We are supportive of Bristol City Council’s declaration of a Climate Emergency and an Ecological Emergency and the goals detailed in the One City Climate Strategy, including the commitment to carbon neutrality by 2030 and doubling the abundance of wildlife by 2050. We are also supportive of their commitment to doubling the tree canopy by 2046.
However, we have a real concern that the commendable words are not being matched by effective actions.
A principle aim of the BTF is to promote the planting and preservation of trees in Bristol for the well-being of its citizens, the sustainability of urban habitation, the enhancement of nature in the cityscape and as our contribution to combating climate change (see A Manifesto for protecting Bristol’s existing Urban Forest).
A recurrent concern we have is the continued loss of trees as a result of environmentally insensitive developments that are not sympathetic to the City’s declared commitments outlined above. On the other hand, the BTF supports developments that favour a sustainable environment over high density occupancy, and those that prioritise retention of existing trees.
Bristol’s policy on replacing trees lost to development – adhering to the Bristol Tree Replacement Standard (BTRS) – is widely well regarded. As such, decision makers believe that tree loss is mitigated by subsequent tree replacement. However, recent studies undertaken by the BTF have shown that this is not the case over the timescales committed to by Bristol City Council and the Green Party.
Typically, tree planting undertaken under the BTRS takes between 30 and 50 years to recover the biomass (and therefore the CO2e) lost by felling, well beyond the 10-year commitment on carbon neutrality, and even beyond dates set for doubling the tree canopy or doubling wildlife abundance.
The BTF study has been developed into a versatile online tool for calculating the extent and timescale of the carbon deficit, with a wide range of inputs. This can be accessed via the link Tree Carbon Calculator, and we encourage you to try this yourself. See also the BTF blog Tree replacement and carbon neutrality.
In the example shown here, a mature tree felled in 2020 is replaced by four trees (as per BTRS) of the same species. The carbon released (2 tonnes CO2e) is not recovered until 2064, a full 34 years beyond the date Bristol aims to be carbon neutral.
This model can also be used to determine how many replacement trees are needed to recover lost carbon within a particular timescale. In the example shown, to be carbon neutral by 2030, a reasonable expectation as this is the declared aim of BCC, the felled tree would need to be replaced by 37 plantings of the same species. Scaled up to, for instance, 500 trees, new plantings would need to number 18,500 to mitigate the lost carbon.
This new information represents a fundamental change in the evidence base for tree replacements, and emphasises the need to retain existing mature trees, and not to consider replacement by new plantings as adequate mitigation.
We request that you consider this new information with urgency and make a commitment to oppose developments where mature trees are removed and tree replacements do not deliver carbon neutrality by 2030.