Urban tree cover is critical for the good health of humans and other species, but to ensure we have such a benefit in the future, the type of trees selected for cities needs to change. Hannah Gardner looks at the likely candidates

Securing the eco-system benefits of successful tree planting for the future relies on utilising recent research data. While the rate and unpredictability of climate change is quickly testing resilience, climate projections and studies in plant biology should inform selections of species that can survive and thrive, particularly in urban environments.

‘Urban trees are a frontline adaptation tool, providing cooling, shade, air quality improvements, stormwater regulation, and essential biodiversity support,’ says Kevin Martin, Head of Tree Collections at the Royal Botanic Gardens Kew, where he shoulders responsibility for its living tree collection. He is also a Research Fellow at the Urban Plant Lab, a not-for-profit organisation led by Directors Dr Andrew Hirons, Dr Henrik Sjöman, and Dr Harry Watkins, that was set up to aid people through research, guidance, events, and training in the selection and establishment of plants for urban environments. 

Since 2015, the Lab team, together with various collaborators, has published a number of papers and books and in November 2025, it delivered its final report, Future Climate Suitability of London’s Public Realm Trees, which was commissioned by the Greater London Authority and the Forestry Commission to assess how trees planted in the public realms of Greater London and the City are likely to cope with projected climate conditions in 2090, and was co-authored by Dr Hirons and Kevin.

London is the first city in the world to commission such a comprehensive climate suitability assessment of its public trees. Although specific to Britain’s capital (the report’s authors stress that the findings 'should not be applied to other cities or regions, even within the UK, as climate projections and growing conditions vary substantially’), the findings are of interest in a wider context. Eighty per cent of people in England live in urban areas1, where trees are an essential infrastructure, and street trees account for a large proportion of that. 

Working to a scenario whereby, by 2090 in London, the annual Potential Evapotranspiration (PET) value will be more than 750mm, with an annual precipitation count of 600mm and a mean annual temperature of 14C, the report finds that understanding a taxa’s projected growth rate and canopy structure matters as trees that efficiently cool the air will provide essential climate-regulating services as heat intensifies. However, they need the space in which to do so and, as the report’s conclusion states, ‘Climate risk to trees is further compounded by poor growing environments. Together, these factors present a substantial and strategic challenge for urban forest managers to address over the coming decades.’

EXPERT TIPS FOR ESTABLISHMENT AND LONGEVITY
‘Understand what you are trying to achieve,’ says Eliot Barden. ‘Select the right tree in the right place and, critically, for the right reason.’

Perform correct tree-planting practises: use the shallow-planting technique in square holes and allow sufficient root protection area as the tree matures. Carefully consider staking and irrigation during the establishment period, which should be at least two seasons.

‘Budget and plan for a full, proactive aftercare schedule before planting,’
says Guy Watts.

Disease resistance is also key. ‘Many familiar species have traits that leave them vulnerable to hotter, drier summers and prolonged heatwaves,’ says Kevin. ‘Their decline may not be immediate but over time, reduced growth, canopy dieback, and even premature mortality are likely.’ 

The models in the report also highlight species (both local and exotic) that have the physiological ‘toolkit’ to withstand the challenges of a changing climate, and its key findings highlight the scale of that task. If no changes to tree species selection are made, 73 per cent of London’s public trees may struggle to thrive or survive. Only 0.38 per cent of the capital’s currently existing trees are considered highly suitable for future climate conditions while 22 per cent of them are moderately suitable, 62 per cent are rated as having low suitability, and 10.6 per cent are considered vulnerable. 

Trials for new plant material
While Future Climate Suitability of London’s Public Realm Trees is a call to arms to ‘strategically diversify London’s urban forest’, to ‘intentionally design excellent rooting environments for new trees [and] develop policies to ensure pathways for new plant material, well-matched to future climates, to be brought into cultivation’, it is a clarion call to key stakeholders in all Britain’s towns and cities. 

Indeed, specialist nurseries are already pro-actively trialling new species. Barcham Trees, for example, has commissioned the Exeter-based social enterprise Treeconomics to analyse data gathered by internationally recognised systems such as i-Tree Eco methodology so the nursery can calculate the specific benefits of each taxa.

Following on from their awareness-raising presence at RHS Chelsea earlier this year, I asked both Eliot Barden, of Majestic Trees, and Guy Watts, of Architectural Plants, for their recommendations for climate-resilient tree selection and insights into tree establishment and management. 

I then considered resilient taxa for specific situations, as this targeted approach may be useful for professional designers. You can read the results on these pages.  

ENDNOTE
¹ Environment Agency, Chief Scientist’s Group. (2021). The state of the environment: the urban environment, (Updated 2023) gov.uk.

Photograph, (London skyline) Getty Images/Richard Newstead

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