Role of the urban plant environment in the sustainable protection of an ancient city wall

Abstract Cultural heritage sites are exposed to urban environmental phenomena and various forms of deterioration that degrade their historical and cultural value. As an important element, plant landscaping can be a potential regulator of the microenvironment, mitigating the adverse effect of the local climate to cultural heritage. The influence of evergreen trees on the weathering deterioration of the Nanjing City Wall was studied and evaluated through field measurements and numerical modeling. A two-dimensional hygrothermal ‘City Wall–plant’ model was developed to simulate the shaded and unshaded surfaces. The results showed that compared to the unshaded case, the shaded surface showed smaller temperature fluctuations with an increase in the minimum temperature by 0.5°C-0.8 °C, smaller water content fluctuations with the standard deviation decreasing by 0.017 kg/kg at the height of 0.15 m, and a lower evaporation rate by 8–18%. This means that evergreen trees can effectively reduce the risk of deterioration on wall surfaces due to freeze–thaw cycles, efflorescence, and subflorescence. These findings provide the theoretical basis for the sustainable preservation of sites with cultural heritage.