Tree growth, physiology, and ecosystem services across a sealing gradient in Munich, Germany

Urban trees provide essential ecosystem services, but impervious surface cover is associated with altered growing conditions and tree performance. We quantified mean imperviousness within a neighbourhood-scale 500 m buffer and classified 128 Acer platanoides , Robinia pseudoacacia , and Tilia cordata trees across the Munich–Freising region, Germany, into four categories: mostly unsealed (MU, <25%), partially sealed (PS, 25–49%), medium sealed (MS, 50–75%), and highly sealed (HS, >75%). Structural attributes, leaf physiology, local environmental conditions, and indicators of carbon storage, habitat provision, and surface-temperature reduction were assessed. Physiological measurements from two annual campaigns enabled interannual comparison but not assessment of intra-seasonal dynamics. Mean structural attributes did not differ significantly among sealing categories, although the explanatory strength of some allometric relationships varied descriptively across the gradient. Gas-exchange patterns differed descriptively among species, categories, and sampling campaigns; however, continuous imperviousness was not significantly associated with chlorophyll content (SPAD), transpiration, or stomatal conductance in the final models. Stomatal conductance was instead associated nonlinearly with shallow soil moisture and positively with precipitation and tree size. During physiological sampling, continuous imperviousness was positively associated with air temperature, corresponding to an estimated difference of approximately 0.20 °C per 10-percentage-point increase in imperviousness, whereas shallow soil moisture, relative humidity, and vapour pressure deficit showed no significant associations. Aboveground carbon storage was related primarily to DBH and species rather than sealing category; a 10% increase in DBH corresponded to an estimated 23.4% increase in carbon storage. Model-estimated microhabitat abundance was highest at partially sealed sites and was greatest for T. cordata . Model-adjusted surface-temperature reduction was descriptively higher over asphalt than over grass, although the surface materials were analysed separately; neither sealing category nor species was significantly associated with surface-temperature reduction over either surface material. Overall, neighbourhood-scale imperviousness was not a universally dominant predictor of urban-tree performance. Structural, physiological, and ecosystem-service patterns were associated with different combinations of species, tree size, sampling conditions, and local environmental characteristics. The findings support site- and service-specific urban-tree management while treating neighbourhood imperviousness as a contextual indicator rather than a direct measure of individual-tree growing conditions.