New research from the Royal Horticultural Society (RHS) and Frank P Matthews has revealed the ability of garden trees to deliver a broad suite of benefits under the UK’s changing climate.

A total of 19 trees were chosen by gardeners for their aesthetics, which were tested by the charity’s scientists at RHS Garden Wisley, and found to also deliver environmental benefits in at least one area – from cooling, flood mitigation, carbon capture or support for wildlife.

With the UK set to see hotter summers over the long term, the deciduous trees in the study provided highly effective cooling via transpiration and shading when in leaf, with ‘Callery’ pear (Pyrus calleryana ‘Chanticleer’) closely followed by flowering cherry (Prunus ‘Fugenzō’) and red maple (Acer rubrum ‘Brandywine’). Italian cypress and western red cedar (‘Cole’s Variety’) were the most effective evergreens. Effectiveness was linked to large dense canopies and high water uptake.

The cherry maintained its capacity to transpire and cool even when temperatures were around 35° C and humidity was low, while the other trees in the experiment plateaued or declined. The cypress (Cupressus sempervirens ‘Garda’), holly (Ilex aquifolium ‘J.C. van Tol’) and pear provided the most transpirational cooling relative to canopy size – a useful attribute for smaller gardens.

On account of its dense canopy, the cypress also proved the most effective for canopy rainfall storage, wind shelter and screening.  

As autumn marks the start of tree planting season, the partners recommend that gardeners consider what services they might need trees to perform in their garden and select varieties accordingly, also taking into account soil conditions and garden location.

Dr Mark Gush, head of environmental horticulture at the RHS, comments:

“In considering potential trees to grow, gardeners are increasingly mindful of looking beyond just the aesthetic, towards species that will also provide a range of benefits while being resilient to changes that we are now experiencing in the climate. Long-term detailed and rigorous field monitoring studies like this one are extremely valuable in providing evidence-based guidance on this complex topic.”

Nick Dunn, managing director of Frank P Matthews tree nursery, also comments:

“This important project has offered an opportunity to accurately endorse garden trees both native and non native as key contributors to a broader environmental benefit than was previously accepted.”

The complete guide to the environmental benefits of the trees tested can be found here.