S07 - Session O3 - Provision of ecosystem services by garden trees

Authors: Elisabeth Larsen *, Tijana Blanusa, Rachael Tanner, Paul McAleer, Andrew D. Hirons, Mark Gush

The majority of the world's population now live in urban areas. This leads to competition between grey and green infrastructure, reduction in permeable surfaces and rising temperatures in urban landscapes. Trees play a vital part in thermal regulation, water recycling and carbon storage. However, there are large species-specific differences. While domestic gardens provide 25% of urban tree cover in the UK, there is little advice for gardeners on what trees to plant to buffer adverse effects of dense urban landscapes and a changing climate. Thus, there is a need to understand which tree species are associated with different ecosystem services, as well as a measure of the effectiveness to which the service is delivered. This study focused on a range of tree species suitable for a domestic garden context, to understand what characteristics are important for flood mitigation, cooling capacity and carbon storage. Nine species/cultivars of small to medium-stature garden trees, including Crataegus persimilis 'Prunifolia Splendens' , Cupressus sempervirens 'Garda', Ilex aquifolium 'J.C. van Tol' , Magnolia 'Galaxy' , Malus toringo 'Scarlett' , Picea pungens ' Erich Frahm' , Prunus 'Shirofugen' , Pyrus calleryana ' Chanticleer ' and Sorbus ulleungensis ' Olympic Flame' , were planted in 130 l containers in a large irrigated outdoor experiment which commenced in February 2021. Measurements included continuous records of sap flux density, meteorological parameters and substrate soil moisture, with regular discrete measurements of canopy size, leaf area, woody biomass and gas exchange. The Malus and Prunus emerged as strong candidates for summer cooling, with large transpiration volumes (0.9 and 1.1 l tree -1 day -1 in June), large projected crown- and leaf area. The Ilex emerged as a strong candidate for summer cooling, despite its smaller size, as judged by high sap flux density in warm scenarios (4.1 cm 3 cm -2 d -1 in June). The Picea and the Cupressus emerged as stronger candidates for flood mitigation, due to high transpiration rates during cooler periods. Current observed diversity in transpiration responses indicate notable differences in physiology as well as in responses to meteorological drivers.