Comparing the transpirational and shading effects of two contrasting urban tree species

Adaptive forest management improves stand-level resilience of temperate forests under multiple stressors

Forests are expected to be strongly affected by modifications in climate and disturbance regimes, threatening their ability to sustain the provision of essential services. Promoting drought-tolerant species or functionally diverse stands have recently emerged as management options to cope with global change. Our study aimed at evaluating the impact of contrasting stand-level management scenarios on the resilience of temperate forests in eastern North America and central-western Europe using the individual process-based model HETEROFOR. We simulated the evolution of eight stands over 100 years under a future extreme climate according to four management scenarios (business as usual - BAU; climate change adaptation - CC; functional diversity approach - FD; no management - NM) while facing multiple disturbances, resulting in a total of 160 simulations. We found that FD demonstrated the greatest resilience regarding transpiration and tree biomass, followed by CC and then BAU, while these three scenarios were equivalent concerning the net primary production. These results were however dependent on forest type: increasing functional diversity was a powerful option to increase the resilience of coniferous plantations whereas no clear differences between BAU and adaptive management scenarios were detected in broadleaved and mixed stands. The FD promoted a higher level of tree species diversity than any other scenario, and all scenarios of management were similar regarding the amount of harvested wood. The NM always showed the lowest resilience, demonstrating that forest management could be an important tool to mitigate adverse effects of global change. Our study highlighted that tree-level process-based models are a relevant tool to identify suitable management options for adapting forests to global change provided that model limitations are considered, and that alternative management options, particularly those based on functional diversity, are promising and should be promoted from now on.

Modifying temperature-related cardiovascular mortality through green-blue space exposure

Green-blue spaces (GBS) are pivotal in mitigating thermal discomfort. However, their management lacks guidelines rooted in epidemiological evidence for specific planning and design. Here we show how various GBS types modify the link between non-optimal temperatures and cardiovascular mortality across different thermal extremes. We merged fine-scale population density and GBS data to create novel GBS exposure index. A case time series approach was employed to analyse temperature-cardiovascular mortality association and the effect modifications of type-specific GBSs across 1085 subdistricts in south-eastern China. Our findings indicate that both green and blue spaces may significantly reduce high-temperature-related cardiovascular mortality risks (e.g., for low (5%) vs. high (95%) level of overall green spaces at 99th vs. minimum mortality temperature (MMT), Ratio of relative risk (RRR) = 1.14 (95% CI: 1.07, 1.21); for overall blue spaces, RRR = 1.20 (95% CI: 1.12, 1.29)), while specific blue space types offer protection against cold temperatures (e.g., for the rivers at 1st vs MMT, RRR = 1.17 (95% CI: 1.07, 1.28)). Notably, forests, parks, nature reserves, street greenery, and lakes are linked with lower heat-related cardiovascular mortality, whereas rivers and coasts mitigate cold-related cardiovascular mortality. Blue spaces provide greater benefits than green spaces. The severity of temperature extremes further amplifies GBS's protective effects. This study enhances our understanding of how type-specific GBS influences health risks associated with non-optimal temperatures, offering valuable insights for integrating GBS into climate adaptation strategies for maximal health benefits.

Comparable diameter resulted in larger leaf area and denser foliage in the park trees than in street trees: A study on Norway maples of Karlsruhe city, Germany

The leaf area of trees is the main surface of energy and matter exchange between the plant canopy and the atmosphere. A better understanding of canopy structure variations in cities is a prerequisite to evaluating leaf area and ecosystem services. We selected 58 single-standing and healthy Norway maple trees (Acer platanoides L.), equally distributed between the park and street at the same tree size for canopy structure and leaf area measurements. The canopy structures of street trees and park trees were different. Street trees had significantly higher dieback (p < 0.01), crown damage (p < 0.01), and branch-free bole length (p < 0.001) than park trees. Even though we sampled trees with similar diameters, park tree crowns tended to be healthier and denser than street trees. The crown volume, crown projection area (CPA), light availability (Crown Light Exposure or CLE), and foliage density were lower in street trees than in park trees. The average foliage density of street trees is 20 % lower than park trees. All the above differences in crown volume and foliage density lead to a significantly lower leaf area in street trees. The total leaf area of a single street tree was only 83 m2 on average, compared to 186 m2 among park trees. We demonstrated that crown volume and growing habitats (i.e., park or street) are important explanatory variables for leaf area. We conclude that a precise and site-specific evaluation of leaf areas is a prerequisite for accuracy in quantifying ecosystem services from urban trees.

Assessment of vertical cooling performance of trees over different surface covers

Tree-induced cooling benefits are associated with various factors, such as canopy morphology, surface cover, and environmental configuration. However, limited studies have analyzed the sensitivity of tree-induced cooling effects to the combination of such factors. Most studies have focused on 1.5-m cooling performance, and few studies on the variability of the under-tree vertical cooling performance. Therefore, this study aims to investigate the vertical cooling performance of different combinations of trees and surface covers. The study was completed in Chongqing, China, with field experiments capturing vertical air temperature and wind speed at 0.5, 1.0, 1.5, 2.0 and 2.5 m under two typical combinations of "tree + grass" (ComA) and "tree + shrubs" (ComB), and capturing 1.5 m microclimatic environments of a control group with hard pavement without tree shade (REF). The results show that at an average ambient temperature of 33 °C, the maximum air-cooling temperatures for ComA and ComB were 2.46 °C and 1.78 °C, respectively. An increase in the ambient temperature corresponded to a decrease in the cooling effect difference between ComA and ComB. ComA had a maximum vertical temperature difference of 1.01 °C between H1.5m and H2.0m. Between H2.5m and H2.0m, the maximum vertical temperature difference for ComB was 1.64 °C. This study explored the changing patterns of under-tree vertical temperatures under different tree and surface cover combinations, conducive to clarifying the key elements affecting tree cooling performance. The results have implications for accurate thermal comfort assessments and provide a theoretical basis for fine-tuning the design of under-tree spaces.

Soil CO2 and CH4 fluxes from different forest types in tropical peat swamp forest

Information on temporal and spatial variations in soil greenhouse gas (GHG) fluxes from tropical peat forests is essential to predict the influence of climate change and estimate the effects of land use on global warming and the carbon (C) cycle. To obtain such basic information, soil carbon dioxide (CO2) and methane (CH4) fluxes, together with soil physicochemical properties and environmental variables, were measured at three major forest types in the Maludam National Park, Sarawak, Malaysia, for eight years, and their relationships were analyzed. Annual soil CO2 fluxes ranged from 860 to 1450 g C m⁻2 yr⁻1 without overall significant differences between the three forest sites, while soil CH4 fluxes, 1.2-10.8 g C m⁻2 yr⁻1, differed. Differences in GHG fluxes between dry and rainy seasons were not necessarily significant, corresponding to the extent of seasonal variation in groundwater level (GWL). The lack of significant differences in soil CO2 fluxes between the three sites could be attributed to set-off between the negative and positive effects of the decomposability of soil organic matter as estimated by pyrophosphate solubility index (PSI) and GWL. The impact of El-Niño on annual CO2 flux also varied between the sites. The variation in soil CH4 fluxes from the three sites was enhanced by variations in temperature, GWL, PSI, and soil iron (Fe) content. A positive correlation was observed between the annual CH4 flux and GWL at only one site, and the influence of soil properties was more pronounced at the site with the lowest GWL and the highest PSI. Variation in annual CH4 fluxes was controlled more strongly by temperature where GWL was the highest and GWL and plant growth fluctuations were the least. Inter-annual variations in soil CO2 and CH4 fluxes confirmed the importance of long-term monitoring of these at multiple sites supporting different forest types.

Urban green space and albedo impacts on surface temperature across seven United States cities

Extreme heat represents a growing threat to public health, especially across the densely populated, developed landscape of cities. Climate adaptation strategies that aim to manage urban microclimates through purposeful design can reduce the heat exposure of urban populations, however, it is unclear how the temperature impacts of urban green space and albedo vary across cities and background climate. This study quantifies the sensitivity of surface temperature to landcover characteristics tied to two widely used climate adaptation strategies, urban greening and albedo manipulation (e.g. white roofs), by combining long-term remote sensing observations of land surface temperature, albedo, and moisture with high-resolution landcover datasets in a spatial regression analysis at the census block scale across seven United States cities. We find tree cover to have an average cooling impact of -0.089 K per % cover, which is approximately four times stronger than the average grass cover cooling impact of -0.021 K per % cover. Variability in the magnitude of grass cover cooling impacts was primarily a function of vegetation moisture content, with the Land Surface Water Index (LSWI) explaining 89 % of the variability in grass cover cooling impacts across cities. Variability in tree cover cooling impacts was primarily a function of sunlight and vegetation moisture content, with solar irradiance and LSWI explaining 97 % of the cooling variability across cities. Albedo cooling impacts were consistent across cities with an average cooling impact of -0.187 K per increase of 0.01. While these interventions are broadly effective across cities, there are critical regional trade-offs between vegetation cooling efficiency, irrigation requirements, and the temporal duration and evolution of the cooling benefits. In warm, arid cities, high albedo surfaces offer multifaceted benefits such as cooling and water conservation, whereas temperate, mesic cities likely benefit from a combination of strategies, with greening efforts targeting highly paved neighborhoods.

Evidence-based guidelines for greener, healthier, more resilient neighbourhoods: Introducing the 3-30-300 rule

The important contributions of urban trees and green spaces to for example, climate moderation and public health have been recognized. This paper discusses guidelines and norms that promote the benefits of viewing green, living amongst green, and having easy access to green spaces for recreational use. Having trees and other vegetation in sight from one's home, place of work, or school has important mental health and performance benefits. Local tree canopy cover is positively associated with cooling and other aspects of climate moderation. With public green spaces in proximity to one's home stimulates regular use of these areas and results in positive impacts on mental, physical, and social health. After analyzing existing guidelines and rules for urban green space planning and provision, a new, comprehensive guideline is presented, known as the '3-30-300 rule' for urban forestry. This guideline aims to provide equitable access to trees and green spaces and their benefits by setting the thresholds of having at least 3 well-established trees in view from every home, school, and place of work, no less than a 30% tree canopy in every neighbourhood; and no more than 300 m to the nearest public green space from every residence. Current implementation of this new guideline is discussed, as well as the advantages and disadvantages of using this evidence-based but also clear and simple rules.

Crown Shapes of Urban Trees-Their Dependences on Tree Species, Tree Age and Local Environment, and Effects on Ecosystem Services

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.

A Comparative Study of Cooling Performance and Thermal Comfort under Street Market Shades and Tree Canopies in Tropical Savanna Climate

Walking through street markets is the most popular outdoor activity in Thailand, promoting local economies and tourism. In the year-round hot and humid conditions, living outdoors with long heat exposure throughout the midday can result in heat-related illness. Artificial shade structures and tree shade canopies are typical cooling strategies to protect market sellers and pedestrians from direct sun exposure and improve outdoor human thermal comfort in the street market. This study investigates microclimate conditions and cooling benefits of typical street market shade structures with different settings—three roofing materials, two roof shapes, and surrounding trees with dense and sparse canopies. The dimension of the single artificial shade was 2 m × 2 m with heights varying 2–2.5 m. The vertical air temperature and sky view factor profiles were measured on winter and summer days. The calculated physiological equivalent temperatures (PET) and thermal comfortable hours beneath different shade structures were assessed using RayMan 1.2 software. A cluster of trees with a dense canopy provided more effective cooling (with a satisfied thermal condition of 9 h) than artificial shade structures. Thermal conditions under the galvanized steel roofing and HDPE tarpaulin plastic roofing shades were cooler than those of polycarbonate roofing shade. Meanwhile, the space beneath the sparse tree canopy had the warmest condition. The temperature reductions beneath the artificial shade structure varied throughout the day, with the maximum reduction occurring during midday and the lowest reduction found in the late morning and late afternoon. Our study demonstrates that the tree canopies and artificial shade structures had limited application for providing comfortable conditions throughout midday. To reduce such extreme heat, a combination of shade structures with other cooling techniques is suggested, which should be the focus for further studies.

Spatial and temporal changes of outdoor thermal stress: influence of urban land cover types

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.

Effects of tree plantings and aspect ratios on pedestrian visual and thermal comfort using scaled outdoor experiments

Urban trees ameliorate heat stress for urban dwellers. However, it is difficult to quantitatively assess the integrated impacts of tree planting and street layouts on visual and thermal comfort in simulations and urban field experiments. We conducted scaled outdoor experiments in Guangzhou to investigate the influence of tree plantings on pedestrian visual and thermal comfort in street canyons with various aspect ratios (H/W = 1, 2, 3; H = 1.2 m). We considered the effects of tree crown covers (big and small crown) and tree planting densities (ρ = 1, 0.5) on pedestrian illuminance level and two thermal comfort indices (Physiological Equivalent Temperature: PET and Index of Thermal Stress: ITS). When ρ = 1, trees in most cases reduce pedestrian illuminance (maximum 140.0klux) and improve visual comfort. Decreasing ρ from 1 to 0.5 increases the illuminance (maximum 179.5klux) in the streets with big crown trees (H/W = 1, 2) and in the street with small crown trees (H/W = 2). When ρ = 1 (H/W = 1, 2), big crown trees decrease the peak daytime PET (by about 4.0 °C) and ITS (by about 285 W). Small crown trees (ρ = 1, H/W = 1, 2) produce a warming effect on peak daytime PET (2.0-3.0 °C), but a reduction in ITS is observed when H/W = 2, 3. After reducing ρ from 1 to 0.5, big crown trees increase peak daytime thermal stress according to both indices when H/W = 1, 2. Small crown trees exhibit a similar PET cycle between ρ = 0.5 and ρ = 1 across various H/W, but their daytime reduction of ITS is less effective when ρ = 0.5 (H/W = 2). The discrepancies between PET and ITS are attributed to their different approaches to modelling radiation fluxes. The narrower the street, the lower the illuminance, PET, and ITS, while their increases caused by reduced ρ are limited in narrow streets. Our study informs some potential urban tree planting strategies and produces high-quality validation data for numerical simulations and theoretical models.

The role of urban trees in reducing land surface temperatures in European cities

Urban trees influence temperatures in cities. However, their effectiveness at mitigating urban heat in different climatic contexts and in comparison to treeless urban green spaces has not yet been sufficiently explored. Here, we use high-resolution satellite land surface temperatures (LSTs) and land-cover data from 293 European cities to infer the potential of urban trees to reduce LSTs. We show that urban trees exhibit lower temperatures than urban fabric across most European cities in summer and during hot extremes. Compared to continuous urban fabric, LSTs observed for urban trees are on average 0-4 K lower in Southern European regions and 8-12 K lower in Central Europe. Treeless urban green spaces are overall less effective in reducing LSTs, and their cooling effect is approximately 2-4 times lower than the cooling induced by urban trees. By revealing continental-scale patterns in the effect of trees and treeless green spaces on urban LST our results highlight the importance of considering and further investigating the climate-dependent effectiveness of heat mitigation measures in cities.

Urban Heat Island and Its Interaction with Heatwaves: A Review of Studies on Mesoscale

With rapid urbanization, population growth and anthropogenic activities, an increasing number of major cities across the globe are facing severe urban heat islands (UHI). UHI can cause complex impacts on the urban environment and human health, and it may bring more severe effects under heatwave (HW) conditions. In this paper, a holistic review is conducted to articulate the findings of the synergies between UHI and HW and corresponding mitigation measures proposed by the research community. It is worth pointing out that most studies show that urban areas are more vulnerable than rural areas during HWs, but the opposite is also observed in some studies. Changes in urban energy budget and major drivers are discussed and compared to explain such discrepancies. Recent studies also indicate that increasing albedo, vegetation fraction and irrigation can lower the urban temperature during HWs. Research gaps in this topic necessitate more studies concerning vulnerable cities in developing countries. Moreover, multidisciplinary studies considering factors such as UHI, HW, human comfort, pollution dispersion and the efficacy of mitigation measures should be conducted to provide more accurate and explicit guidance to urban planners and policymakers.

Detecting Tree Species Effects on Forest Canopy Temperatures with Thermal Remote Sensing: The Role of Spatial Resolution

Canopy temperatures are important for understanding tree physiology, ecology, and their cooling potential, which provides a valuable ecosystem service, especially in urban environments. Linkages between tree species composition in forest stands and air temperatures remain challenging to quantify, as the establishment and maintenance of onsite sensor networks is time-consuming and costly. Remotely-sensed land surface temperature (LST) observations can potentially acquire spatially distributed crown temperature data more efficiently. We analyzed how tree species modify canopy air temperature at an urban floodplain forest (Leipzig, Germany) site equipped with a detailed onsite sensor network, and explored whether mono-temporal thermal remote sensing observations (August, 2016) at different spatial scales could be used to model air temperatures at the tree crown level. Based on the sensor-network data, we found interspecific differences in summer air temperature to vary temporally and spatially, with mean differences between coldest and warmest tree species of 1 °C, and reaching maxima of up to 4 °C for the upper and lower canopy region. The detectability of species-specific differences in canopy surface temperature was found to be similarly feasible when comparing high-resolution airborne LST data to the airborne LST data aggregated to 30 m pixel size. To realize a spatial resolution of 30 m with regularly acquired data, we found the downscaling of Landsat 8 thermal data to be a valid alternative to airborne data, although detected between-species differences in surface temperature were less expressed. For the modeling of canopy air temperatures, all LST data up to the 30 m level were similarly appropriate. We thus conclude that satellite-derived LST products could be recommended for operational use to detect and monitor tree species effects on temperature regulation at the crown scale.

On the cooling potential of irrigation to mitigate urban heat island

Urban overheating is the most documented phenomenon of climate change, causing severe energy problems. The study aims to evaluate the mitigation potential of irrigation as a response to the urban overheating and heatwaves in large cities, using simulation-based techniques. Mesoscale simulations are conducted for a 32.5 km × 22.5 km metropolitan region of Sydney, Australia, and it is modelled based on the moderate resolution imaging spectroradiometer (MODIS) 500 m resolution land surface dataset. To better represent the Sydney metropolitan area, the New South Wales Land Zoning dataset is used to remap the land surface. The weather research forecast model (WRF) combined with the urban canopy model (UCM) is used as the simulation tool. The results show that a daily irrigation scheme results in a maximum daily temperature drop of approximately 1.3 °C and an average daily air temperature decrease close to 0.5 °C. It is also found that the cooling effect due to the additional irrigation is strongly correlated to the ambient temperature, urban fraction, and the soil moisture state before irrigation. The irrigation induced cooling effect tends to be higher in the urban areas where the soil is drier before irrigation, or in a larger portion of the area that is covered with vegetation, or where the ambient temperature is higher.

Identifying Tree Traits for Cooling Urban Heat Islands—A Cross-City Empirical Analysis

Research Highlights: This paper presents a cross-city empirical study on micro-climatic thermal benefits of urban trees, using machine-learning analysis to identify the importance of several in situ measured tree physiognomy traits for cooling. Background and Objectives: Green infrastructure and trees in particular play a key role in mitigating the urban heat island (UHI) effect. A more detailed understanding of the cooling potential of urban trees and specific tree traits is necessary to support tree management decisions for cooling our progressively hot cities. The goal of this study was to identify the influence and importance of various tree traits and site conditions. Materials and Methods: Surface temperature, air temperature at 1.1 m and at tree crown height, as well as wet bulb globe-temperature of shaded and fully sun-exposed reference areas, were used to study the cooling effect of seven different urban tree species. For all 100 individuals, tree height, crown base, trunk circumference, crown volume, crown area, leaf area index (LAI) and leaf area density (LAD) were measured. Measurements were conducted in the cities of Dresden, Salzburg, Szeged, and Vienna as representatives for middle European cities in different climate zones. Results: Beside site conditions, tree species, height, height of crown base, as well as trunk circumference, have a great influence on the cooling effect for city dwellers. The trunk circumference is a very valuable indicator for estimating climate regulating ecosystem services and therefore a highly robust estimator for policy makers and tree management practitioners when planning and managing urban green areas for improving the availability and provision of ecosystem services.

Role of Species and Planting Configuration on Transpiration and Microclimate for Urban Trees

Research Highlights: To demonstrate the effectiveness of configuration modes and tree types in regulating local microclimate. Background and Objectives: Urban trees play an essential role in reducing the city’s heat load. However, the influence of urban trees with different configurations on the urban thermal environment has not received enough attention. Herein we show how spatial arrangement and foliage longevity, deciduous versus evergreen, affect transpiration and the urban microclimate. Materials and Methods: We analyzed the differences between physiological parameters (transpiration rate, stomatal conductance) and meteorological parameters (air temperature, relative humidity, vapor pressure deficit) of 10 different species of urban trees (five evergreen and five deciduous tree species), each of which had been planted in three configuration modes in a park and the campus green space in Xi’an. By manipulating physiological parameters, crown morphology, and plant configurations, we explored how local urban microclimate could be altered. Results: (1) Microclimate regulation capacity: group planting (GP) > linear planting (LP) > individual planting (IP). (2) Deciduous trees (DT) regulated microclimate better than evergreen trees (ET). Significant differences between all planting configurations during 8 to 16 h were noted for evergreen trees whereas for deciduous trees, all measurement times were significantly different. (3) Transpiration characteristics: GP > LP > IP. The transpiration rate (E) and stomatal conductance (Gs) of GP were the highest. Total daily transpiration was ranked as group planting of deciduous (DGP) > linear planting of deciduous (DLP) > group planting of evergreen (EGP) > linear planting of evergreen (ELP) > isolated planting of deciduous (DIP) > isolated planting of evergreen (EIP). (4) The microclimate effects of different tree species and configuration modes were positively correlated with E, Gs, and three dimensional green quantity (3DGQ), but weakly correlated with vapor pressure deficit (VpdL). (5) A microclimate regulation capability model of urban trees was developed. E, Gs, and 3DGQ could explain 93% variation of cooling effect, while E, Gs, VpdL, and 3DGQ could explain 85% variation of humidifying effect. Conclusions: This study demonstrated that the urban heat island could be mitigated by selecting deciduous broadleaf tree species and planting them in groups.

Tree Transpiration and Urban Temperatures: Current Understanding, Implications, and Future Research Directions

The expansion of an urban tree canopy is a commonly proposed nature-based solution to combat excess urban heat. The influence trees have on urban climates via shading is driven by the morphological characteristics of trees, whereas tree transpiration is predominantly a physiological process dependent on environmental conditions and the built environment. The heterogeneous nature of urban landscapes, unique tree species assemblages, and land management decisions make it difficult to predict the magnitude and direction of cooling by transpiration. In the present article, we synthesize the emerging literature on the mechanistic controls on urban tree transpiration. We present a case study that illustrates the relationship between transpiration (using sap flow data) and urban temperatures. We examine the potential feedbacks among urban canopy, the built environment, and climate with a focus on extreme heat events. Finally, we present modeled data demonstrating the influence of transpiration on temperatures with shifts in canopy extent and irrigation during a heat wave.

Process based simulation of tree growth and ecosystem services of urban trees under present and future climate conditions

Global processes of urban growth lead to severe environmental impacts such as temperature increase with an intensification of the urban heat island effect, and hydrological changes with far reaching consequences for plant growth and human health and well-being. Urban trees can help to mitigate the negative effects of climate change by providing ecosystem services such as carbon storage, shading, cooling by transpiration or reduction of rainwater runoff. The extent of each ecosystem service is closely linked with the tree species as well as with a tree's age, size, structure and vitality. To evaluate the ecosystem services of urban trees, the process-based growth model CityTree was developed which is able to estimate not only tree growth but also the species-specific ecosystem services including carbon storage, transpiration and runoff, shading, and cooling by transpiration. The model was parametrized for the species small-leaved lime (Tilia cordata), robinia (Robinia pseudoacacia), plane (Platanus×acerifolia) and horse chestnut (Aesculus hippocastanum). The model validation for tree growth (stem diameter increment, coefficient of correlation=0.76) as well as for the water balance (transpiration, coefficient of correlation=0.92) seems plausible and realistic. Tree growth and ecosystem services were simulated and analyzed for Central European cities both under current climate conditions and for the future climate scenarios. The simulations revealed that urban trees can significantly improve the urban climate and mitigate climate change effects. The quantity of the improvements depends on tree species and tree size as well as on the specific site conditions. Such simulation scenarios can be a proper basis for planning options to mitigate urban climate changes in individual cities.

Whether Urban Development and Ecological Protection Can Achieve a Win-Win Situation—The Nonlinear Relationship between Urbanization and Ecosystem Service Value in China

Most of the existing research on urbanization suggests that urbanization leads to a decline in ecosystem services values (ESV). However, the impacts of industrial structure and changes in land use patterns on ESV have often been ignored. Using provincial data in China from 2003 to 2015, this study demonstrates the possibility of achieving a win-win situation regarding urbanization and ESV enhancement at the global and regional scales. The negative effect from production processes and the influence of residents’ preferences are considered in the evaluation of ESV. The impact of urbanization on ESV is empirically analyzed by using a spatially adaptive semi-parametric model in order to mitigate both endogeneity of the parametric model and the curse of dimensionality in nonparametric model. The results show that there is a U-shaped curve relationship between urbanization and ESV for the whole country. However, most provinces of China are still located at the left side of the U-shaped curve where urbanization reduces the ESV per capita. Central and local governments should strengthen differentiated land use policies, environmental regulations, and finance and tax policies to transform the industrial structure, so that each province may achieve a win-win situation regarding urbanization and ESV enhancement. Such policy changes would promote sustainable development in China.