Urbanization associated with greater tree growth declines in urban than in rural forests

Summary

As temperatures continue to rise, the effects of climate variation and urbanization on tree growth are not entirely clear. This study compared the radial growth and climate sensitivity of black locust (Robinia pseudoacacia) and black pine (Pinus thunbergii) in urban forest parks and rural mountain areas in Qingdao, eastern China. Results from four tree-ring width chronologies indicate significant disparities in growth and climate sensitivity between urban and rural areas for both tree species. Trees in urban areas grew slower, likely due to greater water stress. Specifically, urban black locust growth was limited by water availability during the current growing season (April–September), while urban black pine growth was constrained by water availability in the late-growing season (August–September) of the previous year. Growth-trend analysis revealed a significant decline in tree growth since the early 21st century, with urban trees showing a more pronounced decline, highlighting that recent warming and drying likely affected by urbanization and inhibited urban tree growth. Identifying and planting tree species adapted to the changing climate is important for long-term urban forest management. Irrigation of the existing trees to reduce water stress is important to retain the current tree canopy during a several-decade period of transition to more urban tolerant tree species.