Increasing Cambridge's tree canopy and the great ash hunt

By Dr Matthew Ling, Cambridge City Council

By 2050, it is estimated that nearly 70 per cent of the global population will live in urban areas. In our current situation, facing an uncertain amount of further time under lockdown conditions to stem the spread of coronavirus, the value we place upon our urban green spaces and vegetation has been realised like never before. The joy and calming affect that can be found in being among trees and plants, or taking a walk in a park, is being increasingly highlighted in these times of uncertainty, anxiety and stress.

The need to plan, adapt, and prepare our urban environments to be fit for purpose for their residents has been increasingly emphasised too during this lockdown period. Urban centres, by their nature, are predominated by engineered, built or grey solutions. While this building and engineering is often remarkable, evermore technologically advanced, and facilitates our modern ways of living, it can also bring about a host of unplanned problems. Asphalt and concrete in particular, are impervious to rainfall, causing rapid runoff, and absorb and store heat from solar irradiation, causing localised heat attenuation – often referred to as the urban heat island effect. An overreliance on these materials, coupled with a climate that is projected to expose the UK to more frequent hot, dry summers, suggests that we need to explore alternative approaches for our urban environments.

Cambridge City Council has recognised the important role green infrastructure can have in addressing some of these issues. In 2019 the council declared both climate and biodiversity emergencies, committing to tackling both through its actions and decisions. The same year, the council also joined a project consortium under the European Territorial Cooperation ‘Interreg 2 Seas’ programme to pilot a range of green infrastructure solutions to help adapt to climate change. This led to the launch of the Cambridge Canopy Project, the green infrastructure focus of which is trees.

The Cambridge Canopy Project seeks to help the city adapt to a changing climate by cultivating a resilient urban forest with increased tree canopy cover. Specifically, this will be achieved through a two percentage point increase in tree canopy cover (17 per cent rising to 19 per cent) by the 2050s – as trees are relatively slow growing, it will take 30 years to realise this canopy development.

The main objectives of the project are: contributing to, and encouraging, increased levels of tree planting and protection and, making a measurable contribution to the sustainability of the city’s urban forest.

More and more, people are coming to realise the huge range of benefits we receive from trees, and just how valuable they can be in our changing climate. Some of the more obvious factors include shade, fruit and timber provision, and carbon sequestration for example. Whereas, some of the less well-known benefits include positive influence on primary school educational attainment, reduced levels of violent crime, positive health benefits such as less marked ADHD (attention deficit hyperactivity disorder) in children, and increased mental wellbeing, as many of us are appreciating under the current lockdown period.

There is a huge wave of momentum and enthusiasm behind tree planting at the moment, as demonstrated in the 2019 UK general election, which saw all of the main political parties making ambitious manifesto commitments around increased tree planting efforts. For example: the Labour Party – 2bn trees to be planted by 2040; the Green Party– 700m trees by 2030; and, the Conservative Party – 30m trees planted per year by 2024. With trees so firmly in the public psyche, the time really is now for the Cambridge Canopy Project to seize the momentum and engage with the city’s residents.

Average tree canopy cover across cities in the UK is approximately eight per cent. At 17 per cent Cambridge is already doing quite well, and has the feel of a leafy and green city. But canopy cover across the city is not evenly distributed, with some wards being comparatively poorly provided for (ranging from 12.8 per cent to 22.6 per cent). As a result, not everyone will realise the range of benefits flowing from trees. The project will therefore seek to prioritise planting in these areas to ensure that, in the decades ahead, the urban forest will cater for everyone on some level.

Other specific measures the project will focus upon include proposing a number of ‘shadeways’ where pedestrians and cyclists will be able to commute and travel on paths and roads with substantial levels of shade provided by tree canopy cover. To achieve this, greater numbers of street trees will be planted, alongside a selection of larger species that will cast more shade.

These factors, in combination, are intended to make Cambridge as well suited as possible for its residents and visitors under climatic conditions in the years ahead which will be hotter and drier, and with more frequent and intense storm and rainfall events. Having a larger and more resilient urban forest with greater canopy cover will positively contribute to the alleviation of many of the effects realised through climate change.

The greatest challenge for the project in terms of achieving its aims will be to engage with the public in such a way that they are moved into action. Cambridge is a relatively small city council, with limited land on which to plant additional trees. Of the total land area of the city, only 13.5 per cent of it falls under council ownership, with 77 per cent being privately owned. Analysis indicates that within the private land ownership group there are approximately 44,000 houses with gardens in the city. Through engagement, outreach, and awareness-raising activities it is hoped that at least 12,500 of these will plant one new tree in their gardens.

Many of the public engagement elements of the project have had to be postponed due to the coronavirus pandemic. However, the public can still get involved and contribute during the lockdown period, while ensuring adherence to government social distancing guidance. As outlined above, the majority of trees, and the majority of land, in Cambridge are privately owned. We would like to understand more about the public’s perception relating to trees in private gardens and have developed a survey to gather this information. If members of the public would like a short distraction, it would be a great help if they could spare 5-10 minutes to complete the survey (the link is below).

Linked to this, we would also like help from the public to map the city’s trees which will contribute to their better management in the long-term. To achieve this, we are asking for members of the public to download our map of the city’s trees on an app called Curio-xyz and plot the trees in their gardens or other private land (again, more information can be accessed via a link below).

One specific tree we are asking the public to look out for is the ash (Fraxinus excelsior) due to the threat posed to it by ash dieback. Ash, which are just coming into flower now, are the most numerous trees across the city, and if many are lost to this disease it will have a substantial impact on our urban forest. If residents have ash trees in their gardens, they can map them via the ‘Cambridge Ash Hunt’, again using the Curio-xyz app (link below).

Gathering this information will be critical in drawing up an action plan setting out how to deal with the impacts of Ash Dieback.

A core principal exists in arboriculture, that of ‘the right tree in the right place’. Cambridge City Council employs a team of highly skilled and knowledgeable tree officers that oversee all things tree-related. Being able to draw upon this expertise ensures that the right tree is always selected for each planting location, based on size, micro-climatic and environmental conditions, and any nearby constraints or stresses. With this same approach, it is possible to find a tree to suit almost any sized garden. The project will develop guidance to help residents select and plant a tree to meet their needs.

While garden centres are closed at the moment, it is the perfect time to plan what tree you would like to plant in your garden, and where you will position it once the lockdown is over.

By collectively realising the benefits provided by trees and the urban forest, and taking action to help grow and maintain it, Cambridge’s residents can help to make the city more robust, self-sustaining, and prepared for the future impacts of climate change.

For further details on the Cambridge Canopy Project, visit cambridge.gov.uk/cambridge-canopy-project. You can also keep updated via Twitter at twitter.com/CamCanopyProj.

For the residents’ survey – trees in your gardens – visit cambridge.gov.uk/consultations/cambridge-canopy-project-residents-survey.

To help map the city’s trees, visit cambridge.gov.uk/help-us-map-the-citys-trees.

For the Cambridge Ash Hunt, visit cambridge.gov.uk/ash-trees.

The Cambridge Canopy Project has received funding from the Interreg 2 Seas programme

2014-2020 co-funded by the European Regional Development Fund under subsidy contract No. 2S05-048.