Street Trees Research Articles

Monitoring drought impacts on street trees using remote sensing - Disentangling temporal and species-specific response patterns with Sentinel-2 imagery

Healthy street trees provide important ecosystem services to cities, but are under increasing stress from urbanisation and climate change, including drought. Traditional field observations are limited in their ability to provide city-wide and regular monitoring of the drought response of street trees, which is essential for their effective management. To overcome this, we propose a novel workflow using freely available remote sensing imagery from Sentinel-2 to identify temporal and species-specific drought response patterns of street trees. We evaluate the workflow on a sample of 2514 mature street trees of the seven most common street tree species in Leipzig, Germany. For each tree, we generate time series of eight vegetation indices from 2017 to 2022, namely enhanced vegetation index (EVI), normalised burn ratio (NBR) and normalised difference vegetation index (NDVI), each using the 10 m and 20 m resolution near-infrared band (EVI-10, EVI-20, NBR-10, NBR-20, NDVI-10, NDVI-20), as well as red edge normalised difference vegetation index (RENDVI) and red-green vegetation index (RGVI). They form the basis for a correlation analysis with the meteorological drought indicator standardised precipitation evapotranspiration index (SPEI) and for annual growing season integrals, which we subtract from those of the base year 2017. We use boxplots and statistical hypothesis testing to examine differences between and within tree species and years. The results show positive relationships between the eight vegetation indices and the SPEI, with the NBR-20 having the highest correlation coefficients. We also find significant differences in the drought response of several tree species, with Quercus robur being the most drought responsive and Platanus x acerifolia being the least. While most tree species have significantly smaller growing season integrals in the drought years 2018 and 2020 than in the non-drought years 2017 and 2021, the effects are not as pronounced in the drought years 2019 and 2022. Uncertainties arise, for example, from spectral signal variations caused by adjacent land use. Nevertheless, the proposed workflow holds promise for incorporation into holistic urban green management solutions and mixed-method approaches for further research into the causes and consequences of drought-induced damage to street trees.

Genome evolution of the ancient hexaploid Platanus × acerifolia (London planetree)

Whole-genome duplication (WGD; i.e., polyploidy) and chromosomal rearrangement (i.e., genome shuffling) significantly influence genome structure and organization. Many polyploids show extensive genome shuffling relative to their pre-WGD ancestors. No reference genome is currently available for Platanaceae (Proteales), one of the sister groups to the core eudicots. Moreover, Platanus × acerifolia (London planetree; Platanaceae) is a widely used street tree. Given the pivotal phylogenetic position of Platanus and its 2-y flowering transition, understanding its flowering-time regulatory mechanism has significant evolutionary implications; however, the impact of Platanus genome evolution on flowering-time genes remains unknown. Here, we assembled a high-quality, chromosome-level reference genome for P. × acerifolia using a phylogeny-based subgenome phasing method. Comparative genomic analyses revealed that P. × acerifolia (2n = 42) is an ancient hexaploid with three subgenomes resulting from two sequential WGD events; Platanus does not seem to share any WGD with other Proteales or with core eudicots. Each P. × acerifolia subgenome is highly similar in structure and content to the reconstructed pre-WGD ancestral eudicot genome without chromosomal rearrangements. The P. × acerifolia genome exhibits karyotypic stasis and gene sub-/neo-functionalization and lacks subgenome dominance. The copy number of flowering-time genes in P. × acerifolia has undergone an expansion compared to other noncore eudicots, mainly via the WGD events. Sub-/neo-functionalization of duplicated genes provided the genetic basis underlying the unique flowering-time regulation in P. × acerifolia. The P. × acerifolia reference genome will greatly expand understanding of the evolution of genome organization, genetic diversity, and flowering-time regulation in angiosperms.

Effect of street trees shade on perceived thermal comfort in a south temperate climate: The sidewalks of Montevideo (Uruguay)

The use of vegetation in cities is one of the most promising strategies for urban climate change adaptation and mitigation. Tree shade influences heat storage from surfaces reducing long wave radiation emission which directly affects people. People 's heat perception depends more on insolation and the temperature of surrounding objects than on air temperature itself. There is a need for analyzes that include the combined effects of physical and human variables on thermal comfort, as well as location-based studies to address its climatic and social conditions. In order to compare the effect of the trees on microenvironmental temperature and perceived thermal comfort, we measured physical parameters and performed structured interviews on three downtown streets of Montevideo, Uruguay, which had sections with and without trees on four dates during the summer. Generally, people surveyed under both treatments stated they did not feel fully comfortable due to summer heat, but the proportion of people who stated feeling in thermal comfort under tree shade was more than double than the unshaded sections.The seasonal ARIMA analysis supported that the tree shade reduced the microenvironmental temperature by its effect on radiant temperature. By using a statistical decision tree methodology that combines all the variables in the same analysis, we found a greater impact of physical variables than personal variables on people's thermal comfort and thermal preferences. We also identified gender as a significant variable that affects people's thermal preferences, where 46.4 % of females preferred a slightly colder environment.

국내․외 가로수 조성 및 관리 체계에 관한 연구†

국내․외 가로수 조성 및 관리 체계에 관한 연구†

The challenges of urban street trees and how to overcome them

The challenges of urban street trees and how to overcome them

Evaluating the effects of different tree species on enhancing outdoor thermal comfort in a post-industrial landscape

A frequently emphasized strategy to reduce the burden of heat in cities across the world is the implementation of street trees. Here, we examine the effects of deciduous and coniferous tree deployment on meteorological variables and pedestrian thermal comfort through analysis of the new dynamic thermal comfort (dPET) index, using the latest version of the computational fluid dynamics model ENVI-met. We performed on site observational measurements of air temperature (Ta), relative humidity (Rh), wind speed (Ws), and mean radiant temperature (MRT) at five different locations on the hottest day of summer 2023, in a post-industrial urban landscape located in Tehran, Iran. Observations were used to evaluate ENVI-met simulation performance and served as a baseline against which sensitivity experiments—based on a minimum (35%) and maximum (75%) intervention scenario for deciduous and coniferous trees—were compared against. Our analysis indicates that 35% and 75% deployment reduced Ta by 1.2 °C and 4.2 °C, respectively, for deciduous tree species, compared to a 0.9 °C and 3.1 °C reduction for coniferous species, during the hottest day of summer 2023. The maximum deployment scenario decreased MRT by approximately 60 °C and 43 °C for deciduous and coniferous tree deployment, respectively. The maximum tree deployment scenario decreased dPET by nearly 16 °C and 14 °C for deciduous and coniferous trees, respectively, during the time of day that diurnal heating is maximized. Our findings highlight micrometeorological and personalized thermal comfort effects associated with variable tree species type and extent through examination of a pedestrian’s ambulatory experience across diverse urban microclimates in a region of the world that is particularly understudied.

The ManhattAnt: identification, distribution, and colony structure of a new pest in New York City, Lasius emarginatus

An unidentified ant species was discovered in the heart of New York City in 2011, which garnered national headlines and created the memorable nickname “ManhattAnt.” New York City is one of the oldest and largest cities in North America and has been the site of introduction for some of North America’s most damaging invasive pests. Nevertheless, there has been little follow up research on the ManhattAnt since its discovery, and it has yet to be formally identified. Here we use genetic and morphological approaches to confirm the identity of the ManhattAnt and characterize its introduced range and colony structure. Results from genetic analyses placed the ManhattAnt within the Lasius emarginatus species complex, and morphological comparisons ruled out closely related species to identify the ManhattAnt as the European ant L. emarginatus with 93–99% certainty depending on the nest sample. Since its initial discovery in the region, the ManhattAnt has become one of the most common ants in New York City and has spread at a rate of 2 km/yr into New Jersey and onto Long Island. Based on the climate it inhabits within its native range, L. emarginatus could expand to cover much of the eastern United states from Massachusetts to Georgia. Although many successful invasive ants display supercoloniality with little aggression between neighboring nests, we found no evidence that L. emarginatus colonies in New York City are supercolonial. Continued monitoring of L. emarginatus is warranted, as it has been increasingly reported as an indoor pest and is known to form mutualisms with honeydew producing pests of street trees.

Study Roadmap Selection Based on the Thermal Comfort of Street Trees in Summer: A Case Study from a University Campus in China

The intensification of the urban heat island effect, characterized by persistent high temperatures in Chinese cities during summer, has led to notable shifts in urban residents’ activity patterns and travel preferences. Given that street trees, as fundamental components of urban road networks, have significant interaction with residents, it is imperative to investigate their thermal comfort impact. This study aims to enhance the comfortable summer travel experience for urban dwellers. Fujian Agriculture and Forestry University (FAFU) was selected as the case study site, with eight street tree species identified as measurement points. The summer solstice (21 June 2023) served as the representative weather condition. Through monitoring temperature and humidity, the study explored the correlation between street tree species, their characteristic factors, and thermal comfort. Utilizing ENVI-met and ArcGIS, the thermal comfort of campus travel routes was assessed, leading to the development of a summer travel guide based on thermal comfort considerations. The research novelty lies in applying a combined ENVI-met 5.0.2 and ArcGIS 10.8 software approach for modelling and visualizing the microclimate, which enables a more precise analysis of the thermal comfort variations of different campus paths, thus improving the accuracy and applicability of the results in urban planning. The findings reveal several points. (1) Different street trees possess varying capacities to enhance human comfort, with Falcataria falcata and Mangifera indica exhibiting the strongest cooling and humidifying effects, whereas Bauhinia purpurea and Amygdalus persica perform the poorest. Additionally, the research confirms ENVI-met’s scientific accuracy and practicality for microclimate studies. (2) The contribution of street trees to the comfort of campus road travel is primarily determined by the Sky View Factor (SVF), which negatively correlates with cooling and humidifying intensity and positively with thermal comfort. (3) During midday, travel comfort conditions on campus roads are better. Based on the thermal comfort assessment, a summer roadmap was created for the campus. In this case, the campus roads indicated by road A are considered the best travel routes in summer, and the roads indicated by roads B and C are considered alternatives for travelling. This practical application demonstrates how theoretical research results can be translated into practical tools for daily commuting and urban planning. It provides data references and empirical cases for the scientific optimization and enhancement of urban roads.

Uncovering the Role and Labor of Volunteer Leaders within a Community-Led Urban Tree Planting Initiative

Urban forestry programs across North America rely on volunteers to lead urban forest stewardship activities and encourage participation in tree planting and general maintenance. We examined the leadership structure of a tree planting initiative (TPI) in the greater Philadelphia region to understand the role and labor contributions of volunteer leaders, and the current challenges of achieving equitable urban tree canopy within community-led TPIs. Using an online survey, we found that leaders contribute unpaid labor, time, and skills within the following categories: group organization and communication, tree-planting and event coordination, tree care and maintenance, and broader environmental education and advocacy. Volunteer leaders also face challenges related to leadership and administrative tasks. This study deepens understandings of the labor needs within volunteer TPIs and potential ways to support the equitable growth of these initiatives moving forward. Future research is needed to understand recognitional equity gaps in volunteer leadership more broadly.

Dynamic Analysis of Street Trees in Vehicle-mounted LiDAR Point Clouds

Street trees, as key elements of urban road scenes, play a significant role in the overall ecological environment and aesthetics of city roads through their dynamic growth and changes. With the continuous development of urban roads, the growth conditions of street trees are also constantly changing. Therefore, studying how to infer the dynamic changes of roads through the variations in street trees is a highly valuable technical issue. This paper delves into several critical parameters of street trees, including diameter at breast height (DBH), tree height, trunk height, crown volume, and crown spread. By updating these parameters, determining transplantation and replanting decisions, and analyzing growth states, we comprehensively analyze the dynamic changes of street trees. To achieve this goal, we integrated multiple parameters into the analysis process of street trees and established a comprehensive analysis system centered on the DBH parameter. Combining this with data visualization technology, we provide an intuitive dynamic analysis method. Experimental results indicate that, compared to single-parameter analysis methods, the multi-parameter comprehensive analysis method demonstrates higher accuracy and stronger persuasive power in the study of dynamic changes in street trees, thereby validating the superiority and practicality of the proposed research algorithm. This research can provide more scientific and reliable references for urban road planning and management.

Exploring the spatial association between the distribution of temperature and urban morphology with green view index.

Urban heat islands will occur if city neighborhoods contain insufficient green spaces to create a comfortable environment, and residents' health will be adversely affected. Current satellite imagery can only effectively identify large-scale green spaces and cannot capture street trees or potted plants within three-dimensional building spaces. In this study, we used a deep convolutional neural network semantic segmentation model on Google Street View to extract environmental features at the neighborhood level in Taipei City, Taiwan, including the green vegetation index (GVI), building view factor, and sky view factor. Monthly temperature data from 2018 to 2021 with a 0.01° spatial resolution were used. We applied a linear mixed-effects model and geographically weighted regression to explore the association between pedestrian-level green spaces and ambient temperature, controlling for seasons, land use information, and traffic volume. Their results indicated that a higher GVI was significantly associated with lower ambient temperatures and temperature differences. Locations with higher traffic flows or specific land uses, such as religious or governmental, are associated with higher ambient temperatures. In conclusion, the GVI from street-view imagery at the community level can improve the understanding of urban green spaces and evaluate their effects in association with other social and environmental indicators.

Colletotrichum cliviicola as a new causal agent causing leaf spot disease on Tilia tomentosa moench (silver linden) in China

Tilia tomentosa Moench (silver linden) is a globally preferred option for landscaping and street tree planting. Its intentional introduction to China in recent years has led to widespread cultivation. In 2021, a leaf spot disease significantly impacted silver linden trees in a sentinel garden in China, with an average incidence and disease severity of 94.3% and 5.0, respectively, adversely affecting the trees' growth and development. In this investigation, potential fungal pathogens were isolated from the affected leaves, and Koch's postulate was subsequently employed to validate the pathogenicity of the fungal isolates (TM-1 and TM-2). The pathogen was unequivocally identified as Colletotrichum cliviicola through a combination of morphological observation and a multi-locus analysis (ITS, ACT, ApMat, CAL, CHS-1, GAPDH, and TUB2). This marks the first record of C. cliviicola affecting silver linden in China. The information provided a valuable foundation for the rapid detection and effective prevention and control of the diseases affecting linden trees.

Multistakeholder governance and community engagement in urban greening

Simone Borelli leads the Forestry Division at the Food and Agriculture Organization (FAO-ONU). He is one of the creators of the Tree Cities of the World Program and was invited to a conference at the “Congresso Brasileiro e Ibero-Americano de Arborização Urbana. Urban Forestry in the Decade of Ecosystem Restoration”, in sept-oct 2021. This event took place at the Federal University of Mato Grosso do Sul, and was promoted by the Graduate Program in Natural Resources (PGRN_UFMS), in partnership with the Graduate Program in Local Development, from the Catholic University D. Bosco (PGDL_UCDB) and the Brazilian Society of Urban Forestry (SBAU), the Brazil Chapter of International Society of Arboriculture (ISA). The interview was conducted after the event ended and reflects its commitment to the theme of green infrastructure and community involvement.

Estimation of the Living Vegetation Volume (LVV) for Individual Urban Street Trees Based on Vehicle-Mounted LiDAR Data

The living vegetation volume (LVV) can accurately describe the spatial structure of greening trees and quantitatively represent the relationship between this greening and its environment. Because of the mostly line shape distribution and the complex species of street trees, as well as interference from artificial objects, current LVV survey methods are normally limited in their efficiency and accuracy. In this study, we propose an improved methodology based on vehicle-mounted LiDAR data to estimate the LVV of urban street trees. First, a point-cloud-based CSP (comparative shortest-path) algorithm was used to segment the individual tree point clouds, and an artificial objects and low shrubs identification algorithm was developed to extract the street trees. Second, a DBSCAN (density-based spatial clustering of applications with noise) algorithm was utilized to remove the branch point clouds, and a bottom-up slicing method combined with the random sampling consistency iterative method algorithm (RANSAC) was employed to calculate the diameters of the tree trunks and obtain the canopy by comparing the variation in trunk diameters in the vertical direction. Finally, an envelope was fitted to the canopy point cloud using the adaptive AlphaShape algorithm to calculate the LVVs and their ecological benefits (e.g., O2 production and CO2 absorption). The results show that the CSP algorithm had a relatively high overall accuracy in segmenting individual trees (overall accuracy = 95.8%). The accuracies of the tree height and DBH extraction based on vehicle-mounted LiDAR point clouds were 1.66~3.92% (rRMSE) and 4.23~15.37% (rRMSE), respectively. For the plots on Zijin Mountain, the LVV contribution by the maple poplar was the highest (1049.667 m3), followed by the sycamore tree species (557.907 m3), and privet’s was the lowest (16.681 m3).

Urbanizational impact on climatic variables and geographical analysis of physical land use land cover variation of a city using Remote Sensing.

<p>Climate change has serious implications foron the rise and variation of the average earth’s temperature, and intensified rainfall. In urban areas, temperatures and intensified rainfall variation are noticeably seenin the city which disrupts the normal life of a living things. Also, it affects the storage of rainfall runoff water in tanks and lakes. Green cover reduction due to the increase ofagriculture, industrialization, population explosion and urbanization have a direct impact on the climate pattern.The average temperature of a city is increasing in every decade due to a drastic reduction in the green cover.This is visible today from the abnormal melting of glaciers. The rainfall pattern is highly intensified, and the frequency of rainfall is on the a decreasing trend. This intensified rainfall creates high surface runoff during rainfall and disrupts the normal life in a city. The Standard Precipitation Index (SPI) for a city indicates a noticeable shift in its climatic pattern, particularly with consistent rainfall during the southwest monsoon. Over the span of four decades, LULC research has revealed an increase in residential areas and a decrease in green cover. This urbanization process is associated with changes in LULC, resulting in decreased vegetation and diminished storage water bodies.Variations in the temperature of a city are on an increasing trend. Urban forestry or the dense green coverof an area reduces the temperature and creates cool pockets in the city. The regression model for temperature and vegetation indicates the negative correlation of temperature with high vegetation growth. Keywords: Urbanization, Climate change, Rainfall-runoff, Temperature, Green Cover</p>

Considering the composite tree attributes extracted by UAV can improve the accuracy of street tree species classification

Considering the composite tree attributes extracted by UAV can improve the accuracy of street tree species classification

Quantitative Study on the Effects of Street Geometries and Tree Configurations on the Outdoor Thermal Environment

Global warming and the urban heat island effect has aroused the attention of research on the outdoor thermal environment. As outdoor spaces often used by citizens, streets play an important role in improving the thermal environment. In this study, six factors relating to street geometries and tree configurations in Busan are measured and quantified to form 32 typical scenarios. The degree of importance of these six factors is evaluated based on ENVI-met simulation results, and GeoDetector is introduced to evaluate the interactions between the factors and their impacts on the outdoor thermal environment. This study confirms the significantly higher impact of street geometry factors on the air temperature and physiological equivalent temperature compared to tree configuration factors. Particularly, Hb/Ws shows the most significant impact during the research period. The impact of interactions between any two factors of street geometry is much higher than that of interactions between the geometry and tree configuration factors and that of interactions between the tree configuration factors. We recommend dynamically adjusting the relationship between street geometry and tree configurations in different situations to improve the outdoor thermal environment, especially at noon and in the afternoon.

Analysis of the Impact of Urban Green Spaces on Mitigating the Urban Heat Island Effect

The Urban Heat Island (UHI) effect, characterized by higher temperatures in urban areas compared to their rural surroundings, poses significant challenges for energy consumption, air quality, and public health. This study examines the impact of urban green spaces on mitigating the UHI effect in four major Spanish cities: Madrid, Barcelona, Seville, and Valencia. Using high-resolution satellite imagery, ground-based temperature measurements, and advanced GIS and statistical modeling techniques, we quantified the temperature differences between green and non-green urban areas. Our findings indicate that green spaces, including parks, street trees, and green roofs, significantly reduce urban temperatures, with parks exhibiting the highest cooling effects. The spatial analysis revealed that UHI hotspots are concentrated in densely built-up areas, while green spaces effectively mitigate these effects. Seasonal variations show that the cooling benefits of green spaces are more pronounced during the summer months. This study highlights the importance of incorporating diverse and well-distributed green spaces in urban planning to enhance thermal comfort, reduce energy consumption, and improve urban livability. Policy recommendations are provided to guide the integration of green infrastructure in climate adaptation strategies for Spanish cities.

Feasibility of constructed soils for tree planting – A pilot study in New York City

Constructed soils are soils that are created with a mixture of various materials. An innovative soil exchange program - the Clean Soil Bank (CSB) in New York City allows recycling of clean glacial outwash sediments excavated from depth at construction sites. One previous study showed that soils constructed from CSB sediment and compost can effectively support crop growth in community gardens, but no research has been conducted on its potential usage as a medium for tree growth. Moreover, biochar has been used to improve soil quality, but its efficacy for street trees incorporated into constructed soils has largely not been quantified in the field. The objective of this project was to evaluate the feasibility of using soils constructed from the CSB and compost for tree planting and to investigate the impact of biochar on tree performance. Thirty-six trees of two species (Maackia amurensis and Zelkova serrata) were planted in 2019, on the sidewalks of a residential-business neighborhood in Bronx, New York. Each tree pit contains one of three soil types: type A - existing and purchased topsoil mixed with 33% compost and biochar, type B - CSB sediment mixed with 33% compost, and type C - CSB sediment mixed with 33% compost and biochar. Soil samples were collected in 2019 (before planting) and in 2021. Tree health assessments were conducted in September 2020 and July 2021 using a protocol developed by the USDA Forest Service. Other tree health parameters collected include diameter at breast height (DBH), crown diameter, tree height, photosynthetic capacity, and foliar chemistry. Significant differences in bulk density, water holding capacity, and K, Fe, and Zn concentrations were found among the three soil types. However, comparison of tree performance and foliar chemistry showed no systematic differences among the three soil types. The results indicate that CSB sediment mixed with compost can be an effective replacement for purchased topsoil for tree growth. No evidence was found that biochar provides additional benefits to street tree performance. Considering the abundant availability of glacial outwash sediment at low cost to the city, as well as access to locally produced compost, constructed soils can be a reliable source of material for urban forestry programs.

Urban treescapes as everyday workplaces and knowledge battlegrounds: Lessons from Bangkok, Thailand

Urban greening expertise and programs are pursued and circulated globally to enhance urban livability and sustainability, but the outcomes are often mixed and are accompanied by side effects. Drawing on the concept of “worlding,” this paper examines the processes and outcomes of a training program that introduced tree climbing techniques from overseas to reduce the aggressive pruning practices by the municipal workforce in Bangkok, Thailand. Steered by Thai civil society organizations (CSOs) and international arborists, the training program was supported by the city government and local forestry experts. However, the outcomes were limited. A variety of temporal, logistical, and place-specific factors (including traffic, weather, size and accessibility of trees), constrained the applicability of the introduced techniques for pruning street trees in Bangkok. These crucial urban contextual factors were neglected in the training program design due to knowledge conflicts between the “civic experts” and “lay practitioners,” which undermined the potential of the training program. Illustrating urban treescapes as everyday workplaces and knowledge battlegrounds, this paper argues that aspirations for world-leading expertise might hamper the expression of tacit knowledge that stems from and coordinates with a specific urban context. The conclusion highlights the importance of inclusivity to achieve successful transnational circulation of greening expertise and broader urban transformative attempts involving global knowledge exchange.