In Part 2 of this series of articles, Ben Kite explained how the concept of ‘biodiversity offsetting’ came in to being as a potential answer to the failure of the planning system to stem the loss of biodiversity; he also discussed how it raised more questions than it answered. Here, in part 3, he examines how the weaknesses in biodiversity offsetting led to its downfall, and how its proponents have sought to address these when fashioning its successor.

The failure of ‘biodiversity offsetting’, as it was initially presented, to be welcomed into mainstream ecological practice, was in my view at least in part due to some rather awful high-profile examples of the concept being grossly misused. One well-respected ecologist wrote angrily in a widely read periodical for example[i], about two projects where perverse ecological outcomes were only narrowly averted, thanks to determined and informed opposition.

The first example was a project in Kent, where anticipated damage to a fantastically biodiverse complex of ancient woodlands, scrub and species-rich calcareous grasslands, collectively providing the exacting conditions required to support a very large population of Nightingales Luscinia megarhynchos, was proposed to be ‘offset’, mainly by some scrub planting in another County (on land that itself had other ecological value that could have been displaced). Why on Earth the proponents of this project thought that creating more of an already super-abundant habitat type, in a different County, might somehow be an adequate substitute for the loss of irreplaceable biological complexity, developed over great lengths of time, or that it might perhaps cause Nightingales to appear out of ‘thin air’ in the new location, I may never know.

Nightingale - Luscinia megarhynchos

Above: Nightingale – in terminal decline? Photo © Paul Sterry/Nature Photographers Ltd

The second example, in Oxfordshire, concerned an ancient, species-rich and unimproved (in the agricultural sense) wet grassland, that first had its value artificially deflated through misrepresentation in a biodiversity offsetting calculator, before insult was added to injury through the ludicrous assertion that a grassland of higher biodiversity value could somehow be created simply by sowing purchased wildflower seeds on an alternative area of arable land. As an ecologist who has been involved in several large-scale grassland restoration and creation projects and having struggled with the inherent difficulties this entails, I find the pretence in that particular claim astonishing. Biodiversity calculators are clearly vulnerable to misuse – either through understatement of the value of what is being lost, or the overstatement of the value of what is being offered in their place.


Photo 11 (002)Above: species-rich unimproved grassland. Photo © Ben Kite

Notwithstanding the above, and in fairness to the originators of ‘biodiversity offsetting’ as a more formalised approach in the UK, they had always been clear that any application of the methodology should adhere to a number of important ‘key principles’. At least two of these key principles were conspicuously disregarded in the two wayward case studies outlined above.

The first principle that went unobserved, is that the so-called ‘mitigation hierarchy’[ii] should always be followed. This forms the bedrock of every good ecologist’s approach to their work, if they are engaged in the business of ecological impact assessment. It holds that any impacts on important ecological features should be avoided first, if possible (e.g. by adjusting the development layout to enable something important to be retained), then mitigated (reduced – for example by fitting directional cowls to lights to minimise light spill onto an important habitat), and finally only then compensated for, if it is not possible to reduce an impact to the point of insignificance. Compensation is provided by creating a new feature of ecological value to replace the one that could not be retained.

Crucially, the mitigation hierarchy holds that the above steps should be applied in the order that they are listed.  Biodiversity offsetting, of course, occurs where something has been lost or damaged as a result of development, so it is classed as ‘compensation’ in the hierarchy – i.e. the last resort. An ecologist should be able to demonstrate that they have exhausted any reasonably feasible opportunities at each preceding stage of the hierarchy.

The second key principle that went unobserved in the above case examples is that, by definition, biodiversity offsetting cannot be used to ‘replace’ habitats that are in truth irreplaceable.

It is a basic principle of ecology that, broadly speaking, the older a habitat is, the more biodiverse it is likely to be. This is because as time passes new species arrive into a habitat, become established, and then themselves provide the ‘niche’ needed for other species to establish. A recently colonised plant species for example may provide a food source for several species of new invertebrate, which in turn then provide food for new birds (this phenomenon is known as a ‘bottom up’ trophic cascade). This cumulation of complexity produces habitats that are often described in terms of their uniqueness and antiquity as being the natural equivalent of cathedrals or castles – and are often every bit as beautiful.

There are exceptions to the rule that antiquity is correlated with biodiversity, such as where a habitat has been impacted by abnormal negative influences, such as artificial fertiliser application (see Ben’s blog The Fat of the Land) that diminishes its ecological interest (these are known in technical parlance as ‘stochastic events’); but in general, the principle holds good.

In view of the above, and of the fact that any land use change at all requires some existing features to be lost, the practice of ecological impact assessment has needed to develop ways to distinguish between features of high and low importance. Ecologists often refer to young, simple, common and easily replaced habitats as ‘constant natural assets’ – it may well be appropriate to compensate for the loss of such features through the process of biodiversity offsetting. Ancient habitats however, or those reliant on unique environmental conditions, such as a particular hydrological regime, simply cannot be meaningfully recreated, at least within a human lifespan. Not even the most skilled ecologist could possibly replicate the extraordinarily complex assemblage of plants, animals, fungal mycorrhiza, bacteria and other soil microorganisms and structures that develop over centuries in an ancient woodland or grassland, for example.

Photo 12 (002)Above: Ancient woodlands like the one pictured here, has antique habitat features such as veteran trees, standing deadwood rich in fungi, beetles and other invertebrates, and a richly woven carpet of ground flora comprising  slow-colonising species such as Bluebell and Wild Garlic, as seen here. Once lost it cannot be replaced once lost. Photo © Ben Kite

Ecologists sometimes refer to such habitats as ‘critical natural capital’, and the originators of biodiversity offsetting always intimated that such places should occupy a somewhat sacrosanct status that exempted them from being ‘offset’. Again, this key principle was somehow overlooked in the two case examples outlined above. 

Closing the Loopholes

As momentum behind biodiversity offsetting began to stall in the wake of cases like those mentioned above, and in the face of growing professional and public disapproval, the proponents of biodiversity offsetting evidently set to work behind the scenes closing some of the more egregious loopholes that had been exploited in their process.

A herald of what was to come appeared in July 2018 when the Government’s National Planning Policy Framework (NPPF) was overhauled. Two discrete changes were made during this update that went unnoticed by many and which, without hindsight, might have seemed only tangentially relevant to biodiversity offsetting as a methodology.

The first change was that the previously stated objective of achieving ‘no net loss’ in biodiversity (see Part 1 of this article), was replaced by new text (paragraph 170(d)) stating:

“Planning policies and decisions should contribute to and enhance the natural and local environment by….minimising impacts on and providing net gains for biodiversity…..”

Although similar wording existed in the previous (2012) version of the NPPF, the words “if possible” followed; effectively making the requirement for biodiversity net gain aspirational rather than mandatory. The change made in 2018 thus raised the bar, as development was now expected to provide an overall enhancement to the natural environment.

The second change concerned the treatment of ‘irreplaceable habitats’ (regarding the second key principle I outlined above). The original text of the NPPF required development causing the ‘loss or deterioration’ of such habitats to be refused “…unless the need for, and benefits of, the development in that location clearly outweigh the loss..”. This caveat left it open to a decision maker to decide, on a purely subjective and perhaps uninformed basis, that a development was more beneficial than the irreplaceable habitat it sought to remove. The second change in 2018 to the NPPF (paragraph175(c)) tightened up on this caveat, requiring such justifications for the loss of irreplaceable habitats to now be “wholly exceptional”. An example of the sort of project that might fit this description was also given as being a “nationally significant infrastructure project”.

Although this change does not entirely close the second of the two loopholes identified above, and regrettably appears designed to enable exemptions for the Government’s own flagship projects, it does nonetheless make it harder for the average development proposal to justify impacting an irreplaceable habitat.

Notwithstanding these positive changes, it ought to be noted that both the original and revised versions of the NPPF specify that ecological impacts should be addressed through the ‘mitigation hierarchy’, in accordance with the first of my key principles mentioned above

This fact did not of course stop the proponents of the two wayward projects mentioned above from overlooking this expectation. What it did do, however, was enable informed opposition to highlight the resultant non-compliance with policy, and in so doing prevent those proposals from achieving consent. To me, this emphasises the reliance of the planning system upon the intervention of informed individuals, be they professional ecologists or otherwise, in reaching satisfactory outcomes. A key potential danger of biodiversity metrics or calculators therefore, is that they can provide the illusion of robustness – as if the spreadsheet one is looking at can somehow replace expert ecological knowledge.

In the next and final article in this series, I will introduce the successor methodology to ‘biodiversity offsetting’ that followed on from the above policy amendments – a process that is now branded as ‘Biodiversity Net Gain’ (BNG).  I will explain how it differs from its first incarnation, and offer my thoughts on its prospects for making a positive difference.

[i] Woodfield D (2018) ‘Biodiversity Accounting’ – a tool for transparency or for dumbing down?. British Wildlife. December 2018 pp117-120.

[ii] Chartered Institute of Ecology and Environmental Management (CIEEM, 2018) Guidelines for Ecological Impact Assessment in the UK and Ireland: Terrestrial, Freshwater, Coastal and Marine.