Management of tropical urban parks informed by divergent stomatal regulation of trees

As climate change intensifies urban environmental challenges, cities increasingly rely on urban green spaces as climate adaptation infrastructure. Urban trees provide critical ecosystem services through root water uptake and leaf water loss, yet how their stomata respond to atmospheric drivers in tropical urban environments remains poorly understood. This research examines how ten dominant tree species in Chulalongkorn University Centenary Park, Bangkok regulate stomatal conductance (g_s) in response to vapor pressure deficit (VPD) and photosynthetically active radiation (PAR) across wet and dry seasons. We identify two functional groups-VPD-tolerant species and VPD-sensitive species-and translate these patterns into practical recommendations for species selection and irrigation in tropical urban parks. VPD-tolerant species (Afzelia xylocarpa, Bauhinia purpurea, Tabebuia rosea, Dipterocarpus alatus, and Hopea odorata) maintained high g_s throughout the day regardless of rising VPD, sustaining continuous gas exchange and ecosystem service provision across seasons. VPD-sensitive species (Dalbergia cochinchinensis, Millettia leucantha, Homalium tomentosum, Millingtonia hortensis, and Samanea saman) reduced g_s in response to increasing VPD during the dry season but shifted toward PAR sensitivity under the wet season, reflecting greater drought tolerance. Our findings have implications for management, suggesting early morning is the most physiologically effective irrigation window. Also, VPD-tolerant species would be best suited for high-service planting zones benefitting from sustained gas exchange, while VPD-sensitive species are appropriate where lower maintenance and drought resilience are priorities. These findings provide physiologically based and actionable recommendations for urban tree species selection, irrigation scheduling, and long-term green infrastructure planning under future climate uncertainty.