Land at Wheal Martyn, St Austell China Clay area, Biodiversity Net Gain
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The natural choice for good advice
Land at Wheal Martyn,
St Austell China Clay area,
Cornwall
Biodiversity Net Gain
May 2021
A report by
James Gilroy BSc (Hons), MSc - Ecologist
Western Ecology, 1 Geffery Close, Landrake, Cornwall, PL12 5HA Telephone: 0800 622 6828
email: office@westernecology.co.ukReport details
Site address: Land at Wheal Martyn, Stenalees, St Austell, Cornwall PL26 8XH
Grid reference: SW 99935 56269
Report date: 27th May 2021
Report author: James Gilroy BSc (Hons), MSc
Report reviewer: Colin Hicks BSc (Hons), MCIEEM
Report Reference: WOR-2254.2
Declaration of compliance
BS 42020:2013
This study has been undertaken in accordance with British Standard 42020:2013
Biodiversity, Code of practice for planning and development.
Code of Professional Conduct
The information which we have prepared is true, and has been prepared and provided in
accordance with the Chartered Institute of Ecology and Environmental Management’s Code
of Professional Conduct. We confirm that the opinions expressed are our true and
professional bona fide opinions.
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 2 of 12Table of contents
1. Introduction .................................................................................................................... 4
2. Methodology .................................................................................................................. 4
3. Biodiversity Net Gain Summary Figures ......................................................................... 5
4. Biodiversity Net Gain Summary ..................................................................................... 6
Linear habitats ..................................................................................................... 7
5. Biodiversity Net Gain technical details ........................................................................... 8
6. Conclusion ................................................................................................................... 12
7. References .................................................................................................................. 12
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 3 of 121. Introduction
Western Ecology has been commissioned to complete a Preliminary Ecological Appraisal of
a parcel of land within the Wheal Martyn operational area of the Imerys china clay workings,
near Stenalees in mid-Cornwall. A single wind turbine, up to 135m in height, with associated
infrastructure and access track is proposed.
This biodiversity net gain report accompanies the Biodiversity Net Gain (BNG) calculation
using Defra Metric 2.0 (as of 25/05/2021).
This report includes the BNG calculations for this site and the mitigation areas on which
these calculations are based, as detailed in Map 1.
2. Methodology
A walkover of the site was completed by James Gilroy BSc (Hons), MSc on 26th May 2021
between 20:00 and 21:00 with an air temperature of 12oC, with a very light westerly breeze,
dry and with 10% cloud cover.
The existing habitats were classified using the Phase 1 Habitat Survey methodology
developed by the Joint Nature Conservation Committee (JNCC, 2010) and modified by the
Institute of Environmental Assessment (IEA, 1995). The main plant species were recorded,
and broad habitat types mapped. Habitats encountered are described within the Results
section, with a map included within the report. Plant species were identified according to
Stace (1997).
The DEFRA Biodiversity Net-gain Metric 2.0 was then used to calculate the overall value of
habitats (baseline and existing/proposed), in terms of habitat units. Habitats were
characterised as described above and mapped using a combination of OS background
mapping and aerial imagery. Habitat condition assessments were made by assessing each
habitat against a specific list of criteria as defined by the habitat condition tables provided in
the Biodiversity Net Gain Technical Supplement (Crosher et al. 2019). Professional
judgement was used to make condition assessments of habitats, when applicable.
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 4 of 123. Biodiversity Net Gain Summary Figures
Summary of biodiversity net gain in units and percentage change, a detail taken from
Biodiversity Net Gain metric 2.0 calculation for land at Wheal Martyn, ‘Detailed Results’
sheet (Biodiversity Metric 2.0 Land at Wheal Martyn 0521).
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 5 of 124. Biodiversity Net Gain Summary
A total biodiversity net gain of 13.09% has been achieved through a combination of on-site
habitat creation and enhancement and off-site habitat enhancement. Locations of on and off-
site habitat creation and enhancement are detailed in Map 1.
Onsite biodiversity net gain will be met as follows:
• The area serving as the crane pad will be used to create 0.24ha of lowland acid
grassland, once construction of the turbine has been completed. This habitat will be
created by hydroseeding the bare ground using a seed mixture containing acid
grassland species. Lowland acid grassland creation will achieve moderate condition
(as per Metric 2.0 technical supplement) through the implementation of a
management plan. This will provide 1.63 habitat units.
• An area of 0.7ha of existing scrub habitat will be enhanced. This scrub habitat is
currently assessed as in ‘poor’ condition due to lack of age/structural diversity,
dominant species and cover of undesirable species. Enhancement of this area will be
achieved by improving the condition to ‘moderate’. A management plan will be
developed and implemented in order to secure this enhancement. This will provide
5.66 habitat units.
Off-site biodiversity net gain will be met as follows:
• An area of existing lowland heathland totalling 0.61ha, located adjacent to the site’s
northern boundary and currently assessed as ‘fairly poor’ condition will be enhanced
to moderate condition. This will largely involve removal of invasive scrub (such as
Rhododendron) and reduce cover of native scrub to more beneficial levels. Without
this enhancement, this heathland would be lost to encroaching scrub and will
therefore provide a useful enhancement. This will be achieved through the
implementation of a heathland restoration management plan and will provide 7.68
habitat units.
• An area of 0.58ha of mixed scrub will be enhanced to lowland heathland. This area
of scrub is currently assessed as poor condition (due to lack of age/structural
diversity, dominant species and cover of undesirable species), and has in most
places naturally succeeded former heathland habitat. This will provide an area of
heathland that will connect to the areas of heathland to be improved, thereby
contributing towards a larger overall extent of better quality heathland habitat. This
enhancement is anticipated to achieve a lowland heathland habitat of moderate
condition through implementation of a management plan and will deliver 4.65 habitat
units.
• An area of 0.14ha of mixed scrub, located adjacent to the site’s north west boundary
and currently assessed as poor condition will be enhanced to moderate condition.
Enhancement will involve removing undesirable species such as Rhododendron,
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 6 of 12opening the canopy and subsequent rotational thinning, achieved through delivery of
a management plan. This will provide 1.13 habitat units.
Linear habitats
The site baseline does not feature any linear habitats such as hedgerows. Introducing new
linear habitats in order to achieve a gain in linear habitat units would not provide a useful
ecological benefit to this site and would not be appropriate for the existing habitats.
Therefore, the gain achieved in habitat units alone is considered to be sufficient to meet the
biodiversity net gain requirements, as well as providing a functional improvement to the
habitats within this area, post-development.
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 7 of 125. Biodiversity Net Gain technical details
Placement of habitat provision, loss and gain area and lengths in the accompanying metric provided by ‘sheet/cell’. Habitat
creation/enhancement for BNG in green, habitat lost to development in red.
Habitat/species1 Existing provision ha/km Loss ha/km and metric Gain ha/km and metric position Comments
and metric position position
Onsite baseline 1.05/cell 11E 0.48/cell 11Y N/A Total heathland within site – 0.48ha lost to
Heathland and shrub- development, 0.57ha retained. Fairly poor
Lowland heathland condition due to failing 3-4 criteria, as per Metric
2.0 technical supplement. Ecologically desirable
due to broader restoration objectives associated
with wider pit.
Heathland and shrub – 1.36/cell 12E 0.08/cell 12Y 0.7/cell 12T - enhanced – see on- Total scrub habitat within the site. Loss of a small
Mixed scrub site enhancement area of dense woody scrub to permanent
development footprint (0.08ha), 0.58ha retained,
0.7ha enhanced. Assessed as poor condition due
to failing a number of criteria e.g. presence of
undesirable species, lack of structural diversity.
Ecologically desirable due to broader restoration
objectives associated with wider pit.
Onsite habitat creation N/A N/A 0.32/cell 13D – built structures – no Permanent development footprint of access track
Urban - Developed gain and turbine. Sealed surface likely to be
land; sealed surface hardstanding.
Grassland – other, N/A N/A 0.24/cell 12D Temporary development area – area seeded with
lowland acid grassland acid grassland mix. Acid grassland considered to
be acceptable creation due to association with
heathland habitats in other parts of local area. Will
serve to increase diversity in site, post
development. Moderate condition achieved
through management plan.
1 Habitat type from Defra BNG 2.0 metric (different to JNCC Phase 1 habitat classification). UKHab/Phase 1 translation can be found in the Metric under ‘technical data’ menu.
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 8 of 12Onsite habitat 1.32/cell 12E – see on-site 0.70/cell 12S enhanced from ‘poor’ Area of existing scrub within site assessed as poor
enhancement baseline to ‘moderate’ condition - improved to achieve moderate
Heathland and shrub – condition through delivery of management plan.
Mixed shrub
Off-site baseline 0.61/cell 11E N/A N/A Area of existing heathland adjacent the site,
Heathland and shrub – containing high concentration of young
Lowland heathland Rhododendron saplings and very dense areas of
native scrub, which will engulf heathland if not
managed. Assessed as fairly poor condition due to
failing 3-4 condition criteria. Ecologically desirable
due to broader restoration objectives associated
with wider pit.
Heathland and shrub – 0.58/cell 12E N/A N/A Area of very dense woody scrub featuring
Mixed scrub connectivity to Site. Likely to have succeeded
former heathland habitat in most areas. Assessed
as poor due to lack of structural/age diversity,
presence of undesirables (Rhododendron) and
dominant species Ecologically desirable due to
broader restoration objectives associated with
wider pit.
Heathland and scrub – 0.14/cell 13E N/A N/A Area of existing scrub adjacent to site’s NW
Mixed scrub boundary, featuring dense scrub cover;
Rhododendron, Willow & E. Gorse. Assessed as
poor condition. Ecologically desirable due to
broader restoration objectives associated with
wider pit.
Off-site enhancement 0.61/cell 12S – see off-site N/A 0.61/cell 12S enhanced from ‘fairly Area of heathland adjacent to site, featuring dense
Heathland and shrub - baseline poor’ to ‘moderate’ cover of undesirable scrub such as Rhododendron
Lowland heathland and Willow. Young Rhododendron colonising and
will engulf heathland if not managed. Improve
condition to moderate by removing
Rhododendron, thinning native scrub, sowing bare
ground with acid grass/seed mix - through delivery
of management plan.
Heathland and shrub – 0.58/cell 13S – see off-site N/A 0.58/cell 13S enhanced from mixed Area of dense scrub, including Rhododrendron,
Lowland heathland baseline scrub to Lowland heathland over N slopes of tip, likely to have succeeded
former heathland. Scrub enhanced to heathland
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 9 of 12by removing scrub, scraping litter and
hydroseeding with acid grassland & heath mix.
Moderate condition achieved through appropriate
management. This will link with heathland
restoration areas to create a larger, connected
area of better-quality heathland, post
development.
Heathland and shrub – 0.14/cell 14S – see off-site N/A 0.14/cell 14S enhanced from ‘fairly Poor quality scrub, improved by removing
Mixed scrub baseline poor’ to ‘moderate’ Rhododendron, thinning canopy and rotational
cutting through management plan delivery. This
will add an area of better-quality scrub with
connectivity to adjacent heathland - will contribute
to an overall improvement to the site and
surrounding area.
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 10 of 12Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
Page 11 of 126. Conclusion
The mitigation and enhancement recommended within this report is of a sufficient scale to
ensure that the proposed development provides the required net gain for biodiversity,
thereby aligning it with the National Planning Policy Framework and Cornwall Council’s
‘Cornwall Planning for Biodiversity Guide’.
7. References
Crosher, I, Gold, S., Heaver, M., Heydon, M., Moore, L., Panks, S., Scott, S., Stone, D. and
White, N. (2019) The Biodiversity Metric 2.0: Auditing and accounting for biodiversity value:
technical supplement (Beta version July 2019). Natural England.
Institute of Environmental Assessment (IEA), 1995. Guidelines for Baseline Ecological
Assessment, Institute of Environmental Assessment. E&FN Spon, aJn Imprint of Chapman
and Hall. London.
Joint Nature Conservation Committee, 2010. Handbook for Phase 1 Habitat Survey - a
Technique for Environmental Audit. Reprinted by JNCC, Peterborough
Stace, C., 1997. New Flora of the British Isles. 2nd edition. Cambridge University Press,
Cambridge.
Land at Wheal Martyn, St Austell China Clay area, Cornwall – Biodiversity Net Gain, May 2021
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