In his previous article, Ben outlined how past attempts to achieve ‘no net loss’ of biodiversity through the planning system in England were frustrated by competition for space and the limitations of land ownership. In Part 2, he outlines the first, but ultimately unsuccessful, serious attempt to overcome these constraints – known as ‘Biodiversity Offsetting’, and touches on some of the flaws that led to it being redesigned as an approach.

Ecologists working with developers, planners, planning authorities and regulators have been pondering for years now, how to overcome the problem of developers having insufficient space within the land that they control to be able to provide for the needs of both people and wildlife.

Despite National policy requiring ‘no net loss’ of biodiversity for some time, in practice the pressing need for homes and infrastructure meant that, broadly, only ecological features of significant importance had any real bearing on the outcome planning decisions – lower value features were often either overlooked or shoe-horned into the ‘space left over after planning’ (SLOP). As other influences meant that an ever-growing proportion of the countryside was comprised of such lower-value habitats and features, their incremental loss through development began to raise the real prospect of a ‘death by a thousand small cuts’ for the natural environment in the UK.

An earlier attempt to change the modus operandi was made shortly after the Conservative / Liberal Democrat coalition took power in 2010, when the idea of ‘biodiversity offsetting’ was thrust into the limelight by its proponents and then subject to pilot studies sponsored by DEFRA.

‘Biodiversity offsetting’ as a process attempts to quantify the ‘value’ of component parts of the natural world on more of an objective rather than subjective basis, so that features of equal or greater value can be created elsewhere to compensate for their loss. Due to the practical impossibility of accounting for all species that may be present in a given area, this is usually done by auditing the areas of different habitat types that are present and using them as proxy measures for biodiversity. The resultant assumed value is then generally expressed as a number of either biodiversity ‘units’ or ‘credits’.

photo 5 - heathland (002)

Biodiversity offsetting uses habitats as a proxy measure for biodiversity, distilling wildly different habitats such as heathland (above) and chalk grassland (below) into a common measure of ‘biodiversity units’. Photos © Ben Kite.

photo 6 - chalk grassland (002)

The thinking that underlies this approach owes much to the academic concept of ‘ecosystem goods and services’, which refers to the benefits that humanity receives from nature for free, which would otherwise have to be purchased through artificial means. These are such things as; clean air and water, climate regulation, food, fibres, pharmaceuticals, flood attenuation, carbon sequestration, healthy soils, natural crop pest control, improved physical and mental well-being, amenity, and much more besides. Disciples of this thinking make the persuasive argument that if we recognise the true financial value of such ‘natural assets’, through processes such as ‘natural capital accounting’, they will carry greater weight in society’s decision-making and are then more likely to be protected.

photo 7 - amenity (002)Above: Nature as amenity – how much is it ‘worth’ to you? Photo © Ben Kite.

Biodiversity offsetting, and the ‘biodiversity units’ that stem from it, are a rogue offshoot of this thought experiment. They are an attempt to represent or ‘capture’ the overall importance of habitats in as simple a way as possible, so that the consequences of a proposed land use change in terms of losses or gains of biodiversity units can be compared with other hypothetically possible outcomes (e.g. choosing to locate development elsewhere, or arranged in a different layout). The twin purposes of this exercise are to find the outcome that is preferable, but also to highlight where ecological value is being lost, so that new habitats of equal or greater value elsewhere can then be created elsewhere, by way of compensation.

As it is not possible to audit all species that are present in an area, data pertaining to the typical ‘species richness’ of different habitat types is instead used to calculate value as function of the type and area of the habitats that are affected. The number of biodiversity units that any area is then presumed to be ‘worth’ is determined using a ‘calculator’ or ‘metric’, that generates a value (in biodiversity units) based on a function of the assumed rarity and/or species richness of the habitat type in question, multiplied by the area that the habitat area covers. Calculators also commonly allow for adjustments to the calculation to be made in order to account for factors such as the condition, distinctiveness and the ‘connectedness’ of the habitat(s) being assessed.

Photo 8 - cladonia

 It is not possible to audit all species present, particular those of diminutive stature such as a Cladonia lichen species (above), or invertebrates like the Four-spot Orb Weaver Spider Araneus quadratus(below). Consequently, species-richness data for different habitat types is used as a proxy measure. Photos © Ben Kite.

Photo 9 - 4 spot orb weaver

When applied in a development context, the biodiversity offsetting methodology requires an ecologist to calculate the value in biodiversity units of whatever habitats are being lost, and then compare this with the presumed value of whatever is proposed to be created – usually a combination of built form and new habitat creation or ‘Green Infrastructure’. If the number of biodiversity units increases, a net gain in biodiversity is indicated and the development may be allowed to proceed, but if the number decreases, a net loss of biodiversity is indicated, and some form of additional compensation (habitat creation elsewhere) would in theory be sought before consent could be granted.

The potential benefits of such a system are obvious in terms of the consistency, repeatability, simplicity and speed of decision-making that is likely to result. Additionally, the proposed approach has the benefit of accounting even for ‘low value’ habitats that might otherwise be overlooked when decisions are made. As I feel certain the reader must now be contemplating, however, attempting the somewhat audacious and arrogant feat of defining the ‘value’ of something as complex as nature in such simplistic terms as ‘number of biodiversity units’ is fraught with difficulty at both the practical and philosophical levels and contains a degree of inherent absurdity.

Notwithstanding the appropriateness of doing this at all (which I will explore), vast numbers of perfectly reasonable questions abound as to the basic practicalities of this approach, such as:

  • How can something as impossibly complex, rich, intricate and differentiated as a natural system be distilled into a mere number?


  • How, for example, can the value of a small semi-natural woodland be meaningfully weighed against the value of a similarly sized traditionally managed old orchard? Would doing so not just be ‘comparing apples with pears’, in both the literal and metaphorical sense?


  • Is it really possible to adequately represent not only the measurable values of nature in this way, but also the intangible ones, such as beauty or cultural significance?


  • How can a practitioner adequately account for the fact that British habitats are complex at the small scale, with even very similar examples of ostensibly the same habitat type sometimes supporting markedly different complements of species?


  • How can one adequately account for the fact that, in reality, different areas of the same broad habitat type will have very different values, depending on their position and function in the landscape? For example, if one woodland is used as a wildlife corridor between two other areas, and another otherwise identical woodland is not?


  • Can the system be wrongly used to favour a particular outcome, either deliberately or accidentally, by manipulation or misrepresentation of the data fed into the calculator?

To my mind the above problems, whilst certainly thorny issues, are wholly overshadowed by the more fundamental and troubling questions of whether the entire approach is philosophically justifiable and logically defensible in the first place.

On the philosophical front – by abandoning our defence of the instinctively received wisdom that living systems have value that simply cannot be measured, have we as conservationists unwittingly conceded something crucially important? Have we opened the door to those who would (given half a chance) diminish our relationship with the natural world to a mere transaction – finally making society’s detachment from nature complete and irreversible?

On the logical front, we all accept (I think!) that the natural environment as a whole is priceless, because nothing else (including the economy) could exist without it. How therefore can it be a sound rationale to intellectually dismantle this priceless system into component parts, that are then each assigned a finite value? Is doing this not simply the economic equivalent of smashing a priceless antique Ming vase into a thousand small pieces, and attempting to sell each piece off individually, naively expecting a profit?

More profoundly perhaps, does the very act of trading biodiversity actually invert the true hierarchy of importance between the environment and the economy in the minds of decision makers, by framing the former as simply a collection of commodities to be traded under the umbrella of the latter?

Biodiversity offsetting, as the first tangible incarnation of this new approach to ecological decision-making for land use change, posed more questions than it answered. Although the pilot studies run by DEFRA did yield some encouraging results (notably including a significant increase in funding from development for nature conservation initiatives), the concept ultimately failed to galvanise sufficient support amongst ecologists and nature conservation professionals to enable it to be fully accepted in the form in which it was originally posited.

In Part 3 of this article, I will explore further some of the flaws in the Biodiversity Offsetting process that led to its downfall, and explain how its proponents have begun to address these as they have worked towards its successor methodology.