Cambridge City Council: the Cambridge Canopy Project - building climate resilience for the future

The Cambridge Canopy Project – part of the Interreg 2 Seas ‘Nature Smart Cities’ project – seeks to grow Cambridge’s urban forest, increasing tree canopy cover from 17% to 19% by the 2050s. The project uses trees as a form of green infrastructure to make the city more climate-resilient for the future, helping to combat the urban heat island effect and lowering the risk of flooding. By utilising a nature-based solution like this, the Cambridge Canopy Project is helping the city adapt to, and mitigate against, the likely impacts that will be brought about under future climate change scenarios.

The challenge

As a relatively small and already green city, the challenge faced by the Cambridge Canopy Project to realise a 2% increase in tree canopy cover across the city is, where to fit in more trees. 2,000 locations on council-owned land across the city have been identified where new trees can easily be planted. These are primarily in roadside grass verges, parks, and other open spaces. However, modelling suggests that 16,000 new trees across the city are required to achieve 2% more canopy cover. However, planting alone cannot meet this challenge. Unnecessary tree removal should be reduced, thereby protecting canopy distribution from gradual diffusion over time. The urban forest must also be made more resilient to the impacts of climate change by encouraging greater diversification of species to be planted.

The solution

Analysis of Cambridge’s land area shows that 77% of the city is privately owned. The single greatest land use is residential, accounting for 39% of the land area. This land use component consists of approximately 54,000 properties, of which more than 40,000 have at least a front or back garden. Considering this, and the fact that 74% of the current tree canopy cover falls within the privately-owned part of the city, the greatest opportunity for increasing tree numbers and canopy cover exists in privately owned gardens.

To realise the Project’s 2% canopy cover increase target, 14,000 additional trees over those being planted in the public realm are needed, and the residents of Cambridge hold the key to achieving this. Through several free tree giveaway schemes (‘Free Trees for Babies’ and the ‘Neighbourhood Canopy Campaign’), more than 1,500 trees will be gifted to residents. On top of this, through a range of targeted engagement, awareness raising, and capacity building communications and processes, the many positive virtues and benefits provided by trees and their canopy cover are being championed. By doing so, it is hoped that residents will be catalysed to take action and plant a new tree in their gardens and care for the ones they already have.

The impact

There is a plethora of positive benefits provided to us from Cambridge’s urban forest. It is estimated that all the existing trees across the city store more than 88,000 tonnes of carbon, sequestering more than 2,000 tonnes per year. They also have the potential to filter out air pollutants exceeding 64 tonnes in mass annually, and to reduce surface runoff resulting from rainfall by more than 97,000 cubic metres per year.

Additional benefits which are more difficult to quantify include: the positive physical and mental health impacts we realise from being around trees – including lower rates of anti-depressant prescriptions; increased footfall and willingness to spend in retail areas; increased property values; enhanced social cohesion and sense of community; and, decreased rates of violent crime. All of these attributes derived from having trees in our cities are now well understood and researched.

Lessons learned

Awareness raising is essential to sustaining the health and integrity of the urban forest. It is a vital process that requires investment over the long-term to ensure our trees are understood, appreciated, valued, and protected into the future. Doing so will maintain and enhance the flow of ecosystem services from our urban forest now and into the future for the benefit of all residents and those working in and visiting Cambridge.

Young trees are extremely susceptible to drought stress. Whilst measures are implemented to water newly planted trees as well as possible, they will always benefit from more watering. Factoring this into planting budgets and activities is of critical importance to successful establishment.