Our proposal for a new Bristol Tree Replacement Standard

The Bristol Tree Replacement Standard (BTRS), which was adopted nearly a decade ago in 2013, provides a mechanism for calculating the number of replacements for any trees that are removed for developments. It was ground-breaking in its time as it typically required more than 1:1 replacement.

The presumption should always be that trees should be retained. The application of BTRS should only ever be a last resort. It should not be the default choice, which it seems to have become.

The starting point for any decision on whether to remove trees (or any other green asset) is the Mitigation Hierarchy[2] which states, firstly, avoid; then, if that is not possible, minimise; then, if that is not possible, restore; and, as a last resort, compensate (the purpose or BTRS). BCS9 adopts this approach and states that:

Individual green assets should be retained wherever possible and integrated into new developments.

However, with the emergence of a new Local Plan for Bristol, we believe that the time has come for BTRS to be revised to reflect our changing understanding of the vital importance of trees to the city in the years since the last version of the Local Plan was adopted in 2014.

In addition, Bristol has adopted Climate and Ecological Emergency Declarations so a new BTRS will be an important part of implementing these declarations. Nationally, the new Environment Act 2021 (EA 2021) is coming into force late next year.

Our proposal provides a mechanism for complying with the new legal requirement for 10% Biodiversity Net Gain (BNG) which will be mandatory when EA 2021 takes effect.

Background

Under current policy – BCS9 and DM17 – trees lost to development must be replaced using this table:

Table 1 The Current BTRS replacement tree table

However, when the balance of the Environment Act 2021 (EA 2021) takes effect late in 2023, the current version of BTRS will not, in most cases, be sufficient to achieve the 10% biodiversity net gain (BNG) that will be required for nearly all developments. Section 90A will be added to the Town and Country Planning Act 1990 and will set out the level of biodiversity net gain required ( Schedule 14 of the EA 2021).

The Local Government Association says of BNG that it:

…delivers measurable improvements for biodiversity by creating or enhancing habitats in association with development. Biodiversity net gain can be achieved on-site, off-site or through a combination of on-site and off-site measures.[3]

GOV.UK says of the Biodiversity Metric that:

where a development has an impact on biodiversity, it will ensure that the development is delivered in a way which helps to restore any biodiversity loss and seeks to deliver thriving natural spaces for local communities.[4]

This aligns perfectly with Bristol’s recent declarations of climate and ecological emergencies and with the aspirations of the Ecological Emergency Action Plan,[5] which recognises that a BNG of 10% net gain will become mandatory for housing and development and acknowledges that:

These strategies [the Local Nature Recovery Strategies] will guide smooth and effective delivery of Biodiversity Net…

Our proposed new BTRS model

We propose that the Bristol Tree Replacement Standard be amended to reflect the requirements of the EA 2021 and BNG 3.1 and that the BTRS table (Table 1) be replaced with Table 2 below:

Table 2 The proposed new BTRS tree replacement table

The Replacement Trees Required number is based on the habitat area of each of the three BNG 3.1 tree categories (Table 7-2 below) divided by the area habitat of one 30-year old BNG 3.1 Small tree (Table 3 below) plus 10% net gain. This is rounded up to the nearest whole number since you can’t plant a fraction of a tree.

The reasoning for our proposal is set out below:

Applying the Biodiversity Metric to Urban trees

The most recent Biodiversity Metric (BNG 3.1) published by Natural England, defines trees in urban spaces as Urban tree habitats. The guidance states that:

the term ‘Urban tree’ applies to all trees in urban situations. Urban trees may be situated within public land, private land, institutional land and land used for transport functions.

Table 7-1 divides Urban tree habitats into three categories:

Paragraph 8.5 of the 3.1 BNG Guidance makes it clear that lines of trees in an urban environment should not be treated as a linear habitat:

Urban trees are considered separately to lines of trees in the wider environment, since they generally occur in an urban environment surrounded by developed land. 

Calculating Urban tree habitat

Urban tree baseline habitat area is measured in hectares and is based on the Root Protection Area[7] (RPA) of each tree impacted by a proposed development. RPA is used instead of tree canopy because it is considered to be the best proxy for tree biomass.

In most cases, RPA is obtained from an Arboricultural Impact Assessment (AIA), which complies with British Standard 5837 2012 – Trees in relation to design, demolition and construction (BS:5837).

Where no AIA is available, Table 7-2 is used:

Note that the tree’s size will still need to be ascertained, and that any tree with a stem diameter (DBH) 75mm or more and of whatever quality (even a dead tree, which offers its own habitat benefits) is included . Under BTRS, trees with a DBH smaller than 150 mm are excluded, as are BS:5837 category “U” trees.

The guidance also makes it clear that, given the important ecosystem services value provided by trees, where possible like-for-like compensation is the preferred approach, so that lost Urban trees are replaced by Urban trees rather than by other types of urban habitat.[8]

Replacing lost trees

To calculate the number of trees required to replace Urban tree habitat being lost, table 7-2 above is used on this basis:

Size classes for newly planted trees should be classified by projected size at 30 years from planting.

We have used the median DBH sizes for new stock trees as set out in BS 3936-1: Nursery Stock Specification for trees and shrubs as the basis for calculating the eventual size of a newly planted trees after 30 years and assumed that a tree adds 2.54 cm (1”) to its girth annually.

This results in a predicted stock tree size after 30 years’ growth. This is then assigned to one of the three Urban tree categories set out in table 7-2: Small, Medium or Large. In all cases save for Semi-mature tree stock, the eventual size of stock trees after 30 years falls within the BNG 3.1 size category Small, which has a habitat area of 0.0041 hectares. This value is then used to calculate how many new trees will be required to replace trees lost to the development, plus a 10% biodiversity net gain. This gives a compensation size per replacement tree of 0.0045 ha (0.0041 hectares + 10%).

Table 3 below shows the basis our our calculation:

Table 3 Annual stock tree growth predictions

The Trading Rules

It may be that a notional positive biodiversity net gain can be achieved by replacing fewer trees than this analysis indicates. However, this is not enough. The calculation should also comply with the Trading Rules that apply to Urban tree habitats.

Paragraph 7.6 of the 3.1 BNG Guidance states:

The mitigation hierarchy and trading rules apply to Urban trees. Given Urban trees are a ‘Medium’ distinctiveness habitat, trading rules stipulate that the same broad habitat type (or a higher distinctiveness habitat) is required. However, given the important ecosystem services value provided by trees, where possible ‘like for like’ compensation is the preferred approach (i.e. where possible any loss of Urban trees should be replaced by Urban trees – rather than other urban habitats).

Rule 3 of the User Guide states: ‘”Trading down’ must be avoided. Losses of habitat are to be compensated for on a ‘like for like’ or ‘like for better’ basis. New or restored habitats should aim to achieve a higher distinctiveness and/or condition than those lost…’

The likely impact of this policy change

We have analysed tree data for 1,038 surveyed trees taken from a sample of AIAs submitted in support of previous planning applications. Most of the trees in this sample, 61%, fall within the BNG 3.1 Small range, 38% within the Medium range, with the balance, 1%, categorised as Large.

Table 4 below sets out the likely impact of the proposed changes to BTRS. It assumes that all these trees were removed (though that was not the case for all the planning applications we sampled):

Table 4 Proposed BTRS impact analysis

The spreadsheet setting out the basis of our calculations can be downloaded here – RPA Table 7-2 Comparison.

Our proposed changes to BTRS (published in the Planning Obligations Supplementary Planning Document, page 20) are set out in Appendix 1.

This article was amended on 7 November 2022 to include references to Lines of Trees in the urban environment, the application of the Trading Rules to Urban tree habitats and fix a broken link.

Appendix 1

Our proposed changes to BTRS, set out in the Planning Obligations Supplementary Planning Document, page 20.

Trees – Policy Background

The justification for requiring obligations in respect of new or compensatory tree planting is set out in the Environment Act 2021, Policies BCS9 and BCS11 of the Council’s Core Strategy and in DM 17 of the Council’s Site Allocations and Development Management Policies.

Trigger for Obligation

Obligations in respect of trees will be required where there is an obligation under the Environment Act 2021 to compensate for the loss of biodiversity when Urban tree habitat is lost as a result of development.

Any offsite Urban tree habitat creation will take place in sites which are either on open ground or in areas of hard standing such as pavements.

Where planting will take place directly into open ground, the contribution will be lower than where the planting is in an area of hard standing. This is because of the need to plant trees located in areas of hard standing in an engineered tree pit.

All tree planting on public land will be undertaken by the council to ensure a consistent approach and level of quality, and to reduce the likelihood of new tree stock failing to survive.

Level of Contribution

The contribution covers the cost of providing the tree pit (where appropriate), purchasing, planting, protecting, establishing and initially maintaining the new tree. The level of contribution per tree is as follows[9]:

  • Tree in open ground (no tree pit required) £765.21
  • Tree in hard standing (tree pit required) £3,318.88

The ‘open ground’ figure will apply where a development results in the loss of Council-owned trees planted in open ground. In these cases, the Council will undertake replacement tree planting in the nearest appropriate area of public open space.

In all other cases, the level of offsite compensation required will be based on the nature (in open ground or in hard standing) of the specific site which will has been identified by the developer and is approved by the Council during the planning approval process. In the absence of any such agreement, the level of contribution will be for a tree in hard standing.

The calculation of the habitat required to compensate for loss of Urban trees is set out in Table 7-2 of the Biodiversity Metric (BNG), published from time to time by Natural England. This may be updated as newer versions of BNG are published.

The following table will be used when calculating the level of contribution required by this obligation:


A copy of this blog can be downloaded here:

BTF proposal for a new Bristol Tree Replacement Standard


[1] Biodiversity Metric 3.1 – Auditing and accounting for biodiversity – USER GUIDE.

[2] https://nationalzoo.si.edu/ccs/mitigation-hierarchy.

[3] https://www.local.gov.uk/pas/topics/environment/biodiversity-net-gain.

[4] https://www.gov.uk/government/news/biodiversity-30-metric-launched-in-new-sustainable-development-toolkit.

[5] https://www.bristol.gov.uk/documents/20182/5572361/Ecological_Emergency_Action_Plan.pdf/2e98b357-5e7c-d926-3a52-bf602e01d44c?t=1630497102530.

[6] DBH = Diameter at Breast Height. RPAr = Root Protection Area radius. Area = the calculated BNG habitat area.

[7] RPA area = π × r2 where r is 12 x the tree’s DBH for a single stemmed tree. For multi-stemmed trees, the DBH of the largest stem in the cluster should be used to determine r.

GOV.UK advice is that r should be at least 15 times larger than DBH – https://www.gov.uk/guidance/ancient-woodland-ancient-trees-and-veteran-trees-advice-for-making-planning-decisions.

The Woodland Trust also recommends that r be set to 15 x DBH for ancient and veteran trees – https://www.woodlandtrust.org.uk/blog/2021/04/root-protection-areas.

[8] Paragraph 7.8 – Trading Rules.

[9] These values should be updated to the current rates applicable at the time of adoption. The current indexed rates as of April 2022 are £1,041.6 & £4,517.89 respectively.

[10] DBH = Diameter at Breast Height. RPAr = Root Protection Area radius. Area = the calculated BNG habitat area.

Trees under threat at the Eastgate Centre!

Bristol’s trees are constantly under threat from development, especially when the commercial value of the land they grow on is so great and the public amenity value they offer is not thought worthy of consideration.

Here is (yet) another example.

An outline planning application – Number 17/01580/P – has been made to at the Eastgate Centre on Eastgate Road  for the demolition of the existing drive-thru restaurant. It will be replaced by new retail units with a health and fitness club above and a replacement drive-thru restaurant.

Part of this application will require the destruction and removal of a delightful stand of trees that grow on a triangle of land between the roundabout on Eastgate Road and the existing retail park. This is so that larger retail units can be built and goods vehicles can more easily gain access to the rear of the site. This is a plan of the trees affected.

Eastgate Trees

This is the proposal for what will be planted in their place – a souless echo of what is already there:

Eastgate Trees2

The Council’s own arboricultural officer has objected to the proposal. He advises:

“I have conducted a site visit and reviewed the supporting arboricultural documentation. The trees on site are located on the edge of the proposed development area and provide a significant screen to the already extensive retail development. The group of trees fall within 2 distinct age ranges, a mature group of ash, oak and poplar and a young understorey of secondary infill planting.

The mature trees are protected by TPO 282. The ash and oak are a historic remnant of a landscaped garden (Circa 1900) from the former gas works that occupied the site, the ash appear to of been managed as old pollards which have now grown out. They are historic trees with potential veteran tree characteristics that warrant the TPO status and must be retained. Due to poor management or lack of management the trees have a number of less than satisfactory defects associated with them that have in part been identified within the supporting tree survey from February 2015. The understorey planting appears to date back to the original development of the retail park, this understorey now has a more complex relationship with the larger TPO trees. They reduce the target area of people and property by the restriction of movement within this area and they also provide shade to the lower portions of the main stems which when considering the potential veteran tree characteristics offer significant ecological benefits. The management of this area for the benefit of the mature TPO’d trees would need careful consideration.

The supporting arboricultural survey is out of date and only provides basic survey detail that does not consider age and historic relevance of the TPO’d trees. The survey in not a full BS5387 report as required with DM17: Development Involving Existing Green Infrastructure.

The proposal seeks to redevelop the current Burger King site to increase the number of commercial units with associated HGV delivery bays to the rear.

This proposal would remove the vast majority of the historic TPO’s trees and associated understorey, This would be detrimental to the TPO status of the trees. The final design would be in constant conflict with the trees identified for retention leading to further applications to remove the tree following occupation of the individual units.

The Mature Oak T10 is a key amenity feature located in an elevated position over the roundabout at the gateway of the Eastgate centre; this is a TPO’d tree and no evidence has been provide to justify its removal.

I object to the proposed and would recommend refusal of the application on the grounds of a detrimental impact to the only green infrastructure on site and historic environment. Insufficient detail has been presented in accordance with BCS9, DM15 & DM17. There has been no consideration of the TPO status of the trees or their current or future management.

The arboricultural documentation is poor, out of date and insufficient to support an application, the tree planting plan produced to mitigate the loss of such significant trees has not considered the “Planning obligation SPD, Tree.” (Bristol tree replacement standard (BTRS). I hope you find these comments of use.

Matt Bennett Arboricultural Officer (Planning) City Design Group – Place Directorate City Hall.”

We agree with Matthew! We shall be lodging our objections.

If you also agree, please lodge your objections here in the Planning application comments section. These are the Important dates:

Eastgate Trees3

Bristol’s trees in crisis!

With Bristol City Council’s budget cuts, two decisions have been made regarding the management of Bristol’s treescape that make no economic sense, and threaten the reputation of the City as a Green and pleasant place to live and locate a business.

With Bristol City Council’s budget cuts, two decisions have been made regarding the management of Bristol’s treescape that make no economic sense, and threaten the reputation of the City as a Green and pleasant place to live and locate a business.

Decision 1: Slashing of street tree management budget

  • The budget for managing street trees has been cut by nearly 78% from £240,000 to £53,000.
  • As a result there will be no pollarding of street trees or removal of epicormic growth around the tree.
  • Emergency cover outside normal working hours is no longer being provided through the tree management contract, despite having no cost benefit.
  • Tree management will be limited to felling to address safety risks, despite greater initial costs and the long term consequent loss of tree sites – felling costs the same as 16 years of maintenance.  As a result, Bristol’s street tree population will rapidly fall into decline as they are steadily removed, never to be replaced.

Decision 2: No planting of street trees, either replacement or new, even when cost neutral

  • Bristol City Council has operated a number of innovative schemes allowing residents or community groups to sponsor replacement or new street trees. Despite fully funding the planting, and maintenance for two years, such planting will no longer be permitted.
  • At the moment, when a tree is replaced in an existing tree pit it costs £295. This covers regular watering until the tree is established and two years maintenance. If the trees dies whilst establishing itself, it is replaced at no extra cost.
  • If the Council can be persuaded to change its mind about not planting new trees, then this cost could to increase to the £765 that developers are required to pay – the overall costs of planting a tree and maintaining it during its lifetime. Planting a tree at a brand new site could add around £2,000-£2,500 if a special tree pit needs to be installed.
  • Currently there is huge support from the community for replacing lost trees. Around £200,000 of developers’ money is set aside for this purpose, Metrobus is committed to planting 200-300 trees as part of their planning condition, and Bristol University has donated funds to plant 60-100 public street trees.
  • It makes little sense, in times of budget constraints, to renounce external funding sources that fully cover planting and maintenance costs.

These decisions are a false economy for Bristol City Council

  • With no pollarding of street trees, increased tree growth will lead to more subsidence claims against the Council, and create more highway damage, pavement trip hazards, and infrastructure damage.
  • New tree growth from previous pollarding points will become unstable, increasing the probability of personal injury and property damage claims against the Council.
  • Just a couple of additional subsidence or injury claims could negate the Council’s entire “cost saving”.
  • This short-term decision makes no sense – if a tree can be maintained for some 16 years – the one-off cost of felling it, then surely it makes better economic sense to spread this inevitable cost and maintain the tree rather than fell it as a short-term ‘solution’ – a ‘solution’ which loads all the costs up front and will lead to greatly increased and unavoidable expenditure in not very many years time?

These decisions will threaten Bristol’s reputation as a Green City

These decisions were taken with no consultation with stakeholders

There has been no consultation regarding these decisions with other Departments within Bristol City Council, who will have to deal with the foreseeable consequences, with insurers, who will face additional damage claims, Avon and Somerset Police, who will have to address public order consequences of mass felling, or Bristol Tree Forum, with its wide-reaching understanding of tree issues.

What you can do

  • Contact your Councillor and email the Mayor and demand that these decisions be overturned.
  • Contact us here at Bristol Tree Forum to register your support and offer to help defend Bristol’s public tree spaces.
  • Spread the word and forward this blog to others interested in saving trees.

Green space and our health

The evidence for physical and mental health benefits from contact with nature, such as reducing rates of non-communicable diseases is clear.

A range of bodies, including Government agencies, have promoted the potential physical and mental health benefits of having access to green spaces.

The evidence for physical and mental health benefits from contact with nature, such as reducing rates of non-communicable diseases is clear. So are the challenges for preserving and extending urban green spaces.

Green space is natural or semi-natural areas partially or completely covered by vegetation that occur in or near urban areas and provide habitat for wildlife and can be used for recreation. They are many and varied – from tree-covered streets & avenues to squares, play areas, schools, cemeteries, parks, woodlands, nature reserves and allotments.
Sadly, only half of us live close to green space. Green space is expected to decrease as urban infrastructure expands.

Key benefits include:

  • Physical and mental illnesses associated with sedentary urban lifestyles are an increasing economic and social cost.
  • Areas with more accessible green space are associated with better mental and physical health.
  • The risk of mortality caused by cardiovascular disease is lower in residential areas that have higher levels of ‘greenness’.
  • There is evidence that exposure to nature could be used as part of the treatment for some conditions.
  • There are challenges to providing green spaces, such as how to make parks easily accessible and how to fund both their creation and maintenance.

Crisis for the Bristol Environment

Trees, parks and the financial crisis

The recent decisions made by the City Council in response to the drastic cuts made by the government will create a dramatically changed world for the whole Bristol environment. We have got used to our street trees being manicured, our parks being regularly mown and tended, new trees being widely and enthusiastically planted, developer’s plans being closely monitored. We may have moaned about minor inefficiencies, criticised delays and decisions, but we have expected to be listened to and mostly we have been.

It is all going to change. By 2020 Bristol parks are going to have to find their own finance, parks users will have to pay for the privilege of using them and parks groups will have to take over maintenance. Street trees will cease to be pollarded. Last winter leaves were not swept until they had all fallen, and only now have most gutters been cleared. Next autumn sweep your own gutters and keep your own gutters clear, the Council won’t be able to do it!

And it will be no use protesting, shouting, writing rude e-mails to your local Councillor. There is little that they can do. Its put-your-money-time-and-effort-where-your-mouth-is time. Getting out there, talking and co-operating with your neighbours, getting wet, doing the stuff that needs to be done – as many are already doing. There are lots of dangers in this. There will be a degree of chaos, there will be mistakes. But it is also an opportunity to ‘act local’ and show that we are all responsible for where we live, that the parks are our parks, that we value trees and our public spaces, that we don’t expect “them” to solve all our problems.

And there will be some ‘up side’. The natural world is an exuberant world. Things may be less tidy, but biodiversity thrives in messy places. Unswept gutters and untrimmed hedges may cause problems, but we can help ourselves to resolve these issues – and hedge trimmings and fallen leaves makes great leaf mould.

Here is the a “dead hedge” on the downs, rebuilt by volunteer labour last month to help protect the wildflower meadow beside it from joggers; just one example of what self-help can do.

downs-hedging

Who knows, we might even get our urban sparrows back.

Richard Bland  March 2017

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