Let's make the city cooler: The importance of leaf traits in urban planning

Research Highlight discussing: Wang X, Rahman MA, Cadotte MW, Mokroš M, Pauleit S, Rötzer T, Chen B, Liang X, Shen G, Wan Y, Dong X, Xu J, Da L, Song K. (2025). Integrating forest inventory and LiDAR observations to uncover the role of plant traits on cooling effects in urban areas. Journal of Applied Ecology, https://doi.org/10.1111/1365-2664.70102. As cities face rising temperatures due to climate change and urban expansion, urban forests have become increasingly vital for regulating microclimates. Wang et al. employ a trait-based ecology approach to demonstrate that leaf nutrient traits may be even more influential in cooling urban areas than canopy structure. By integrating drone data, laser scanning and detailed trait data from nearly 4000 trees across 77 species in Shanghai, the study reveals that leaf nitrogen and phosphorus explain more variation in cooling and humidifying effects than canopy structure. Structural shading was most effective at midday, while nutrient-driven transpiration dominated in the morning and late afternoon. Surprisingly, high potassium levels reduced cooling, likely due to water loss through excessive stomatal opening. Based on these results, the authors propose a new framework for selecting tree species in urban greening, emphasizing both leaf function and structure. With emerging remote sensing tools capable of estimating leaf traits at the landscape scale and large trait databases, this study marks a shift from planting more trees to planting the right trees, offering a replicable and scalable path towards climate-resilient urban design.