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Biodiversity offsets: possible methods for measuring biodiversity losses and gains for use in the UK


Abstract and Figures

There has been increasing interest in the use of biodiversity offsets to reverse residual adverse effects of development. This paper proposed a metric framework for biodiversity offsetting in the UK, subsequently adopted by Defra as the basis for its offset and biodiversity net gain policies. We proposed a habitat-based approach to measuring impacts and determining offset requirements which is based on hectares of habitat of particular type and level of intrinsic 􏰕􏰃􏰁􏰇􏰈􏰁􏰌􏰏􏰈􏰁􏰄􏰅􏰌􏰅􏰇􏰇􏰖􏰑distinctiveness, adjusted to account for differences in condition ( in UK habitats often closely linked to suitability of management). 􏰛􏰈 For purposes of illustration we present a hypothetical worked example, but recommend rigorous testing to ensure that the approach is fit for purpose. At the end of the paper we identify some potential pitfalls and issues that might need further consideration, including the need to ensure that the species populations associated with UK habitats receive targeted attention as necessary to ensure that they remain viable and have access to habitat of equivalent area, type and suitability when habitat trade-offs occur..
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Biodiversity offsets: possible methods for measuring biodiversity losses and gains for
use in the UK
Jo Treweek CEnv, MIEEM and Bill Butcher, Treweek Environmental Consultants
Helen Temple, The Biodiversity Consultancy
There is increasing interest in biodiversity offsetting to achieve no net loss (or preferably a net
gain) of biodiversity, when development might otherwise result in residual adverse effects
despite appropriate avoidance and mitigation measures. There are now laws requiring
enhancement policies. Development of similar systems in the UK and the EU is being explored
(Defra, 2009; EU, 20101), making it important to consider the risks and opportunities presented
by biodiversity offsetting. There is a growing body of theoretical and practical experience to
draw on: an extensive overview can be found on the Business and Biodiversity Offset
In determining what constitutes a reasonable and fair offset, we need to consider the extent to
which losses (due to impacts) and gains (due to offsets or compensation) balance out to
 as a minimum. An essential ingredient of a robust biodiversity offset
system is therefore a credible method for measuring biodiversity losses and gains. This is the
main focus of this paper.
The challenge is to develop methods which will be straightforward to apply in practice without
sacrificing the precision required to ensure that all important aspects of biodiversity are
captured. In the absence of an agreed, universal measure of biodiversity and for entirely
pragmatic reasons, most offset systems are habitat-based. Compared with species populations,
habitats are relatively stable over time, can be adequately described with fewer types and are
normally used as the primary focus of biodiversity conservation.
Recognising that some important ecological attributes will not be adequately reflected using
habitat as a surrogate (population decline caused by traffic collisions, for example), we suggest
a habitat-based approach to measuring impacts and determining offset requirements which
might lend itself to the UK situation. This draws on a version first published in Defra (2009) and
companies. It is based on hectares of habitat of particular type3 or intrinsic 
adjusted to account for differences in condition (which in UK habitats is often closely linked to
suitability of management). 
system and the requirements of the UK BAP (1995) and should be seen as a starting point for
purposes of discussion and debate rather than a recommended final solution. For purposes of
illustration we present a hypothetical worked example, but rigorous testing would be required to
ensure that the approach  At the end of the paper
we identify some potential pitfalls and issues that might need further consideration.
3 IHS is suggested because it encompasses all UK terrestrial, freshwater and marine habitats, including European
and BAP habitats ( It is also now widely used at local and regional scales for mapping and
collating habitat data recorded in other classifications (e.g. Butcher, 2008; SERC 2007).
Some key principles and assumptions
There are some circumstances in which use of offsets will never be appropriate: offsets should
not be used for impacts on biodiversity which needs to be conserved in situ for it to survive, for
example. In the UK, offsets might therefore be inappropriate for any BAP habitat with 
habitat which takes so long to establish and mature that it is effectively
irreplaceable in any reasonable human timeframe, such as ancient woodland or raised bog.
Another key concept in biodiversity offsetting is additionality, or the requirement for offsets to
deliver conservation outcomes which can be shown to be additional to those that would have
occurred anyway, or which are the responsibility of statutory bodies to deliver. Additionality
might be achieved by protecting lowland deciduous woodland that would otherwise have been
rapidly destroyed, or by creating a diverse habitat on intensive arable cropland. On the other
hand, there would be no additional value in buying woodland that was not under any immediate
threat and then doing nothing with it. Even if the woodland improved in quality over time, for
example through succession, this could not be claimed as an outcome or benefit of the offset
per se.
Biodiversity offsets can't be used to solve every conservation challenge and should be used
intelligently in conjunction with other conservation policies and tools. We have therefore
assumed that any UK offset system would have to complement existing requirements for
ecological compensation under the Habitats Directive and would only apply to losses of habitat
occurring outside the Natura 2000 network.
Possible approach/ framework
The approach 
habitat which will be exposed to an impact and also to land which might be used for an offset.
It is possible to draw on established methods to assess habitat condition, such as those used on
nationally designated sites (Natural England, 2008), but there are no universally agreed
methods for assessing levels of biological distinctiveness. A consultation exercise is currently
underway through the auspices of the Natural Capital Initiative4 to test the extent to which
consensus can be reached if ecologists assign UK habitats to distinctiveness categories a priori
and without in depth assessment on a case-by-case basis, but this is an area where further
research is likely to be necessary.
A potential scoring system is set out in the offset matrix shown in Figure 1. We propose a four
point scale from 0 to 3 in which a score of zero would be assigned
to e.g. as applied by Kyläkorpi et al., 2005) and a score of 3 to
BAP and Annex 1 habitat categories (EU Habitats Directive5). For current purposes we have
doubled the distinctiveness score in the matrix to account for the fact that intrinsic biological
distinctiveness is a more fundamental and less alterable property than current condition. Again,
this requires testing to ensure that reasonable outcomes result in practice. Scores can be
normalised on a scale of 0 to 1 as shown in square brackets. A score of 1 results in cases
where habitat with high distinctiveness and optimum condition is affected.
5 Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora
Figure 1: Offset scoring matrix
Biodiversity Distinctiveness
Very Low (0)
Low (2)
High (6)
Optimum (4)
8 [0.33]
24 [1.00]
Good (3)
6 [0.25]
18 [0.75]
Moderate (2)
12 [0.50]
Poor (1)
2 [0.08]
6 [0.25]
The area of habitat to be lost, multiplied by the score from the matrix gives the credits, or
required for the offset. If several habitat types are present, the assessment must
be repeated for each one and the results summed to give the overall offset requirement.
offset must deliver an overall ratio of 1:1 (or better) when offset
gains are compared with the predicted losses due to development. To quantify gains on
potential offset land the final predicted outcome in terms of area x matrix score must be
compared with the baseline or starting condition of the land to be used.
Generating measurable biodiversity gains
In a system such as the one proposed here, the main ways to generate measurable biodiversity
gains are by improving condition of a particular habitat (e.g. by bringing a degraded lowland
heathland into appropriate management) or by elevating distinctiveness category (e.g. by
converting a Category 2 grassland to a Category 3 grassland
Lowland Meadow BAP habitat).
Gain on the distinctiveness scale involves a movement to the right in the matrix (e.g. a low level
of distinctiveness to a high level), while gain on the condition scale involves an upwards
movement (e.g. improvement in condition from poor to good). Use of the matrix to determine
offset requirements means that every offset should contribute to requirements under the UK
BAP to:
1. Achieve condition in existing (priority) BAP habitat.
2. Restore relict/degraded habitat to a BAP habitat type.
3. Expand area of BAP habitats through creation effort.
A hypothetical worked example
Figure 2 shows 14 ha of land near Aberdeen which has been mapped using IHS (NESBREC,
2007) and is due to be lost as a result of a hypothetical development proposal. Hypothetical
condition scores have been assigned to habitat parcels.
Figure 2: habitat types and condition on land to be affected by the development
Figure 3 summarises the losses that will occur and the credits required.
Habitat type
Matrix Score
Offset credits or
Hard surface
Very Low
Neutral grassland
(non BAP)
Dry heath (BAP)
Dry heath (BAP)
Total area of
impact and
credits required
Figure 3: Credits or habitat units to be lost
Figure 4 shows 32 hectares of land, also near Aberdeen. In our hypothetical example this area
has been offered as a potential offset and we need to decide whether it is able to provide the
required credits or habitat units.
Figure 4: habitat types and condition on potential offset site
Figure 5 summarises the habitats on the potential offset area and their baseline levels of
distinctiveness and condition. The offset needs to deliver gains commensurate with the losses
identified in Figure 3. There are various options for achieving this, the most obvious being
through gains in condition.
Habitat Type
justification for
level of
HE1 (Dry Heath)
BAP habitat
EM4 (Purple Moor
Grass and Rush
BAP habitat
GA1 (Lowland Acidic
BAP habitat
GA0 (Acidic
Non BAP habitat
CR0 (Crops)
Non BAP habitat
G10 (Improved
Non BAP habitat
Figure 5: Baseline assessment of potential offset
Impacts should be offset by actions on specific parts of the proposed offset area, with the final
status of the offset land always equal or better on both distinctiveness and condition scales than
the corresponding impacted land. This means that losses of BAP habitat extent or condition
would have to be offset through gains in extent or condition of the same or a different BAP
habitat. On the other hand, loss of extent or condition in a non-BAP habitat could be offset
through gains in extent or condition in a BAP habitat.
Figure 6 summarises potential enhancements, based on the assumption that all land will be
maintained at, restored to or created as BAP habitat (thus scoring high on the distinctiveness
scale); and that the offset must result in achievement of  when it is
mature (suggested rules which are open to debate). There may be a time lag involved in
achieving the required condition, hence the likely need to consider using multipliers in any
eventual UK system (beyond the scope of this paper).
Habitat Type
Action to deliver gain
(change from poor to
good condition in
habitat units)
Potential enhancement
(change from poor to
optimum condition in
habitat units)
HE1 (Dry Heath)
Achieve condition
EM4 (Purple Moor Grass
and Rush Pastures)
Achieve condition
GA1 (Lowland Acidic
Achieve condition
GA0 (Acidic Grassland)
Restore BAP habitat
CR0 (Crops)
Expansion (create BAP
G10 (Improved Grassland)
Expansion (create BAP
Figure 6: options for delivering gains
Offset options vary. Focusing on one habitat only, a
the Dry Heath or creating BAP habitat in optimum condition on the Improved Grassland could
deliver the required gain of at least 6.73 credits/ habitat units (see Figure 3). Another option
might be to achieve optimum condition on EM4, and GA1 and create BAP habitat in optimum
condition on CR0 and G10, resulting in a composite offset delivering 7.28 habitat units.
Most biodiversity offset systems in use worldwide include rules relating to allowable exchanges
between habitats when determining offset requirements. Most h-assumption
for replacement of lost habitat, but allow offsets based on different types provided that these are
In our example a similar rule might be to
require the offset to deliver the same habitat as the impacted one, unless there is gain on the
distinctiveness scale. This 
ation, to offset the loss of 5.8ha. Creation of other BAP habitat (for example additional
Purple Moor Grass and Rush Pasture) would only be possible once losses of Dry Heath had
been offset.
Possible unintended consequences and issues requiring further consideration
This paper has focused on just one aspect of biodiversity offsets; there are many others which
will require careful consideration and testing in practice before a robust system can be assured.
Some issues requiring further consideration are outlined here, as well as some possible
unintended consequences of the proposed approach.
Based on review of methods in use worldwide, we conclude that it would be possible to develop
a workable method to assess losses and gains as part of an offset system which could deliver
demonstrable gains in BAP habitat extent and condition. Any UK system for biodiversity offsets
would probably apply only in certain prescribed circumstances, however. It is likely that offsets
would apply to losses of habitat occurring outside the Natura 2000 network and that impacts on
 as discussed earlier in this paper. The
method suggested here could apply to any impact (however small) on any habitat (whether
considered important or not), with potential benefits in terms of tackling cumulative impacts
(such as those highlighted in a recent article on development creep in The Guardian 6) but 
use for small scale impacts on habitats of low distinctiveness and condition would only be
practicable if a straightforward system for requiring and identifying offsets could be established
to ensure an acceptable bureaucratic load for numerous smaller transactions (a system of
It might be necessary to put safeguards in place to avoid an outcome in which impacts are
always offset by condition enhancement on existing habitat, rather than by gains in
distinctiveness (which are likely to be harder to achieve in practice). This could be avoided by a
rule requiring offsets to include an equivalent area of habitat expansion and/or restoration to
ensure that there is no loss of extent of BAP habitat, where impacts will result in deterioration on
the biodiversity distinctiveness scale.
Another necessary safeguard might be a requirement for the final condition of any offset to be
good or optimum. Clearly further work is required to identify suitable criteria for determining
when such a condition has been achieved and to establish a reasonable timeframe for this. It
may be necessary to establish indicators which can be used to determine whether
implementation of appropriate management does indeed deliver demonstrable gains in
condition and/or distinctiveness, for example. Whatever system is introduced, and whoever
delivers the offsets ("habitat banks" or some other agency), it will be essential to have
independent, trusted auditing or verification.
Recognising that habitat expansion, restoration and condition achievement carry varying levels
of outcome uncertainty, it may be necessary to consider use of appropriate multipliers to ensure
a robustly fair offset. Similarly there may be long delays in achievement of prescribed outcomes.
In some cases it will not be appropriate to replace habitat lost now with the same habitat units in
viability could be compromised by temporary loss of habitat. Multipliers could also play a part
here, but this is a controversial area, beyond the scope of this paper.
The proposed metric (area x condition x distinctiveness) is a general metric that can be applied
to all UK sites/habitats and is fungible. In effect it represents a kind of "lowest common
denominator". Supplementary methods would be necessary to ensure that high-priority
biodiversity features for which habitat is not a good surrogate are appropriately measured and
offset. Risk of impacts on habitats with high distinctiveness or the presence of BAP species
might be the trigger for further consideration of this kind.
If a biodiversity offset system allows impacts on one habitat type to be offset through actions to
enhance another (as suggested here), it is important to check that the overall balance of
habitats is maintained with impacts and offsets in place over time and that some habitats do not
gain at the expense of others (perhaps those which are more challenging to restore). This
exchange rules such as the one suggested earlier. A reliable system of strategic spatial
planning might also be important to ensure that offsets are delivered on suitable land or that
opportunities to develop habitat networks are realized. This is an aspect which will require
careful consideration given recent changes in regional planning.
References and web links
Butcher, B (2008) Regional Habitat Data Project, Stage 2. West Midlands Biodiversity
Partnership, unpublished report.
Defra (2009) Scoping study for the design and use of biodiversity offsets in an English Context.
Final Report, Contract NEE 0801,
eftec, IEEP (2010) The use of market-based instruments for biodiversity protection The
case of habitat banking Technical Report to European Commission DG Environment. (accessed 08.08.2010).
Kyläkorpi K, Rydgren B, Ellegård A, Miliander S, Grusell E (2005) The Biotope Method 2005. A
method to assess the impact of land use on biodiversity. Vattenfall, Sweden.
Natural England (2008) SSSI condition assessment: A guide for owners and occupiers. NE 61
Natural England, Peterborough.
North East Scotland Biological Records Centre (NESBReC) (accessed 08.08.2010)
SERC 2007 SERC (2007) Integrated Habitat System Regional Dataset for SE England, South
East England Local Records Centres. Somerset Environmental Records Centre, Wellington.
UK BAP ( (accessed 08.08.2010)
UK BAP (2006). Review of BAP Targets Target Type Definitions, UK BAP 2006
... A DEFRA 2013 Green Paper on biodiversity offsetting discusses these precedents as demonstration projects and in the absence of empirical studies conflates their existence for policy success. Much of this scoping report was subsequently recycled into the technical guidance for the design of the biodiversity metric 'currency' within English offsetting systems (Treweek et al., 2010). ...
... Early offset projects, however, tended to rely on area alone (such as wetland mitigation banking). Many biodiversity offset projects, including and the ones in England and the EU, use metrics that assess several dimensions across habitat distinctiveness, condition and sometimes ecosystem function (Gonçalves et al., 2015;Treweek et al., 2010) as well as the spatial area (like hectares or acres) in compound metrics. 4. BBOP personal communication, 2015. 5. Other sources of funding included environmental taxes, NGO sector funding and private payment for ecosystem services (PES) schemes 6. ...
Full-text available
Policies for biodiversity no net loss and net gain underwrite narratives for green growth through advancing reparative logics to ongoing habitat impacts. By enabling offsetting practices that risk accommodating rather than averting land change developments, net principles are said to resemble modes of ‘accumulation by environmental restoration’. Biodiversity net principles are frequently depicted visually as a diagram of the mitigation hierarchy for communicational ease and have proliferated over recent decades despite little evidence for their ecological effectiveness. This paper combines economic sociology, visual media analysis of the net diagram and political ecology to account for the stabilisation of net principles in policy frameworks. It highlights the upstream imaginative work that this visual tool and its wider assemblages perform to support offsetting and habitat banking practices on the ground. The paper positions the NNL diagram as a conceptual and ideational technology. It traces the practices through which biodiversity is rationalised by the Cartesian coordinates of an XY schematic, and en-framed as a measure of numerical value on a vertical scale. The effect is to engender coherence to the idea of netting out differences in aggregate sums of biodiversity unit value, making nature conceptually offset-able. I develop this account through a history of the diagram as well as the broader processes that have shaped the policy and its arrival in English planning frameworks. Observers increasingly question how biodiversity offsetting and no net loss/ net gain have become so popular when their empirical foundations are so weak. This paper proposes that within the wider assemblages of actors, one answer is located in the potency and mobility of conceptual technologies such as diagrams of no net loss or net gain of biodiversity and the logic of balance-sheet accounting that is imbricated within the visual design.
... Developers in England will have to demonstrate their proposals achieve a net gain in biodiversity (measured using a government-prescribed biodiversity metric) to receive planning permission from local planning authorities (LPAs), who ultimately assess all of the development plans associated with the site (which can include various economic, social and environmental impact assessments, construction plans, feasibility studies, etc.) and decide whether projects have the right to proceed. Currently, BNG assessments align with the ecological impact assessment (EcIA) process, taking information routinely collected during predevelopment ecological surveys and feeding this through an Excel-based biodiversity calculator tool, the "Biodiversity Metric 2.0″ (Crosher et al., 2019;Treweek et al., 2010). The Metric is a multiplicative composite indicator converting inputs including the area, habitat condition, habitat distinctiveness, and various multipliers (capturing elements including the risk of project failure, the expected time taken for the proposed habitat to reach its desired condition level, and the landscape-scale ecological importance of the site) for each habitat patch within the development footprint into an overall biodiversity score measured in "biodiversity units" (Supporting information). ...
... Another mechanism might be capping how much urban land take is permitted by the policy. When the Metric was first designed, the authors recommended a 1:1 minimum area be established, so that a loss of habitat area could not solely be compensated for through promises of future condition increases (Treweek et al., 2010). On the other hand, a mandatory area target might disincentivize delivering higher condition habitats. ...
Full-text available
Net outcome‐type biodiversity policies are proliferating globally as perceived mechanisms to reconcile economic development and conservation objectives. The UK government's Environment Bill will mandate that most new developments in England demonstrate that they deliver a biodiversity net gain (BNG) to receive planning permission, representing the most wide‐ranging net outcome type policy globally. However, as with many nascent net‐outcome policies, the likely outcomes of mandatory BNG have not been explored empirically. We assemble all BNG assessments (accounting for ∼6% of England's annual housebuilding and other infrastructure) submitted from January 2020 to February 2021 in six early‐adopter councils who are implementing mandatory no net loss or BNG requirements in advance of the national adoption of mandatory BNG, and analyze the aggregate habitat changes proposed. Our sample is associated with a 34% reduction in the area of nonurban habitats, generally compensated by commitments to deliver smaller areas of higher quality habitat years later in the development project cycle. Ninety‐five percent of biodiversity units delivered in our sample come from habitats within or directly‐adjacent to the development footprint managed by the developers. However, we find that these gains fall within a governance gap whereby they risk being unenforceable, a challenge that is shared with other net outcome type policies implemented internationally.
... Our results support the view that there are some downsides of using a simple approach like the matrix method even though it may be more straightforward and quicker to use than more complex ones (Treweek et al. 2010). However, it should Environmental Management be noted that the simplicity and labor intensity of the matrix method heavily depends on the metric which determines the condition score. ...
... The calculation methods have differences in dealing with the substitutability of individual components. The matrix method assumes that all biodiversity values are commensurable (Treweek et al. 2010), although, this is dependent on the metric the condition score is calculated with. The additive function allows substitutability between different components (McCarthy et al. 2004), whereas, in the ELITE index, the use of multiplicative function aims to reduce substitutability. ...
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The rates of ecosystem degradation and biodiversity loss are alarming and current conservation efforts are not sufficient to stop them. The need for new tools is urgent. One approach is biodiversity offsetting: a developer causing habitat degradation provides an improvement in biodiversity so that the lost ecological value is compensated for. Accurate and ecologically meaningful measurement of losses and estimation of gains are essential in reaching the no net loss goal or any other desired outcome of biodiversity offsetting. The chosen calculation method strongly influences biodiversity outcomes. We compare a multiplicative method, which is based on a habitat condition index developed for measuring the state of ecosystems in Finland to two alternative approaches for building a calculation method: an additive function and a simpler matrix tool. We examine the different logic of each method by comparing the resulting trade ratios and examine the costs of offsetting for developers, which allows us to compare the cost-effectiveness of different types of offsets. The results show that the outcomes of the calculation methods differ in many aspects. The matrix approach is not able to consider small changes in the ecological state. The additive method gives always higher biodiversity values compared to the multiplicative method. The multiplicative method tends to require larger trade ratios than the additive method when trade ratios are larger than one. Using scoring intervals instead of using continuous components may increase the difference between the methods. In addition, the calculation methods have differences in dealing with the issue of substitutability.
... Below we give an overview of the Development by Design process used to implement the process at Barrick's Kanowna Belle operations. Many studies have outlined the offset design process [16][17][18][19][20], and our intention here was not to do an in depth review of these methodologies. Instead, in this paper we focus on the challenges of determining and implementing offsets using a real world example to highlight those challenges and potential solutions. ...
... Establishing goals for mitigation (i.e., what is necessary to offset impacts) first requires an estimate of expected direct and indirect impacts [19]. These impacts, which may be due to a proposed project, expanded resource use or, as with the case of Barrick's Kanowna Belle mine, the result of existing impacts, are analyzed at a site-level to understand the specific nature of potential impacts. ...
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Biodiversity offsets can be an important tool for maintaining or enhancing environmental values in situations where development is sought despite negative environmental impacts. There are now approximately 45 compensatory mitigation programs for biodiversity impacts worldwide, with another 27 programs in development. While offsets have great potential as a conservation tool, their establishment requires overcoming a number of conceptual and methodological hurdles. In Australia, new policy changes at the national and state (i.e., Western Australia) level require that offsets follow a set of general principles: (1) Environmental offsets may not be appropriate for all projects and will only be considered after avoidance and mitigation options have been pursued; (2) Environmental offsets will be based on sound environmental information and knowledge; (3) Establishing goals for offsets requires an estimate of expected direct and indirect impacts; (4) Environmental offsets will be focused on longer term strategic outcomes; (5) Environmental offsets will be cost-effective, as well as relevant and proportionate to the significance of the environmental value being impacted. Here we focus on the challenges of determining and implementing offsets using a real world example from a voluntary offset process undertaken for Barrick Gold's Kanowna Belle mine site in Western Australia to highlight those challenges and potential solutions.
... These mapped and classified sites are then scored according to their observed condition and biodiversity distinctiveness with the scoring matrix of the BDO metric (Table 1). Distinctiveness is determined based on the guidelines in Treweek et al. (2010) and especially on species richness, diversity, rarity, and the unique potential for the area to support species rarely found elsewhere (DEFRA 2012b). The habitat condition grades are adapted from the Higher Level Agri-Environment Scheme (HLS) Farm Environment Plan Manual (FEP). ...
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This paper describes and analyses applied practices creating numerical equivalence between sites of development impact and proposed conservation offset sites in the new conservation technology of biodiversity offsetting. Application of biodiversity offsetting metrics in development impact and mitigation assessments is considered to standardize biodiversity conservation outcomes, sometimes termed 'biodiversity yield' by consultants conducting these calculations. The youth of biodiversity offsetting in application, however, means that little is known about how biodiversity valuations and offset contracts between development and offset sites are agreed in practice, or the long-term implications for conservation outcomes. We respond to the first of these gaps in particular by demonstrating how sites were made commensurable and biodiversity gains or yields were calculated and negotiated for a specific offset contract in a government-led pilot study into biodiversity offsets in England. Observations over 24 months were based on repeat site visits, 50 transcribed semi-structured interviews subjected to textual analysis using a qualitative data analysis computer software programme, and review of biodiversity offsetting calculation spreadsheets and planning documents. The technical calculations made and negotiated in different iterations of a specific Biodiversity Impact Assessment using the biodiversity offsetting metric developed by the UK's Department for Environment, Food and Rural Affairs constitute a particular focus of the paper. We highlight three main findings. First, biodiversity offsetting metrics are being amended in creative ways as users adapt inputs to metric calculations to balance and negotiate conflicting requirements. Second, the practice of making different habitats equivalent to each other through the application of biodiversity offsetting metrics is giving rise to commensuration outcomes that may be questionable in terms of projected conservation outcomes. Third, the pressure of creating value for money in compensation strategies for conservation can diminish conservation 'yields' in the competitive search for less expensive mitigation options. This article is protected by copyright. All rights reserved.
... It quantitatively aligns the qualities of a habitat's ecological distinctiveness against its condition in a matrix that produces the quantitative value of a hectare of biodiversity habitat as a numerical surrogate. Distinctiveness includes parameters such as species richness, diversity, rarity (at local, regional, national and international scales) and the degree to which a habitat supports species rarely found elsewhere (Treweek et al. 2010). DEFRA (2012) guidance for measuring habitat condition is to use the Farm Environmental Plan manual for the Higher Level Stewardship Scheme (Natural England 2010) which is designed to give a specific output categorising habitats into three states, namely "favourable, favourable recovering, and unfavourable". ...
In light of ongoing global biodiversity loss, there is an increasing need for restoration-based activities to complement conventional nature conservation activities. Building on this premise, the paradigm of “no net loss” has risen to prominence in a worldwide context and particularly with respect to EU policy. In this scope, biodiversity offsets are increasingly explored and promoted to reach the no net loss goal.
Technical Report
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Biodiversity metric 2.0 provides developers, planners, land managers and others with a tool to help limit damage to nature in the first place and to help it thrive. The metric uses habitat features as a proxy measure for capturing the value and importance of nature. It uses a simple calculation that takes into account the importance of these features for nature: their size, ecological condition, location and proximity to nearby ‘connecting’ features. The metric enables assessments to be made of the present and forecast future biodiversity value of a site. This can be applied to an individual field or an entire river catchment. The biodiversity metric 2.0 enables developers and land managers to better understand and quantify the current value of a place for nature and how proposed changes to that site, either from development or land management practice, will impact on that value. In short, it provides a way of calculating biodiversity gains and losses. The metric enables developers and land managers to see how they might be able to design a site or implement a land management change in a way that increases its value to nature over time. The biodiversity metric 2.0 is the successor to the biodiversity metric published by Defra in 2012 and commonly referred to as the ‘Defra biodiversity metric’. Biodiversity metric 2.0 builds upon that original metric. Co-developed with the help of industry, environmental NGOs, planners and land managers biodiversity metric 2.0 represents a significant advance in our ability to account for and measure biodiversity losses and gains. This new metric can be used in all terrestrial development and land management scenarios. It can measure the value of habitats ranging in scale from individual street trees and green roofs through to very important priority habitats. The biodiversity metric 2.0 includes all terrestrial habitats including linear habitats (hedgerows, lines of trees, rivers and streams) whose biodiversity value is calculated separately to the main metric calculation.
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In many countries, biodiversity compensation is required to counterbalance negative impacts of development projects on biodiversity by carrying out ecological measures, called offset when the goal is to reach "no net loss" of biodiversity. One main issue is to ensure that offset gains are equivalent to impact-related losses. Ecological equivalence is assessed with ecological equivalence assessment methods taking into account a range of key considerations that we summarized as ecological, spatial, temporal, and uncertainty. When equivalence assessment methods take into account all considerations, we call them "comprehensive". Equivalence assessment methods should also aim to be science-based and operational, which is challenging. Many equivalence assessment methods have been developed worldwide but none is fully satisfying. In the present study, we examine 13 equivalence assessment methods in order to identify (i) their general structure and (ii) the synergies and trade-offs between equivalence assessment methods characteristics related to operationality, scientific-basis and comprehensiveness (called "challenges" in his paper). We evaluate each equivalence assessment methods on the basis of 12 criteria describing the level of achievement of each challenge. We observe that all equivalence assessment methods share a general structure, with possible improvements in the choice of target biodiversity, the indicators used, the integration of landscape context and the multipliers reflecting time lags and uncertainties. We show that no equivalence assessment methods combines all challenges perfectly. There are trade-offs between and within the challenges: operationality tends to be favored while scientific basis are integrated heterogeneously in equivalence assessment methods development. One way of improving the challenges combination would be the use of offset dedicated data-bases providing scientific feedbacks on previous offset measures.
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Biodiversity offsets are compensatory mechanisms increasingly used to address ecological impacts resulting from human activities. We review the scientific literature on biodiversity offsets, published between 1999 and 2014. We found that biodiversity offset studies have increased through time. The majority of studies have been carried out in the USA. The development of biodiversity offsets schemes faces conceptual and practical challenges. The conceptual challenges discussed in the literature are: choice of metric, spatial delivery of offsets, equivalence, additionality, timing, longevity, ratios and reversibility. The practical challenges reported in the literature are: compliance, monitoring, transparency and timing of credits release. Amongst these, choice of metric and location are paramount and are related to the multidimensional nature of biodiversity and the values society places on biodiversity. Harmonized metrics such as the Essential Biodiversity Variables (EBVs) help to address these challenges by providing comparability of biodiversity loss and gain amongst locations.
Regional Habitat Data Project, Stage 2. West Midlands Biodiversity Partnership
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