Category: Bristol Trees

Biodiversity gain: will urban nature become hollowed out?

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:

Bristol Tree Forum representations in relation to the Bristol Local Plan 2023 Publication Version consultation & BTF Representations on the Bristol Local Plan 2023 publication version – Addendum.

A shorter version of this article was published by 24/7 as:

‘It seems inevitable Bristol will see a steady, inexorable biodiversity decline’

Why Bristol needs a Biodiversity Net Gain SPD

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.

This is what the Council currently requires from developers: Biodiversity Net Gain for major development and small site planning applications. At best, this is only advisory, unlike an SPD which would be part of the Local Plan and so compel the developer’s compliance.

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.

A shorter version of this blog was published in 24/7 as: ‘Without enforcement, Bristol’s nature will be exported bit-by-bit‘

How to assess the condition of a tree

There are special rules for assessing the condition of Individual trees habitat, as set out in the biodiversity gain guidance.

The criteria set out in the  Statutory biodiversity metric condition assessments table must be used to decide on the condition of Individual trees habitat, which is scored as follows:

ConditionScore
Good3
Moderate2
Poor1

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:

BNG – valuing habitats

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:

Very High8
High6
Medium4
Low2
Very Low (hedgerow module)1
Very Low (area module) 0

The Condition of a habitat is assessed using the various matrices set out in Statutory biodiversity metric condition assessments published by Defra. These are the scores:

Good3
Fairly Good2.5
Moderate2
Fairly Poor1.5
Poor1
Condition Assessment N/A 1
N/A – Other0

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 the scores:

High1.15
Medium1.1
Low1

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. 

CategoryValue
Low1
Medium0.67
High0.33
Very High0.1

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.

Other Blogs in the series

Tree Habitat Area Calculation

The Trading Rules Explained

The trading rules explained

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 1 of the Statutory Metric and the Small Sites Metric (SSM) guides state that the trading rules must be followed.

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.

Other Blogs in the series

Calculating habitat units

Tree habitat area calculation

Our City book launch

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.

We can only hope that that will change.

Why we must protect the trees we love

Paul Sander-Jackson, who helped to plant the Baltic Wharf trees, returns to Bristol shocked to learn that they will now be felled.

We came back to live in Bristol nearly two years ago. After living in Somerset for 32 years, and in Bristol 12 years before. Much has changed in the city, but much has remained – the best bits, and especially the trees.

Our new home backs on to Oldbury Court – which has an astonishing range of trees and plants, as well as a river and rocks and old quarries. Our garden has a lime tree – probably about 80 to 90 years, just outside its boundary fence.

In Somerset, we became very involved, in the later stages of life there, in planting new trees and woodlands, hedges and copses. The organisation we were involved with – Reimagining the Levels – has been responsible for planting over 100,000 trees in the past few years. But that is addressing a major problem in Somerset – a tree cover of only between 6% and 7%.

Coming back to Bristol, I wondered where my energy should go. But a few months ago, an old friend mentioned that I might like to get involved in Bristol Tree Forum. The rest is (personal) history. My partner and I are now joint Tree Champions for the Frome Vale ward.

It was a great shock when I was made aware of the application then pending on the Baltic Wharf Caravan Club site, particularly because when I used to do landscaping and gardening for a livelihood in the late eighties and early nineties, I had helped plant trees on that site, and carefully undertaken structural pruning and maintenance. And now a planning application was threatening to fell 80 of them.

“The Baltic Wharf trees were at least 35 years old, providing numerous ecological ‘services’ to the area”

As I made further enquiries, it turned out that there were over 590 objections to the application, with six statements in support. Six!! The trees represented over a quarter of the tree cover in the immediate area. They were at least 35 years old, providing numerous ecological “services” to the communities of Bristol.

And then the terrible shock of a unanimous – yes unanimous – planning committee decision to go ahead without amendments to the felling of the trees, with no objection from the responsible tree officer.

This left me realising many things. How naïve I have been about the problems nature, and especially trees, face in this lovely city. How we need to struggle and advocate for every one. Trees offer so many positive benefits for all creatures, including humans. I reflect on the wonderful life in ‘our’ lime tree.  Pigeons, starlings, sparrows, crows, squirrels. Life in all its varied forms. Leaves, blossoms, growth.

And perhaps most of all, I recognise that in Bristol, in 2024, there is perhaps an equal if not greater task to planting new trees. To protect the ones we have, and love. And to share that love with as many people, in our local communities and beyond, that we can.

“Maybe we can teach even more people how important it is to retain trees and how we should never allow a good tree in a good place to be arbitrarily felled”

My partner and I began our life in Bristol in St Werburghs, starting the City Farm there in 1980. As it got going, with great help from some wonderful City Council officers in the planning and parks departments, we planted trees with children from six local primary schools. Those children, I hope, will always carry the memory of that planting. And I hope they go and visit the trees – now over 40 years old and flourishing in the wondrous environment of the City Farm.

It is about a will, an attitude, a set of values. Above all, it is about respect for our fellow plants and creatures, who share this planet and this city with us.

Interested in becoming a Tree Champion like Paul? Click below to learn more.

Find out about tree champions

Our 2024 tree giveaway – free saplings for planting

Last year we were able to provide – free of charge – over 2,000 tree saplings for tree lovers to plant in and around Bristol…. and beyond!

This year we plan to give away pedunculate oak (Quercus Robur) and downy birch (Betula Pubescens), each native and supporting lots of wildlife.

Would you like some to plant out in 2024? We have 2,000 to give away.

First come, first served, tho!

Stop Press – We have now distributed all available trees, so this offer is now closed. Thanks for all your support.

Watch out for our offer next year!

Few of us will forget that 2023 was the hottest year ever recorded and far exceeded previous temperature records, both locally and nationally, coming close to the average world temperature of 1.5C that we have all been challenged to avoid!

The Met Office reports that in early September 2023, the UK experienced a significant heatwave with daily maximum temperatures exceeding 30°C somewhere in the UK for seven consecutive days from 4th to 10th and reaching 31 to 32°C across south-east England. While this heatwave would not have been particularly unusual had it occurred during the high summer months (July or August), this was, for September, the longest run of days exceeding 30°C on record.

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 sun and releasing it as heat. This “heat island” effect can raise temperatures by as much as an additional 12C. Trees can 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. This cooling greatly enhances our resilience to the dangerous heat waves that are predicted to increase in severity and frequency.

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. It is therefore disappointing that neither the council’s Climate Emergency Action Plan or the ‘Adaptation to a changing climate’ section of the recent draft Bristol Local Plan review make any mention of trees.

We are one of the most biodiversity depleted countries in the world, and have lost nearly 70% of our biodiversity since the industrial revolution. Trees are vital in supporting biodiversity, with oak trees capable of supporting over 2,300 different species, including birds, mammals, invertebrates, mosses, lichen and fungi.

What is 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.

As well as advocating the retention of life-saving trees in our city, Bristol Tree Forum have been encouraging tree planting by holding an annual tree giveaway since 2020. In that year we purchased 1,600 oak saplings from Maelor Forest Nurseries which we distributed free of charge. In 2021/2022 we initially gave away 600 white birch and 400 alder, as well as 900 oak saplings, the latter thanks to a partnership with the Arkbound Oakupy project. We were then contacted by the Forest of Avon Trust who had a surplus of 4,500 tree saplings, over 4,000 of which we were able to distribute through our network of tree planters. Overall, that year we gave away around 6,000 trees including 1,600 oak, 740 silver birch, 860 white birch, 55 grey birch, 600 alder, 100 alder buckthorn, 950 rowan, 45 Scots pine, 60 sweet chestnut, 300 sycamore, 50 spindle and 630 wild cherry. Last year, we manage to distribute 2,102 trees.

Trees planted in Bristol. Trees were also planted as far afield as West and North Wales, South Devon and Wiltshire.
Just some of the trees given away in 2021/22

Flushed with the success of last year’s project, we have ordered another two thousand saplings – pedunculate oak (Quercus Robur) and downy birch (Betula Pubescens) – which we are ready to give away. Each species is a native tree of great benefit to wildlife and is tolerant of urban and rural conditions.

Trees can be ordered using the form below

We will get delivery in late February, when the trees can be collected from a site in Redland, Bristol.

The saplings come bare-rooted (i.e. out of the soil) and 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 and how many, and for you to provide basic contact details (email and/or phone number) for us to organise collection of the trees. Contact details will not be used for any other purpose.

Our response to the proposed changes to the allotment agreement

We urge the Bristol City Council Cabinet to reject the current draft. More nuanced rules, that meet identified real needs, need now to be developed following a proper consultation with Bristol’s allotmenteers. The PGSS must be also integrated into the new Local Plan so that all the sites that have been identified are protected either as Local Green Space or as Reserved Open Green Space and given proper planning weight when decisions about their future use and development are made.

We are particularly concerned that the draft rules relating to trees on allotments are too narrowly drawn and will result in the loss of allotment tenants’ ability to make the best use of the particular conditions of their plot. We urge the relaxation of these proposed limits on the number and types of trees which can be planted.

Food growing as part of the draft Parks and Green Spaces Strategy

We are concerned that the Strategy for Food Growing and Allotments has been included as Chapter 6 of the draft Parks and Green Spaces Strategy (PGSS). This is a departure from the 2008 PGSS, which makes it clear that such spaces are not included, since they are not public spaces: ‘The Strategy does not consider green spaces that are not freely accessible to the public, including allotments, city farms, school grounds, or Sites of Nature Conservation Interest in private ownership.’

The proposed PGSS recognises that: ‘There are other green spaces managed by the council that are not included because they do not offer full public access for recreation …’ [our underlining]. Given that allotments and other land used for growing food (including grazing land) are subject to private tenancies, with rental payments and mutual rights and obligations agreed between tenant and Council, it is hard to understand why they have been included in the strategy proposal.

We need to recognise the importance of this specific type of land use and ensure that it is not made an ancillary element in the PGSS. It deserves greater attention, which is why we suggest that it should have been integrated into and protected by the current proposals for the new Local Plan (as, indeed, Parks and Green Spaces should also be) rather than treated as an add-on to the proposed PGSS.

In particular, the current status of and strategy for market gardens, smallholdings and grazing land (and other land not used for food growing), which have an area greater than all current allotments combined, get only passing consideration. Little or no thought is given to the opportunities these sites present for nature recovery, biodiversity enhancement and other environmental gains.

Instead, we are told that these sites:

… have limited benefit beyond the individual users … and many smallholdings tend to use less than 10% of their site for food growing … we now need to review our current landholding agreements so that we can start to explore opportunities to repurpose land to diversify our food growing spaces and ensure land is being used effectively to meet Bristol’s food growing targets. … Once suitable land has been identified we will review how these opportunities are promoted to ensure that the system of securing land is fair and equitable. We are particularly interested in opportunities that will not only ensure land is being sustainably and efficiently managed but that also delivers social value and benefits the residents of Bristol.

In the face of the demand for allotments and the need to increase local food production, which has led at least in part to the proposed changes in the tenancy agreement, these areas must surely warrant greater protection than is given them in the proposed PGSS. These areas also contain many trees (often veterans) and other ecologically sensitive habitats, and many are in SNCIs. It is vital that these matters are properly considered when planning any change of use of such land. This ought to be addressed properly in the proposed new Local Plan, not in this draft strategy.

Trees on allotments

Trees on allotments fall into two categories: those within allotment plots and those on allotment sites but outside the plots.

  • Trees outside allotment plots

From our analysis of data on the Council’s Open Data site, we estimate that allotment sites total some 105 hectares when community orchards are included. However, only about 87 hectares of these sites are productive. This means that around 17% of allotments, some 18 hectares, are unproductive. We welcome the clarification in the new tenancy agreement that trees in these unproductive areas remain in the care of the Council and may not be damaged by tenants.

  • Trees within allotment plots

Proposed allotment Rule 4.0 Trees deals with trees growing within allotment plots. We distinguish between newly planted trees and existing trees below.

  • New trees

Regulation 4.4 limits the height of trees to 2.5 metres (a common constraint in other councils). The limit in Regulation 4.3 of one tree per allotment sized between band B and band C is far too restrictive, particularly since the majority of plots fall within these bands.

Rule 3.1 requires that the tenant uses at least 75% of the plot for ‘a cultivated crop of vegetables, fruit bushes [not fruit trees], ornamental flowers, and herbs.’

Rule 3.3 states that fruit trees will occupy the non-cultivated area of the plot (which may be no more than 25% of the plot) unless they are underplanted with a productive crop, in which case they will be counted as being part of the cultivated area. No trees are permitted on band A or Micro Plots, nor is any consideration given to whether it is possible to underplant ‘a productive crop’. This implies that the food value of the tree does not warrant the space they occupy. According to the RHS, having fruit trees on an allotment adds both structure and permanence, while fruit tree crops have a higher value than many other allotment crops and are easier to manage.

The transitional arrangements require that all trees, except the permitted dwarf rootstock fruit trees, be removed from plots within three years, though mature trees may be permitted.

These rules devalue the role of trees on allotments, not only for their contribution to the ecology of the area but also their food production value. These rules also effectively exclude such fruit-tree-growing techniques as cordons, espaliers or step-over planting.

Regulation 4.3 also constrains the type of fruit trees that may be grown.  Since only rootstocks M27 and M26 are allowed (though not the intermediate M9 rootstock), it seems that that only apple trees may be grown, even though dwarfing rootstocks are available for a number of other fruit trees such as Pear, Quince (Quince C), Cherry (Gisela 5), Plum (including Gages and Damsons), Peach and Apricot (VVA-1, Pixy).

The exclusion of hazel and other non-fruit trees (most trees bear fruit) removes the ability of tenants to grow valuable nut crops or to provide locally grown stakes through coppicing – a good way to reduce our carbon footprint. This restriction also precludes the use of allotment space for growing trees from seed with a view to planting them out elsewhere, at a time when there is a great need for locally grown trees for local tree planting.

Established trees

  • Fruit trees

Many fruit and other trees are already growing on many allotment sites. They provide not only good-value food, but they also provide biodiversity, a rich ecological resource for insects, birds and mammals and are important legacy features of the site. The allotment and its users have adapted to the presence of these trees and their removal would not only be counterproductive to the value of the site and cause distress to tenants but would also risk damaging the soil and the allotment more broadly.

  • Non-fruit trees

Although such trees may not have obvious value for food production, other considerations apply. We agree that allotments should not be taken over by trees, resulting in the reversion of productive land to woodland and the attendant loss of statuary allotment protection for such land. However, it would be a mistake to create rules which put biodiversity, nature and ecology in conflict with food production; trees are crucial for biodiversity, which in turn is essential for the productivity of the places where we grow food.

Site-appropriate regulations

Allotment plot conditions both within allotment sites and across Bristol vary widely. The gradient and aspect of each plot, its soil type, soil depth and historical development all pose different challenges to tenants, requiring a localised approach to the best way to utilise a site. Imposing a one-size-fits-all set of regulations, based on some notional idealised allotment plot, will not provide sufficient scope to allow for these variations. Tenants’ associations also need to be able to vary the regulations to fit their local conditions. Indeed, arguments in favour of the distribution of local decision making, which we endorse, have recently been made by the Bristol Mayor.

Here is a copy of this response

Calculating tree habitat area

A key factor in calculating the value of a habitat under the new Statutory Biodiversity Metric is to work out its size. In the case of trees, their habitat size can be of critical importance to the calculation of their biodiversity valuation which will, in turn, help to preserve our precious tree habitats.

As a result, individual trees in an urban setting are often the most important habitat present.

Unfortunately, developers may be tempted to allocate all trees on their planned development site (especially those in groups) to Woodland and forest habitats rather than to Individual trees habitat, because this gives the trees and the site a lower biodiversity value. An example of this is the proposed development by Goram Homes of Hengrove Park in Bristol, as shown in the image above and discussed below. The whole site was granted outline planning permission in October 2019.

Unfortunately, the Statutory Biodiversity Metric User Guide (the Metric) definitions of these habitats are ambiguous and can make such allocations hard to counter, even in settings that are clearly urban.

The User Guide defines two broad tree habitats types whose areas are measured in hectares (ha):

  • Woodland and forest
  • Individual trees

Defining woodland and forest habitat

There are conflicting definitions of ‘woodland’. The Metric User Guide does not define Woodland and forest habitat.

However, the UK Habitat Classification, UKHab, upon which the Metric is based, defines it as ‘Land with 25% or more cover of trees that are five metres or more in height.’ This definition doesn’t mention the minimum land area required.

The UK National Forest Inventory 2015 (NFI) defines woodland as:

‘a minimum area of 0.5 hectares under stands of trees with, or with the potential to achieve, tree crown cover of more than 20% of the ground. Areas of young trees, which have the potential to achieve a canopy cover of more than 20%, will also be interpreted as woodland and mapped. The minimum width for woodland is 20 m, although where woodlands are connected by a narrow neck of woodland less than 20 m wide, the break may be disregarded if less than 20 m in extent.‘

Bristol City Council also uses area to define woodland in its 2008 Biodiversity Action Plan (Chapter 5, page 65), which states that ‘this action plan covers all woodlands over 0.5 hectares in extent found in Bristol.‘ As this is a local policy, and aligned with the NFI definition, we have adopted it.

The habitat area of Woodland and forest habitats is based on its total measured canopy area.

Defining individual trees habitat

The Metric User Guide (page 53) advises when to record Individual trees habitat:

Individual trees are classed as ‘urban’ or ‘rural’. You should consider the degree of ‘urbanisation’ of habitats around the tree and assign the best fit for the location. 

Use the broad habitat type ‘Individual trees’ to record: 

  • individual rural trees 
  • individual urban trees 
  • lines, blocks or groups of trees found within and around the perimeter of urban land.

In all circumstances ‘Individual trees’ should be used to record ancient and veteran trees, regardless of location. This could include ancient and veteran trees within hedgerows, ‘rural’ lines of trees and woodlands. 

Other clarifications

Do not use the hedgerow module classifications ‘line of trees’ and ‘ecologically valuable line of trees’ to record linear formations of trees in the urban environment.

These classifications should only be used for rural lines of trees.
Trees within overgrown non-native and ornamental hedges (for example, leylandii) should not be classified as individual trees, or as lines of trees. Record these as nonnative ornamental hedges within the hedgerow module.

Trees recorded as individual trees that will be removed for any purpose, including development, disease, or safety must be recorded in your baseline and recorded as lost.

Do not otherwise record individual trees if they occur within a habitat type characterised by the presence of trees, unless specified within the section on ‘recording individual trees at baseline’, which covers: 

  • trees within private gardens 
  • removal of trees within hedgerows 
  • removal of trees within rural lines of trees 
  • removal of trees within orchards and wood-pasture and parkland 

Recording individual trees at baseline 

The biodiversity metric uses set values to represent the area of individual trees depending on their diameter at breast height. 

This value is a representation of canopy biomass, and is based on the root protection area formula, derived from BS 5837:2012. 

Table 14 sets out class sizes of trees and their area equivalent. 

The User Guide then deals with specific instances where individual tree habitats also need to be recorded:

Recording baseline trees within private gardens

A private garden is a garden within the curtilage of a privately owned or tenanted dwelling house. Private gardens can contain important features for biodiversity, including mature trees and hedgerows. 

record all medium, large and very large trees within private gardens as individual trees 

Recording baseline trees within hedgerows and lines of trees 

  • if any medium, large or very large trees within a hedgerow or ‘rural’ line of trees are being removed, record these in the area baseline as individual trees 
  • the removal of trees may influence the linear value of hedgerows and ‘rural’ lines of trees within the hedgerow module 

Recording baseline trees within orchards and wood-pasture and parkland 

  • if any medium, large and very large trees within these habitats are being removed, record these in the area baseline as individual trees 
  • this does not change the way in which you would record the area of orchard or wood-pasture and parkland area habitat (see ‘Recording habitat mosaics’ section) 

Calculating the number of post-development trees required

Post-development size classes 

When planting trees post-development size class is determined by the size of the tree at site-planting. When using the tree helper: 

  • record newly planted individual trees as ‘small’, unless ‘medium’ size or above at the time of site-planting 
  • record trees planted with a DBH less than 7.5 cm as ‘small’ 

You should not: 

  • record natural size increases of retained trees within post-development sheets 
  • record natural size increases of planted trees within post-development sheets 

The post-development private garden has no public access, and biodiversity net gains cannot be legally secured. As these gains cannot be secured you should only record created private gardens as either: 

  • ‘urban – vegetated garden’; or 
  • ‘urban – unvegetated garden’ 

You should not: 

  • record the creation of any other new habitats within private gardens 
  • record enhancement of any habitat within private gardens 

However, habitats which are recorded in the baseline and remain within a private garden may be recorded as retained. 

A garden within the curtilage of a privately owned or tenanted dwelling house.  The post-development private garden has no public access, and biodiversity net gains cannot be legally secured. 

How these rules affect the tree habitat area calculation

As a result, this approach places a higher value on the areas of all but the largest Individual trees habitats than those that form part of a Woodland and forest habitat. The following graph shows this, with RPA, derived from DBH, representing the canopy biomass of both broad habitats.

We analysed 12 recent planning applications involving 2,116 trees, 612 (29%) of which were identified for removal. Using the Metric User Guide, they have a combined habitat area of 20.2 ha. If they are measured by canopy area it would only be 8.3 ha (41% of their habitat size). If their combined Root Protection Areas (RPA) were used, they would cover only 8.6 ha (43% of their habitat size).

On the basis that all these trees are in poor condition and have no strategic significance, we calculate that, with the minimum 10% biodiversity net gain now required, a total of 1,925 new trees would need to be planted to replace the habitat lost by the removal of these 612 tree – a ratio of just over 3:1.

To illustrate how this can affect actual applications, here’s a pending application by Goram Homes at Hengrove Park in Bristol. The area edged in red is the development site.

This next image shows how the applicant’s ecologists have defined each habitat: the woodland and forest habitats are shown as a diamond pattern on a dark green background. They cover 2.44 ha.

They’ve also identified 0.19 ha of Individual trees habitat, that is, trees not growing within the woodland and forest habitats.

Area 8 in the south of the site (0.99 ha) might legitimately be designated Woodland and forest habitat, but, given that all the remaining trees are growing separately and in groups in an urban park, they should be designated Urban Individual tree habitat.

The site is complex, with many trees growing in groups but, by excluding the trees in area 8 and treating all the other onsite trees as Urban Individual tree habitat, we calculate that their habitat area is 6.42 ha. This is 4.78 ha more than the applicant’s calculation. This difference will clearly have a significant impact on the final biodiversity net gain calculation, valuing these habitats at 34.07 area habitat units (or 2,989 Small size trees) as opposed to the applicant’s 12.11 (or 1,063 Small size trees).

To give the applicant their due, they at least attempted to calculate the tree habitat area. We have seen other applications where the trees were simply ignored, or were classified as another habitat – bramble scrub in one case, or the method by which the Individual trees habitat area was calculated bore no relationship to the evidence submitted. We must remain ever vigilant against such tricks.

This blog was amended on 09 May 2024 to include the comments of the Nature Conservation Officer dated 03 May 2024 about whether the trees on the Hengrove Park development site are Individual trees habitat or Woodland and forest habitat. The officer writes:

This blog was amended on 14 February 2024 following the obligation for most planning applications to achieve at least 10% biodiversity gain becoming obligatory on 12 February 2024.

Further changes have been made following updates published in July and August 2024, in particular the clarification of the application of BNG in private gardens.

Other Blogs in the series

Calculating habitat units

The trading rules explained