‘The Bristol Zoo development will result in a biodiversity net loss’

On Wednesday, Bristol City Council’s development control committee will decide the future of Bristol Zoo Gardens and the fate of the many mature trees growing within it.

The 376 trees on the site have enormous habitat and environmental value, and yet the trustees propose to remove 156 of them.

The resulting loss of biodiversity will be profound, and this is just one of the reasons why we at the Bristol Tree Forum hope the committee will reject the application.

(According to the applicant’s own calculation, these 156 trees represent 48 per cent of the site’s biodiversity value.)

How can this be permitted in a city that has declared an ecological emergency?

Bristol Tree Forum’s chair says the development of the Bristol Zoo Gardens site will see a profound loss of biodiversity – photo: Mia Vines Booth

We’ve commented on this application extensively – firstly in June 2021 and, more recently, in March this year.

Bristol Zoo Gardens opened in 1836, while the construction of the nearby Clifton Suspension Bridge was also happening, and was in continuous use until it closed late last year.

The gardens were a major attraction in their own right. They are of historic, cultural and botanical importance, not just to Bristolians but also to the wider horticultural and botanical community across both the UK and globally.

The site houses a nationally recognised collection of plants, including “Champion Trees” recorded on the National Tree Register, and it’s home to the National Conservation Collection of Plants and Gardens/Royal Horticultural Society plant collections such as Caryopteris and Hedychium.

Despite this, the zoo’s trustees want to destroy this rich heritage and turn the site in a space primarily for housing.

There are many reasons why this should not be allowed to happen, but we focus on just one: the loss of biodiversity (either minus 22 per cent or minus 12 per cent depending on what model is used) that will result from the removal of nearly half the trees on the site – in our experience, the proposal to transplant mature trees is unrealistic and unlikely to be successful.

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Read next: Bristol Zoo boss defends redevelopment of Clifton site ahead of decision day 

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The zoo trustees have used Biodiversity Metric BNG 3.0, which does not work for calculating the habitat size of the trees.

When BNG 3.0 was first published by Natural England, we immediately saw its glaring errors and pointed them out – Valuing our Urban trees – part 1.

While the process of calculating biodiversity net gain is complex, these simple errors were obvious.

Our statement to the development control committee explains why BNG 3.0 does not work and why the development would result in a net loss of biodiversity.

We have tried to point this out both to the trustees and to planning officers, and set out our reasons in great detail, but without success.

We’ve asked them to show us their workings but have had no response. Neither the trustees nor council officers have tried to engage with our objections above.

We have simply been ignored.

We are shocked that the trustees do not appear to understand how the biodiversity metric works.

They have employed experts to advise them, and we would have expected that they would be one of the first organisations in Bristol to commit to ensuring their plans at least achieve net gains in biodiversity.

What has gone wrong?

We wonder if they have, instead, decided to turn a blind eye to these errors, hoping that others would not notice them?

Bristol Tree Forum’s Mark Ashdown hopes the application to build new homes on the historic site of Bristol Zoo will be rejected due to the number of trees that would be lost – photo: Bristol Tree Forum

We are frustrated that biodiversity net gain calculations done by developers are not being checked by the local planning authority.

Natural England expects that they should. This means that developers can produce whatever figures they want or sometimes hide their workings from detailed scrutiny so they cannot be properly checked.

When the Tree Forum has raised this in the past, the response from the planning authority was that it is the result of differences of opinion, leaving the planning committee members with no ruling on what is correct and what is incorrect.

You cannot have differences of opinion on facts – facts speak for themselves.

We are hopeful that Wednesday’s committee will see through this and refuse the application.

This is an opinion piece written by Mark Ashdown, the chair of Bristol Tree Forum 

Read next:

• Wild Place to become Bristol Zoo Project
• Hundreds march to protest plans for former Bristol Zoo site
• Campaigners accuse Bristol Zoo of misleading the public 

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