Abstract
Background
Plants are sensitive to air pollution by altering their vital processes such as growth or photosynthesis. Leaf characteristics reflect the adaptive mechanism of plants to their ...environment. This mechanism is demonstrated through changes in anatomical, morphological, and physiological characteristics relative to environmental changes.
Methods
Samples were taken from 2 species of
Platanus orientalis
L. and
Celtis caucasica
Willd. in 10 urban forests of Tehran, Iran. In each study area, 50 leaves were collected from different directions of the canopy of each tree, and their area was measured by a leaf area meter instrument in a laboratory. Leaf moisture and specific leaf area (SLA) were also calculated. The data of air pollutants were obtained from the nearest pollution measurement stations to each study location.
Results
The average percentage of moisture for
P. orientalis
and
C. caucasica
was calculated as 49.6% and 41.9%, respectively. The averages of SLA were estimated 9.2 and 6.5 cm
2
/g, respectively. The average leaf area was 36 and 6.04 cm
2
, respectively. The correlation between quantitative variables of leaf (leaf area and SLA) and air pollutant appeared in both study species, only there was a significant negative relationship between leaf area and O
3
. This relationship was stronger in
C. caucasica
(
R
2
= −0.78).
Conclusion
The results of this research showed that both species showed similar behavior against air pollutants, but
C. caucasica
showed more reaction.
Intensifying the proportion of urban green infrastructure has been considered as one of the remedies for air pollution levels in cities, yet the impact of numerous vegetation types deployed in ...different built environments has to be fully synthesised and quantified. This review examined published literature on neighbourhood air quality modifications by green interventions. Studies were evaluated that discussed personal exposure to local sources of air pollution under the presence of vegetation in open road and built-up street canyon environments. Further, we critically evaluated the available literature to provide a better understanding of the interactions between vegetation and surrounding built-up environments and ascertain means of reducing local air pollution exposure using green infrastructure. The net effects of vegetation in each built-up environment are also summarised and possible recommendations for the future design of green infrastructure are proposed. In a street canyon environment, high-level vegetation canopies (trees) led to a deterioration in air quality, while low-level green infrastructure (hedges) improved air quality conditions. For open road conditions, wide, low porosity and tall vegetation leads to downwind pollutant reductions while gaps and high porosity vegetation could lead to no improvement or even deteriorated air quality. The review considers that generic recommendations can be provided for vegetation barriers in open road conditions. Green walls and roofs on building envelopes can also be used as effective air pollution abatement measures. The critical evaluation of the fundamental concepts and the amalgamation of key technical features of past studies by this review could assist urban planners to design and implement green infrastructures in the built environment.
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•Green infrastructure can play a significant role in mitigating urban air pollution.•Air quality changes in local built environments due to vegetation are assessed.•Low-level hedges improves air quality in street canyons unlike high-level trees.•Green green walls and roofs are effective to reduce pollution in streets/open roads.•Prior design of green infrastructure should be performed for improving air quality.
Catastrophic windstorms attributed to climate change are expected to increase in the upcoming period, causing damage to trees, particularly in tropical climates where most damage arises during ...storms. In October 2019, the city of Viçosa (Minas Gerais, Brazil) was affected by heavy rain and winds of 82.4 km/h. It provoked extensive damage to the urban trees on the university campus, where individuals of the Spathodea campanulata were affected. The objective of this study was (1) to determine tree failure parameters - previous studies were used to assess the tree risk failure of the species and its diagnosis after an extreme climatic event - and (2) to classify the damage as: irreversible, intermediate and without damage according to the parameters on the evaluation form. An analysis was carried out considering whether the damage class parameters were observed, discarding the weights assigned to each one (originally applied by the methodology). Later these weights were used in the application of Fisher's statistical tests and Pearson's Chi-Square. The general analysis indicated that among 28 parameters used in the visual evaluation, nine were associated with the occurrence of irreversible damage to the trees. After the statistical analysis, the conclusions indicated that six of the parameters were significant.
Greenspaces and urban trees play an important role in moderating and improving urban environments to make them more comfortable and healthy for people. While trees provide important wellbeing ...benefits to people, urban planning and maintenance practices can create inhospitable and stressful environments where trees are unable to flourish or reach their potential. As the impacts of climate change intensify, the health of urban trees will become increasingly important. To explore how planning and maintenance practices are affecting urban trees, we draw on a case study of 31 street and park trees adjacent to high-use pedestrian areas in Wellington, New Zealand. We analysed these trees using six key factors that influence tree health to identify how planning and maintenance practices could be adjusted to support tree health and ecosystem function. We suggest that the six key factors have planning and maintenance implications for urban trees which are relevant to a variety of urban contexts, but particularly space-constrained urban streets requiring multiple functions and infrastructure. We argue that as climate impacts intensify, using these six key factors can help promote urban tree health and ecosystem function and avoid mal-adaptive planning and maintenance practices.
Moderation of thermal energy balance through the canopies of urban trees is well known. However, a more functional and quantitative view of the heterogeneous urban environment and their influence on ...the below-canopy vertical air temperature gradients is largely missing. Throughout the summer 2016 we continuously measured air temperature at three different heights (at 1.5, 3 and 4.5m from the ground) under the canopies of two common but contrasting street tree species in respect of eco-physiology and morphology in Munich, Germany: Robinia pseudoacacia L. (ring porous) and Tilia cordata Mill. (diffuse porous). Along with air and surface temperature we also measured meteorological and edaphic variables and categorized summer time as cool, mild, summer and hot days. Global radiation, vapour pressure deficit and soil temperature increased as the days got warmer but precipitation, soil moisture and wind speed showed the reversed pattern. Overall, T. cordata trees with higher leaf area index and sap-wood area provided three times more transpiration than R. pseudoacacia. On an average air temperature gradient of outside to inside canopy dropped from 1.8°C to 1.3°C for T. cordata but from 1.5°C to only 0.5°C for R. pseudoacacia as the days got warmer. Vertical decline of air cooling effect was around 1°C from canopy to the near-ground (1.5m). Lower soil moisture but higher soil temperature suggested that cool air from the canopy mixed with a higher amount of sensible heat flux under the canopies of T. cordata compared to the R. pseudoacacia as the days got warmer. The study indicated a threshold for extreme hot days when grass surface evapotranspirational cooling will not be as effective and act like built surfaces rather deep shading from tree canopies will be important.
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•Below-canopy cooling benefits of tree species can vary depending on weather types.•We studied air temperature from the tree canopies to the ground under tree shades.•20 Robinia pseudoacacia and Tilia cordata trees were studied during the summer 2016.•Shading is the prominent cooling benefits when the days are very hot.•Transpirational cooling from trees and grasses are prominent in mild or summer days.
•Three greening species were exposed to 5 O3 concentrations in 15 open-top chambers.•A stomatal multiplicative model was individually parameterized for the three species.•Concentration and flux-based ...O3 response relationships for Asat were established.•The performance of both types of metrics for risk assessment was similar for any species.•Current ambient O3 concentration in China damages plant photosynthesis.
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The relationships of CO2 assimilation under saturated-light conditions (Asat) with exposure- (AOTX, Accumulated Ozone exposure over a hourly Threshold of X ppb) and flux-based (PODY, Phytotoxic Ozone Dose over a hourly threshold Y nmol·m−2·s−1) O3 metrics was studied on three common urban trees, Fraxinus chinensis (FC), Platanus orientalis (PO) and Robinia pseudoacacia (RP). Parameterizations for a stomatal multiplicative model were proposed for the three species. RP was the species showing lower species-specific maximum stomatal conductance (gmax) and experiencing lower cumulative O3 uptake along the experiment, but in contrast it was the most sensitive to O3. PODY was slightly better than AOTX metric at estimating relative Asat (R-Asat)for PO and RB but not for FC. The best fittings obtained for the regressions between R-Asat and AOTX for FC, PO and RP were 0.904, 0.868, and 0.876, when the thresholds of X were 60ppb, 55ppb and 30ppb, respectively. However, AOT40 performed also well for all of them, with R2 always >0.83. For PODY, the highest R2 values for FC, PO and RB were 0.863, 0.897 and 0.911 at thresholds Y=7, 5 and 1nmolO3m−2s−1, respectively. Given the potentially higher O3 removal capacity of FC and PO by stomatal uptake and their lower sensitivity to this pollutant than RP, the former two species would be appropriate for urban gardens and areas where O3 levels are high. Parameterization and modeling of stomatal conductance for the main urban tree species may provide reliable estimations of the stomatal uptake of O3 and other gaseous pollutants by vegetation, which may support decision making on the most suitable species for green urban planning in polluted areas.
•Current methods to map urban trees are hindered by high costs or poor resolution.•Computer vision is used to quantify urban tree cover from street view images.•A multi-step algorithm accurately ...segments the percent of tree cover in an image.•Modeling the relationship between neighbouring images increases predictive accuracy.•Computer vision can map urban tree cover at high spatial resolution with rapid throughput.
Traditional tools to map the distribution of urban green space have been hindered by either high cost and labour inputs or poor spatial resolution given the complex spatial structure of urban landscapes. What’s more, those tools do not observe the urban landscape from a perspective in which citizens experience a city. We test a novel application of computer vision to quantify urban tree cover at the street-level. We do so by utilizing the open-source image data of city streetscapes that is now abundant (Google Street View). We show that a multi-step computer vision algorithm segments and quantifies the percent of tree cover in streetscape images to a high degree of precision. By then modelling the relationship between neighbouring images along city street segments, we are able to extend this image representation and estimate the amount of perceived tree cover in city streetscapes to a relatively high level of accuracy for an entire city. Though not a replacement for high resolution remote sensing (e.g., aerial LiDAR) or intensive field surveys, the method provides a new multi-feature metric of urban tree cover that quantifies tree presence and distribution from the same viewpoint in which citizens experience and see the urban landscape.
Abstract
The importance of urban tree diversity for improving resilience is
increasingly understood by decision makers. Urban foresters want to prevent
the overrepresentation of species on their ...streets and in their city, which
could result in a significant loss of canopy cover in the event of a
large-scale disturbance such as a drought or an exotic pest or disease.
Although numerous software and tools exist to visualize tree inventories and
plan tree maintenance work, only a few offer support for increasing tree
diversity. After reviewing the existing tools available for urban forest
managers, we present SylvCiT, a novel decision-support and open-source
software available on a web platform designed to consolidate information
related to the urban forest in one place and facilitate decision-making at
different scales. While the first interfaces provide the user with a
spatially explicit portrait of the urban forest (species richness,
functional diversity, structural diversity, i.e., diameter classes) and
associated ecosystem benefits (e.g., stored carbon, ornamental value), the
software is designed to produce a list of functional groups and appropriate
species to plant considering tree species already present. Based on an
artificial intelligence algorithm, SylvCiT identifies the types of trees
(species and functional groups) that are absent or underrepresented at
different scales to make recommendations that increase species and
functional diversity to improve resilience to global change. SylvCiT will
continue to be developed to evaluate other ecosystem benefits and integrate
criteria such as site characteristics into the recommendation
algorithm.
Urban forests are recognized for their multiple benefits to society, and increasingly so with climate change. However, they too are threatened by increased heat, pollution, and higher risks of pest ...outbreaks. Increasing the diversity of tree species in urban forests is crucial for enhancing their resilience by reducing the risk of mass tree losses. Yet, we lack the most important ingredient to act: knowledge. Traditionally, urban tree inventories only include trees on public land. This study describes the first urban forest research plot established in Montreal, Canada, encompassing 1567 trees on public and private (residential and institutional) lands from 84 species and 43 genera. Our paper significantly contributes to the existing body of knowledge by providing empirical data that enhances our understanding and provides a clearer picture of urban forests, particularly concerning total tree diversity, across public and private lands. We found that tree abundance and diversity differed depending on land ownership: the public urban forest included more trees and was slightly more diverse than the private urban forest. Acer emerged as the most abundant genus, and small trees dominated all ownership categories. Importantly, the species composition of trees in public and private spaces differed, increasing the overall diversity. Of particular interest was the presence of three species on private property that were not recorded in the larger public tree inventory. Developing inventory practices that include private trees can provide insight to strategically enhance tree diversity where needed and maximize the benefits that diverse urban forests provide.
•Diversity in the urban forest improves resilience and enhances ecosystem services.•Most urban tree inventories only include trees located on public land.•Focusing on public trees may lead to underestimating diversity and resilience.•Tree abundance and diversity differ depending on land ownership type.
Urban trees are often not considered in air-quality models although they can significantly impact the concentrations of pollutants. Gas and particles can deposit on leaf surfaces, lowering their ...concentrations, but the tree crown aerodynamic effect is antagonist, limiting the dispersion of pollutants in streets. Furthermore, trees emit Biogenic Volatile Organic Compounds (BVOCs) that react with other compounds to form ozone and secondary organic aerosols. This study aims to quantify the impacts of these three tree effects (dry deposition, aerodynamic effect and BVOC emissions) on air quality from the regional to the street scale over Paris city. Each tree effect is added in the model chain CHIMERE/MUNICH/SSH-aerosol. The tree location and characteristics are determined using the Paris tree inventory, combined with allometric equations. The air-quality simulations are performed over June and July 2022. The results show that the aerodynamic tree effect increases the concentrations of gas and particles emitted in streets, such as NOx (+4.6 % on average in streets with trees and up to +37 % for NO2). This effect increases with the tree Leaf Area Index and it is more important in streets with high traffic, suggesting to limit the planting of trees with large crowns on high-traffic streets. The effect of dry deposition of gas and particles on leaves is very limited, reducing the concentrations of O3 concentrations by −0.6 % on average and at most −2.5 %. Tree biogenic emissions largely increase the isoprene and monoterpene concentrations, bringing the simulated concentrations closer to observations. Over the two-week sensitivity analysis, biogenic emissions induce an increase of O3, organic particles and PM2.5 street concentrations by respectively +1.1, +2.4 and + 0.5 % on average over all streets. This concentration increase may reach locally +3.5, +12.3 and + 2.9 % respectively for O3, organic particles and PM2.5, suggesting to prefer the plantation of low-emitting VOC species in cities.
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•The aerodynamic effect impacts significantly concentrations of species emitted in streets.•Biogenic emissions induce mainly an increase in organic particles concentrations.•Dry deposition on leaves induces a low decrease in gas and particle concentrations.•Planting of trees with large crowns on high-traffic streets should be avoided.•Tree species that emit few terpenes should be favored in cities.
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