Green infrastructure (GI) has emerged as a feasible strategy for promoting adaptive capacities of cities to climate change by alleviating urban heat island (UHI) and thus heat stress for humans. ...However, GI can also intensify the winter cold stress. To understand the extent of UHI within a city as well as the link between outdoor thermal stress both diurnally and seasonally, we carried out an empirical study in Würzburg, Germany from 2018 to 2020. At sub-urban sites, relative humidity and wind speed (WS) was considerably higher and air temperature (AT) lower compared to the inner city sites. Mean AT of inner city sites were higher by 1.3 °C during summer and 5 °C during winter compared to sub-urban sites. The magnitude followed the spatial land use patterns, in particular the amount of buildings. Consequently, out of 97 hot days (AT > 30 °C) in 3 years, 9 days above the extreme threshold of wet bulb globe temperature of 35 °C were recorded at a centre location compared to none at a sub-urban site. Extreme heat stress could be halved with 30-40% cover of greenspaces including grass lawns, green roofs, and green walls with little compromise in increasing winter cold stress.
A more detailed understanding of the micro-climatic thermal benefits of different urban tree species and the retrospective species characteristics is necessary to guide management decisions. In this ...review, we focused specifically on empirical data collected at ground level for below-canopy surface temperature (ST) and transpiration cooling (AT), using a meta-analysis method. Tree canopy density was clearly identified as the most influential driver of different mechanisms of cooling benefits. Secondly, climate of the cities where the trees were grown showed significant impacts on cooling potentials: trees grown in Oceanic and Continental climates showed a higher cooling potential compared to trees grown in Mediterranean climate for AT and sub-tropical climate for ST. Thirdly, tree growth in size and ground surface cover showed significant impact. ST decreases almost linearly with the increase of canopy density; however, the rate is significantly lower over transpiring grass surfaces. Transpiration of trees planted over grass was ten times higher (4.15 g m−2 min−1) compared to a tree planted in paved cut-out pits (0.44 g m−2 min−1). Moreover, diffuse porous wood anatomy and trees originating from temperate and resource-rich forests showed better cooling potentials. Among the leaf traits, dark green leaves, < 0.15 mm of thickness showed higher AT and ST benefit. The review pointed out the lack of standardized study protocols in determining tree cooling benefits and empirical data, particularly at tropical and sub-tropical climate. Finally, the study suggested some recommendations for plantings that optimize the cooling benefits from urban greenspaces.
•Determinant variables about tree species cooling potential have been investigated.•Surface (ST), transpiration air-cooling (AT) and human comfort (TC) was reviewed.•Leaf area index showed a positive correlation with all three mechanisms of cooling.•Surface temperature reduction was more over asphalt than grass or building walls.•Darker, thin leaved species with diffuse porous wood anatomy provided better AT.
•Human thermal comfort (PET) under different tree species have been investigated.•Eco-physiological and bio-meteorological data were measured across the city.•Tree species with higher leaf area index ...showed better below-canopy surface cooling.•Along with higher tree transpiration, they provided better PET reduction.•Cluster tree planting design provided better PET even they reduced the tree growth.
The potential of urban greenspaces in regulating temperature is widely known; however, in the heterogeneous urban landscape the process and the magnitude of human thermal comfort as well as the cumulative effects of natural and built surfaces are not yet well understood. We selected two ecologically contrasting species Tilia cordata Mill. and Robinia pseudoacacia L. planted in eight plots across five different sites in Würzburg, one of the major cities in Northern Bavaria, Germany. We monitored meteorological and edaphic variables and tree sap-flow along with the air temperature, relative humidity, within tree canopy and outside, between January 1 and December 31, 2018. Additionally, we measured surface temperature, meteorological variables below the tree canopies and outside, during the hottest summer days of 2018 (July 23 to 31). With 35% higher leaf area index, T. cordata tree canopies prevented higher incoming radiation compared to R. pseudoacacia trees. Moreover, with diffuse porous wood anatomy, T. cordata trees provided four times more transpiration compared to R. pseudoacacia, therefore, up to 2.8 °C air temperature reduction (ΔAT) within the tree canopy, and increase in absolute humidity (ΔAH) up to 2.6 g m − 3 compared to the 1.9 °C of ΔAT and 1.9 g m − 3 of ΔAH for R. pseudoacacia respectively. Thus, physiological equivalent temperature reduction was up to 4 °C under the shade of a R. pseudoacacia tree compared to 11 °C under a T. cordata tree. Finally, the research showed the importance of urban topography, such as street orientation, surrounding environment such as geometry, urban design to reduce the hindrance of wind flow and proportion of greenspaces in terms of outdoor human thermal comfort.
Large-scale urban growth has modified the hydrological cycle of our cities, causing greater and faster runoff. Urban forests (UF), i.e. the stock of trees and shrubs, can substantially reduce runoff; ...still, how climate, tree functional types influence rainfall partitioning into uptake and runoff is mostly unknown. We analyzed 92 published studies to investigate: interception (I), transpiration (T), soil infiltration (IR) and the subsequent reduction in runoff. Trees showed the best runoff protection compared to other land uses. Within functional types, conifers provided better protection on an annual scale through higher I and T but broadleaved species provided better IR. Regarding tree traits, leaf area index (LAI) showed a positive influence for both I and T. For every unit of LAI increment, additional 5% rainfall partition through T (3%) and I (2%) can be predicted. Overall, runoff was significantly lower under mixed species stands. Increase of conifer stock to 30% in climate zones with significant winter precipitation and to 20% in areas of no dry season can reduce runoff to an additional 4%. The study presented an overview of UF potential to partition rainfall, which might help to select species and land uses in different climate zones for better storm-water management.
Urbanization and climate change are two inevitable megatrends of this century. Knowledge about the growth responses of urban trees to climate is of utmost importance towards future management of ...green infrastructure with the aim of a sustainable provision of the environmental ecosystem services. Using tree-ring records, this study analyzed growth response to climate by stem diameter at breast height (DBH) of 1178 trees in seven large cities worldwide, including Aesculus hippocastanum L. in Munich; Platanus × hispanica Münchh. in Paris; Quercus nigra L. in Houston; Quercus robur L. in Cape Town; Robinia pseudoacacia L. in Santiago de Chile, Munich, and Würzburg; and Tilia cordata Mill. in Berlin, Munich, and Würzburg. Climate was characterized following the de Martonne aridity index (DMI). Overall, trees showed an 8.3% lower DBH under arid than humid climate at the age of 100. Drought-tolerant tree species were overall not affected by climate. However, R. pseudoacacia showed a lower diameter when growing in semi-dry than humid climate. In contrast, drought-sensitive tree species were negatively affected by arid climate. Moreover, the effect of drought years on annual diameter increment was assessed. P. × hispanica and R. pseudoacacia appeared as the most drought-resistant species. The highest sensitivity to drought was detected in T. cordata and Q. robur. A. hippocastanum and Q. nigra showed a lower diameter growth during drought events, followed by a fast recovery. This study’s findings may contribute to a better understanding of urban tree growth reactions to climate, aiming for sustainable planning and management of urban trees.
Our aim is to contribute to understanding the role of subtropical trees on carbon storage and CO2 removal in the city of Sao Paulo/Brazil, besides highlighting the surrounding environment ...implications to sibipiruna trees (Cenostigma pluviosum)’s performance. The case study was conducted with three trees, one planted on a sidewalk in Pinheiros neighborhood, a highly sealed area, and two in a green area, the Ibirapuera Park. To define the stem basal area growth and its pattern, local measurements were taken over a year and a segmented linear regression model was adjusted. The stem growth dependency on microclimate was tested by a Spearman Correlation. The trees’ active stem growth presented a similar pattern. The soil volumetric water content and soil temperatures were the variables with more impact. The total mean radial stem growth for the IBIRA1 and IBIRA2 trees was 1.2 mm year−1 and 3 mm year−1, while at PIN1 it was 1.3 mm year−1. The total biomass increment in IBIRA1 and IBIRA2 was 4.2 kg C year−1 and 12.8 kg C year−1, while in PIN it was 4.9 kg C year−1 and the removal was 15.3 C year−1, 47.1 kg CO2 year−1 and 17.9 kg CO2 year−1, respectively. The results indicated that the land cover difference implies a significant interference with the promotion of carbon fixation and CO2 removal, demonstrating that planting urban trees in soils with better water storage conditions is more efficient.
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 Forest and Urban Microclimate Rötzer, Thomas; Moser-Reischl, Astrid; Rahman, Mohammad A. ...
Forests,
12/2023, Letnik:
14, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Urban environments are challenging places for urban greenspaces, especially for trees, which have the greatest impact on ecosystem service provisions ...
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.
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