Living Lab raw data

Climate change is projected to increase the frequency and intensity of heatwaves, exacerbating the urban heat island effect and contributing to vegetation decline. Urban vegetation plays a critical role to improve thermal comfort, yet the physiological responses of common species to heat and drought stress remain poorly understood. · We examined water relations and thermal tolerance of eight widely planted urban tree and shrub species in a common garden in western Sydney, Australia, over two average austral summers (2022-2023, 2023-2024) with periods of mild to moderate water deficits. · Two vulnerable shrub species, Melaleuca thymifolia and Westringia fruticosa, experienced drought stress as evidenced by their low predawn (Ψpre <-1.5 MPa) and midday leaf water potential (Ψmid) exceeding their turgor loss point. Leaves of shrub species were prone to overheating during hot, dry periods, likely due to reduced transpirational cooling from lower water availability and/or limited stem water storage. Common functional traits (e.g. wood density, leaf size, Tcrit, leaf thickness) did not reliably predict species vulnerability. · Notably, thermal safety margins (TSM) were smaller in tolerant species, questioning their utility as vulnerability metric under field conditions. · These findings highlight the importance of species-specific physiological responses to compound climate stressors for climate-adaptive urban greening strategies.