Urban forests are considered a key element in the ecological structure of cities, contributing to the provision of ecosystem services such as carbon sequestration and climate regulation. However, few studies have investigated these regulating services in small Neotropical cities. The aim of this study was to estimate the biomass supply and carbon sequestered by urban trees, as well as to evaluate the capacity of trees in thermal regulation during the hottest season in 2021 (from December 2020 to May 2021) in Puerto Carreño - Colombia. Accordingly, we implemented random sampling through 200 circular plots to estimate the biomass and carbon storage of trees. Moreover, we used 16 digital iButton sensors located in paired sites (unshaded and tree-shaded) in eight ground covers in the city to measure hourly temperature and humidity for six months. We find that urban forests in Puerto Carreño have relatively high tree diversity and complex vertical structures, greater than that of more populated cities in the region, and high carbon storage (in a range between 37 - 51 tC/ha). Thermal regulation by urban forests increases exponentially with the ambient temperature i.e. 7,5°C at 44 °C but 2°C at 34,9°C. Specifically, during higher daily heat extremes, cooling effects are maximized by neotropical urban forests. Relative humidity is generally greater in shaded areas versus unshaded areas, which is even more pronounced during critical hot periods. Under a global context, Puerto Carreño has a high risk to develop a deadly combination of climatic conditions for temperature and humidity. Very high discomfort indexes are considerably mitigated by urban forests by a factor of 10 during the hottest hours (9 a.m. to 4:00 p.m.). On site surveys confirmed that people perceive the well-being effects of trees and their climate regulating services: tree shade and fruit provision were the key ecosystem service benefits mostly identified by residents. Our study shows that tropical urban forests are key local and global mitigation (carbon stocks) and adaptation (extreme heat reduction) measures to fight climate change.
