In its Information Statement of October 2025 concerning its recent fencing works at Stoke Lodge Playing Fields, Cotham School has chosen to misunderstand our concerns about the welfare of the trees at Stoke Lodge Playing Fields.
‘In planning the work to reinstate the fence, the School wanted to respond to feedback, to improve safety by removing muddy paths, to respond to the Bristol Tree Forum concerns regarding footpaths impacting on the roots of trees protected by Tree Preservation Orders, to reduce any other ecological impact and to create an enhanced local open space.’
Our complaints about the detrimental impact caused by the school’s original fencing layout on all the trees – not just the trees protected by Tree Preservation Orders (TPOs) – growing around the boundary of the site and on the playing fields were made in February 2020, nearly six years ago, in this blog: The trees at Stoke Lodge Park and Playing Fields – a letter to the Council. Cotham School has ignored these complaints and has never approached us to discuss our concerns.
Furthermore, Cotham School’s decision to drive its new fencing through the root zones of several TPO trees, one of which is a veteran boundary oak, and to destroy other trees, some of which are protected by a TPO, makes it clear to us that the school continues to ignore the welfare of the trees growing at Stoke Lodge.
We have reported these most recent breaches of TPO legislation to the Local Planning Authority. We have also made clear to Bristol City Council our concerns about the welfare of the Stoke Lodge trees generally. We have been ignored.
As a result of this neglect, the long-term welfare of all the trees growing on and around the playing fields is at risk.
To calculate the biodiversity value of a habitat, it’s important to assess its strategic significance. A habitat’s strategic significance takes into account both its type and its location. If strategic significance is high, then the habitat’s value will be uplifted by 15%. However, as this article explains, the opportunities for doing this are limited.
A habitat parcel is an area of habitat which is all of the same distinctiveness, condition and strategic significance. Strategic significance refers to the importance of a habitat parcel based on its location and type.
Each habitat parcel needs to be assessed both before, when the baseline habitat is surveyed, and after development, on or off site.
This flowchart sets out how to assess the strategic significance of a habitat parcel. It uses the tables, shown below, from the Statutory Biodiversity Metric User Guide.
WEMCA’s Local Nature Recovery Strategy (LNRS) will fail to provide Bristol with the benefits promised for nature. While the new Biodiversity Net Gain (BNG) rules require most development in the city to increase biodiversity by at least 10%, unfortunately the LNRS will not apply to most potential development sites.
The LNRS is a locally led and evidence-based strategy which aims to target action and nature investment where it’s most needed. We’re told that the strategy will also focus on biodiversity net gain by increasing the strategic significance of specific habitats. However, it is hard to imagine how the LNRS will help to enhance biodiversity net gain in most, if not all, potential development sites in the city.
We might have been better off, at least as far as the application of biodiversity net gain to new development is concerned, by asking the LPA to specify alternative documents (such as those listed at the end of this article) for assigning strategic significance instead.
The issue
When calculating the impact of a proposed development on biodiversity, one factor taken into account is the strategic significance of any habitat found on a focus area for nature recovery site (coloured purple in the map above). If strategically significant habitats are created or enhanced, then their strategic significance is set to High in the Statutory Metric calculator tool and a 15% uplift to the calculation of its value is applied. Subject to which of the six LNRS areas is being considered, these are the strategically significant habitats in the city:
Ditches
Ecologically valuable lines of trees
Ecologically valuable lines of trees – associated with bank or ditch
Grassland – Floodplain wetland mosaic and CFGM
Grassland – Lowland calcareous grassland
Grassland – Lowland meadows
Heathland and shrub – Mixed scrub
Heathland and shrub – Willow scrub
Individual urban or rural trees
Lakes – Ponds (priority habitat)
Priority habitat (on the River Avon and the Riparian buffers)
Species-rich native hedgerow with trees – associated with bank or ditch
Species-rich native hedgerow with trees
Species-rich native hedgerows – associated with bank or ditch
Species-rich native hedgerows
Urban – Open mosaic habitats on previously developed land
Urban – Biodiverse green roofs
Woodland and forest – Lowland beech and yew woodland
Woodland and forest – Lowland mixed deciduous woodland
Woodland and forest – Other woodland; broadleaved
Woodland and forest – Wood-pasture and parkland
However, a detailed examination of the LNRS map reveals that not all parks and green spaces have been designated as focus area for nature recovery sites. It’s only those which are in one or both of the following:
a location where they can make a greater contribution to ecological networks
deprived areas with a lack of access to nature.
These designations were based on Bristol’s previous work on ecological networks within the city and where wildlife-friendly interventions are most likely to be feasible. This means that the existence, creation or enhancement of these special habitats outside these areas will not attract the 15% strategic significance uplift.
The BNG requirements
The now compulsory Statutory Metric Guide, used for calculating Biodiversity Net Gain (BNG), advises (at page 27) that: ‘Strategic significance is the local significance of the habitat based on its location and habitat type. You should assess each individual habitat parcel, both at baseline and at post-intervention, for on-site and off-site.’
If the LPA has adopted an LNRS then only the High or Low strategic significance multipliers can be used (High – formally identified in local strategy = 1.15. Low – area compensation not in local strategy = 1). If it has not adopted an LNRS, then the Medium strategic significance multiplier may also be used (Location ecologically desirable but not in local strategy = 1.10).
Where an LPA has adopted an LNRS, all those sites which have not been identified as a focus area for nature recovery site will be designated as having Low strategic significance and so attract no uplift, even if they’ve been identified as important habitats in the Local Plan or in another strategic document adopted by the Council. These documents (used where an LPA has not adopted an LNRS) can include:
Draft Local Nature Recovery Strategies
Local Plans and Neighbourhood Plans
Local Planning Authority Local Ecological Networks
Parks and Green Spaces Strategies
Tree and Woodland Strategies
Area of Outstanding Natural Beauty Management Plans
Biodiversity Action Plans
Species conservation and protected sites strategies
Green Infrastructure Strategies
River Basin Management Plans
Catchment Plans and Catchment Planning Systems
Shoreline management plans
Estuary Strategies
Baseline habitats cannot be uplifted
Despite the BNG strategic significance guidance, Defra has stated that LNRS designations only apply to the creation or enhancement of post-development biodiversity mitigation habitats. They don’t apply if these habitats – called the baseline habitats – are found on the site before development begins.
This means that the 15% strategic significance uplift can only be applied where offsite biodiversity mitigation is being delivered in a focus area for nature recovery site. If these habitats are being delivered elsewhere, the uplift may not be applied.
However, even if the baseline habitats were included, it is unlikely to make any difference This is because the focus area for nature recovery sites identified in Bristol are, for the most part, located in public parks or green spaces, on river banks, in riparian buffers or on railway margins, none of which are likely ever to be developed or, in many cases, used to offset habitat lost to development elsewhere.
So far, no announcement has been made as to whether any of Bristol’s focus area for nature recovery sites will be made available for offsite habitat mitigation and the proposed new Local Plan does not commit to using these sites for this purpose.
This, combined with the challenge of finding LNRS suitable for offsite habitat mitigation, registering them as biodiversity gain sites and then managing them, effectively, in perpetuity, suggests that few feasible LNRS sites will be found, especially as many sites are also in demand for public access for recreation.
Many thanks for of of you who have asked for trees – over 1,200!
We have now closed the offer.
Planting a tree is, perhaps, one of the most significant things we can do to help protect our future environment, promote nature and make the world a better place for the generations to come. The trees we plant today will continue to provide benefits for the environment, wildlife and people, for hundreds of years.
A veteran chestnut
We all know the value of trees in sequestering carbon, and they still represent the most effective and widespread means of removing CO2 from the atmosphere. For instance, a single mature oak tree is the equivalent of 18 tonnes of CO2 or 16 passenger return transatlantic flights. However, it is in our cities that trees provide the greatest benefits; cleaning our air, reducing flooding, improving our physical and mental health, and, crucially, reducing temperatures during heat waves.
Our cities suffer additional problems during heat waves, with all of the concrete and tarmac absorbing a lot of energy from the cooling sun and releasing it as heat. This “heat island” effect can raise temperatures by as much as an additional 12 degree centigrade. Trees can greatly reduce, or even eliminate, this effect, partly through shade but also actively cooling the air by drawing up water from deep underground, which evaporates from the leaves… a process called evapotranspiration. According to the US Department of Agriculture, this cooling effect is the equivalent to 10 room sized air con units for each mature tree. This cooling greatly enhances our resilience to the dangerous heat waves that are predicted to increase in severity and frequency.
A veteran Beech
A stand of Silver birch
Also, Trees improve air quality by absorbing both gaseous (e.g., NO2) and particulate pollution. They reduce traffic noise and flooding and improve physical and mental wellbeing.
Thus, trees are a crucial, but often ignored, element in increasing our resilience to climate change.
What are the Bristol Tree Forum doing to help?
It is said that the best time to plant a tree is 20 years ago, and the second-best time is now.
Unfortunately, important mature trees are constantly being lost to development, damage and disease. Though these might easily be replaced by new trees, what is less easy is replacing the decades or even centuries that the tree has taken to grow, the carbon that the tree has sequestered, the ecosystems the tree supports and all of the other benefits trees provide. For these reasons, most of the work of the Bristol Tree Forum focuses on protecting our existing trees. These efforts are particularly crucial in the urban environment where our trees are under the greatest threat.
However, as well as advocating the retention of life-saving trees in our city, Bristol Tree Forum have been encouraging new tree planting by holding an annual tree giveaway since 2020; the ancient trees of the future are being planted today! Most of Bristol’s trees are sited in private land and gardens, so the trees we have are mostly thanks to the efforts of Bristol residents, and it is those residents we must look to if we want to increase our tree canopy.
Over the last four years, we have given away around 10,600 trees, with species as diverse as English and Sessile oak, Downy birch, Silver birch, Grey birch, Alder, Alder buckthorn, Rowan, Scots pine, Sweet chestnut, Sycamore, Spindle, Wild cherry, apple, pear and plum.
This year’s Tree Giveaway has been made possible by the generous support ofMaelor Forest Nurseries, based on the Welsh borders, and Protect Earth whose aim is to plant, and help people plant, as many trees as possible in the UK to help mitigate the climate crisis.
Thanks to Maelor, we are able to offer a variety of species with a wide range of sizes and preferred habitats, including Pedunculate (English) oak, Red oak, Sweet chestnut, Silver birch, Sycamore, Hawthorn, Beech, Hornbeam, Wild cherry, Alder, Red alder, Field maple and Norway maple.
Trees can be ordered using the form below
We will get delivery of trees in February, when the trees can be collected from a site in Redland, Bristol. We will email you when they are ready.
The saplings come bare-rooted (i.e. out of the soil) and will need to be planted as soon as possible after collection, although the viability of the trees over winter can be extended by storing the trees with the roots covered in damp soil.
The form below is to find out who would like to have saplings for planting, which species, how many and where you plan to plant them.
Please provide your email so we can contact you organise collection of the trees. Your contact details will be kept private and will not be used for any other purpose than to process your request.
In a boost for the environment, new legislation now obliges most developers to set out how they will achieve at least 10% more biodiversity than already exists on their proposed development sites.
Developers must now show how they will improve the biodiversity of their development site as a result of their works. Developers must record the (baseline) on-site habitats that exist before development starts and show how they will either enhance or replace these on site. If their proposals fail to reach the 10% threshold, the developer may provide the shortfall elsewhere. This post-development mitigation should be done as closely as possible to the development site, or at least within the Local Authority. However, if this isn’t possible, they can use approved sites anywhere in England.
This approach is called the Biodiversity Gain Hierarchy (found in Schedule 7A of the Town and Country Planning Act 1990 at section 37A). The Hierarchy says it’s a priority to avoid the ‘adverse effects’ to ‘onsite habitat with a habitat distinctiveness score … equal to or higher than four.’ If this can’t be avoided, only then is mitigation permitted. In our experience, nearly all developers ignore the requirement to avoid adverse effects and move straight on to mitigation.
Since the introduction of the Bristol Tree Replacement Standard in 2013, developers (and planners) have ignored the policy requirement to avoid tree removal where at all possible. Instead, they’ve moved straight on to providing compensation for the trees lost to the development. As a result, the money set aside for replacement tree planting was not spent (on occasion reaching nearly £1 million) and many of the lost trees were never replaced.
Under the Hierarchy, habitats that score four are designated as having medium distinctiveness. While many habitats have medium distinctiveness, many don’t. For example, managed grassed areas (called ‘modified grassland’) are often found on urban sites but have a low distinctiveness score. So, too, do many other urban habitats such as allotments and gardens. Developers are not required to avoid harming these, though losses to these habitats must still be mitigated.
There’s no definition of what an ‘adverse effect’ is or any guidance on how it is assessed. However, recent advice from the Bristol’s Chief Planner about the meaning of ‘harm’ suggests that this could be interpreted very broadly or simply ignored because some sort of mitigation will always be available.
In the last extreme, developers may purchase biodiversity credits. We wait to see how this and the offsite biodiversity mitigation market evolves, but a 2012 paper published in the Harvard Environmental Law Review suggests that such environmental markets are prisoners of their own geography because the space available is always constrained:
Markets for water quality, biodiversity, endangered species, fisheries, air quality, and aquatic resources, to name a few, must recognize that the commodities they trade exist at particular geographic scales, and set appropriate spatial limits on the redistribution of environmental quality. The size of geographic trading areas has significant implications for the economic viability of markets and the ecological quality of their offsets.
This will be a particular challenge when providing biodiversity mitigation in urban areas.
The squeeze on green spaces
Land use in Bristol is subject to intense competition by many stakeholders. This is especially true for our green and open spaces, which offer many ‘services’ beyond just habitat provision. There is very little, if any, space available for new biodiversity to be created. At best, some green spaces might be enhanced, but opportunities to do this are likely to be very limited.
For example, Bristol Tree Forum’s examination of the three proposals to develop Bedminster Green shows that, if these proposals are allowed, then nearly 400 new trees will need to be planted to compensate for the lost tree habitat – a medium distinctiveness habitat. There’s no room to plant these trees on site, so offsite provision will be needed. There are very few opportunities for doing any new tree planting (as opposed to replacing lost trees) in the surrounding wards or even across Bristol, let alone, as is usually required, within a mile of a development site.
Instead, these replacement trees will have to be planted somewhere else: ‘in some foreign field that is forever Bristol’. This will inevitably lead to a net loss of biodiversity across the city as nature is ‘hollowed out’. This is unacceptable. The whole purpose of the new biodiversity gain regime is to improve overall local biodiversity, but it seems inevitable that Bristol will instead see a steady, inexorable decline.
We are disappointed that the current draft of the new Local Plan addresses none of these issues and have said so in our responses to the latest consultation:
The new Biodiversity Net Gain (BNG) obligations, which came into force last February, aim to improve our natural environment by requiring that all new developments have a positive impact (a net gain of at least 10%) on biodiversity.
For this reason, we believe that Bristol urgently needs to follow the lead of the other west of England councils, B&NES, South Gloucestershire and North Somerset, and adopt a Biodiversity Net Gain Supplementary Planning Document (SPD). A list of other local authorities that have adopted their own biodiversity SPDs can be seen here on the Local Government Association planning advisory service website – Biodiversity Net Gain in Local Plans and Strategic Planning.
Councils are encouraged to develop a locally specific SPD as part of their Local Plan. This would:
set out local priorities and strategies that require developers to deliver BNG locally
ensure that BNG contributes to wider nature recovery plans such as the newly launched Local Nature Recovery Strategy (LNRS) and other local objectives, and help ensure that the right habitats are provided in the right places
link BNG requirements to other strategic objectives and place-making policies in the Local Plan, to ensure a more holistic approach
set requirements for managing and maintaining habitats provided through development.
Having such a document would clarify exactly what developers need to do in terms of the BNG requirements. While these requirements have many gaps, they are now, as it were, the only game in town and we must try to make the best of them. We believe that developing a robust BNG SPD could help mitigate these problems by adding tougher conditions that developers must meet.
With the launch of the LNRS – a collaborative effort to help people and organisations within WECA and North Somerset take effective action for nature – it has become more important than ever for Bristol City Council to bring this strategy into action, especially where new development is planned.
Two factors causing us the most concern (there are others) are the exclusion of stakeholders from the BNG decision process and the lack of enforcement of BNG requirements.
Consulting stakeholders
We’ve long been concerned that the new BNG regime excludes stakeholder groups such as ours from engaging with and commenting on the approval process for Biodiversity Gain Plans (BGPs) because of the way the planning rules work.
The BGPs are a post-approval requirement (see Schedule 7A of the TCPA ’90, Part 2, section 13(1)), which means there’s no obligation for a developer to demonstrate how it will meet its BNG responsibilities during the application stage (although the Council could require this).
Under current rules, BGPs only need to be submitted for approval to the Planning Authority after an application has been approved. However, there’s no statutory requirement to consult any statutory bodies on BGPs or to publicise or consult on the submission of a BGP prior to its approval. It seems, therefore, that we (and other stakeholders who, like us, are fighting for everyday nature) will have no say in what is proposed, or even have any idea of what a BGP contains or how it could affect us.
Surely this goes against the principles of open governance and localism which councillors should be fighting to defend, especially where it’s likely to have a direct impact on the very places that we Bristolians love and value?
Improving enforcement
As a recent article in Local Government Lawyer magazine points out, there are serious issues around BNG enforcement that need to be resolved.
We’ve been trying to engage with council officers over this issue for some time, but so far without success. Maybe the time has come for the Council to seize the initiative? With the proposed new Local Plan moving towards its public hearings stage early next year and the likelihood that the plan will be adopted next April, maybe now is the time for the reconstituted Local Plan Working Group to take this in hand.
One of our fears is that some planning conditions, such as this one from the recent, pre 12 February 2024, Bristol Rovers Memorial Grounds application are unenforceable. In this case they only oblige the club to submit a proposed Landscape Ecological Management Plan (LEMP). They did this last June. However, the wording of the condition means that the club is not obliged to perfect this or even to carry it out.
Readers may recall that the development had been completed and the new stands occupied long before the main application was made, well before this and other conditions had been submitted or approved. In addition, as part of the eventual approval, the club agreed to plant a wood on a piece of unused land it owns to the south of the new stadium (the area shaded green below), but this has not yet been done.
As part of this agreement, the club is expected to enter into a LEMP to plant the wood and then maintain it in perpetuity. The LEMP Condition says:
Within 6 months of the date of consent, the applicant shall submit a 30-year Landscape and Ecological Management Plan (LEMP). This should address retained features of ecological interest, together with mitigation and enhancements to be provided. The LEMP should set out management compartments, objectives, and prescriptions for all new proposed soft landscaping/planting to demonstrate how all habitats will be managed to their target condition (as specified in the BNGA). It should also show how management of the site will be resourced and monitored.
In this example, all that can be enforced is a failure to submit the LEMP within six months, which, in this case, has been done. There is a S106 imposing LEMP obligations but this is toothless and, anyway, only the Council can enforce it – which it is not obliged to do.
There’s also the practical effect of the Biodiversity Gain Hierarchy – Biodiversity net gain Guidance Paragraph: 008 Reference ID: 74-008-20240214. This effectively means that the developer need not achieve any net gain on site, or even locally, but can instead deliver it anywhere in England or, as a last resort, simply buy BNG credits, though at a premium.
For example, the grant conditions – 11 (The BGP condition), 12 & 14 – in the recent, post-12 February Council application, The White Hall, Glencoyne Square, are unenforceable given their wording as there is only an obligation to submit; again, approval is not required. We assume that a s106 agreement and a Habitat Management and Monitoring Policy (HMMP) will need to be produced, but, at the moment, we still have no idea how the self-acknowledged 38.09% habitat loss will be mitigated, or where.
Given the intense competition for space in the city, it seems inevitable that, as a result of the application of the Biodiversity Gain Hierarchy, Bristol’s nature will, bit by bit, be exported to some far-off field that no one knows or cares about. In theory, a BNG SPD could at least try to ensure that habitats lost to development are replaced locally wherever possible.
It’s been suggested that new SPDs can’t be delivered until after the new Local Plan has been examined and formally adopted. Maybe, but we see no reason why we can’t at least start a conversation about this. As it is, the proposed Local Plan will need substantial redrafting to align with the new BNG rules, having been adopted by the Council before these had been finalised.
It’s also been suggested that there are neither the funds nor enough officer time available to develop this new SPD. However, since all the adjacent councils (members of WECA), and many farther afield, have developed, or are developing, their own SPDs, we can surely save time and expense by looking on these as templates from which to build our own. The examples above alone make it all the more urgent for issues such as this to be resolved with the early adoption of a BNG SPD. We urge the Council to commission officers to draft an SPD as a matter of urgency.
There are six criteria for assessing a tree’s condition. If a tree passes five or six of the criteria, it is in good condition. If it passes three or four of the criteria, it is in moderate condition. If it passes two or fewer of the criteria, it is in poor condition.
These are the six criteria to consider:
A – The tree is a native species (or at least 70% of the block are native species). B – The tree canopy is predominantly continuous, with gaps in canopy cover making up <10% of total area and no individual gap being >5 m wide (individual trees automatically pass this criterion). C – The tree is mature (or more than 50% of the block are mature). D – There is little or no evidence of an adverse impact on tree health by human activities (such as vandalism, herbicide or detrimental agricultural activity). And there is no current regular pruning regime, so the trees retain >75% of expected canopy for their age range and height. E – Natural ecological niches for vertebrates and invertebrates are present, such as deadwood, cavities, ivy and loose bark. F – More than 20% of the tree canopy area is oversailing vegetation beneath.
The ‘Fairly Good’ and ‘Fairly Poor’ condition categories are not available for this habitat type.
Enhancement of this habitat is only possible by improving it so that it meets the criteria B, D and F. It is not possible or appropriate to enhance individual tree/s through meeting just one or two of these criteria, nor by meeting only A or C or E.
It is important that the species of each tree on site is properly listed by the developer. Here is the list of the native species defined by the Statutory Metric:
With the introduction of the Biodiversity Metric, all existing (i.e. baseline) habitat parcels on proposed development sites are given a calculated habitat value, called Habitat Units (HUs).
Baseline habitat parcels
Baseline habitat is the habitat that exists before a site is developed. Development sites often contain a mosaic of baseline habitats each of whose condition may vary. These are called habitat parcels.
The area of a habitat parcel is measured in hectares (or square metres when using the Small Sites Metric). Linear habitats parcels are measured in kilometres (or metres when using the Small Sites Metric).
The sum of all the ground-based area habitat parcels should equal the area of the proposed development site (the redline boundary).
Calculating HUs
The HU calculation uses the following formula:
HU = Habitat area/length x Distinctiveness x Condition x Strategic Significance.
The Distinctiveness of each habitat is predefined. These are the Distinctiveness scores:
The Strategic significance of a habitat is its importance according to its location and habitat type. Each of these elements is given a score which is then used in the HU formula. These are thescores:
High
1.15
Medium
1.1
Low
1
For example, an area habitat parcel covering a hectare, which is of medium distinctiveness, in moderate condition and of medium strategic significance, is calculated as follows:
1 ha (area) x 4 (distinctiveness) x 2 (condition) x 1.1 (strategic significance) = 8.8 HUs.
Individual trees habitat
There is a special formula for individual trees habitats. This is because they oversail the habitat on the ground and so are non- ground-based habitats, which need to be treated differently from ground-based habitats.
This table shows the four size classes for Individual trees habitats:
It uses the diameter at breast height (DBH measured 1.5 metres above the ground) of each tree growing on a proposed development site (if the tree is multi-stemmed, the largest DBH recorded is used) and assigns a ‘Biodiversity metric area equivalent’ to calculate its habitat area. This value represents canopy biomass, and is based on (but not the same as) the root protection area formula, derived from BS 5837:2012.
For example, a medium-size individual trees habitat covers an area of 0.0163 ha and has medium Distinctiveness. If it is in moderate Condition and of medium Strategic significance the HU value is calculated as follows:
0.0163 ha (area) x 4 (distinctiveness) x 2 (condition) x 1.1 (strategic significance) = 0.14344 HUs.
Post-development habitat creation and enhancement
The biodiversity metric also applies three additional risk factors to all post-development enhanced and created habitat parcels, across all three habitat types – Area, Hedgerow and Watercourse – using this formula:
HU = Habitat area/length x Distinctiveness x Condition x Strategic Significance x Temporal Risk x Difficulty factor x Spatial Risk
Temporal risk
This represents the average time lag between the start of habitat parcel creation or enhancement works and the target outcome date. This is known as the ‘time-to-target condition’ and is measured in years.
If there is a delay in creating or enhancing the habitat parcel, or it has already been enhanced or created, this can be factored in to adjust the time-to-target period either up or down.
The temporal risk period is automatically applied by the biodiversity metric and changes depending on target habitat condition. As a result, the temporal risk multiplier, based on the 3.5% discount table below, sets the current value of the future habitat being created.
Difficulty of creation or enhancement
The creation and enhancement categories represent the uncertainty of the effectiveness of techniques to create or enhance habitat parcels.
The biodiversity metric automatically assigns the delivery risk and score for each habitat parcel, based on its habitat intervention category.
Category
Value
Low
1
Medium
0.67
High
0.33
Very High
0.1
Spatial risk
Where a project cannot achieve a net gain in biodiversity units on site, then offsite HUs can be used to meet the BNG requirement.
The spatial risk penalty (SRM) reflects the relationship between the location of on-site biodiversity loss and the location of off-site habitat compensation. It affects the number of biodiversity units provided to a project by penalising proposals where off-site habitat is located at a distance from the development site.
If the offsite area is within Local Planning Authority (LPA) boundary or National Character Area (NCA), the penalty is x 1.0.
If it is in a neighbouring LPA or NCA, the penalty is x 0.75.
If it is elsewhere (anywhere in England), the penalty is x 0.5.
The effect of this is that it costs more HUs to achieve the BNG requirement the farther away the offsite mitigation is from the location of on-site biodiversity loss.
Post-development Individual trees habitat creation
When creating Individual trees habitat, post-development size class of a tree is determined by its size when it is planted. Newly planted trees should be recorded as small-sized, unless the tree is actually medium-sized or above at the time of planting.
In our experience, nearly all nursery-grown trees are small-sized, as this table, derived from BS 3936-1, demonstrates.
For example, a small-sized tree covers an area of 0.0041 ha and has medium Distinctiveness. The difficulty of creation factor is preset at Low.
If it is planned for it to achieve a moderate Condition, the time-to-target period will be 27 years. If it is planted within the LPA in an area of medium Strategic significance, its HU value will be calculated as follows:
0.0041 ha (area) x 4 (distinctiveness) x 2 (condition) x 1.1 (strategic significance) x 0.382 (temporal risk) x 1 (difficult factor) x 1 (spatial risk) = 0.01378 HUs.
Much has been made of the new rules that require most developments to add at least 10% more biodiversity to a site than was present before development took place. This requirement is known as biodiversity net gain (BNG).
However, a much-overlooked aspect of the new rules is the requirement also to comply with so-called trading rules.
These trading rules set minimum requirements for habitat creation and enhancement to compensate for specific habitat losses resulting from a new development.
If these rules are not followed, a developer cannot claim that there is biodiversity net gain, even if the planning application has achieved the minimum 10% BNG required.
Rule 2 states that biodiversity unit outputs for each habitat type – Area, Hedgerow or Watercourse – must not be added together, traded, or converted between types. The requirement to deliver at least a 10% net gain applies to each separate habitat type.
The trading rules only apply to the point of no net loss of a specific habitat. Once the trading rules have been met for this habitat, the biodiversity net gain requirements can be met by the creation and enhancement of any other habitat, provided it is the same habitat type.
This table from the Statutory Metric sets out how they apply:
The trading rules for the SSM are slightly different. This is because the SSM does not cater for high and very high distinctiveness habitats (if these are present, the Statutory Metric must be used):
Although the calculator warns of any breaches of the trading rules, the design of the SSM does not allow users to identify where the breaches have occurred. However, the Statutory Metric does. So, if the habitats input into the SSM calculator are transposed to the Statutory Metric calculator, this will reveal where the trading rules breaches are and allow the user to consider how to mitigate the losses whilst still complying with the trading rules.
There are special rules for very high distinctiveness habitats and for compensating for loss of watercourses and high distinctiveness woodland, which are not addressed here.
How the trading rules apply to urban tree habitats
Individual trees habitat has medium distinctiveness. This means that this habitat can only be replaced like for like, although higher distinctiveness habitats can be substituted when the Statutory Metric is used.
Other broad habitats with the same distinctiveness cannot be substituted. For example, Woodland and forest habitat cannot be used to replace lost Individual trees habitat unless it has a higher distinctiveness and the SSM is not being used.
As a result, the requirement to replace lost trees can result in many more trees having to be planted (often off site) than will be lost. In one recent example we examined, 116 replacement trees were needed to comply with the trading rules, even though only 12 were being removed.
Hopefully, developers will now think twice before seeking to remove trees to make way for their plans.
On Thursday 26 September 2024 Waterstones at The Galleries launched Our City. This book chronicles community activism in Bristol through multiple campaigns described in eighteen individually authored chapters.
Suzanne Audrey pulled the whole project together, edited the book and contributed the introduction and conclusion. The book is well worth buying. It tells a story of the diversity and resilience of Bristol communities when faced with threats usually emanating from the council which should be looking after them. The Bristol Tree Forum was asked to contribute. During the launch event, contributors were each given three minutes to describe their work. This is what we said:
Saving Bristol’s Urban Trees by Vassili Papastavrou
In Bristol we are seeing the loss of hundreds of important urban trees each year. They cannot be replaced and it will create a city that is unliveable – we need them to keep us cool now.
I’d like to illustrate the problem with two willow trees which grew not far from here. Two years ago, during National Tree Week, they were chainsawed by Bristol City Council. Highly visible and next to Temple Meads, the trees should have had Tree Preservation Orders but the council does not TPO its own trees, claiming that it is a responsible landlord and that its trees are safe.
I was brought up in Cambridge. Along the banks of the river Cam, willows are such a feature of the city that no one in their right mind would consider chopping them down. But in Bristol they were removed without a moment’s thought.
The removal was filmed by Martin Booth and got a lot of coverage but in reality it was just another ordinary day of tree removal in Bristol. Martin tweeted, “This is so sad to watch. One of Bristol’s most beautiful trees, a majestic weeping willow is being chopped down this morning”.
Trees compete for space with other uses of the city. In Bristol mature urban trees are given lowest priority, so when plans come up, trees are removed. As this incident demonstrates, they have zero value to the Local Planning Authority or the council.
The willows never went in front of the Planning Committee where there could have been a debate as this was a “delegated decision”. Effectively Bristol City Council was giving planning permission to itself in a backroom deal. The planning application was snuck through with no mention of the trees in the title, no arboricultural report from the council, no tree officer report from the local planning authority. The council passed judgement on itself.
And after the deed had been done, was there any recognition that a terrible act had been committed? An inquiry to make sure that this kind of thing would never happen again?
Silence. For in Bristol there is no one in a position of power who cares about retaining important urban trees.
Bristol Tree Forum 