An individual, mechanistic and dynamical model to simulate urban tree growth and ecosystem services supply under...

Urban trees represent a key nature-based solution and an essential component of green infrastructure, providing multiple ecosystem services but increasingly subjected to environmental stressors. We present a dynamic, mechanistic, and individual-based model designed to simulate growth of urban trees and associated ecosystem services supply under varying climate conditions. The model is modular, runs at daily temporal resolution and incorporates key biological processes including photosynthesis, water limitation and biomass allocation. It simulates single-tree growth and quantifies ecosystem services, e.g., carbon sequestration, air filtration, local climate regulation, using species-specific parameters and climate forcing. The model was calibrated and tested in a pilot application in Milan, simulating long-term growth of three common broadleaved species (Platanus x acerifolia, Populus nigra and Robinia pseudoacacia) across different planting ages and climate scenarios. This approach advances urban tree modelling by combining individual-based daily simulation of mechanistic processes with operational calibration using standard inventory data. A multi-objective calibration was used to fit stem diameter and crown width, and sensitivity analyses assessed parameter robustness and uncertainty propagation. Results show realistic growth trajectories with clear species-age contrasts. Tree growth declines under stronger climate forcing, and ecosystem service provision scales non-linearly with age, with mature trees providing substantially greater benefits. Carbon sequestration and air filtration decrease under extreme scenarios, whereas local climate regulation exhibits a compensatory response: lower productivity is offset by higher evaporative demand, yielding stable or slightly increased evapotranspiration-based cooling. Thus, the model provides a novel tool to support urban forestry planning, species selection, and long-term service assessment.