EMROP: Waihi North Project WAI-985-000-PLN-LC-0001_Rev0 clean 2.3.3 Explanation of BOAM: Accounting Model Features The BOAM compares the biodiversity features at the impact site(s) to a ‘benchmark’. The benchmark provides a reference point for a similar biodiversity type in a ‘natural’ condition, against which to evaluate the biodiversity losses and gains. Due to historical land use practices, the affected ecosystem type (broadleaved species scrub- VS5, (Singers & Rogers 2014)) within the southern SNA166 fragment is a highly modified seral community that will be expected to naturally transition to its original cover, (kauri, podocarp, broadleaved forest, Type WF11, Singers & Rogers 2014). The broadleaved species scrub within the WNP is generally deficient of many elements of a future WF11 forest (such as future canopy saplings). Therefore a key conservation objective for the BOAM actions is to facilitate succession of SNA 166 towards its historic state (in addition to counterbalancing loss in extent of protected vegetation). The benchmarks for broadleaved species scrub are explained here. Benchmarks and justification are presented in Table 6. 2.3.3.1 Biodiversity Type and Benchmarks The biodiversity type is classified as ‘broadleaved species scrub’- VS5, (Singers & Rogers 2014). This is a regenerating ecosystem type - a community of pioneer flora and fauna that occur or regenerate following disturbance (human or natural). Diversity of broadleaved species scrub is highly variable, and is influenced by many factors, including fragment isolation, topography and seed source. It can be dominated by a mosaic of species commonly found in the subcanopy and edges of more mature forests. It can also be dominated by few species, such as tree ferns (e.g. SNA 165 / Ngatikoi Domain), kāmahi, māpou or kōhūhū (Singers et al. 2017). Given the highly fragmented, isolated and poor condition of many naturally occurring, regenerating ecosystems throughout both the Waikato Region and Waihi Ecological District, a benchmark for broadleaved species scrub with similar bioclimatic and topographic influences is not known. Therefore, a conservative model is described here, whereby a very good condition example of a broadleaved species scrub will support a high species richness, with future kauri podocarp broadleaved canopy species present in the understorey. 2.3.3.2 Biodiversity Component The biodiversity components are based on the two dominant vegetation communities within the broadleaved species scrub / forest (rewarewa dominant scrub and tree fern dominant scrub). These have been measured separately, but share the same benchmark. A third component of the offset considers the non-SNA Western fragment, which supports a mixture of rewarewa scrub and pōhutukawa trees, as distinct from the composition of the adjacent SNA vegetation. 2.3.3.3 Biodiversity Attributes Five biodiversity attributes (‘Currencies’) were selected for the Accounting Model for vegetation and habitats that collectively describe the key values of the biodiversity components (Cells 1.1a-e, Table 5; 1.2a-e, Table 6; 1.3a-e, Table 7). These attributes are canopy height, native canopy native canopy cover, native canopy diversity, native understorey diversity, and avifauna diversity. These attributes were measured from vegetation plots and counts, and are summarised in Table 6.
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