This policy this is the most controversial element of the “Biodiversity and green spaces” portion of the Local Plan.
While I, like so many others, am of course in favour of increasing biodiversity in Greater Cambridge, there are a lot of questions around the measurement of biodiversity net gain, the imprecision of the indicator, and, most troubling, the option to use off-site contributions to increase net gain. Indeed, I am surprised that the “First Conversation consultation” showed “very strong support for biodiversity net gain including use of off-site contributions” – I believe that there was strong support for biodiversity net gain but would question if there is truly ‘strong support’ for off site contributions.
I think the policy should also be clearer that the Plan’s biodiversity objectives are about controlling development impacts, and not about improving biodiversity on existing sites (even a goal of ‘no net loss’ would be something, and given that biodiversity has been degraded across the country in recent decades, seeing some goals for increased biodiversity on existing sites would be welcome). The 20% gain is only being sought if nature is damaged as part of development on new sites. The policy says that it will “seek wider environmental net gains” so perhaps there are greater ambitions, but this should be spelled out. The current policy only addresses space impacted by development and seems like a missed opportunity to set goals for increasing biodiversity overall.
On new development sites, developers will of course seek to show either that there is no net loss (or if this is impossible, to mitigate offsite), and the methodology – using DEFRA’s new BNG (biodiversity net gain) calculator 3.0 for determining damage to a site seems weighted in developer favour.
While I appreciate that biodiversity is very difficult to measure, especially for use in a regulatory/market framework, new DEFRA’s BNG 3.0 algorithm seems excessively simplistic, looking only at habitat features and excluding species measurement (I understand that habitat is seen as a proxy for species). The metrics used to calculate ‘biodiversity units’ – there are only four – of size, distinctiveness, condition, and strategic habitat are very subjective and are measured in a difficult-to-understand way – why is distinctiveness measured along a scale of 0 – 8, while condition is on a scale of 1 -3, and strategic significance is 1 – 1.15 (this last on a scale which seems incapable of capturing any real difference). Moreover, DEFRA 3.0 (unlike 2.0) explicitly excludes the metric of “connectivity,” and this is at odds with the corridors and connectivity themes of both the Green Infrastructure policy (BG/GI) and the River Corridors policy (BG/RC). Developers will hire ‘environmental consultancies’ to gauge these metrics, which are likely to come in at the low end, given the complicity between these consultancies and the developer industry.
Where developers are not able to provide 20% net biodiversity gain onsite, they are allowed to make contributions to off-site projects. This provides no advantage for residents of the local area either in terms of biodiversity or connectivity, and it is questionable whether at the nationwide level biodiversity benefits would be delivered, as it is entirely possible that sites with a lower base line biodiversity elsewhere could be chosen for the mitigation efforts.