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

Urban trees represent a key nature-based solution and an essential component of green infrastructures, providing multiple ecosystem services but increasingly subjected to environmental stressors. Here we present a dynamic, mechanistic, and individual-based model designed to simulate growth of urban trees and the associated provision of ecosystem services under varying climate conditions. The model is modular, runs at daily time steps and incorporates key biological processes such as photosynthesis, water limitation and biomass allocation. It simulates single-tree growth and quntifies ecosystem services, such as carbon sequestration, air filtration, and local climate regulation using species-specific parameters and local climate forcing. The model was calibrated and tested in a pilot application in Milan, simulating the long-term growth of three of three common broadleaved species (Platanus x acerifolia, Populus nigra and Robinia pseudoacacia) across different planting ages and climate scenarios. A multi-objective calibration was used to fit stem diameter and crown width, and sensitivity analyses were conducted to assess 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 delivering far greater benefits. Carbon sequestration and air filtration decrease under more 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. The model offers a promising tool for supporting urban forestry decisions related to planning, species selection, and long-term ecosystem service provision.