempt to describe something as complex as biodiversity; and
  2. the respective weightings and values given to different habitat types within the metric itself.

The first point is a valid one—of course, the natural world that sustains all life can’t be encapsulated in a simple spreadsheet. This isn’t, however, what biodiversity metrics are attempting to do and to claim otherwise is somewhat disingenuous.

The primary purpose of the metric approach is to provide a simple, consistent set of rules against which all developments can be fairly assessed. In this regard, the Statutory Metric does a good job of balancing a near-endless list of variables.

To satisfy my own curiosity about the impact of the metric, I have revisited a handful of pre-metric projects and retrospectively run the numbers to determine what their BNG outcome would have been. Without exception, where biodiversity enhancements were described qualitatively (mostly in the “no net loss” era), they failed to achieve a meaningful net gain under the metric. While this must be interpreted with a degree of caution, it reinforces the view that although the metric is not the answer in and off itself, it provides ecologists with a useful tool with which to leverage more nature-positive outcomes.  

The second point is a symptom of diversity and complexity of the ecosystems that sustain us, and, by association, the diversity and complexity of viewpoints held by ecologists.

A common point of debate around previous metrics is that they valued grassland habitats too highly at the expense of woodland habitats, leading to vast swathes of wildflower seed being scattered across the country in the name of BNG (some of dubious origin). This argument has flipped 180° with the statutory metric, leading to accusations that trees (particularly scattered individual trees) are given a disproportionally high value.

Ultimately, this is a circle that can never truly be squared and is a genuine case of comparing apples with oranges. What is true, however, is that the optimal ecological outcome will always be dictated by the geography and underlying environmental conditions at any given site and that working with nature to put the right habitat in the right place will always stand the greatest chance of success.

The Statutory Metric will always have its detractors and will never be perfect. As with any tool, its value is entirely dependent on the way it is applied by the end user—an area in which the industry is still finding its way. Careful and considered use of the metric as part of a holistic biodiversity solution is, in my view, a powerful approach and a reason for optimism.

Coming soon: In part two of BN Genius or Biodiversity Net Pain, Tom explores whether the BNG system is fair to council ecologists.

In the meantime, get beyond the legislative jargon and unravel the layers of BNG’s complexity in Tom’s ‘Decoding Biodiversity Net Gain’.