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Biodiversity Compensation Models: An Overview

A key principle of biodiversity offsets is that No Net Loss (NNL) or preferably Net Gain (NG) of indigenous biodiversity values is demonstrably achieved through the quantification of losses and gains. However, it is often difficult to demonstrate these outcomes with confidence, particularly for projects where the biodiversity gains at offset sites are based on future predictions, e.g., predicted tūī counts 20 years after commencement of offset actions. Because of such difficulties, measures to address residual effects at the consent application or plan change phase of a project ordinarily default to compensation.

To this end, we have developed the Biodiversity Compensation Model (BCM). The BCM is intended for use as a decision support tool to provide guidance on the type and amount of compensation required for a project to achieve  positive effects that outweigh the adverse effects on biodiversity values.

We consider the BCM approach to strike the best balance between offsetting theory and practice at the plan change or consent application stage. Through transparency and rigour, the BCM has the potential to facilitate significantly better ecological outcomes than the status quo for determining quanta of compensation: i.e. the sole reliance on professional opinion or arbitrarily applied multipliers or compensation ratios. Importantly, this approach is intended to be at the ‘as close to offset as possible’ end of the compensation continuum.

The BCM approach builds on the foundations of the Biodiversity Offset Accounting Model (BOAM) developed by Maseyk and others (2015). However, it is intended for use only when the information required for the BOAM or other offset accounting models cannot be reliably quantified and effects cannot be demonstrably offset with adequate precision. These BCMs are not used instead of the BOAMs but rather as a precursor to these more comprehensive tools.


The BCM is intended for use only in accordance with biodiversity offsetting or compensation principles: in particular, only once adherence to the effects management hierarchy and limits to offsetting principles have been demonstrably achieved.

As with any method or tool, it is up to the practitioner to justify its use for their assessment based on their relevant experience, professional judgement, and the applicability of the tool to the project site and scale of assessment.

The BCM is not intended to be a formulaic tool applied in the absence of a robust ecological assessment. The appropriateness and validity of its use stands or falls on the practitioner(s) who apply it.

The BCM can (and should) be converted to BOAM to verify that offsets have been achieved (or not) once real data are available, e.g., via biodiversity outcome monitoring programmes at the proposed offset sites after offset actions have commenced.

The following BCM documentation and the model spreadsheet can be downloaded below

Baber, M Christensen, J Quinn, J Markham, G Kessels, G Ussher and R Signal Ross (2021): The use of modelling for terrestrial biodiversity offsets and compensation: a suggested way forward. Resource Management Journal April 2021: 28 – 33. View here.

Baber, M, Dickson, J, Quinn, J, Markham, J, Ussher, G, Heggie-Gracie, S, and Jackson, S (2021). A Biodiversity Compensation Model for New Zealand – A User Guide (Version 1). Prepared by Tonkin & Taylor Limited. Project number 1017287.0000P. View here.

Baber, M, Dickson, J, Quinn, J, Markham, J, Ussher, G, Heggie-Gracie, S, and Jackson, S (2021). Biodiversity Compensation Model for New Zealand– Excel Calculator Tool (Version 1). Prepared by Tonkin & Taylor Limited. Project number 1017287.0000P. View example below.

The BCM calculator tool can be provided on acceptance of the conditions below.

Conditions of use: The User Guide (A Qualitative Biodiversity Model for New Zealand) and the Excel Calculator Tool have been developed by Tonkin & Taylor Limited (T+T) for the purposes set out in the User Guide, by reference to applicable standards, guidelines, procedures and practices at the date of issue of the User Guide. While we intend to update and refine the User Guide and the Excel Calculator Tool from time to time, T+T is under no obligation to do so. T+T accepts no liability to any person in relation to the User Guide or the Excel Calculator Tool (Baber et al. 2021b) other than to its clients in the context of a specific engagement. The application and interpretation of the User Guide and the Excel Calculator Tool by others is outside the control of T+T and is at the sole risk of the user. The User Guide and Excel Calculator Tool are copyright © Tonkin & Taylor Ltd. All rights reserved.

If you would like use our BCM Calculator and by doing so agree to our Terms and Conditions please contact us here or hit the button below.