Calculation overview

This section presents the essential features of the BA metric in terms of how assessments are made. The figure below presents an overview of how the SGBA estimates Biodiversity Net Change (BNC). Post-development is ‘weighed’ or compared against pre-development habitat biodiversity. Post-development habitat biodiversity is constituted by three factors, namely, baseline retention and either habitat creation or enhancement, or both. In essence, net positive BNC is ideally targeted, reflecting the delicate balance and difference between habitat biodiversity gained and lost in the process of development or related interventions. 

More specifically, proxy estimates of habitat biodiversity in the form of Habitat Biodiversity Units (HBU; explained below) are calculated for habitat baseline retention, creation and enhancement initiatives. The latter two contribute to and counter-balances baseline proxy estimates of pre-development habitat biodiversity lost to developmental and related interventions (see figure below).

At the heart of the estimation of HBU for habitat baseline (retention or loss), creation and enhancement are the consideration of  three main variables: habitat area, distinctiveness and condition. For each variable, the products of these are multiplied in order to generate HBU scores. Distinctiveness and condition variables are additionally multiplied together with  risk-related weights (discussed in a later section together with example calculations).