Valuing our urban trees – part II

Assessing the condition of urban tree habitats using Biodiversity Metric 3.0

Our recent blog – Valuing our urban trees I, pointed out the failings of the methodology for calculating the size of urban tree habitats as set out in Biodiversity Metric 3.0 (BNG 3.0). We would now like to show how this is compounded by the inappropriate assessment criteria used to determine the condition of Urban Tree habitats, as also set out in BNG 3.0 (see Annex 1).

We use the following example – taken from a recently approved planning application [1] which will result in the removal of 13 urban trees – to demonstrate why this is approach is inappropriate.

Figure 1 The example tree – Google Street View 2020

This street tree is a London Plane (Platanus × acerifolia) with a stem diameter (called DBH) of 118 cm. It is a non-native species planted in hard standing on Bridge St, Bristol BS1 2AN in about 1967. Using BS 5837:2012Trees in relation to design, demolition and construction – Recommendations (a BSI Standards Publication), it has been categorised as A,1,2 (see Annex 2). The developer’s Arboriculturalist described it as having a ‘Large, broad crown with excellent form and vigour.’

The tree’s BS 5837:2012-calculated Root Protection Area (RPA) radius[3] is 14.6 metres, so it has an RPA of 630 square metres. The tree has an average crown radius of 9.88 metres and a calculated canopy area of 306 square metres.

Using BNG 3.0 TABLE 7-2: Urban tree size by girth and their area equivalent (see Annex 1), the calculated RPA of the tree is set at Large, so its habitat size is limited to just 113 square metres – a discount of 82% of its calculated RPA and 37% of its canopy area.

Notwithstanding categorisation of the tree as A,1,2, the BNG 3.0 Condition Assessment Criteria categorises the condition of this tree as Poor because it meets only two of the six criteria, as shown below:

Using BNG 3.0, the calculation of the baseline habitat (called Habitat Units) of this tree is as follows:

Had the BS 5837:2012 condition of the tree been allowed for and its condition set to ‘Good’, then the habitat units of this tree would be three times the habitat unit value of 0.0452, i.e., 0.1356 as shown below.

Not only has the true size of the urban tree habitat been significantly undervalued (because its actual RPA has not been used), but its assessed condition using the BNG 3.0 criteria is also clearly inappropriate given that this tree has been assessed at the highest category under BS 5837:2012:

Category A – Trees of high quality with an estimated remaining life expectancy of at least 40 years …that are particularly good examples of their species, especially if rare or unusual; or those that are essential components of groups or formal or semi-formal arboricultural features (e.g., the dominant and/or principal trees within an avenue).

The proposed solution

BNG 3.0 is seriously flawed when it comes to evaluating Urban Tree habitats. We have already commented on this when it comes to calculating habitat size.

In our view, the solution to the issue of assessing the correct condition of urban tree habitats is already available in BS 5837:2012. The standard may require some amendment to align it with BNG 3.0, but it is a well-established and practical approach used by the arboricultural community. This British Standard gives recommendations and guidance on the relationship between trees and design, demolition and construction processes and is used whether or not planning permission is required.

A copy of this blog can be downloaded here.


Our third blog dealing with habitat selection is available here – Valuing our urban trees – part III.


Annex 1

The Biodiversity Metric 3.0 – auditing and accounting for biodiversity

USER GUIDE (page 68)

TECHNICAL SUPPLEMENT (pages 193-194)


Annex 2

BS5837:2012 – 4.5 Tree categorization method – tree category definitions


[1] The Developer used BNG 2.0 in its submissions and applied a different Condition assessment to the one used here.

Mislabelling Bristol’s crucial open spaces as “brownfield” sites to justify development

A recent landmark Council motion to Protect the Green Belt and Bristol’s Green Spaces, was approved with cross-party support and no dissensions. As a result, vital green spaces within Bristol now have additional protection, in line with the City’s declarations of Climate and Ecological Emergencies, the recently published Ecological Emergency Action Plan and the new Environment Act 2021.

However, a consequence of the adoption of this motion is that there is greater pressure to develop on  other sites.  Those advocating development on open spaces within Bristol have begun, arbitrarily and without proper justification, to declare such open spaces to be brownfield. To inaccurately describe a development site as brownfield places Development Committee members under undue pressure to approve a planning application when, as greenfield, a site should fall under the additional protection engendered by the landmark motion.

Baltic Wharf Caravan Park

Recent examples (see below) where the term brownfield has been misused  are the Bristol Zoo Gardens car park on College Rd, Clifton and the Baltic Wharf Caravan Park on the Floating Harbour in Hotwells, each of which have been mislabelled as brownfield sites despite not falling within with the recognised legal definition.

Bristol Zoo Gardens car park

The term brownfield site is used to describe certain types of previously developed land. Most dictionary definitions refer to this land as being currently or previously occupied by a permanent structure which generally includes the potential for contamination. In planning law there is a definition which must apply when considering planning proposals. This is detailed in the National planning policy framework (NPPF – called ‘Previously developed land’, p.70) as:

Land which is or was occupied by a permanent structure…. and any associated fixed surface infrastructure”.

The definition excludes land which is maintained as a garden:

….. land in built-up areas such as residential gardens, parks, recreation grounds and allotments…

In addition to the definition, there is a statutory requirement for local authorities to maintain an up to date register of brownfield sites which are appropriate for development:

Regulation 3 of the Town and Country Planning (Brownfield Land Register) Regulations 2017 requires local planning authorities in England to prepare, maintain and publish registers of previously developed (brownfield) land”.

Brownfield land registers will provide up-to-date and consistent information on sites that local authorities consider to be appropriate for residential development having regard to the criteria set out in regulation 4 of the Town and Country Planning (Brownfield Land Register) Regulations 2017.” 

“Regulation 17 requires local planning authorities to review their registers at least once a year“.

The Town and Country Planning act also addresses the situation where a fragment of the site might be considered brownfield, but other parts of the curtilage is green space:

Greenfield land is not appropriate for inclusion in a brownfield land register. Where a potential site includes greenfield land within the curtilage, local planning authorities should consider whether the site falls within the definition of previously developed (brownfield) land in the National Planning Policy Framework. Where it is unclear whether the whole site is previously developed land, only the brownfield part of the site should be included in Part 1 of the register and considered for permission in principle”.


Mislabelling as brownfield examples in recent planning applications

Bristol Zoo Gardens car park, College Rd, Clifton (21/01999/F)

The planning proposal makes the statement “The application site is brownfield, previously developed land, as it is a car park“. Mayor Marvin Rees similarly defined the site in a subsequent tweet criticising some members of the Development Committee for voting against the proposal.

This site fails to comply with the proper planning definition of a brownfield site. In relation to the NPPF definition, 7.4% of the site is occupied by buildings whereas tree canopy covers about 17% of the site. Much of the site is covered by unfixed surface, which does not qualify under the definition of a brownfield site. Therefore, according to the Town and Country Planning Act only 7.4% of the site could be considered brownfield, with the remaining 92.6% being classified as greenfield. The site does not appear on the Council’s register of brownfield sites, and therefore cannot legally be classified as such.

Baltic Wharf Caravan Park (21/01331/F)

This planning proposal has also been inappropriately described as a brownfield site in the planning application. Only 2.6% of the site is occupied by a permanent structure, whereas the 100 trees that occupy this site cover over 30% of its area. Thus, only 2.6% of the site could possibly be defined as brownfield, with the remaining 97.4% falling under the classification of greenfield. Furthermore, as much of the site is maintained as a “residential garden”, the site is exempt from the NPPF definition. This site, also, is absent from the necessarily up-to-date register of brownfield sites.

Whilst there may be arguments to develop some parts of some of these sites, the existing trees should be retained in order to comply with Local Planning Policy BCS9.  The current approach  of flattening all trees, including those  on the edge of the site results in third rate developments.  Instead, new developments should be built around existing trees.


Petition

If you agree that this mislabelling should stop, please sign this petition to protect Bristol’s green spaces from the Council’s mislabelling of them as “brownfield sites”:

Protect Baltic Wharf and Bristol’s Other Green Spaces

%d bloggers like this: