Biodiversity Metric 3 Training for Planners

PAS hosted a Natural England webinar for local authority planners on the Biodiversity Metric 3 in October 2021. You can access a recording of the event, download a PDF of the slides and view questions and answers from the session here.

October 2021

Biodiversity Metric 3 is a biodiversity accounting tool that can be used to calculate losses and gains for terrestrial and/or intertidal habitats associated with a development or other project. Biodiversity Metric 3 was released in July 2021; updating and replacing the beta Biodiversity Metric 2.0. It can be used now and is intended to underpin the Environment Bill’s provisions for mandatory biodiversity net gain.

This event was aimed at Planners working within Local Planning Authorities to help better their understanding of Biodiversity Metric 3, including how to interpret outputs from this tool, and identify where errors may have occurred in completion of the tool. The event was hosted by PAS with training provided by Natural England.

The training covered:

  • An introduction to Biodiversity Metric 3
  • Using Biodiversity Metric 3
  • Interpreting the outputs
  • Case study
  • Top tips
  • Bad practice and error messages

After the presentation there was a question and answer session. This included questions and useful answers on broader issues relating to the application of biodiversity net gain and the new requirements coming in through the Environment Bill. The Q&As are posted below.

A recording is available on YouTube and the slides from the event can be downloaded as a PDF below.


The following questions and answers are taken from this training session on Biodiversity Metric 3 with some updates to reflect more recent information in June 2023.

Is there an online option to login and access the Biodiversity Metric spreadsheet? 
In what form will the metric report be submitted with a planning application?  It will need to be made available to the public - online tool might be difficult.

Currently, and for the immediate future, the Biodiversity Metric is a Microsoft Excel-based tool and therefore requires Excel to operate. It is expected that the full metric spreadsheet should be submitted by developers to LPAs for consideration, with a planning application. Defra will be exploring options to digitise the metric in the future.

Who is expected to complete the habitat condition assessment sheets? If LPAs, will there be any training on identifying habitats and their condition?
Will developers be responsible for providing the relevant outputs from the metric for LPAs consideration rather than the LPA being responsible for inputs?
Do we need to verify that the metric has been completed by qualified ecologists? Particularly if we, as reviewers, are not qualified in recognising habitat types etc.

The metric calculations/spreadsheets are technical and beyond the capability or time resources of existing planning officers to scrutinise, who will do this?

The value of a site's habitat can be a subjective view. Does the metric recognise if a site has been under or overvalued?

How is the default condition value assigned to a habitat type assigned? I note this is auto populated when you select a habitat type.
If the LPA does not have access to ecological expertise, how do they assess whether the assessment of condition is accurate?
How are LPAs supposed to know what undervaluing or overvaluing the habitat baseline/proposed would look like?

Responsibility for completing the Biodiversity Metric assessment and calculations

For habitat condition assessments in association with development, it is the developer's responsibility to provide the Biodiversity Metric calculations to include in the Biodiversity Gain Plan. The Biodiversity Gain Plan will require a statement of competency for a named person who has carried out the assessment and metric calculation. So, developers will need to employ a ‘competent person’ to conduct the habitat survey and assessments and complete the metric tool. The developer will then share the full spreadsheet with the LPA, alongside other required documents for the application. LPAs will not be responsible for completing the metric.

‘Competency’ to use the metric

A 'competent person' is defined as: being able to confidently identify the positive and negative indicator species for the range of habitats likely to occur in a given geographic location at the time of year the survey is undertaken. For a full metric application, the competent person should be an ecologist. However, in circumstances where the development fits with the criteria to use the Small Sites Metric it is not necessary for the metric to be completed by an ecologist but by someone who is competent to use that metric. It is the developer or applicant's responsibility to ensure that the person they appoint to complete the metric fulfils this criteria and is suitably competent, as described in the metric User Guide. Biodiversity metric users will not be required to have received formal training or accreditation, but a training course must be completed and accreditation achieved by those using the watercourse element of the metric. Defra and Natural England are working with industry to provide training and further guidance on the Biodiversity Metric. Natural England has also been looking at the potential for assurance schemes for BNG more generally.  We will add more information on this as it becomes available.

LPA responsibilities and how to meet these

It is expected that LPAs will review and check the metric spreadsheets. In order to verify the habitat surveys, LPAs could refer back to aerial photos, Local Environmental Record Centres or other data sources and seek the advice of local ecologists (where available).

Natural England and Defra recognise that resources within LPAs are stretched and we hope that there will be more information on new burdens funding for LPAs soon. PAS produced a short guide on resourcing BNG for local authorities to help identify what skills and expertise are needed to meet the new requirements.

Assessing the values ascribed by the metric

The values ascribed to individual habitat types within the metric are based on the ‘distinctiveness’, condition, spatial location and importance of those habitat features. The metric cannot recognise whether a habitat type has been correctly identified or the condition and strategic significance assessed accurately. This is reliant upon the competence and integrity of the individuals entering the data. Detailed guidance has been provided to assist in assigning the correct habitat type and condition to a habitat.

The habitat distinctiveness scores are set within the metric and are based on ecological evidence that will be kept under regular review. Fixing the distinctiveness scores in the metric ensures greater consistency and reduces the scope for subjectivity and dispute.

Habitat condition is established by undertaking a habitat survey and ascribing a condition score to a habitat, based on the judgement of a suitably competent person (usually an ecologist). Condition sheets have been published with the metric to allow for greater consistency of assessment. In the case of rivers and watercourses, the person undertaking the condition assessment must be accredited in the use of the condition assessment methodology. For a small number of habitats, the condition is fixed and prepopulated in the metric and a condition assessment is not required.

Spatial location can also affect a habitat's value, in particular whether or not the habitat is of, or in a location that is of, ‘strategic significance’. This is determined by published local plans and strategies and can be specified by the LPA. It is expected that Local Nature Recovery Strategies (LNRS) will standardise strategic significance by mapping and describing those habitats of particular local importance (for creation and/or enhancement). See also above under Local Plans for further information on ‘strategic significance’ in policy and below on LNRS.

Should the use of the metric be explicitly required in Local Plan policy?

Under mandatory BNG, there will be a requirement to use the latest version of the statutory Biodiversity Metric so there is no need to repeat this in Local Plan policy. Prior to mandatory BNG, there is no requirement to use the Biodiversity Metric and projects can continue to use an alternative metric (unless the LPA has specified which metric to use). If the LPA does not specify the use of another metric, then we would recommend using the most recent version of the Biodiversity Metric.

What level of info will be required for Plan Making? Would allocations need to be supported by assessments? Is a strategic approach required for mitigation?
Is the Metric required during the Local Plan process, i.e. assessing potential site allocations, or is it more geared towards planning applications?

It would be helpful if potential site allocations could be assessed for their biodiversity value as this will help ensure application of the mitigation hierarchy by flagging up any high value (for biodiversity) sites before these get allocated. It will also help to give an indication of how easy (or otherwise) developers will subsequently find it to deliver BNG solely within the allocated site baseline, or whether they will likely need to go off-site to meet the local BNG % requirement i.e. if the allocated site has a low biodiversity unit baseline score it is likely that BNG could be delivered entirely within the site. If it has a high score, then it will be very difficult and the developers will likely need to look for off-site opportunities. LPAs could then think about how to encourage strategic habitat banks to provide the supply of offset units developers will need – the baseline assessment will have provided sufficient intel to be able, with some confidence, to anticipate what types of habitats and unit types will be required.

In addition to such uses the metric can also be used to track changes in the biodiversity value of land overtime and, as such, can be used for performance monitoring and reporting purposes.

Is there to be any standard guidance produced to inform applicants how to use the metric? This will save LPAs producing separately for example as part of SPD.

It is not expected that LPAs will need to produce their own metric guidance. There is currently a simple user guide for the metric embedded within the tool (click the “Instructions” tab on the opening page). This is also available on the Biodiversity Metric web page, along with two substantial guidance documents: the ‘User Guide’ and ‘Technical Supplement’. Natural England has produced some case studies (available on the metric webpage) to assist in the interpretation of this guidance with more to come and there are plans to update the user documents alongside the statutory metric.

Is there a requirement for a plan showing how the various area calculations have been made to be submitted with the metric? Big job to check this otherwise.

It is strongly recommended that a plan is supplied, and that information provided in the plan enables habitat parcels shown to be clearly identified in the associated metric calculation. There is a facility to attach a plan to the metric on the start page. LPAs should encourage developers to submit as much information as possible within the “assessor comments” section of the metric to justify their decision-making regarding each habitat parcel. It is expected that Biodiversity Gain Plan requirements for mandatory net gain will include pre- and post-development maps.

How can it be applied to an outline application where the layout has not been established?

The metric is intended to be used early in the design process, in order to quantify and evaluate the impacts of different design options when there is more scope to influence design changes and achieve better ecological outcomes. The metric can be applied on an indicative basis and by adopting a precautionary approach when ascribing habitat condition and distinctiveness values.

Is the metric climate change-proofed as some habitats will be lost or inevitably change over time?

The metric accounts for a variety of risk factors within it which can influence whether or not a particular habitat will be successfully established. These risk factors are standardised, evidence based and will be kept under review.

Does every type of habitat which is reduced have to be re-provided? Or can a balance be done, e.g. hedgerows +50% grassland -10%?

The minimum percentage requirement (e.g. 10%) should be applied to all area and/or linear unit types found within the development site red line boundary and should be applied irrespective of whether the habitat in question was directly or indirectly impacted by the development. Area, hedgerow and watercourse habitat units are all considered separately and are not interchangeable; you cannot address a loss of one type by providing another. The metric trading rules should always be followed, for example there should be no trading down in habitat distinctiveness. All high distinctiveness habitats require re-creation on a like-for-like basis should they be lost, whereas there is more flexibility for lower distinctiveness habitat types in terms of what habitat can be delivered if they are lost. 

Is urban tree canopy cover a habitat in its own right or should there be double accounting of site areas, e.g. trees over grassland or hardstanding? 
Within Defra Metric 4.0, Traditional Orchards come under the grassland broad category. Should you consider these trees separately?

Urban tree canopy cover should be considered separately to the habitat that it stands on. For example, if there was a one-hectare area of grassland with five trees, then you would record both the one-hectare of grassland and the five trees separately. 

Individual trees should not be recorded separately where they occur within habitat types characterised by the presence of trees, such as orchards, lines of trees or wood-pasture and parkland, but can be recorded where they do not form part of a primary habitat description.

Why does some high distinctiveness woodland creation not generate many biodiversity units in the metric?

Less biodiversity units will be generated where higher distinctiveness woodland is being proposed, compared to a lower distinctiveness woodland type (e.g. ‘other woodland; broadleaved’).  This is due to the difficulty of successfully creating a new woodland from scratch and the associated inbuilt risk multipliers within the metric, such as the time taken for high distinctiveness woodland to reach good condition. Providing the trading rules are adhered to, aiming for a lower condition, or a lower distinctiveness woodland, is more realistic and therefore will generate more biodiversity units within the Biodiversity Metric. As a rule of thumb, when creating new woodland from scratch, unless required to do otherwise to compensate for the loss of an existing area of high distinctiveness woodland, use the ‘other woodland; broadleaved’ category and ascribe a target condition of no greater than ‘moderate’. This is explained further in the metric guidance. Another reason behind this is to encourage retention of the most valuable habitats as part of the mitigation hierarchy before compensating for their loss.

Should site size influence decisions about measuring the area of nominally linear habitats?

All habitats inputted into the Biodiversity Metric need to be measured in hectares, unless they are part of the two linear tabs for either watercourses, or hedgerows and lines of trees, which need to be measured in kilometres. The exception to the above is sites that meet the requirements that allow them to use the small sites metric, in which case area and length is measured in square metres and metres respectively.

Surely, you can't include gardens to deliver BNG as there is no guarantee that gardens will be retained or appropriately managed?
If gardens are counted as 'net gain' how do we prevent habitat loss, through residents converting gardens to hard surfaces and outbuildings allowed as permitted development?

Gardens are included in the Biodiversity Metric for use in biodiversity net gain calculations. Their pre-defined distinctiveness is set at 'low' or 'very low' (depending on whether the garden is vegetated or un-vegetated), and the condition for gardens is set at no greater than 'poor'. The metric also assumes that a significant amount of any gardens established will be ‘lost’ over time i.e. due to decking, etc. Therefore, although gardens can be included within calculations, their low biodiversity unit value accounts for the assumption that a large proportion will potentially be lost, reflecting the fact that these are largely private spaces and so they cannot be legally secured in the same way. That said, gardens can and do provide locally important spaces for biodiversity and their retention and incorporation into design is to be encouraged, hence their inclusion in the metric.

Guidance is provided on how suburban housing should be accounted for in the metric using a precautionary assumption that a housing development would be in the proportion 70:30 developed land/sealed surface to vegetated garden. This can be negotiated up or down by the consenting body or if sufficient justification can be provided by the applicant to deviate from this. 

There is no scope for adding any other habitat as well as/instead of vegetated garden. If a developer wants to try and deliver habitats other than garden through BNG on-site then it should be in the public realm with an appropriate management plan and commitment to deliver and maintain – thus giving a greater degree of certainty than could be achieved in a private garden.

Does the metric incentivise the inclusion of ecological features such as green roofs and walls and street trees within new development?

Yes, Green Infrastructure (GI) features can contribute to a project’s BNG calculations and there are a range of GI features included within the tool, including green roofs, green walls and Sustainable Drainage Systems (SuDS). All such features, whether found on the baseline or included in the post-intervention proposal, should be included in the metric calculations.

Is the metric going to be updated to deal with identified issues calculating BNG for mineral sites as well as the long-term nature of minerals development?
What approach is taken to mineral sites which restore large areas of land after extraction and can take decades to complete their restoration scheme?

It is not Defra or Natural England's intention to alter the Biodiversity Metric specifically for minerals projects. However, Natural England have been working closely with the minerals industry to ensure that the metric is applicable and suitable for mineral sites and projects. Natural England will also be publishing specific case studies, developed in conjunction with the sector, to illustrate how best to approach metric calculations on minerals sites and how this will work in practice.

Once the Statutory Biodiversity Metric is released, the intention is to update it every 3 to 5 years to incorporate industry feedback.

Further information on the application of the BNG policy requirement to minerals sites. e.g. s73 and ROMPs, is outlined in the 2022 BNG consultation from Page 34 and Section 4.1 of the 2023 BNG consultation response. This was also covered at our deep-dive session on the BNG process in TCPA development in Spring 2022.

Five years after development is complete, how does the Biodiversity Metric assist checks on the BNG achieved? Who is responsible for future evidence? Who pays?
Is the developer/developer's ecologist responsible for the monitoring of the BNG or is the LPA?

Monitoring is the responsibility of the developer and should be set out in the biodiversity gain plan. LPAs will have duties to report on BNG delivery. Some information on monitoring requirements is set out in the BNG consultation from Page 80. Planning authorities will be required to set any specific and proportionate monitoring requirements as part of planning conditions and obligations. A typical monitoring schedule for a project will include reports in years 2, 5,10, 20 and 30 and will include habitat type, extent, and condition. Further guidance on monitoring is expected to be published in Spring 2023. You can also see the slides and recording from our Spring 2022 deep-dive session on BNG monitoring, evaluation and enforcement. 

What is the small sites metric and how does it differ to 4.0?

The Small Sites Metric (SSM) is a simplified version of the Biodiversity Metric which has been specifically designed for use on small development sites where the project chooses to do so, providing there is no priority habitat present on-site. The SSM is not suitable to calculate losses and gains off-site.

Developers should note that the following criteria need to be met to use the small sites metric calculation tool:

  • for residential development: 
    • fewer than 10 residential units on a site area (no more than 9 units) less than 1 hectare
    • when the number of residential units is not known, the site area is less than 0.5 hectares
  • for non-residential development: 
    • the site area is less than 1 hectare.

The biodiversity metric calculation tool must be used, instead of the small sites metric calculation tool, in all cases where

  • priority habitats (high and very high distinctiveness habitats) are within the development site: this does not include the presence of some hedgerows and arable field margins – these are medium distinctiveness habitats;
  • protected sites are within the development site; and/or
  • European protected species are within the development site.

If when using the small sites metric calculation tool, there is a need for off-site units or, as a last resort, statutory credits, complete the calculation instead using the main biodiversity metric calculation tool.

When consulted on major applications, will Natural England analyse the submitted Metric and provide a detailed response?
Will Natural England offer any special advisory service on cases where applicants seek to justify departure from the metric? Will this be important to monitor nationally?

Natural England will not be a statutory consultee on BNG, and so will not be commenting or responding to Biodiversity Metric calculations on a regular basis unless it is a development that triggered Natural England’s involvement as a statutory consultee on other grounds. Dependent on resource, there may be specific cases such as high-risk or high-opportunity case work, where NE may examine metric calculations, likely via their Discretionary Advice Service.