I heard a rather beautiful track the other morning on Radio 3. It turned out to be Ombra mai fu from Handel’s opera Xerces, sung by the wonderful countertenor Andreas Scholl. It’s an ode to the cooling shade of a Plane tree.
Having a very busy day ahead, I wondered if there was much Tree-themed music . This lead to a lively session on our Tree Champions WhatsApp chat, supplemented by input from Claude AI , which actually made some good suggestions.
The result is a bit of a hodge-podge of tracks: some closely tree-related , others less so; some classics , others not so well known and a few quite political. All remind us that the value of trees is not only ecological but also cultural.
The result was this playlist on Spotify
Perhaps we have missed your own favourite Tree-related track . Please let me know what should be added (or removed!) in the comments.
We were pleased to be able to contribution to the Festival of Nature again this year. Here is a report on our contribution by Dave Jones.
A tree walk in Victoria Square Park
I was thinking about a venue for a BTF-led tree walk that we could organise as our contribution to the Bristol Festival of Nature, which in 2026 was focussed on trees! A few months earlier I was on the top deck of a 505 bus going around Victoria Square when I noticed how varied the trees in the square were. I thought this could make an ideal venue for a tree walk, a safe enclosed area for leading a group, easy access when using public transport and plenty of opportunities for a coffee somewhere afterwards.
We did some research and found there should be 50 different tree species, in an area of just over 100m by 100m. There were a variety of trees from temperate regions from all around the world which was considered to provide plenty of interest for a tree walk. We did a trial walk and identified 20 different trees to focus on, and did specific research on those 20 trees for a brief talk. Aiming for a walk time of around 90 minutes, that allows 5 minutes per tree and a few minutes for walking between trees.
The actual Festival of Nature walk event went well, with a full group, some Eventbrite booked people didn’t turn up and some people who didn’t like online booking just turned up and filled the spaces. There was a lot of discussion on each of the planned trees, and the trees in between usually prompted further questions and interest. The time went very quickly and everyone seemed to enjoy the walk and the learning. There was some good questions and input from the guests on the walk which was helpful.
In planning the walk we noticed that there were some dead trees, some invasive species eg holm oak and laurel that was even overtaking a planted tree that wasn’t easy to find, and quite a few self seeded species eg Sycamores. For a city centre park it was starting to look quite wild.
BTF had already had discussions with BCC about finding tasks that volunteers could assist with. Victoria Square could be an opportunity as BCC wouldn’t allow volunteers to work on roadside trees, which many of BCC trees are. BCC have offered lead volunteer training so that BTF could organise an activity when a suitable venue was found.
Helping on the BCC TreeBristol stand
At the end of the Festival of Nature week, BTF were invited to assist with interfacing with the public on the BCC tree stand. One of the people on the stand was responsible for organising the parks lead volunteer training and they were keen that Victoria Square was a potential location to get involved. Also on the stand were senior members of the tree team and they were also keen to support a volunteer-led programme to improve Victoria square. They thought that obtaining trees and materials should be quite easy. The agreed first step was to produce a map of the trees in the square, and a proposal for which trees to remove and where new trees could be placed.
Since 6 August this year, the smallest developments in England (those 0.2 hectares or smaller) no longer have to deliver biodiversity net gain (BNG). To understand what this means for trees, we’ve analysed 505 biodiversity gain plans and 320 readable metric calculations gathered from 59 planning authorities.
The answer is uncomfortable: the exemption removes roughly half of all development sites from the BNG regime, and these are precisely the sites on which trees make up the largest share of the habitat being lost.
In December 2023 we argued for a new Bristol Tree Replacement Standard (BTRS) calibrated to the statutory biodiversity metric. That argument was about making the local standard consistent with national policy. It’s now about something much more critical: on half of all sites, a local standard is the only thing left to protect trees being lost to development.
A site of 0.2 hectares or less, measured by the red-line boundary of the application, is exempt from mandatory BNG unless on-site priority habitat is negatively affected.
Development that’s wholly temporary, with permission granted for five years or less, is also exempt on the same proviso.
For minor development above the area threshold, the mitigation hierarchy has been relaxed: off-site gains are now seen as just as desirable as created or enhanced habitat on the site itself, so a developer may go straight off site without first showing that on-site provision is unachievable.
The self-build and custom-build exemption has also been removed, on the reasoning that most such schemes now fall inside the new small-sites exemption anyway. While applications already submitted before 6 August continue under the old rules, Defra in its 15 April 2026 response to the consultation, estimated that ‘the new area based exemption for sites of less than 0.2 hectares is expected to remove more than 50% of the smallest planning applications which are currently delivering mandatory BNG, from the BNG requirement’.
Trees aren’t priority habitat
The priority habitat proviso sounds protective, and for some sites it is, but it does nothing for trees. Depending on where it is, an individual tree is recorded in the statutory metric as urban tree or rural tree, both of medium distinctiveness; neither is a habitat of principal importance under section 41 of the Natural Environment and Rural Communities Act 2006. Only ancient and veteran trees sit outside these two categories, as irreplaceable habitat, and they are a vanishingly small proportion of the trees felled for development.
So a mature street-side lime, a garden oak, or a row of maturing London planes on the edge of a school playing field — none of these will be protected if they’re in the way of a 0.2 hectare development. Below the threshold, they can be removed without any obligation to count them, replace them, or compensate for their loss anywhere. Unless the tree is protected by a Tree Preservation Order, or unless the local plan says otherwise, nothing now requires their loss to be made good.
This is the gap; and it’s much larger than the word ‘small’ implies.
Half of all development sites now fall outside the system
We measured site area for every gain plan in our dataset that came with a usable metric calculation — 305 sites across 59 authorities. Site area here is the baseline area-habitat total, net of any individual trees, taken from the statutory metric or, for small-sites metrics.
Table 1. Development sites by size, 305 sites with a usable metric calculation
Site size
Sites
Share
Baseline area HUs
Post-development area HUs
On-site change
0.2 ha or smaller
151
49.5%
48.79
48.67
−0.25%
Over 0.2 ha
154
50.5%
506.88
512.82
+1.17%
All sites
305
100%
555.67
561.49
+1.05%
Habitat units are on-site figures from sections 6.3 and 6.4 of the biodiversity gain plan. Hedgerows and watercourses are excluded as linear features.
Just under half of the sites that have been going through the BNG process fall at or below the new exemption threshold — consistent with Defra’s own estimate. Two further things stand out in that table. First, small sites were barely holding their own on site even under the old regime that’s just been withdrawn: a baseline of 48.79 area habitat units became a mere 48.67 after development, a small net loss, with any gain bought off site from elsewhere. Second, the small-site total is dwarfed by the large-site total, which is exactly why the exemption looked politically cheap. In habitat unit terms these sites are a rounding error. In tree terms, though, they aren’t.
Small sites are where the trees are
Of the 320 metric calculations we could read, 163 relate to sites of 0.2 hectares or less. Sixty of these — 36.8% — record individual trees in the on-site baseline. Between them they carry 3.12 hectares of tree canopy ‘oversailing’ 15.22 hectares of land.
Table 2. Individual trees in the on-site baseline, by site size
Site size
Metrics
With trees
Site area (ha)
Canopy (ha)
Canopy as % of site area
Tree baseline HUs
0.2 ha or less
163
60 (36.8%)
15.22
3.12
20.5%
26.71
Over 0.2 ha
157
81 (51.6%)
219.64
13.79
6.3%
133.22
All sites
320
141 (44.1%)
234.85
16.91
7.2%
159.94
Site area is net of individual trees, because tree canopy oversails the habitat beneath it and is not additional land. Canopy can therefore exceed 100% of the site area it overlies.
That last comparison is the heart of it. On sites above the threshold, tree canopy is equivalent to about 6% of the site area. On sites at or below 0.2 hectares it’s 20.5% — more than three times the share. Small sites are disproportionately tree rich, probably because they’re disproportionately urban: they include infill plots, back gardens, corners of school and hospital grounds, and the fringes of existing built-up land. These are the places where we usually find the mature tree canopy of a town.
The concentration is sharper still for twenty of the 163 small-site metrics, which record canopy covering more than half the site area. Seven record canopy exceeding the whole of it. One example is a 0.18 hectare site at 22 York Road in Sutton, which carries 0.33 hectares of canopy across 18 recorded tree entries — canopy equal to 182% of the site, and worth 3.42 habitat units. At an average of 0.019 hectares of canopy each, these are mature trees, not saplings — on the replacement standard set out below, losing 18 medium trees would require 90 replacements. On an application made today, that site would be exempt and the trees could be removed without any obligation to replace them under the new BNG regime.
Expressed as trees rather than hectares, the 3.12 hectares of canopy on small sites is equivalent to 762 small trees, using the 0.0041 hectares the June 2026 metric assigns to a small tree. Because much of that canopy belongs to medium, large and very large trees, the actual number of trees is likely to be lower — and their replacement cost, in the metric’s own currency, correspondingly higher.
And they’re where the new trees were coming from
The exemption removes an obligation to plant as well as an obligation to compensate. Of the 163 small-site metrics, 72 record individual trees created as part of the post-development scheme.
Table 3. Individual trees created in post-development proposals
Site size
Metrics
With tree creation
On-site trees
Off-site trees
Total trees
0.2 ha or smaller
163
72 (44.2%)
597
8
605
Over 0.2 ha
157
97 (61.8%)
3,135
205
3,340
All sites
320
169 (52.8%)
3,731
213
3,944
Tree numbers are the recorded habitat creation area divided by 0.0041 ha per small tree, rounded up. Off-site units bought from a registered gain site do not appear here, because they sit in the seller’s metric.
Over 600 trees across a dataset of a few hundred plans covering barely two years and 59 authorities out of 306. If you scale that across every planning authority in England and across the years ahead, the tree planting foregone is substantial.
BNG was never going to save urban trees anyway
It’s worth being clear that the case for a local tree standard doesn’t rest solely on the exemption. Even where BNG still applies, it often doesn’t keep compensation anywhere near the trees that were lost.
The Biodiversity Gain Sites register as of 19 August 2026 — 2,328 developments across 306 authorities — shows that 87% of developments in urban authorities offset outside their own authority area. Those authorities needed 1,835 area habitat units and hosted 889. In London the pattern is near total: 98% of the 113 registered London borough developments offset elsewhere, requiring 46.8 units and hosting 3.3.
The units are real, and the receiving sites may well be excellent. But a habitat unit delivered in a rural county doesn’t provide shade in Bristol, intercept its rainfall, cool it in a heatwave, or stand outside anybody’s window. Urban tree canopy is a local public good, yet BNG systematically moves its replacement to some distant field that few, if any, will ever visit.
Why we need a tree replacement standard
A tree replacement standard is a local plan policy, not a national biodiversity calculation. It attaches to the tree, not to the site area; it applies whether or not a metric has to be completed; and it keeps the replacement in or close to the place where the loss occurred. It’s the mechanism best suited to fill the gap the exemption has opened.
This is not a novel invention. Bristol has operated the BTRS since 2014 under Core Strategy policy BCS9, and a replacement table is carried forward into proposed local plan policy BG4. What we argued in 2023 was that the ratios should be recalibrated so that the standard delivers what the statutory metric would have delivered, plus the 10% uplift. Our proposal was not adopted then, though our argument stands. What’s changed is who needs it: not just Bristol, but every planning authority that wants any control at all over tree loss on the majority of its planning applications.
We would encourage authorities without such a policy to adopt one, and those with one to check that it’s calibrated to the metric rather than to a historic rule of thumb whose rationale was and remains hard to understand. As the standard is a local plan policy, it can be applied to exempt sites without cutting across the national BNG regime: BNG sets a floor for biodiversity, and a replacement standard sets a separate, local requirement for canopy.
Recalculating the standard against the June 2026 metric
Our 2023 proposal derived replacement numbers from the tree area equivalents then in force. Those figures have since changed. Table 15 of the Statutory Biodiversity Metric User Guide (June 2026), at page 62, now assigns the areas set out below. Applying the same method — the area of the lost tree divided by the area of one small tree, since a newly planted tree is recorded as small, plus the 10% net gain, rounded up because a fraction of a tree is not a tree — gives revised numbers.
Table 4. Replacement trees required, recalculated against the June 2026 metric
Tree size (DBH)
Area equivalent (ha)
Multiple of a small tree
Plus 10% net gain
Replacement trees
2023 proposal
Small (>7.5–30 cm)
0.0041
1.00
1.10
2
1
Medium (>30–60 cm)
0.0163
3.98
4.37
5
3
Large (>60–90 cm)
0.0366
8.93
9.82
10
10
Very large (>90 cm)
0.0765
18.66
20.52
21
20
Areas are from Table 15 of the Statutory Biodiversity Metric User Guide (June 2026), p62. Replacement numbers are the tree’s area divided by the area of one small tree, plus the 10% net gain, rounded up.
Two categories of tree size move. A medium tree is now worth almost four small trees rather than three, so its replacement requirement rises from three to five. A very large tree rises from 20 to 21. Large trees are unchanged at ten.
The small-tree row needs a decision rather than an arithmetic answer. One small tree replaced by 1.1 small trees rounds up to two, which is a real doubling for the commonest category in the surveyed population. The alternative is to hold the small category at one-for-one and take the 10% uplift from the scheme as a whole. We think the honest position is to state the arithmetic and let the policy make the choice explicitly, rather than round the uplift away in silence.
What we’re asking for
That local planning authorities adopt, or retain and strengthen, a tree replacement standard in their local plan, applying to all development including sites exempt from mandatory BNG.
That the replacement ratios be calibrated to the current tree area equivalents in the statutory metric, so that a local standard delivers no less than the national regime would have done.
That replacement be required within the same authority area and as close to the loss site as is practicable, so that canopy is replaced where people live.
That authorities continue to require a BS 5837:2012 tree survey with applications on exempt sites, so that the loss is properly recorded even where no metric is required.
That Defra keep the 0.2 hectare exemption under review, and specifically consider whether the priority habitat proviso should be extended to sites carrying significant tree canopy.
The exemption was introduced to reduce costs and delays for small applications. Whatever one makes of that aim, it shouldn’t be paid for with the mature canopy of our towns and cities. A tree replacement standard is a cheap, well-understood, locally enforceable way of making sure it’s not.
About the data
Figures are drawn from the Bristol Tree Forum biodiversity gain plan dataset (v11): 505 gain plans logged from 59 planning authorities, of which 320 carry a readable statutory or small-sites metric calculation and 305 a usable site area. Plans are dated 2024 (58), 2025 (254) and 2026 (165). Register figures are from the Biodiversity Gain Sites register extract of 19 August 2026, covering 2,328 developments and 2,686 allocations across 306 authorities.
Two caveats:
Site area in this analysis is the metric’s baseline habitat area net of individual trees, which is a close proxy for the red-line boundary the exemption uses but not identical to it; a handful of sites near the threshold may fall on the other side of it in practice.
The sample is of applications that produced a gain plan, so it describes the population the exemption removes rather than all development across the country.
Biodiversity net gain is moving habitat out of towns — but small sites are not the reason why
Two years into mandatory biodiversity net gain, a question worth asking is no longer whether developments are delivering at least 10% BNG — almost all of them do, on paper. The question to ask is: where does the biodiversity go answer what Parliament intended it to go?
Our earlier July blog — When a city builds, where does nature go? — asked where the compensating habitat goes physically, and found it travels a median 36 kilometres from where it was lost, and to less deprived places — this remains true today.
Note: These two blogs analyse their data differently — using a different classification of authorities, and 357 gain plans rather than 202 available in July — so figures should not be read across from one to the other. Where they appear to disagree, the note at the end explains why.
This blog asks a different question: how much habitat moves away, and do small development sites explain this?
We’ve been collecting evidence from the following sources:
357 biodiversity gain plans downloaded from 38 local planning authorities’ planning portals and their FoI responses
We’ve also analysed the published statutory metric calculations, which give measured site areas for 202 of the plans.
We set out two findings that only appear when these datasets are looked at together. They are as follows:
Urban England is a net exporter of habitat units, at scale
The BGS register records, for every development that bought off-site units, whether the gain site sits within the same authority, in a neighbouring one, or somewhere else. We’ve classified each authority by its ONS 2021 Rural Urban Classification. The pattern is stark.
Table1:Area habitat units. ‘Units required’ is what developments in that authority had to buy off-site; ‘Units hosted’ is what gain sites in that authority delivered to developments anywhere. London boroughs are a subset of Urban, not an additional row.
Nine in ten developments in Office of National Statistics (ONS)-defined urban authorities compensate outside their own area. In London it is 98.2% — of 113 developments on the BGS, two compensated at home. Urban authorities between them need 1,435 area units and host 602: a net outflow of 833 units of habitat from towns and cities to the countryside. What that means on the ground: at 192 Beech Hall Road in Waltham Forest, two new houses buy their 0.07 units from a habitat bank at Puddington in Mid Devon — 267 kilometres away — and deliver nothing at all on site. Section 6 of their gain plan, the section that records on-site enhancement, is blank.
Both rural classes are net importers on average, but the averages conceal a very wide spread. For example, the largest single importer is Barnsley (an ONS urban authority) which hosts 101.7 units against the 3.3 its own developments require. At the other end, Cherwell (an ONS Intermediate urban authority) needs 76.2 units and hosts 0.95, Westmorland and Furness (an ONS Intermediate rural authority) requires 61.2 but hosts nothing, while Manchester (an ONS urban authority) needs 48.6 but hosts nothing. What determines whether an authority imports or exports is not how urban it is, but whether anyone has registered a habitat bank inside it.
Note what the table does not show. There is no clean four-step gradient from urban to rural: Intermediate rural (59.3%) sits slightly below Majority rural (61.7%). The gradient is in fact two-step: strongly urban authorities export almost everything; for everywhere else the figure sits at around 60%.
Site size doesn’t explain it
The obvious explanation is that urban sites are cramped. A development on a small plot has nowhere to put lost habitat, so it buys it elsewhere. If that were right, the export pattern would be a led by size rather than policy, but this is not what happens.
Taking the 202 plans for which we hold a measured site area, we can see that between 40% and 47% of measured sites are at or below 0.2 hectares across every ONS class, with the median site between 0.21 and 0.28 hectares, whether the authority is Manchester or mid-Devon. The overall median is 0.243 hectares; a quarter of all sites are below 0.102 ha.
Table1:Small sites are everywhere.
Nor do small sites drive habitat off site. Of the 90 sites at or below 0.2 hectares, 34% use off-site compensation (off-site or both — question 4.6 of the required Biodiversity Gain Plan). Of the 112 larger sites, 42% do. The relationship runs, weakly, the wrong way for the cramped-site theory.So the export of habitat from towns is not a consequence of urban plots being small. It is a consequence of where the available habitat banks are — and they are in the countryside, because that is where land is both cheaper and available. The spatial risk multiplier is meant to discourage distant compensation. On this evidence it is not discouraging it much.
What small sites actually deliver
The small-site analysis is worth reporting in its own right, because percentage compliance conceals what’s happening in absolute terms.
Table 1: Small-site analysis
Small sites are 45% of all measured sites but only 6.6% of the baseline biodiversity. Their median pre-development value is 0.170 biodiversity units — so the minimum statutory 10% BNG required amounts to 0.017 of a unit, equivalent to an area of improved habitat you could easily step across.
They meet the target as reliably as anyone: median on-site net change is +11.5% on small sites against +11.8% on larger ones. That equivalence is the point.
But percentage is not a quantity. Two developments can both report ‘12% net gain’ while one creates a meadow and the other creates a planter, and the 10% BNG test cannot tell them apart.
This matters most in towns, because that is where small sites and high export rates coincide — 44 of the 97 measured urban sites are at or below 0.2 ha, and 90.4% of developments in urban areas send their compensation away. The residual on-site gain left behind in urban England is, in absolute terms, very small indeed.
Our own biodiversity gain plan analysis points the same way. Across all 357 plans analysed so far, 37% use off-site compensation — but that splits 42% in ONS urban authorities against 28% everywhere else. The median on-site net change tells the same story from the other end: +11.0% in urban authorities against +12.5% in non-urban ones. Urban development both delivers less at home and sends more away.
The rules have just changed — but in the same direction as before
From 6 August 2026, three changes take effect for planning applications made on or after that date. Each pushes in the same direction as the pattern set out above.
Development on sites of 0.2 hectares or less is now exempt from mandatory BNG altogether, unless on-site priority habitat is affected. Government expects this to remove around half of residential planning permissions from the regime. In our dataset it would remove 90 of the 202 sites we can measure — 45% of them — and in ONS Urban authorities, 44 of 97.
Those are precisely the sites already contributing least: 6.6% of the baseline biodiversity, and 0.021 of a unit of gain apiece. So the honest reading is that not much is being given up. But not much becomes nothing; the survey that would at least have recorded what was there is no longer required. In towns, where 45% of sites are that small, the regime stops seeing a large part of what gets built.
Minor development no longer has to try on-site compensation first. The biodiversity gain hierarchy is relaxed, so that off-site delivery counts equally with on-site provision. Our data suggests that hierarchy was doing real work: small sites currently use off-site compensation less than large ones — 34% against 42% — which is the opposite of what cost alone would predict. Remove the duty to try on-site first and that gap has only one direction in which to close.
The spatial risk multiplier is being rebased on Local Nature Recovery Strategy areas, cutting the number of habitat trading areas from 306 local planning authorities, or 159 National Character Areas, to 48 LNRS areas.
This is the change that bears most directly on the figures above, and it’s worth being exact about what it does. The BGS already distinguishes compensation that stays inside the development’s own authority from compensation that goes to a different authority in the same LNRS area. We count the second as leaving the authority, because it does, but under the new regime it will attract no spatial risk penalty at all.
Of the 2,328 developments in the current BGS register, 502 — 21.6% — will move from distant to local allocations without a single unit of habitat changing place. In Urban authorities the shift is larger still: 274 developments take the urban share compensating locally from 9.6% to 34.4%.
The reform doesn’t change where the habitat goes. It changes what the metric now treats as local with no spatial risk penalty.
What this does and doesn’t prove
The two datasets count different things. The BGS covers only developments that bought off-site units. It says nothing about the majority of permissions that are met wholly on site. Our 357 gain plans are a hand-collected sample from 38 authorities, not a random one. Where the two are combined above, it’s to test an explanation, not to produce a single national rate.
Hosting is inferred, not stated. The BGS register names the authority of the development but not of the gain site. We place a site in the authority whose developments record an allocation from it as ‘Within (LPA)’, which locates 145 of 212 sites carrying 81% of all units. The remaining 568 units sit on sites used by no development in their own authority; where they are is unknown, so the hosted column is the minimum measurable.
Site area is not the same as the exemption area. Our site areas are based on the baseline habitat area recorded in the statutory metric, not the red line application area against which the 0.2 hectare exemption is measured. The two are close but not identical, so 45% is an estimate of how many of our sites would fall outside the new regime, not a count of them.
Publication is patchy. The BGS register proves the existence of 269 gain plans across 32 authorities, but we hold no local copy of any of these. Each one is a development that cannot have begun without an authority-approved plan. Meanwhile, two authorities have now told us, in answer to FoI requests, about gain plans that are not on their own portals: one listed 60 discharge applications of which 20 could not be found, and the other scheduled six approved gain plans of which two could not be found. That’s a separate issue, but it bears on how much of this picture anyone outside a planning department can see.
Is the BNG regime delivering on its promise?
Biodiversity net gain was sold as a mechanism that would leave development areas richer in nature than it found them. What the BGS register shows, however, is that 833 area units of habitat, net, have left urban England for the countryside, with London exporting 93% of everything its developments require.
That may be defensible ecologically — larger, better-connected habitat banks can be worth more than fragmented urban parcels which may be badly delivered — though the metric’s multipliers are meant to price that in. But it’s not what most people understood the new regime promised, and it’s happening without anyone having decided that it should. The people who lose the nature are not the people who gain it.
If the answer is that urban compensation should stay urban, the levers were there — the spatial risk multiplier, local nature recovery strategies, and the authority’s own discretion over what it accepts. Two of those three have just been loosened. The multiplier is now being based on areas seven times larger than the authorities it replaced, the duty to try on site first has gone for minor development, and a large share of urban sites will shortly sit outside the regime altogether. What is left is local discretion — and an authority that wants nature to stay in its own town will now have to ask for it explicitly, knowing the metric no longer requires it.
Note on our July 2026
Our earlier July post’s figures are not directly comparable with the figures used here. Then, we classified authorities by hand rather than by ONS category, and had only analysed 202 plans. We also reported on-site change as an average weighted by habitat value, which on a dataset with 202 records was decided by two or three large schemes — Plymouth alone moved the current figure by fourteen points. We now use the median values per plan. Our finding that urban schemes rely more on off-site compensation is unaffected.
Dataset: 357 biodiversity gain plans from 38 local planning authorities; Biodiversity Gain Sites BGS register extract of 19 August 2026 (2,328 developments, 2,686 allocations, 3,030.11 area habitat units); statutory metrics giving a measured site area for 202 plans. Authorities are classified by the ONS 2021 Rural Urban Classification of Local Authority Districts, matched by ONS area code. Bristol Tree Forum.
Our detailed analysis is available here –BGP Full Data Extract v11. However, as this is a working document which we are building on all the time, it is likely that many of the figures quoted above will have changed.
By the end of March this year, every council in England had to publish a report on what it is doing for biodiversity. Councils that are also local planning authorities — Bristol among them — must go further, and give details of the biodiversity net gain resulting, or expected to result, from the biodiversity gain plans they have approved.
Some time earlier this year, Bristol City Council published its Biodiversity Duty Report (the Report) covering the period from January 2020 to December 2025. It is a handsome document, and much of it is genuinely positive: it lists 43,523 trees planted, canopy cover up to 18.2%, and pesticide use down 42%.
On the question of BNG, though, it publishes only a single table which can’t answer the question a local resident might ask: Is new development in Bristol leaving our local nature better off or worse off?
What BNG is meant to do
Since February 2024 most new developments in England have had to deliver a 10% increase in biodiversity. Developers measure what’s on a site before they build — using a government metric calculation which converts various habitat types into ‘biodiversity units’ — and then show how they’ll deliver at least 10% more biodiversity than was there before they started.
They can do this in three ways: improve habitat on the site itself; pay for habitat to be created somewhere else; or — as a last resort — buy statutory credits from the Government. Before building can start, the Council must approve the developer’s gain plan showing how the minimum 10% BNG will be achieved.
Each gain plan is a precise record (backed by a metric calculation) of what a development will achieve. Bristol has approved a number of these so far but the Report tells you almost nothing about what’s in them.
What Bristol actually published
Here’s everything the Council’s published about its approved gain plans, as listed in the Report:
Look at the column headed ‘No. of Units post-intervention’. These are the biodiversity units expected after a development is completed. There’s no column for the value of the habitats that were there before (called the baseline). Without a baseline, we can’t know what the net gain percentage is. In the row labelled ‘On-site BNG only’ there’s a reported 275% average % net gain but the other rows are left blank, so it appears not to be an average across the seven plans reported. Three small schemes with very little habitat to begin with can easily produce a number like this: if a site starts with almost nothing, almost any new habitat can produce a large percentage increase. Published on its own, without the baseline values that would put it in proportion, it reads as a triumph but is meaningless because it lacks essential information.
What the gain plans we’ve examined say
Bristol Tree Forum has been collecting biodiversity gain plans from councils across England — 301 of them so far, from 34 authorities. We’ve found 18 for Bristol, 16 of which record a figure for the change in area habitat units on the development site. Twelve of the 16 lose habitat on site. Added together, the 18 Bristol plans show a net loss of 10.9 area habitat units within the red lines of the sites themselves. The four that gain contribute 0.24 units between them. One scheme, at Broomhill Road, records the loss of every unit on the site — 100%.
To be fair to the Council, most of those plans were approved during 2026 and so fall outside the period the Biodiversity Duty Report covers. However, six of them are dated on or before 31 December 2025 and belong squarely inside it; all of these six lose habitat on site, by 4.68 units between them.
Now, an on-site loss is not by itself a breach of anything. That’s exactly what the off-site habitat unit purchase option is for: where a site cannot accommodate the lost habitat on site, the developer is allowed to buy habitat units elsewhere to meet the 10% plus obligation. Nine of Bristol’s 18 plans deliver through a combination of on-site and off-site compensation, and four go entirely off-site. So, on paper, the obligation is met.
But a resident reading the Council’s report would have no idea that any of this was happening. The published table doesn’t state what the baseline habitat was or distinguish between gains and losses. It doesn’t say where the off-site habitat is. And it doesn’t name a single application, so there is no way to look one up.
Where does Bristol’s biodiversity go?
The report does contain one sentence that deserves more attention than it’s had. There’s no registered biodiversity gain site anywhere within the Bristol boundary. The Council’s own candidate sites ‘remain unregistered while a viable solution to procuring a legal agreement is worked towards’, and are still at scoping stage. As far as we’re aware, no Biodiversity Gain Site has yet been registered for the city.
That means every off-site unit bought to offset a Bristol development creates habitat outside the city. Thirteen of our 18 plans use off-site delivery in whole or in part. The habitat lost is in Bristol; the habitat created to compensate for it is not. So far, that compensation amounts to 14.60 units allocated to sites outside the city — 14.55 area units, 0.01 hedgerow units and 0.04 watercourse units. To see them, open https://bgs.bristoltrees.space/bgs-bodies, select LPA Allocation Maps and click on City of Bristol LPA on the map.
Other councils can manage it
Publishing a schedule of all the approved BGP approvals is not difficult. Other authorities are already doing it. For example, Cotswold District Council has published an appendix listing all 24 of its approved gain plans — application reference, date, delivery route, and the units and percentage change for habitats, watercourses and hedgerows on each one. Bolton publishes the same for its four, including the name of the habitat bank each one bought into.
County Durham has not published a schedule of all its approved applications, but it has published the full Government reporting tables, which show, without flinching, that on-site habitat units across its 16 approved plans fell by an average of 30.85%.
Durham’s report is uncomfortable reading for Durham, but it is for that reason worth something; a report that cannot embarrass its author is not really a report.
What we’d like to see
Bristol has met the letter of its duty but it could have gone further and produced a meaningful schedule that would have made sense to the ordinary reader and been used to help inform a proper debate about how the city is (or is not) benefiting from the BNG regime. On our analysis, it’s not.
Three changes would fix this, and none of them requires new data — the Council already holds all of it:
Publish the baseline alongside the post-development figure, so a net change can be worked out.
List the approved gain plans individually, with the application reference, so anyone can find the application and check it.
Say where the off-site units are, and how many have left the city.
There’s some urgency to this. The reporting cycle is five years, by which time a new Local Plan will probably have been adopted. If we have the information now, this might be used in the development of any new Local Plan so that it provides a real benefit to Bristolians. Unless Bristol chooses to publish an update voluntarily, the next time it’s legally required to tell us anything about biodiversity net gain will be 2031 — by which point seven years of development will have been permitted, built and largely finished, on the strength of a table that serves no practical purpose.
Bristol City Council’s Biodiversity Duty Report 2020–2025 is published at bristol.gov.uk. The figures attributed to gain plans in this article are drawn from Bristol Tree Forum’s own collection of biodiversity gain plans obtained from planning registers and freedom of information requests, and are ours rather than the Council’s. We’d be glad to be corrected on any of them.
The cover image above is extracted from the Council’s Biodiversity Duty Report.
Since February 2024 biodiversity net gain has been mandatory for major development in England – and for small sites since April of that year. Two and a half years on, there’s still no publicly available national dataset of the gains that developers promised and say they’re delivering.
While the Biodiversity Gain Sites Register records off-site allocations, these are a small element of the whole BNG regime. The required biodiversity gain plans themselves — the information and documents that state, scheme by scheme, what the baseline biodiversity was and what biodiversity gain the development will deliver — sit dispersed across individual planning portals. Each portal is managed by each of over 300 planning authorities and the information is not nationally collated.
So far, we’ve collected 263 of these biodiversity gain plans from 31 Local planning authorities (about 10% of authorities). We’ve audited them field by field against the published source documents. This is what they show.
How we created the dataset
Every gain plan here was found on a local planning authority’s portal as an approved application, with a published Biodiversity Gain Plan. To date, the earliest is dated 2022; 27 are from 2024, 129 from 2025 and 91 from 2026. The authorities range from Bristol, BaNES and East Suffolk, with 18 or 19 gain plans each, down to several with just one. Site areas, where a statutory metric calculation is published and the baseline habitat area can be read from it, run from a few hundred square metres to several hectares, with a median of 0.225 ha across the 133 gain plans that we have been able to locate so far.
The sample is not representative, and depended on our being able to locate gain plans on planning portals using a variety of search approaches. These searches did not always succeed and we have probably failed to identify all the approved gain plan applications on the portals we were able to interrogate.
How we found the documents
Collecting these 263 plans was harder than analysing them. Once the right application is found, the documents are usually easy to identify: they are labelled ‘Biodiversity Gain Plan’, ‘Net Gain’, ‘metric’ or something equally simple, and the labelling is broadly consistent between planning authorities. The real challenge is finding the application on the authority’s planning portal in the first place.
A gain plan must be submitted to discharge the statutory ‘deemed’ planning condition required under the BNG regime, so it sits within a related discharge application rather than within the original permission. Finding it means knowing which discharge application to look for, and under which application type (assuming there is one). Save for the regulations, there is no guidance on how the biodiversity gain condition should be discharged or what should be published when, so every authority has settled the question differently. A minority have a dedicated application type — e.g. ‘Approval of Details – BNG’ — and one search usually returns everything, but not always : on some planning portals this search returns nothing.
For example, the Bristol City Council planning portal Advanced search option returns no decided results when the ‘Discharge Deemed BNG Condition’ Application Type is used. Only two pending applications are found, but on closer examination, even though one contains the required Biodiversity Gain Plan document, there is no required statutory metric calculation, while the other one relates to an application that predates the BNG regime.
In all other cases the only method is to guess using search terms like ‘biodiversity’, ‘BNG’, ‘gain plan’, ‘net gain’, and hope this produces results. At one authority a search for ‘biodiversity’ returned 16 results, but fewer than half were gain plan applications. At another, three search terms yielded three plans, and we still don’t know whether that’s all of them.
The problem is not that the documents are concealed; it’s that there’s no reliable way to find them, and therefore no way to distinguish an authority with few gain plans from an authority whose search term we’ve not guessed correctly. We recently submitted 41 Freedom of Information requests asking for a list of biodiversity gain plan applications, but so far only one authority has given us the information we requested (Greenwich Borough Council). The others that have replied so far, such as North Somerset Council, have refused our request on the basis that ‘The information you have requested can be found on our Planning Portal’. We have asked for an Internal Review of these refusals.
There are two further obstacles: some plans are published as scans carrying no text layer, so they cannot be searched even once located, and in four decided cases from one authority the metric is published while the gain plan is not. This is not unusual.
The practical consequence is that a member of the public who wants to know how biodiversity net gain is being delivered, say on a development near them — and even when they know the original application reference — will in many cases still not find the answer. The regime may be ‘transparent’ as a matter of law but it is unsearchable as a matter of practice.
How developers deliver the gain plan
Question 4.6 of each gain plan asks the developer how it will reach the target percentage . Across the 263 gain plans we found these answers:
4.6 answer
Gain Plans
On-site
142
Both on and off site
69
Off-site
43
Both boxes ticked (contradictory)
2
Unanswered
7
Total
263
So 112 gain plans — 43% — state that all or some part of the BNG required will be delivered away from the development site. That is a much higher rate of off-site reliance than the Biodiversity Gain Sites Register alone would suggest, because a development that delivers everything on site never appears on the register . The register can tell you where off-site provision is delivered, but not how often off-site provision is used, so it systematically understates it.
Is all the BNG required delivered?
The statutory requirement requires a minimum 10% BNG increase in area, hedgerows and watercourses habitats (it applies separately to each of these habitat modules). A scheme that adds, say, 30% of area units but fails to achieve at least a 10% increase in hedgerow units has not met the BNG requirement.
Taking area habitats, where 224 gain plans state figures we can analyse, the median net gain is +15.1%. That sounds sufficient, and for most schemes it is, but we’ve found that this value is not representative of the whole dataset. Twenty-seven gain plans record an area net gain below 10% on their own figures. Another ten record a negative area net change. The largest recorded loss is −62.7%.
There is also a long tail of very small sites recording enormous percentages: 18 gain plans exceed +100% BNG and two exceed +1,000%. These are almost all sites with a baseline close to zero — say a car park or a concrete garage base — where a handful of new planters produces a percentage gain that means very little. Any analysis that averages percentages rather than pooling units will be dominated by them.
The hedgerow and watercourse modules are where the failures concentrate. Eighty-four gain plans state hedgerow figures; the median is +72.8%, but eight fall below 10%. Only 14 gain plans state watercourse figures at all — and of those 14, five fall below 10%, one of them negative. Watercourses are rare in this sample and poorly served when they appear, so it is hard to draw conclusions from this limited dataset.
Applying the test across all modules shows that 190 gain plans meet 10% everywhere, 35 do not, and 38 cannot be assessed based what the gain plan discloses.
Where do the off-site units go, and do they exist?
One hundred and four gain plans record post-intervention units at section 7.5 of the gain plan — that is, they state an off-site position in figures. Only 73 of those can be matched to an allocation on the Biodiversity Gain Sites Register, totalling 77.88 area habitat units.
The gap between those two numbers is the most consistently troubling thing in the dataset. It has several causes, and we have separated them in the register that accompanies this piece. Some gain plans record the whole habitat bank rather than the units allocated to the development, inflating the figure by a factor of ten or more. Some repeat their section 6 on-site figures in section 7, so the same units are counted twice. Some record a positive off-site uplift with no gain site reference at 7.2 and no allocation on the register at all. Twenty-seven gain plans fall into that last category — an off-site gain asserted in an approved document, with nothing on the statutory register to correspond to it. However, it may be that these sites have yet to purchase their offsite requirements.
The reverse case also occurs: 11 gain plans have units allocated on the register while the plan itself records no off-site gain.
Unit density: more habitat, no more biodiversity
Pooling the metrics we hold — 143 metrics covering 134.5 hectares of on-site area habitat — produces a finding that percentages conceal.
Baseline
Post-development
Habitat area (ha)
134.53
138.25
Biodiversity units
424.65
424.97
Units per hectare
3.157
3.074
This table covers on-site area habitats only and excludes hedgerows and watercourses, which are linear habitats, and off-site purchases. It also predates the most recent additions to the dataset, so treat it as indicative of the 143 metrics we hold rather than of all 263 plans.
Across these sites, habitat area rises by 2.8% while total biodiversity units are flat, and unit density falls by 2.6%. The 10% gains recorded scheme by scheme do not aggregate into a 10% gain in on-site units, because a large share of the recorded gain is bought off site rather than created on it, and because what is created on site tends to be lower in distinctiveness and condition than what was there before. Greener, but with a lower habitat value.
What the documents show
Alongside the dataset, we maintain a register of defects — matters visible in the approved document itself, without site visits or ecological judgement. As of today it records 143 defects across 104 gain plans, from 263 held: a defect rate of 40% across 28 of the 31 authorities.
These are not close calls. They include gain plans dated before the survey they rely on; mandatory fields left blank; section 6 net-change figures that contradict the section 6.3 and 6.4 values above them; post-development values entered in the pre-development box; section 7 left empty on a gain plan that states the gain will be achieved partly off site. Every entry cites the figures it rests on, so any authority that thinks an entry is wrong can check it against its own document.
A distinct category is worth separating out. In four cases from one authority, a search of decided applications returned a statutory metric calculation but no biodiversity gain plan at all. At one of those sites the metric records the development losing 32% of the baseline area units. Off-site provision could in principle make that up — but the document that would say so, the gain plan, was not published. Under paragraph 13 of Schedule 7A, approval of the gain plan is the condition on which lawful commencement rests. It is the document that matters, and it’s the one that’s missing.
That case is worth dwelling on, because it’s the visibility problem meeting the compliance problem . A metric published without a gain plan is not a filing error. Under paragraph 13 of Schedule 7A the approved gain plan is the document on which lawful commencement depends, and it is the one document a reader cannot find. Whether it exists and was not published, or was never required, or was never produced, cannot be determined.
Why the numbers have fallen in our audit
Two months ago this analysis would have reported a defect rate of 49%. It reports 40% because we audited our own dataset before publishing it, and because we corrected it again afterwards when an authority showed us we were wrong. Both times the effect was to remove findings, not to add them.
Machine transcription fails silently. A field the extraction misses looks exactly like a field the applicant left blank, and a blank on our spreadsheet had been turning into a finding against a named authority. We compared 2,409 fields against the source documents and found 58 errors — a rate of 2.4% — of which the largest group were fields recorded as blank that were in fact fully answered.
The worst of it concerns tick boxes. Question 4.6 is a tick box, and so are 4.1, 4.7, 4.13 and 5.2. None of these PDFs stores its ticks as form data: the tick is drawn on the page, and every text extractor reports a ticked box and an empty one identically. A gain plan that answered the question looked exactly like a gain plan that ignored it. We had recorded 30 gain plans as leaving 4.6 blank and had made findings against 27 of them. Re-reading every box by measuring the ink inside it showed that all but one had answered. Thirty-one register entries were withdrawn.
We mention this because anyone building a dataset from these forms by text extraction has the same problem and may not know it. If your BNG data has tick-box fields in it, they are incorrect.
The full method, what was tested, what was found and what remains unverified, is set out in the audit statement published alongside the register. It includes the things we still cannot vouch for: only 4.6 was read in full across the whole set, and 11 of the gain plans are not on the Defra template at all, so questions cannot be said to be unanswered on them.
What this evidence fails to show
Six filters sit between this dataset and the population of approved gain plans in England:
The authorities are self-selecting, being those whose portals expose gain plan applications in some sort of searchable form.
The search of each portal may not have found every application.
Only decided applications are included.
Only published documents can be tested.
Fewer than half the gain plans have a metric published alongside them.
A blank in the dataset is not proof of a blank on the form.
The figures here should therefore be read as a floor on the rate of defects among approved biodiversity gain plans, not an estimate of it. A 40% defect rate among gain plans that were found, decided, published in full and then audited downward says nothing reassuring about the gain plans that were not found.
It is worth being explicit about what the first filter does. The authorities in this dataset are here because their portals let us find gain plans. That is not a neutral criterion. An authority that publishes its BNG documents in searchable, consistently named form is, on the face of it, an authority paying attention to the regime and the obligations it imposes. If anything, this dataset over-represents the diligent.
The dataset, the register and the audit statement are published in full below. In the meantime: we’d like to know which authorities do this well? If your portal makes gain plans easily findable, please tell us. Good practice is easier to copy than to invent.
How to fix this
Two things could make work like this unnecessary:
National guidance from Defra and Ministry of Housing, Communities and Local Government on how the biodiversity gain condition should be discharged and what should be published — the sort of specification the LGA’s Planning Advisory Service could write if funded.
A pre-submission checklist, ideally endorsed by CIEEM, covering the handful of errors that account for most of what we found.
Neither of these solutions would be difficult and both would do more for biodiversity net gain than yet another round of metric revisions. They might also, perhaps, make the life of the poor, beleaguered planning officer a lot easier!
The full dataset (263 gain plans, 31 authorities), the non-compliance register, the BGP Full Data Extract spreadsheet and the audit statement are available via the link below. The register details every defect found, with the figures it rests on.
An earlier version of this piece reported 159 defects across 116 gain plans, a rate of 44%. Nine plans have since been withdrawn from the register because the planning applications they discharge were made before 12 February 2024, when the biodiversity gain condition took effect: the condition did not apply to them, so no requirement of it could have been breached. Following a query from one of the authorities listed (for which, our thanks), the figures above have been amended to 143 defects across 104 gain plans, 40%. Three further entries were withdrawn on the same day after the same authority checked the off-site allocations: in two cases the units are registered and our matching had failed to find them, and in the third an apparent discrepancy is an artefact of the plan reporting to one decimal place. The dataset figures elsewhere in this piece are unaffected, as they record what the plans state rather than whether a legal requirement was met.
The cover image shows the development at Baltic Wharf which was located on the Floating Harbour in Bristol — a former caravan park that has lost 78 well-established mature trees to make way for the development.
Since February 2024, developers in England have had a legal duty to improve the biodiversity of their development site by at least 10%. This Biodiversity Net Gain — BNG — is calculated in ‘habitat units’ using a government spreadsheet. If a scheme cannot achieve this gain on the land it’s actually building on, it can buy the shortfall from a habitat bank anywhere else in England.
The BGS register
The public register of these off-site purchases is called the Biodiversity Gain Sites (BGS) register. It lists both the authority where a development sits and the authority where the compensating habitat is purchased.
We looked at all 2,441 allocations on the register, covering 301 local planning authorities. We found that, across the board, 79% of the allocations send the compensation to a local authority far from the development itself. That is striking enough. But the pattern sharpens dramatically in the more urban areas.
For example, in London, 98% of allocations are delivered outside the borough where the building happens. Just 3% stays within it. London’s boroughs have generated external demand for 46 habitat units and host barely three in return. Metropolitan districts — such as Manchester, Sheffield, Leeds and Birmingham — send 88% of their compensation elsewhere.
By contrast, non-urban authorities send 74%, and keep habitat within their own boundaries in 42% of cases, against London’s 3%.
Taken together, urban authorities are net exporters of habitat. The countryside is where it lands – often in remote rural locations few will ever visit.
How far away does nature go?
The register also records the distance between each development and the habitat bought to compensate for it. The typical distance is 37 km — roughly 23 miles. One allocation in five is more than 100 km away from its development site.
Median distance from development to compensating habitat, by type of authority
For London the median is 86 km, and nearly half of the capital’s allocations are more than 100 km away. Two-thirds fall into the register’s most distant category — the same category the rules are meant to discourage.
Who loses out?
Each site can be placed on a national deprivation scale, from decile 1 (the most deprived tenth of neighbourhoods) to decile 10 (the least deprived). Comparing where a development happens with where its habitat ends up gives a rather uncomfortable picture.
Average deprivation decile of the development, and of the habitat created to compensate for it
Development in metropolitan districts sits, on average, in decile 4.0 — among the more deprived parts of England. The habitat created to compensate for it sits in decile 6.3. Nationally, the shift is from 6.0 to 6.6, and it is almost entirely driven by cities.
Of the 504 allocations where the development is in one of the three most deprived deciles, 99% send their habitat somewhere less deprived — landing, on average, in decile 6.5. For non-urban authorities there is essentially no movement at all.
Displacement, not disappearance — but that is not the whole story
It is worth being careful here. Habitat units are being created. This is displacement, not straightforward destruction, and the register shows real habitat banks being funded and monitored.
Nor is this purely an urban phenomenon. The largest single net exporters on the register are Cherwell in Oxfordshire and Westmorland and Furness — not cities, but high-growth areas under development pressure. Land scarcity, not city status, is the underlying driver.
But displacement still matters, for reasons the metric does not capture. A hectare of habitat in a dense neighbourhood serves thousands of people who can visit it, but the same hectare 50 miles away, on a farm almost nobody visits, scores identically in the register. Access, shade, cooling, birdsong on the way to school — none of these elements appear in the data.
The rules do include a brake: compensation delivered further away is discounted, by a quarter if it’s in a neighbouring area and by half if it’s farther still. On this evidence, though, the brake is not holding, and the latest plans propose to remove it altogether for many developments, making it still worth buying habitat miles away.
What the gain plans show
We also read 205 individual gain plans in detail. The contrast is just as clear on the ground.
Developments in urban authorities lost area habitat on site — down 8% overall between the ‘before’ and ‘after’ figures in their own calculations — while developments in rural authorities gained 16%. Yet both groups have to demonstrate the same 10% or more net gain. Urban schemes get there by buying it: 54% of them use off-site compensation, against 33% elsewhere. Often this is simply because there are just no local Biodiversity Gain Sites, so the developer has no local options.
This is not a story about small development sites. The average development we measured was almost exactly the same size in urban and rural authorities — around 0.7 hectares. It is about the scarcity of available urban land, which is reflected in its cost, not the size of the plots.
The question worth asking
BNG is a real advance on what came before, and the register is a genuine piece of public transparency. This analysis is only possible because the data is published.
But if the policy’s promise is that development leaves nature better off, it is fair to ask: better off for whom? On current evidence, the answer in our biggest cities is someone else, somewhere else — on average 37 kilometres away, in a less deprived place.
Analysis by Bristol Tree Forum, using the Biodiversity Gain Sites register (2,441 allocations to 28 July 2026) and 205 biodiversity gain plans transcribed from local planning authority records. Charts and underlying data at bgs.bristoltrees.space.
