Urban trees support a suite of ecosystem services that benefit human and environmental health. Trees regulate climate, filter air and water, provide habitat, and sequester carbon among other services, including aesthetics. However, urban trees are regularly subject to greater environmental stress and pest infestations that directly reduce physiological functions and ecosystem services. For example, urban warming of just 2°C can increase pest abundance by 200 times and reduce tree condition from ‘good’ to ‘poor,’ indicating a decline in overall structure and health. Although greater pest abundance and poorer health demand increased tree maintenance, these factors are rarely considered when specifying tree species for urban installations. A key challenge to producing sustainable urban landscapes is identifying urban sites that allow trees to thrive with minimal pesticide, water, or other interventions. To meet this challenge, predictions are needed on how site-specific conditions affect long-term tree health. Here we work with urban red maples; previous research has shown that impervious surface cover near planting sites increases temperature, water stress, and pest (Melanaspis tenebricosa) abundance, while downgrading tree condition. We hypothesized that the strength of this effect would vary based on background climate of the city in which trees were measured.
We demonstrate that impervious surface cover adjacent to planting sites can be used to predict pest infestation intensity and health of urban red maples, and that the strength of the effect may differ with the climatic conditions of the city in which the trees are planted. Impervious surface cover significantly predicted urban red maple condition in six southeastern cities. However, we did observe variability in the impervious surface cover thresholds that characterize the suitability (i.e. likelihood of finding a red maple in a given condition [e.g. good, fair, or poor]) of planting sites between cities. Pest infestation intensity was more variable between cities and is likely a result of the climatic requirements of M. tenebricosa. These results further our goal to develop planting recommendations based on impervious surface cover that can be used by landscape professionals and arboriculturists when selecting red maple planting sites. This work importantly provides a framework on how to use impervious surface or other thresholds to identify sustainable planting sites for additional urban tree species.