Assessment of the ecological functions of primary greening tree species in arid and semi-arid urban areas of northern China: a field and UAV-based approach

Abstract In arid and semi-arid regions with limited water, evaluating the ecological functions of urban trees is essential to improve quality greening. This study evaluated the core ecological functions based on the physical traits of arbor species (cooling, species diversity maintenance, and carbon sequestration) of 261 trees from five species ( Salix matsudana, Styphnolobium japonicum, Populus alba, Pinus sylvestris var. mongholica , and Ulmus pumila ) across three arid and semi-arid urban areas: Hohhot, Baotou, and Yinchuan. (1) Among the evaluated morphological traits, crown width (Pearson r = 0.77, P < 0.001) was the significant driver of cooling. Salix matsudana ( EMM : 12.43 °C) and Styphnolobium japonicum ( EMM : 10.48 °C) exhibited the greatest cooling benefits. (2) Compared to morphological traits, tree species identity was identified by random forest (RF) analysis as an important factor influencing understory species diversity maintenance (% IncMSE = 27.84%). Baseline observations showed that Pinus sylvestris var. mongholica provided the highest understory species richness ( EMM : 3.91), Shannon index ( EMM : 1.02), and Simpson index ( EMM : 0.56). (3) Fast-growing Populus alba exhibited the highest individual carbon sequestration ( EMM : 130.86 ± 15.98 kg) and carbon sequestration efficiency ( EMM : 3.95 ± 0.29 kg cm −1 ). Furthermore, within the spatial context of Hohhot, Baotou, and Yinchuan, the functional divergence highlighted significant ecological trade-offs, indicating no single tree species simultaneously maximizes all targeted ecosystem services. Based on Entropy-weight TOPSIS evaluation, Pinus sylvestris var. mongholica (Overall Score: 0.607) and Populus alba (0.533) exhibited the optimal comprehensive performance regarding the three assessed ecological benefits among the selected arbor species in these study areas. These findings provide a scientific reference framework for goal-oriented construction of urban green spaces. When interpreting these conclusions, seasonal constraints of summer-only observations and methodological limitations of relying solely on above-ground biomass must be considered, as they may obscure comprehensive seasonal dynamics and conservatively underestimate the total carbon sink value.