Cooling forests, calmer hearts: Urban forest structure, microclimate and heat relief in adolescents

Source abstract

Urban and peri-urban forests deliver critical ecosystem services under climate warming, yet a fundamental question for evidence-based forest management remains poorly understood: which specific structural forest attributes govern the thermal microclimate and the physiological heat relief experienced by users during physical activity? Answering this question is key to moving forest management beyond general greenspace provision toward structure-targeted interventions that maximize cooling ecosystem services. To the authors‘ knowledge, this study provides the first integrated analysis linking publicly available remote sensing-derived forest structural metrics with continuous mobile microclimatic monitoring and wearable heart rate (HR) measurements, conducted with a large sample of young people walking in real-world peri-urban forest environments. Field measurements were conducted along two peri-urban forest routes in southern Germany, involving 145 participants aged 10-23 years. Universal Thermal Climate Index (UTCI) and HR were analyzed using Random Forest models.Forest stand height emerged as the dominant structural determinant of UTCI — with a management-relevant threshold above 12-15 m —followed by vegetation health. Microclimatic conditions were the primary predictors of HR variability, yet forest structural characteristics alone explained nearly as much variation in HR as models based exclusively on microclimatic measurements (R² = 0.69 vs. 0.70), establishing remote sensing-derived canopy metrics as a monitoring-free proxy for cooling ecosystem services forests provide. Results show that taller and healthier forest stands were associated with lower estimates of cardiovascular heat load through stronger microclimatic cooling. These findings provide forest managers and urban planners with a resource-efficient method for heat-adaptive forest management under ongoing climate change.