Natural capital baseline

This stage involves quantifying the natural capital stocks with the potential to be impacted by proposed scheme. Stocks of natural capital can be conceptualised in different ways; however, the most common and often pragmatic approach is by habitat type. According to the ENCA guidance (Defra, 2023), habitat types most concisely capture the diversity of the UK's ecology, geology and climate in distinct spatial areas. Defining assets by habitat type can also help to identify externalities influenced by the natural environment and ecosystem services supplied by natural capital. As such, a natural capital asset register of habitats relevant to the proposed scheme and their extents was produced. This represents a critical step in informing and interpreting the analysis of ecosystem service benefits, as many of these are directly dependent on habitat extents.

The natural capital asset register baseline was informed by the On-site Habitat Baseline from the Statutory Biodiversity Metric Tool (SBMT) (Defra, 2023) calculation for the DMRB Stage 3 EIAR and consequently, the NCA utilises the same SBMT study boundary (which is henceforth referred to as the ‘NCA boundary’). The use of the On-site Habitat Baseline represents both the most efficient and most accurate quantification of natural capital stocks available for the NCA boundary, informed by UK Habitat Classification (UKHab) surveys for habitats within the proposed scheme.

Baseline habitat areas were extracted from the SBMT. Neither the SBMT calculation, nor the NCA, accounted for any additional impacts to habitats outside of the NCA boundary and the boundary is assumed to capture construction impacts, including temporary works.

Table 2‑1 below presents the sum area of each habitat type within the proposed scheme. The habitat baseline is dominated by the presence of woodland, accounting for >64% of the total area; this is predominantly comprised of coniferous woodland, mixed woodland and lowland mixed deciduous woodland. Second to woodland, grassland dominates with notable areas of other neutral grassland and modified grassland. Small areas of transitional habitat (bracken) are present and there is just under eight hectares of arable land, fairly evenly split between non-cereal crops, temporary grass and clover leys and cereal crops.

Assumptions and limitations

At this stage, linear habitats (hedgerows and watercourses) have not been included within the SBMT for the DMRB Stage 3 Design Fix and are thus not considered as part of the NCA. This is because the methodology is designed for use in English rivers and there is still uncertainty on the suitability and practicality of applying MoRPh assessment methods to assessing river condition in Scotland.