Crown shapes of common European urban tree species differ from tree species to tree species and are modified by the age of a tree and its local environment. A tree’s crown shape has a great influence on the crown volume and thus on the ecosystem service provision of a tree such as the shade area or the shade density. We used the data of 3852 tree individuals from eight German cities and the crown shape data of 528 trees for the species Acer platanoides, Acer pseudoplatanus, Aesculus hippocastanum, Fraxinus excelsior, Platanus × acerifolia, Robinia pseudoacacia and Tilia cordata to analyze tree structural dimensions and the crown volume and shade dependency on a tree’s crown shapes. Ovoid (57% of all tree individuals) and spherical (24%) crown shapes were mostly observed. However, columnar shape was observed for light-demanding R. pseudoacacia in close proximity of objects. The greatest shade areas were measured for spherical shape and the highest shade density for ovoid shape. Logistic regression analysis showed significant effects of age and distance to objects on crown shapes. Significant probability of crown shapes was found for different tree species, e.g., A. hippocastanum strongly showed half-ellipsoid crown shapes.

Urban forests play a critical role in improving the quality of life in cities, but in arid environments, little is known about the potential benefits and growth conditions of different tree species. Our study aimed to fill this gap by investigating the relationships between tree dimensions, above-ground biomass carbon storage, and shading potential in three common urban trees in the arid city of Jericho, Palestine, (i.e., Ficus nitida, Delonix regia, and Phoenix dactylifera). The trees were chosen according to their distribution in urban locations and tree vitality, with ages ranging from 20 to 90 years. Based on the results from tree structure measurements, the carbon storage and shading potential were calculated using the City Tree model. The results indicate a moderate to strong relationship between tree height, crown diameter, and crown volume for F. nitida and D. regia (R² = 0.28–0.66), but no relationship for P. dactylifera (R² = 0.03–0.06). The findings suggest that the analyzed tree species can considerably contribute to the potential benefits of trees in improving the climate of an arid city: D. regia shows a higher median of above-ground biomass carbon storage of 155 kg C tree⁻¹, while P. dactylifera 91 kg C and F. nitida 76 Kg C. D. regia and F. nitida have a higher median of shading potential, (31 m²–41 m²), respectively. Information on the ecosystem services from urban trees and their relationships in terms of species, age, and tree planting urban location are very important for city planners, in relation to sustainable urban green spaces in arid cities.

Urban forests have emerged as a key strategy for promoting adaptive capacities of cities to climate change by mitigating urban heat island (UHI) and thus heat stress for humans. An empirical study in Würzburg, Germany (2018–2020) revealed a significant increase in extreme heat conditions, with nine days exceeding a Wet Bulb Globe Temperature (WBGT) threshold of 35°C in the treeless city center, compared to none in a treed suburban site just five kilometers away.Further research in Munich, Germany, comparing two ecologically contrasting tree species, Tilia cordata and Robinia pseudoacacia, under varying meteorological and soil conditions highlighted that shading is the dominant cooling mechanism, particularly under high atmospheric aridity. In temperate climates with adequate soil moisture, lighter shaded canopies may enhance grass evapotranspiration, suggesting a preference for dense canopies over built environments and lighter canopies over grass surfaces.To explore cooling mechanisms across climates, sensible and latent heat fluxes under tree canopies within various settings (park, street, square) were analyzed in Munich (temperate) and Beer Sheva, Israel (hot arid). Despite irrigation, trees in Beer Sheva exhibited higher hydraulic resistance, limiting transpirational cooling (regression slopes of 0.25–0.44 in Beer Sheva vs. 0.10–0.18 in Munich). Analysing the proportion of latent heat to total available energy, we found transpiration cooling was about 40% less significant at noon hours in summer in Beer Sheva than in Munich. These results suggest that with anticipated higher atmospheric aridity, shading will become even more important, thereby, denser tree canopies would be of higher importance.Additionally, LiDAR scanning revealed that multilayered vegetation enhances cooling benefits more than twofold compared to single-layered vegetation. Thus, increasing vegetation complexity both horizontally and vertically can optimize thermal benefits through shading and transpiration across diverse climates, while also supporting biodiversity and fostering nature connectedness.

Urban trees grow in a very heterogeneous environment. In addition to the demanding growing conditions due to small planting pits with limited rooting space and sparce water availability, heat, pollution and much more, above-ground space requirements because of safety reasons and aesthetic demands affect urban tree growth. Management practices such as pruning are a common measure for many urban tree species to adjust the crown for aesthetic requirements and size constraints such as buildings, other trees or above ground cables. On the other hand, these pruning measures alter tree growth and thus ecosystem services such as cooling, CO2 sequestration and runoff reduction. To maintain or improve growth and the provision of ecosystem services despite the challenging conditions in urban environments, trees can be irrigated, particularly during periods of drought. Our research analyzes the influence of management (pruning and irrigation) on tree growth and the provision of ecosystem services such as cooling on the common urban tree species Platanus x acerifolia in cities. Plane trees are often selected for aesthetic pruning due to their high pruning tolerance, robustness and fast growth. For this study, the tree structures more than 350 pruned and unpruned trees in Munich and in a tree nursery were measured and their growth conditions compared. The modeling tool CityTree was used to calculate the biomass accumulation and provided ecosystem services carbon storage and cooling by shading and transpiration of pruned and unpruned trees, with and without irrigation. The results show clear differences in growth, tree parameters such as leaf area, biomass, photosynthesis and provision of ecosystem services between pruned and unpruned trees, with irrigation helping to survive drought periods. The results can be useful for urban planners regarding management practices in urban tree planning to create more efficient management plans and increase the vitality of urban trees.

As climate change continues, cities are experiencing more heat and drought, causing further deterioration of growing conditions for urban trees. We investigated the growth of the commonly planted urban tree species Tilia cordata, Acer platanoides and Robinia pseudoacacia. The growth analyses are based on dendrometer data from permanent tree laboratories in two German cities with different precipitation levels: Munich with 940 mm/year and Würzburg with 570 mm/year. Species-specific growth patterns (quantity, growth initiation and duration) and the effects of site microclimate on stem increment were analyzed. Due to the high temporal resolution of the dendrometer data and the long recording periods of over 5 years, both long-term trends over several years and short-term reactions of the trees to external influences can be analyzed.Additional to the species-specific differences, with lowest annual growth rates for T. cordata, significant trends show that precipitation and urbanization strongly dictate where trees grow the best. For both cities, cooler and greener sites revealed higher stem increment compared to warmer, highly sealed sites in the historic city centre. During 2021 more precipitation was registered (14 to 19% higher than the long-term average) in both cities. The most beneficial effect on tree growth is clearly shown for Munich, with approximately 50% higher increment for A. platanoides and 30% higher increment of T. cordata compared to the drier year 2022.These results can support planning decisions on the selection of suitable tree species for urban locations.