Urban Tree Health Research Articles

Urban tree health assessment using multifaceted remote sensing datasets: A case study in Hong Kong

Although climate change is impacting various aspects of our environment, it is important to note that the overall risk to trees remains low, especially in urban areas like Hong Kong where the benefits of trees to society are significant. The trees planted in an urban setting are isolated and have several limiting factors including, excessive run-off, urban pollution, physical damage and limited root growth, which sometimes lead for tree failure incidents. The conventional on-site tree health assessment method is time consuming thus, requiring a remote sensing based method to effectively and routinely monitor the health status of urban trees. In this study several types of remote sensing datasets have been exploited to assess the health status of more than 700 Old and Valuable Trees (OVTs) and Stone Wall Trees (SWTs) around Hong Kong. These datasets include the data from Terrestrial LiDAR (Light Detection and Ranging) Surveys (TLS), Handheld Laser Scanner (HLS), Airborne LiDAR Surveys (ALS) and airborne multispectral data. For validation purpose, the in situ tree parameters data was also obtained from the Tree Management Office (TMO) of the Greening, Landscape & Tree Management Section (GLTMS) under the Development Bureau of the Hong Kong SAR Government. The results have indicated that over the period of four years (2017–2020) there has been a decline in the health of some target trees which can be attributed to the increased infestation rate in trees and severe weather conditions. The usage of LiDAR data has supported the fact that different tree structural forms can effectively be extracted and can help making informed decisions on the precise health conditions of urban trees.

Stakeholder exposure to and knowledge of tree pests and diseases and their management in urban areas

Urban trees and forests provide many benefits to the urban environment and are important for climate change adaptation. Yet, they are increasingly threatened by insect pests and diseases, hereafter tree pests/diseases. There is little evidence of the risk awareness and knowledge of different urban stakeholders of this growing threat, how they are affected by tree pests/diseases, and how they might respond to it. To fill this gap, we undertook an online survey of different key stakeholder groups associated with urban trees and forests in Germany. A majority of 75.8 % of the 186 respondents consider urban tree pests/diseases a severe problem and 51.1 % reported high knowledge of tree pests/diseases. There was a lack of knowledge of certain reportable quarantine pests/diseases (e.g., canker stain of plane, emerald ash borer, Xylella) and pest/disease management options (e.g., manual treatment methods and tree diversification). Respondents were most affected by the horse chestnut leafminer (61.3 %), ash dieback (58.1 %) and oak processionary moth (50.0 %). The most widely used pest remedial measures were improvements of tree living conditions (60.8 %) and purchases of plants from certified or trusted local sources (59.7 %). Multiple correspondence analysis showed a significant association between levels of knowledge of tree pests/diseases and pest management responses (11.7 %). Our results suggest that future efforts to improve urban tree health should be enhanced and tailored to the different requirements of various stakeholder groups. The findings of this first comprehensive study with a purely urban focus will inform the development of future activities that prevent or reduce the spread of tree pests/diseases in urban areas. Data AvailabilityThe survey respondents did not give permission for the full data to be accessed or used by third parties.

Trees in Sponge Cities—A Systematic Review of Trees as a Component of Blue-Green Infrastructure, Vegetation Engineering Principles, and Stormwater Management

Combining street trees with stormwater management measures can, in some circumstances, both increase tree vitality and reduce the risk of flooding by directing stormwater into tree pits. Using systematic review methods, this study aimed to provide an overview of the vegetation engineering systems being researched and applied that combine tree planting with urban stormwater management. We also sought to identify the positive as well as possible negative impacts on urban hydrology and tree health. It has been shown that diverting rainwater from impervious surfaces into tree pits has considerable potential for stormwater management and for improving tree health by reducing drought stress in urban trees. Worldwide approaches to optimizing tree pits for rainwater infiltration and water supply are promising. Different systems and substrate types have been tested, and street trees generally show good vitality, although systematic long-term monitoring of tree vitality has rarely been undertaken. There is still a need for research into temporary water storage for dry periods.

Water Availability Determines Tree Growth and Physiological Response to Biotic and Abiotic Stress in a Temperate North American Urban Forest

Warmer temperatures and frequent drought directly affect urban tree health. Both abiotic conditions also affect tree health via increased density of some insect pests. Warming is predicted to benefit urban trees by increasing carbon sequestration and allocation to biomass. However, increased drought and pests are rarely considered despite often co-occurring with heat. To determine the combined effects of these abiotic and biotic factors, we manipulated water availability for established urban red maple trees across a gradient of warming and pest density and measured leaf-level processes and tree growth over two years. We find that water availability is a major determinant of tree growth, physiological processes, and resilience to urban stress factors. Maples performed better with more water, which also made them resistant to effects of temperature and pest density. However, when drought became too severe, leaf-level processes declined with warming. Tree basal area growth was unaffected after two years, but stem elongation increased with increasing water, temperature, and pest density. We discuss potential mechanisms driving these responses and the implications in the context of urban forest management. Urban forest designs that reduce drought and align species adaptations to local conditions are critical for designing more resilient and productive urban forests.

干旱区绿洲城市树木健康评估及影响因素——以乌鲁木齐市为例

PDF HTML阅读 XML下载 导出引用 引用提醒 干旱区绿洲城市树木健康评估及影响因素——以乌鲁木齐市为例 DOI: 10.5846/stxb202106111558 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31770750，31971713） Health assessment of urban trees in arid land oasis cities and its influencing factors: a case study of Urumqi Author: Affiliation: Fund Project: The National Natural Science Foundation of China (31770750，31971713) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:树木作为城市绿色基础设施重要组分，其健康直接影响城市生态系统服务及人居环境质量。城市化进程加快导致生态土地缺失，同时缺乏合理养护加之极端自然条件干扰对树木健康造成严重威胁。为揭示城市树木健康风险及影响因素，对乌鲁木齐市核心城区117个样地绿化树木进行健康评估，从4个维度12个指标构建树木健康分级体系，基于样地调查结果，分析树木组成、结构、关联性、健康状况及影响因素，揭示乌鲁木齐市不同功能区树木健康差异。旨在为研究区树木健康保护、城市绿地可持续经营及城市生态文明建设提供理论依据和数据支撑。结果表明：（1）乌鲁木齐市城市园林树木乔灌比为8.3 ： 1，树木多样性与种间关联程度较低。榆树占比高达43.87%，其中白榆占比22.62%，是主要优势树种；（2）不同树种健康程度呈现差异性，榆树类健康状况呈现圆冠榆 > 大叶榆 > 白榆 > 垂枝榆特征；（3）城市不同功能区树木健康也呈现异质性；以公园和居住小区树木健康分值较高，而行道树和学校庭院树木健康分值相对较低，且冗余分析进一步揭示地面铺装、林木配置结构、生长空间和胸径对树木健康影响程度最为显著。未来优化城市树木生境条件、提升物种丰富度、加强古树名木保育和提高园林绿化管理水平是维护和提升绿洲城市树木健康的重要举措。 Abstract:Urban green space is an important natural and heterogeneous component of urban landscape, which plays an important role in providing urban ecosystem services and improving residents' well-being. As an important component of urban green infrastructure, the health status of urban trees directly affects urban ecosystem services and the quality of human settlement environments. The accelerated urbanization process leads to the loss of ecological land, and the lack of reasonable maintenance and the disturbance of extreme natural conditions pose a serious threat to the health of urban trees, affecting the effective development of the ecological, social and economic benefits of trees. In order to find the risk and influencing factors of urban tree health, a tree health index system was constructed from 4 dimensions and 12 indexes. Based on the survey of 117 sample plots in core urban area of Urumqi, through analyzing the tree composition, structure, association, health status and its influencing factors, the differences of tree health are revealed in different functional zones. The purpose is to provide theoretical basis and data support for tree health protection and sustainable management of urban green space in the study area, which is of great significance to play the landscape service function of green space and improve the degree of urban ecological civilization. The results show that:(1) the average ratio of trees to shrubs in core urban areas in Urumqi is 8.3:1; especially, the tree species diversity, inter and intra correlation of urban green species are low. Elm (Ulmus spp.) accounts for 43.87% of the total urban trees, of which Ulmus pumila accounts for 22.62%, which is the main dominant tree species. (2) There are some differences of the health status between different Elm species. The overall health status of the Elm species elaborates the characteristics of Ulmus densa > Ulmus laevis > Ulmus pumila > Ulmus pumila cv. pendula. (3) The tree health presents heterogeneity in different urban functional zones, which main public parks and residential areas are higher, while roadside and schools are relatively lower. The redundancy analysis further reveals that ground pavement, tree configuration structure, growth space and diameter at breast height (DBH) have the greatest contribution on the tree health. In the future, optimizing urban tree habitat conditions, improving species richness, strengthening conservation of ancient trees and improving landscape planning and management level are important measures to maintain and improve the health status of urban trees in arid land oasis cities. 参考文献 相似文献 引证文献

Preliminary study of canker disease for development of urban tree health standard in Malaysia

Canker disease (CD) mainly infected trees planted in urban areas in Malaysia. This disease is caused by several plant pathogens and may cause tree death and tree failure. The aims of this study are to identify tree species which are susceptible to canker diseases and to identify the causal agents especially plant pathogens of the disease. To perform the study, a survey on planted trees in several urban parks and sites in Malaysia were conducted. In this study, the Canker Disease (CD) assessment procedure was developed and modified from Thousand Cankers Disease Survey Guidelines by the United State Department of Agriculture (USDA). Later, the assessment procedure was improved based on surveys in the ground to fit and get the best quality of data from the observations. As a result, several canker diseases were identified on twenty-three (23) trees, the species were, Acacia sp, Bucida molineti, Cinnamomum iners, Citrus sp, Eucalyptus urograndis, Eucalyptus camaldulensis, Eucalyptus sp, Khaya grandifoliola, Mangifera indica, Manilkara zapota, Mimusops elengi, Peltophorum indicus, Samanea saman, Swietenia macrophylla, Swietenia spicifera, Tabebuia argentea, Terminalia catappa, Terminalia mantaly, Araucaria heterophylla, Casuarina equisetifolia, Gymnostoma sumatrana and Polyalthia longifolia. Based on symptom development the canker diseases known as Sphaeropsis canker, Cryphonectria canker, Chrysoporthe canker, Biscogniauxia canker, Hypoxylon canker, Cypress canker, Nectria canker, Ceratocystis Wilt, Pink disease, and Slime flux disease. This study can be the starting point in developing the Canker Disease (CD) Assessment Standard in Malaysia. It is important for Malaysia to have a Canker Disease (CD) Assessment Standard in order to become a guideline for future study or research that specifies canker disease towards common trees planted in Malaysia especially the urban areas.

Effect of urban tree diversity and condition on surface temperature at the city block scale

Urban forests affect land surface temperature (LST) within a city due to the cooling effect of transpiration. The latter depends on tree health, but it can also be affected by the structure and composition of forest, as a mono-species environment may potentially worsen the health of urban forest. The following hypotheses are therefore proposed: a) greater tree diversity within urban forest results in lower LST at the city block scale; and b) the state of biotic disturbance of urban forest is negatively correlated with LST. The present research explores the relationship between urban forest tree diversity and health based on a survey of 38,950 individuals in the district of Providencia in the city of Santiago, Chile, and compares this information against LST data from the ASTER satellite instrument at the city block scale. The health of the urban forest was determined by expert knowledge means of a field survey that collected data concerning growth stage, phytosanitary state, and state of biotic disturbance. The first hypothesis could not be tested by the lack of urban tree diversity which showed strong domination of three species with more than 52 % of abundance (Robinia pseudoacacia, Platanus orientalis and Acer negundo). The second hypothesis was proved since the results revealed a positive and significant correlation between urban forest diversity and LST, with a Spearman’s correlation coefficient of between 0.56 and 0.7. A positive and significant correlation of 0.55 was found between mean biotic disturbance (BDSm) and median LST (Med), indicating a direct relationship between higher LST and poorer urban forest health. A possible explanation is that, among the trees surveyed within the urban forest, the effect of biotic disturbance is greater than that of species diversity. As such, it may be concluded that planting of trees on city streets as a means of temperature moderation is made less effective if specimens are maintained in a poor general condition of health.

Suggested key variables for assessment of soil quality in urban roadside tree systems

Urban roadside soils are important growth media for roadside trees. However, typical assessment variables are limited in describing the characteristics of roadside soils. We assessed the characteristics of roadside soils using the pre- and new suggested variables and recommended optimal soil variables that are representative of roadside tree health. Seventy-three roadside soils were collected for measurement, while six urban forest soils were prepared as a control. Samples were used to evaluate both pre-suggested and new variables. The former included bulk density, penetration resistance (PR), pH, organic matter (OM), fluorescein diacetate (FDA) activity, and respiration. To improve the pre-suggested variables, we modified the bulk density using PR and investigated the elemental ratios and stable isotopic signatures of particulate organic matter (POM). Two criteria were used to select the variables for urban roadside soils: (1) the variable should identify distinct characteristics of roadside and urban forest soils and (2) the variable should have a high correlation with urban tree health variables: leaf chlorophyll content and tree vigor. The bulk density measured using the conventional method underestimated soil compaction because obtaining intact cores was challenging. The modified bulk density (BDmodified) obtained from the soil PR is suggested to better represent soil compaction. The roadside soils were affected by de-icing materials, construction debris, and atmospheric alkali particles, which increased the soil pH. The unexpectedly higher OM contents in the roadside soils, where tree origins are limited, possibly due to soil OM sources such as vehicular emissions, animal excreta, and sewer flooding. These OM sources may alter the C/H ratio (POM-C/H) and the stable isotopic signature of POM, leading to OM quality changes. Soil respiration better reflected the changes in the microbial activity of the roadside soils, rather than FDA activity. The newly suggested soil variables, BDmofieid, pH, POM-C/H, and RES, were significantly correlated with leaf chlorophyll content and tree vigor (P < 0.05). Using a multiple regression analysis, the newly suggested set of soil variables, including the BDmodified, soil pH, POM-C/H, and soil respiration, showed high predictive power for the growth of urban roadside trees. Future studies should apply these variables to other cities or broader areas and confirm their predictive ability regarding the health of roadside trees.

The Ectomycorrhizal Community of Crimean Linden Trees in Warsaw, Poland

Urban trees provide many ecosystem services essential to city dwellers well-being. Ectomycorrhizal (ECM) fungi are symbionts for trees and may also contribute to urban tree health and thus maintenance of the ecosystem services. However, no studies so far have analysed the composition of the ECM community colonising Crimean linden. In this study we investigated ECM associations of Crimean linden trees in the urban environment, comparing street trees with those growing in a park. Moreover, we studied the ECM community of healthy versus unhealthy linden trees growing along a street. The health status of each tree was assessed using tree health indicators. The smallest degree ECM colonisation was observed in unhealthy street trees (40.5%). Cenococcum geophilum was found to be the most abundant ECM fungal species of the Crimean linden growing in the park (23.9%). Our results suggest that the linden trees growing in the park and those growing along the street but without disease symptoms did not differ in their ECM richness. However, the unhealthy street trees showed less ECM diversity and abundance. Moreover, strong negative correlations between the concentrations of Na and Cl in the soil and ECM colonisation were found. This study describes, for the first time, the ECM fungal community on Tilia “Euchlora” trees grown in Europe. We report novel findings on the ECM associations of Crimean linden trees in an urban ecosystem. Further research should focus on the role of native mycorrhizal fungal communities in nutrient acquisition by urban trees in the presence of salt stress.

Urban Tree Health Classification Across Tree Species by Combining Airborne Laser Scanning and Imaging Spectroscopy

Declining urban tree health can affect critical ecosystem services, such as air quality improvement, temperature moderation, carbon storage, and biodiversity conservation. The application of state-of-the-art remote sensing data to characterize tree health has been widely examined in forest ecosystems. However, such application to urban trees has not yet been fully explored—due to the presence of heterogeneous tree species and backgrounds, severely complicating the classification of tree health using remote sensing information. In this study, tree health was represented by a set of field-assessed tree health indicators (defoliation, discoloration, and a combination thereof), which were classified using airborne laser scanning (ALS) and hyperspectral imagery (HSI) with a Random Forest classifier. Different classification scenarios were established aiming at: (i) Comparing the performance of ALS data, HSI and their combination, and (ii) examining to what extent tree species mixtures affect classification accuracy. Our results show that although the predictive power of ALS and HSI indices varied between tree species and tree health indicators, overall ALS indices performed better. The combined use of both ALS and HSI indices results in the highest accuracy, with weighted kappa coefficients (Kc) ranging from 0.53 to 0.79 and overall accuracy ranging from 0.81 to 0.89. Overall, the most informative remote sensing indices indicating urban tree health are ALS indices related to point density, tree size, and shape, and HSI indices associated with chlorophyll absorption. Our results further indicate that a species-specific modelling approach is advisable (Kc points improved by 0.07 on average compared with a mixed species modelling approach). Our study constitutes a basis for future urban tree health monitoring, which will enable managers to guide early remediation management.

Natural gas leaks and tree death: A first-look case-control study of urban trees in Chelsea, MA USA

Urban vegetation is associated with numerous public health benefits; however, urban tree canopies may be threatened by fugitive methane exposure from leaky natural gas distribution systems. Despite anecdotal evidence of the harmful impacts of natural gas leaks on urban tree decline, the relationship between soil gas exposure and tree health has not been formally quantified in an urban setting. We conducted a case-control study to compare soil natural gas exposure in sidewalk tree pits of healthy and dead or dying trees in Chelsea, Massachusetts, during summer 2019. We measured soil concentrations of methane and oxygen at four points around the trunks of 84 case and 97 control trees. We determined that case trees had 30 times the odds of being exposed to detectable levels of soil methane relative to the control trees sampled (95% CI = 3.93, 229). Among tree pits with elevated soil gas, we also found that methane concentrations were highest on the side of the tree pit closest to the street. These results contribute evidence to support the widespread belief that soil methane exposure can negatively impact urban tree health. They also suggest that fugitive methane leakage from urban natural gas distribution systems beneath the street surface may be responsible for elevated soil gas concentrations in sidewalk tree pits and subsequent tree death.

Prioritization and Planning to Improve Urban Tree Health in the Chicago Region

The Chicago Region Trees Initiative (CRTI) has collected one of the largest data sets on urban forestry in the United States. This data informs where and how CRTI prioritizes its work and capacity building. This data has been incorporated into interactive online resources that communities and neighborhoods can access to help decision makers, landowners, and managers understand where and what to plant, the value of the urban forest, impacts of woody invasive species, heat island challenges, and where opportunities exist for oak ecosystem enhancement. This data helps CRTI and its partners to prioritize action.

Mapping heat and traffic stress of urban park vegetation based on satellite imagery - A comparison of Bucharest, Romania and Leipzig, Germany

Large and comparatively compact European cities such as Bucharest and Leipzig struggle with considerable urban heat island (UHI) effects characterized by heat and drought together with high concentrations of air pollutants (NO2, SO2, O3, CO2). However, a healthy urban green infrastructure is necessary to reduce the impacts of UHI on human health. Therefore, continuous monitoring schemes are required for green infrastructure in order to improve human life in such cities. Satellite remote sensing can provide the means for monitoring urban vegetation status. In this study, vegetation indices, mostly based on the spectral bands located in the red-edge region, were computed from Sentinel-2 imagery, and land surface temperature (hereafter LST) was estimated from Landsat 8 data. The aim was to assess the individual and cumulative effects of both vicinity to roads and estimated LST on tree vegetation health in urban parks using analysis of variance. Vegetation indices indicated stressed vegetation. However, tracking urban tree health required a combination of indices, and therefore of spectral ranges, rather than one specific index alone, as the effect sizes varied between parks, cities and along the centre-periphery gradient. Therefore, spaceborne data can provide spatially-explicit indicators for stressed urban vegetation and, thus, decreasing ecosystem services delivery. Future studies are encouraged to decipher further the relation the spatial configuration of urban systems and remote sensing based stress indicators of urban trees using publicly available datasets to enable comparative studies.

Soil organic matter rather than ectomycorrhizal diversity is related to urban tree health.

Urban trees provide many ecosystem services, including carbon sequestration, air quality improvement, storm water attenuation and energy conservation, to people living in cities. Provisioning of ecosystem services by urban trees, however, may be jeopardized by the typically poor quality of the soils in urban areas. Given their well-known multifunctional role in forest ecosystems, ectomycorrhizal fungi (EcM) may also contribute to urban tree health and thus ecosystem service provisioning. Yet, no studies so far have directly related in situ EcM community composition to urban tree health indicators. Here, two previously collected datasets were combined: i) tree health data of 175 Tilia tomentosa trees from three European cities (Leuven, Strasbourg and Porto) estimated using a range of reflectance, chlorophyll fluorescence and physical leaf indicators, and ii) ectomycorrhizal diversity of these trees as characterized by next-generation sequencing. Tree health indicators were related to soil characteristics and EcM diversity using canonical redundancy analysis. Soil organic matter significantly explained variation in tree health indicators whereas no significant relation between mycorrhizal diversity variables and the tree health indicators was found. We conclude that mainly soil organic matter, through promoting soil aggregate formation and porosity, and thus indirectly tree water availability, positively affects the health of trees in urban areas. Our results suggest that urban planners should not overlook the importance of soil quality and its water holding capacity for the health of urban trees and potentially also for the ecosystem services they deliver. Further research should also study other soil microbiota which may independently, or in interaction with ectomycorrhiza, mediate tree performance in urban settings.

Suspended pavement systems as opportunities for subsurface bioretention

Trees supply numerous ecosystem services to the urban environment, including mitigating the urban heat island, improving air quality, and providing habitat for wildlife. However, due to the structural stability requirements of infrastructure such as sidewalks, roadways, and parking areas, urban soils are commonly characterized by high compaction levels, low porosity, and nutrient deficiency, often to the detriment of urban tree health. By transmitting surface loads to a compacted subbase, suspended pavement systems create a matrix of uncompacted soil that promotes tree health through increased root access to oxygen, water, and nutrients. Recently, interest has grown in making suspended pavement systems multi-functional by designing them to act as subsurface bioretention practices in ultra-urban areas where space may be limited due to concentrated development and high land costs. Despite this interest, only one study has tested suspended pavement systems in this application. Further, the study utilized lined installations to allow a controlled water quality assessment; however, this negated the ability to fully quantify runoff reduction. Two unlined suspended pavement systems designed to function as subsurface bioretention practices were installed in Knoxville, Tennessee, USA, in 2015 and monitored over 27-months. During that period, over 99% of runoff volumes were reduced by the free-drained north system, which completely captured runoff from 79% of storms. The underdrained south system reduced influent runoff by over 88% and captured all runoff from 83% of events during the study. Influent TSS concentrations were significantly reduced by the south suspended pavement system, though no other significant differences between influent and effluent pollutant concentrations were observed, presumably due to low influent concentrations. This study demonstrates the viability of field-scale suspended pavement systems in a stormwater management application and illustrates the hydrologic and pollutant removal capabilities of these systems to manage urban stormwater runoff.

Urbanization drives unique latitudinal patterns of insect herbivory and tree condition

Urban landscapes are characterized by high proportions of impervious surface resulting in higher temperatures than adjacent natural landscapes. In some cities, like those at cooler latitudes, trees may benefit from warmer urban temperatures, but trees in many cities are beset with problems like drought stress and increased herbivory. What drives patterns of urban tree health across urbanization and latitudinal temperature gradients? In natural systems, latitude–herbivory relationships are well‐studied, and recent temperate studies have shown that herbivory generally increases with decreasing latitudes (warmer temperatures). However, the applicability of this latitude–herbivory theory in already‐warmed urban systems is unknown. In this study, we investigated how the interaction of urbanization, latitudinal warming and scale insect abundance affected urban tree health. We predicted that trees in warmer, lower latitude cities would be in poorer health at lower levels of urbanization than trees at cooler, higher latitudes due to the interaction of urbanization, latitudinal temperature and herbivory. To evaluate our predictions, we surveyed the abundance of scale insect herbivores on a single, common tree species Acer rubrum in eight US cities spanning 10° of latitude. We estimated urbanization at two extents, a local one that accounted for the direct effects on an individual tree, and a larger one that captured the surrounding urban landscape. We found that urban tree health did not vary with latitudinal temperature but was best predicted by local urbanization and herbivore abundance. We did not observe increased herbivore abundance in warmer, lower latitudes cities, but instead herbivore abundance peaked in the mid latitudes of our study. This study demonstrates that urban landscapes may deviate from classical theory developed in natural systems and reinforces the need for research reconciling ecological patterns in urban landscapes.

An IoT Tree Health Indexing Method Using Heterogeneous Neural Network

Urban trees provide essential ecosystem services on regulating temperature and humidity, filtering urban pollutants, and improving air quality. However, the increasing number of urban trees put pressure on maintenance and public safety. The total compensatory value of the trees, consisting of inspection, maintenance, and settlement of tree damages, is more than $2 trillion USD. At this point in time, there is no known research on manifesting guidance on automated tree health assessment. The Internet-of-Things (IoT) proliferates the deployment of wireless sensors and networks. A concept of the IoT trees is raised to implement various sensors on the trees for automated health monitoring and assessment. In this paper, an urban tree health index (UTHI) is first developed to indicate the health of urban IoT trees. The index will facilitate preventive measures on urban trees. To construct the indexing model, seven (7) dynamic (time-series) features and seven (7) static features are extracted to explore the ambient effects on urban tree health. Afterward, a heterogeneous neural network (HNN) for UTHI modeling is developed to adopt the heterogeneous feature structure. In HNN, the dynamic features are analyzed in the gated recurrent unit (GRU) layer and the static features are analyzed in a hidden layer. The novel fusion layer then aggregates the outputs computed from those layers and further explores unseen correlations among all features. The experimental result verifies that the HNN-based modeling achieves high accuracy and model fitness with the error rate of less than 5%. In addition, the HNN achieves 34% to 66% improvement of accuracy in comparison with the other machine learning algorithms. The supremacy of the developed model is that all indexing features can be predefined or monitored by the IoT sensors, thus rendering an automated and economic urban tree management.

Volunteering for Forest Health: A Public-Private Partnership in Oakville, Ontario, Canada

The Forest Health Ambassador Program, a joint public-private initiative in Oakville, Ontario, Canada, recruits volunteers from the community to assess municipal street trees for health issues and signs of invasive insects. In partnership with municipal employees, staff from BioForest, a private consultant, trains volunteers to inspect trees for a suite of structural and foliar conditions, as well as for signs and symptoms of infestation by emerald ash borer, gypsy moth, and Asian longhorned beetle. Since 2014, 4,871 street trees have been assessed by a growing base of volunteers. The program effectively increases the number of participants involved in the early detection of invasive pests, beyond what government resources typically allow. Thus, the program entails a low-cost investment that provides multiple ancillary benefits and channels community efforts into a cohesive product. The results provide data with direct implications for municipal forestry operations and help identify trends in urban forest health over time. For example, detections of relatively high numbers of gypsy moth egg masses were reported by volunteers, allowing the municipality to take remedial action and mitigate damage. A variety of media are used to advertise the program, including community newspapers and social media, as well as communications in local schools and at community events. The program is well-suited to high school students, who are able to complete curriculum-mandated volunteer hours through the program, while simultaneously gaining environmental knowledge. The program allows for the proliferation of awareness and education pertaining to municipal urban forest issues, particularly those related to invasive species and urban tree health.

Foliar optical traits indicate that sealed planting conditions negatively affect urban tree health

Urban trees play a key role in mitigating environmental problems in cities, but they often face harsh environmental conditions as they generally grow in sealed soils that have small rooting space and low water availability. In this context, rapid monitoring and assessment of tree health status is critical to maintain urban trees and secure the provisioning of urban ecosystem services. Across three European cities we selected 187 Tilia tomentosa trees growing under following planting conditions: (i) sealed, trees planted in small soil pits or strips surrounded by highly sealed surfaces (concrete, pavement or asphalt); and (ii) unsealed, trees planted in roomy soil surfaces (e.g. parks). We measured leaf reflectance and fluorescence and derived a set of optical traits from the measurements. We examined whether these non-destructively measured optical traits differ between planting conditions and whether they correlate with leaf functional traits, e.g. specific leaf area (SLA), leaf water content (LWC) and leaf water per area (LWA). Compared to the unsealed trees, sealed trees showed decreased SLA and LWC while increased LWA. Leaf optical traits differed between the unsealed and sealed trees. Highly sealed soils accelerated leaf senescence of the sealed trees compared to the unsealed trees, embodied in the temporal trend of optical traits. Sealed planting conditions negatively affect urban tree health status and phenology. These negative effects can be estimated by leaf optical traits, demonstrating the great potential of optical traits in assessing tree health status. Our findings provide insights into facilitating urban green management using optical traits and remote sensing data.

Pedogenic Processes and Urban Tree Health in Engineered Urban Soils in Boston, Massachusetts, USA

Trees provide many ecosystem services in the urban environment. For these benefits to be realized, trees must establish and grow to large sizes. Engineered urban soils (EUS) are intended to promote tree health and sometimes also perform other functions such as supporting infrastructure. Substantial amounts of time and money are invested into these soils and trees, yet data on longitudinal soil developmental processes (i.e., pedogenic processes) and tree performance are limited for these systems. In this research, soil development in seven EUS installations in Boston, Massachusetts, was assessed. The EUS studied included sand-based structural soils, rock-based structural soils, and horticultural mixes. The sites spanned a chronosequence of 6 to 45 years since installation and included five different tree species. The data confirm the hypotheses that pedogenic processes are occurring in these soils at different rates and magnitudes. Illuviation of clay, acidification, and a decrease in the mineralization quotient (qM, or respiration divided by soil organic matter) were observed with increasing site age. The data suggest that overall soil quality may be influential on tree health, and no individual soil physical, chemical, or biological property is driving site differences important for trees. Urban vegetation managers should recognize that these are not static systems and the actions to care for these systems should evolve as the soils develop over time.