Urban Forest Research Articles

Integrating Hyperspectral Reflectance and Physiological Parameters to Detect Urban Tree Stress: A Study of Drought and Simulated Acid Rain

With urbanization and climate change worsening, urban trees are constantly exposed to environmental stress. To enhance the functionality and health of trees, it is crucial to rapidly and non-destructively detect and respond to tree stress. Research utilizing hyperspectral characteristics for detecting various stresses has recently been actively pursued. This study conducted comparative analysis using various leaf physiological parameters (chlorophyll content, chlorophyll fluorescence, leaf water, and gas exchange status) and hyperspectral data (VIS: visible ray; SWIR: short-wave infrared) to diagnose stress in Prunus yedoensis, commonly grown urban trees, by subjecting them simultaneously to different stresses (drought and simulated acid rain). The findings suggest that hyperspectral reflectance proved more responsive in identifying stress compared to the physiological parameters. Initially, VIS was more effective in detecting two stress responses than SWIR through a classification model (PLS-DA: partial least squares-discriminant analysis). Although SWIR initially faced challenges in simulated acid rain stress detection, spectral preprocessing (SNV: standard normal variate, + S.G 2nd: Savitzky–Golay 2nd derivative) enhanced its stress classification accuracy. Over time, the SWIR bands (1437 nm, 1667 nm, and 1949 nm) exhibited characteristics (such as moisture detection) more closely aligned with stress responses compared to VIS, as determined through PCA (principal component analysis). Hyperspectral reflectance also revealed the potential to measure chlorophyll fluorescence (Fo: minimum fluorescence). Building upon the foundational data of this study, the future potential of diagnosing urban tree stress using portable spectrometers is strong.

Selective capture of PM2.5 by urban trees: The role of leaf wax composition and physiological traits in air quality enhancement

Human health risks from particles with a diameter of less than 2.5 µm (PM2.5) highlight the role of urban trees as bio-filters in air pollution control. However, whether the size and composition of particles captured by various tree species differ or not remain unclear. This study investigates how leaf attributes affect the capture of PM2.5, which can penetrate deep into the lungs and pose significant health risks. Using a self-developed particulate matter (PM) resuspension chamber and single-particle aerosol mass spectrometer, we measured the size distribution and mass spectra of particles captured by ten tree species. Notably, Cinnamomum camphora (L.) J.Presl and Osmanthus fragrans Lour. are more effective at capturing particles under 1 µm, which are most harmful because they can reach the alveoli, whereas Ginkgo biloba L. and Platanus × acerifolia (Aiton) Willd. tend to capture larger particles, up to 1.6 µm, which are prone to being trapped in the upper respiratory tract. Leaf physiological traits such as stomatal conductance and water potential significantly enhance the capture of larger particles. The Adaptive Resonance Theory neural network (ART-2a) algorithm classified a large number of single particles to determine their composition. Results indicate distinct inter-species variations in chemical composition of particles captured by leaves. Moreover, we identified how specific leaf wax compositions—beyond the known sticky nature of hydrophobic waxes—contribute to particle adhesion, particularly highlighting the roles of fatty acids and alkanes in adhering particles rich in organic carbon and heavy metals, respectively. This research advances our understanding by linking leaf physiological and wax characteristics to the selective capture of PM2.5, providing actionable insights for urban forestry management. The detailed exploration of particle size and composition, tied to specific tree species, enriches the current literature by quantifying how and why different species contribute variably to air quality improvement. This adds a crucial layer of specificity to the general knowledge that trees serve as bio-filters, offering a refined strategy for planting urban trees based on their particulate capture profiles.

Uniqueness of tree stand composition and soil microbial communities are related across urban spruce-dominated forests

ContextUrban forest soils represent significant reservoirs of biodiversity in cities. Retaining this diversity under urban land-use change requires understanding on how species richness, community assembly and uniqueness of species assemblages are related to local forest characteristics and surrounding landscape structure.ObjectivesOur aim was to assess the significance and relative importance of logging history, tree species composition and urbanization in shaping soil microbial communities across urban spruce-dominated forest landscapes. We investigated responses of microbial diversity from three complementary viewpoints: local diversity, community assembly patterns and community uniqueness.MethodsWe collected soil bacterial and fungal metabarcoding data from 73 spruce-dominated forest sites distributed in three urban centers across southern Finland. We related these data to measurements of logging intensity, tree species composition and degree of urbanization.ResultsLogging intensity, tree species composition and urbanization affected site-scale microbial diversity, but the effects varied between microbial groups. Only logging intensity had a significant imprint on microbial assembly, and this effect was restricted to bacteria. Relative uniqueness of microbial assemblages at the landscape-scale was coupled with the uniqueness of tree species composition in all microbial groups, and further affected by tree diversity in saprotrophic fungi and urbanization in ectomycorrhizal fungi.ConclusionsIn the context of urban spruce-dominated forests, locally diverse tree stands are not necessarily the same as those that contribute the most to landscape-scale diversity. Identifying and preserving contrasting tree stand structures, which support distinctive soil microbial assemblages, may be the winning strategy in maintaining a wide range of soil microbial diversity.

Not population density, but city size and per capita income influence the urban forest carbon sequestration: A case of growing cities in Arkansas, USA

While urban trees provides significant ecosystem services, the impact of increasing urbanization and population on their carbon sequestration potential remains relatively underexplored in interior sprawling cities, highlighting a critical research gap amid growing urban environmental challenges. Although existing studies suggest a strongly correlation between urban forest cover and carbon sequestration, this study aims to investigate how the urban demography factors influence land cover and carbon sequestration across cities with low, medium, and high population densities. Using the i-Tree Canopy tool, we sampled 18,814 random points to estimate city land cover and carbon sequestration in Arkansas, interior state of the US. Results from the principal component analysis revealed that 74% of the variation in a city's land cover among population density classes is attributed to tree and soil cover percentages. The mean annual (1.40 ± 0.08 T ha-1) and total carbon sequestration rates (35.30 ± 5.57 T ha-1) were significantly higher in the areas with low population density due to a higher average tree cover percentage (46%). Carbon sequestration rate was negatively associated with land cover types such as impervious surfaces like buildings (r = -0.44), roads (r = -0.28), grass cover (r = -0.46), and impervious other (r = -0.53). The log-linear model with scaled variables suggested that factors such as city's size and tree cover has positive influence urban trees' annual and total carbon sequestration, while spatial distribution and per capita income negatively affect these ecosystem befits in growing cities, regardless of population density. Travel time within city may have negative impact, while decadal population change may positively impact on carbon sequestration alongside management effort. Valuing this potential urban forest carbon sequestration for emerging carbon market could provide monetary benefits to the urban communities, city managers, and policymakers, enabling the development of effective urban forest management strategies in the context of urban climate change.

Variations in the leaf economics spectrum, anatomical, ultrastructural, and stomatal traits of five tree species in the urban-rural air pollution environment

Rapid urbanization has contributed to global increases in air pollution derived from urban areas. Unlike natural forests, urban forests are exposed to higher concentrations of airborne pollutants due to the strong urban-suburban-rural pollutant emission gradients. However, there remains a pressing lack of available information pertaining to the urban air pollution-related effects on the leaf economics spectrum, anatomical, ultrastructural, and stomatal traits of tree species along an urban-rural gradient. Here, the degree to which urban air pollution impacts the adaption of greening tree species and associated service functions was assessed by sampling five common tree species (Acer pictum, Fraxinus chinensis, Koelreuteria paniculata, Salix babylonica, Sophora japonica) along urban-rural-natural forests in the Beijing metropolitan region of China. These analyses revealed a significant reduction in leaf mass per unit area (–13.4 %), leaf thickness (–16.7 %), and stomatal area (–27.5 %) with increasing proximity to areas of greater air pollution that coincide with significant increases in leaf tissue density (+12.6 %), leaf nitrogen content (+10.1 %), relative chlorophyll content (+2.7 %), and stomatal density (+11.9 %). Higher air pollution levels were associated with organelle changes including gradual disintegration of chloroplasts, larger intercellular spaces and apparent starch and plastoglobuli deposition. Air pollution was conducive to the strengthening of the trade-off potential and adaptation strategies of trees in urban ecosystems, which are associated with trees with a rapid investment return strategy associated with thick leaves and strong photosynthetic capacity. These results provide strong empirical evidence of the profound air pollution-induced changes in leaf functional traits and adaption ability of urban forest tree species.

Perceptions of commercial plants and tree nurseries in the use of native forest tree species for urban landscaping activities in municipalities of Los Baños and Bay, Philippines

Abstract Urban greening using native forest tree species (NFTs) has been increasingly recognized to achieve more livable, healthier, and resilient cities. However, despite having diverse genetic reserves, full utilization of NFTs in the country has not been fully realized. This restricts the mass production of seedlings for urban greening activities. As such, this study was carried out to determine the perceptions of commercial plants and tree nurseries in the use of NFTs for urban greening in municipalities of Los Baños and Bay, Philippines using the snowball sampling technique of Key Informant Interviews (KII). A total of 32 respondents were interviewed. Out of 85 species of trees identified, 51.16% (Los Baños) and 35.29% (Bay) were native. Most buyers planted their seedlings in private gardens (37.62%), subdivisions (12.38%), and private resorts (11.90%). About 18% of respondents sourced out their propagules from local sellers, followed by purchasing ready-to-plant seedlings from nearby towns (e.g. Talisay, Batangas) (14.11%) and Mt. Makiling Forest Reserve (10.58%). Unfamiliarity (21.69%) with the potential of native species seemingly impedes their popularity as urban trees. Over 23% of respondents believed that native trees help enhance the urban biodiversity and more than 43% have mentioned that buyers used leaves as the basis for species selection. Meanwhile, seedlings of seed origin are the most common (about 35%) mode of seedling production. Finally, the study revealed that Pterocarpus indicus is the topmost common native forest tree species being used for urban greening in the subject municipalities and therefore warranted to be used for further studies.

Urban green tree morphology and the problem of minimizing runoff. A case study in Ly Thuong Kiet Street, Hue City, Vietnam.

Abstract Sustainable urban drainage by green infrastructure is emphasized. Trees can change the three processes of interception, evapotranspiration, and infiltration of the hydrological cycle, so they are considered one of the effective solutions to reduce urban flooding. The article applies Minnesota’s Minimum Impact Design Standards (MIDS) Calculator method to compare the ability to reduce surface runoff of urban trees on Ly Thuong Kiet Street before 2009 and 2022. The calculation results show that before 2009 it was 3,406m3; after expanding the road and replacing the type of greenery, it was only 1,570m3 in 2022, a decrease of 2.16 times compared to before 2009. The factors that create the difference are canopy area (CP), leaf area index (LAI), tree species, and soil volume for each tree. The decrease in this ability is due to the greenery replaced after 2010 being unsuitable for local characteristics, so the trees are poorly developed or dead.

Impact of transforming karst mountainous forests into urban parks on plant diversity patterns.

The conversion of urban montane forest resources into urban parks requires careful assessment to understand its impacts on plant diversity over time. This study aims to enhance urban biodiversity conservation strategies by analyzing how habitat type and park age affect woody plant diversity. We surveyed woody plant species in 60 sample plots across two different habitats (remnant forest vs. artificial green space) within three mountain parks in Guiyang, China, established at different times. The alpha diversity of saplings/seedlings was significantly higher in remnant forests than in artificial green spaces. Artificial green spaces exhibited more homogenous woody plant composition compared with remnant forests. Newer parks showed greater variation in plant composition between the two habitats than older parks. Indicative species in remnant forests were predominantly native, whereas those in artificial green spaces were mainly ornamental species. The transformation of karst mountainous forests into urban parks leads to the homogenization of woody plant composition and impedes the regeneration of saplings/seedlings. Therefore, it is crucial to manage these conversions carefully and strive to preserve as many native species as possible to support urban plant diversity conservation.

The Unmanned Aerial Vehicle-Based Estimation of Turbulent Heat Fluxes in the Sub-Surface of Urban Forests Using an Improved Semi-Empirical Triangle Method

The Unmanned Aerial Vehicle-Based Estimation of Turbulent Heat Fluxes in the Sub-Surface of Urban Forests Using an Improved Semi-Empirical Triangle Method

Play tales: Co-creating stories of childhoodnature play in an urban forest school

This article shares several co-created stories of play that we have named ‘Play Tales’. These are about our experiences of researching ‘childhoodnature play’ (playing in a place with more-than-human nature) in an urban forest school in London, England. The article offers insights about the emergence of childhoodnature play. We found out that play changes with the seasons, involves a mix of home, digital, school and outdoor worlds and you know you’re playing because of how you feel. Researching together takes time and space but it is important to work together in research because there are some things only children know.

Green infrastructure as a factor of sustainable urban development: current status and prospects

Abstract The article reflects the results of the assessment of the current state and functioning of the green infrastructure of the urban environment. A thorough survey of the territory and a clear functional zoning were carried out. A study of the features of Landscaping and landscaping of urban forests was conducted and a whole range of issues related to the formation of a full-fledged environment for human recreation was identified. The research has established plants that can withstand high temperature conditions and low humidity, high levels of dust and gases in the air of the urban environment, soil compaction, etc. In the course of research, it was revealed that coniferous plants play a large role in the creation of decorative compositions. For a shaded lawn, special types of herbs are used that can do without direct sunlight. Local creators and artists can be involved in the creation of unusual forest art objects. This will create additional interest in visiting and contribute to the dissemination of information about the city and its attractions on social networks, creating an attractive tourist image. The improvement of the city’s forest area will create opportunities for organizing full-fledged recreation for urban residents, and will have a beneficial effect on their psychological and physical condition. Thus, a sufficient number of well-maintained public spaces have a positive effect on the physical and psycho-emotional health of a city dweller, on the effectiveness of his work.

Identification of the Role of Stakeholders in Sustainable City Forests, Case Study of Beringin Medan City Forest, North Sumatra, Indonesia

Management of forest cities becomes an essential strategy in strengthening environmental and social urban areas, particularly in facing the challenge of urbanization. This study aims to analyze stakeholders' roles, contributions, and strategies to increase synergy in the management of Medan Beringin City Forest. The MACTOR analysis method is used to understand the interaction between stakeholders and the factors influencing them. The results show that the involvement of various parties, including government regions, institutions, self-subsistent society, local community, and private sector, is essential in sustainable city management. City Government and Environment and Forestry Service's key roles in collaboration with other institutions are also seeded. Recommendation strategies can strengthen the effectiveness of management of forest cities, not only in Medan but also in other cities facing similar challenges.

Bioluminescence Inhibition Bioassay for Estimation of Snow Cover in Urbanised Areas within Boreal Forests of Krasnoyarsk City

It has been proposed that the level of air pollution in a city should be estimated based on the accumulation of pollutants in the snow cover of urban forests. This study presents a bioluminescence method for estimating the extent of snow cover pollution in the urbanised areas of boreal forests in Krasnoyarsk city. A bioluminescent assay involving NAD(P)H:FMN oxidoreductase (Red) and luciferase with luminous bacteria (BLuc) was employed to measure the concentrations of six heavy metals (As, Cd, Zn, Co, Hg, and Pb) in the snow cover. The tested snow samples demonstrated a correlation between the reduced activity of the enzyme system and variations in Cd concentration. Furthermore, the research indicated that the period of unfavourable meteorological conditions in Krasnoyarsk city resulted in a notable decline in the activity of the BLuc–Red enzyme system, which may be associated with elevated air pollution levels. This study underscores the potential of the bioluminescence method for monitoring environmental pollution in urban forested areas.

Identifikasi Sumber Belajar Lokal untuk Mendukung Inovasi Pembelajaran Biologi

This research aims to identify local learning resources as an effort to support innovation in high school biology teaching in Mataram City and West Lombok Regency. This study involves exploration using observation and interviews with teachers and students to collect data on the potential of local learning resources and their application in biology education. The results indicate that there are various potential local learning resources, such as school gardens, city parks, urban forests, coastal areas, and local agro-tourism sites. The identification and utilization of these local learning resources have proven to enhance students' interest and motivation, as well as provide a more contextual and relevant learning experience. Data analysis shows that while there is significant potential in utilizing local learning resources, there are still challenges in its implementation.

Is Your Training Data Really Ground Truth? A Quality Assessment of Manual Annotation for Individual Tree Crown Delineation

For the accurate and automatic mapping of forest stands based on very-high-resolution satellite imagery and digital orthophotos, precise object detection at the individual tree level is necessary. Currently, supervised deep learning models are primarily applied for this task. To train a reliable model, it is crucial to have an accurate tree crown annotation dataset. The current method of generating these training datasets still relies on manual annotation and labeling. Because of the intricate contours of tree crowns, vegetation density in natural forests and the insufficient ground sampling distance of the imagery, manually generated annotations are error-prone. It is unlikely that the manually delineated tree crowns represent the true conditions on the ground. If these error-prone annotations are used as training data for deep learning models, this may lead to inaccurate mapping results for the models. This study critically validates manual tree crown annotations on two study sites: a forest-like plantation on a cemetery and a natural city forest. The validation is based on tree reference data in the form of an official tree register and tree segments extracted from UAV laser scanning (ULS) data for the quality assessment of a training dataset. The validation results reveal that the manual annotations detect only 37% of the tree crowns in the forest-like plantation area and 10% of the tree crowns in the natural forest correctly. Furthermore, it is frequent for multiple trees to be interpreted in the annotation as a single tree at both study sites.

Urban foresters’ perceptions about the role of soil and fungi in urban forest management and climate mitigation

The benefits of soil and mycorrhizal fungi in mitigating climate impacts through their vital role in carbon sequestration are well recognised in the academic literature but are not well incorporated in current urban forest planning and policies. We conducted a survey to examine urban foresters’ perceptions about the incorporation of current scientific understanding of the role of soil and fungi, and stakeholders’ engagement in urban forest management. Overall, urban foresters perceive that soil and fungi are important, however, little consideration is given to their incorporation in urban forest management practices and policies. Many stakeholders’ engagement is low in urban forest management. Urban foresters perceive that decision makers have little knowledge about the role of soil and fungi which may pose barriers to its integration in planning and policies. The key challenges revealed by the survey include the lack of funding, conflicting priorities, and the lack of mechanisms to transfer scientific knowledge to urban foresters and inter-departmentally. Municipalities should develop policies that enhance knowledge transfer and integration to enhance the efficacy of urban forest’s strategies that work to support municipal climate goals. Furthermore, collaboration with diverse stakeholder groups may enhance communication and subsequently increase support for urban forest initiatives.

Community perceptions towards the ecosystem services of urban forests in Mekelle, Tigray, Ethiopia

Urban forests are crucial providers of ecosystem services, delivering significant benefits to residents and the environment. This study aimed to investigate how residents in Mekelle, Tigray, Ethiopia, perceive the ecosystem services provided by urban forests. Understanding these perceptions is essential, particularly in developing countries and the study area, where little research has been conducted on this topic. To achieve this objective, a questionnaire-based survey was conducted among randomly selected household heads from two sub-cities within Mekelle. The collected data were analyzed using both descriptive and inferential statistics, including Spearman rank correlation and ordinal regression analysis. These analyses helped identify the factors influencing inhabitants’ perceptions of ecosystem services. The findings revealed that residents placed a high value on the regulating ecosystem services provided by urban forests. In contrast, provisioning, supporting, and cultural ecosystem services were perceived at a medium level. Additionally, the analysis indicated that the level of education and age of respondents were significant factors influencing their overall perception of these ecosystem services. Higher educational attainment and older age were associated with a greater appreciation of the ecosystem services offered by urban forests. This study has important implications for urban forest management and policy. It highlights the necessity of incorporating community perceptions of ecosystem services into urban planning and management efforts. Moreover, the study recommends the need for local governments to focus on raising community awareness about the ecosystem services provided by urban forests. This can ensure more effective and inclusive urban forest management strategies that align with community values and needs.

Shaping Baltimore’s urban forests: past insights for present-day ecology

ContextLand use history of urban forests impacts present-day soil structure, vegetation, and ecosystem function, yet is rarely documented in a way accessible to planners and land managers.ObjectivesTo (1) summarize historical land cover of present-day forest patches in Baltimore, MD, USA across land ownership categories and (2) determine whether social-ecological characteristics vary by historical land cover trajectory.MethodsUsing land cover classification derived from 1927 and 1953 aerial imagery, we summarized present-day forest cover by three land cover sequence classes: (1) Persistent forest that has remained forested since 1927, (2) Successional forest previously cleared for non-forest vegetation (including agriculture) that has since reforested, or (3) Converted forest that has regrown on previously developed areas. We then assessed present-day ownership and average canopy height of forest patches by land cover sequence class.ResultsMore than half of Baltimore City’s forest has persisted since at least 1927, 72% since 1953. About 30% has succeeded from non-forest vegetation during the past century, while 15% has reverted from previous development. A large proportion of forest converted from previous development is currently privately owned, whereas persistent and successional forest are more likely municipally-owned. Successional forest occurred on larger average parcels with the fewest number of distinct property owners per patch. Average tree canopy height was significantly greater in patches of persistent forest (mean = 18.1 m) compared to canopy height in successional and converted forest patches (16.6 m and 16.9 m, respectively).ConclusionsHistorical context is often absent from urban landscape ecology but provides information that can inform management approaches and conservation priorities with limited resources for sustaining urban natural resources. Using historical landscape analysis, urban forest patches could be further prioritized for protection by their age class and associated ecosystem characteristics.

Beyond Urban Forests: The Multiple Functions and the Overlooked Role of Semi-Natural Ecosystems in Mediterranean Cities

Beyond Urban Forests: The Multiple Functions and the Overlooked Role of Semi-Natural Ecosystems in Mediterranean Cities

Alternative uses for urban autumn tree leaves: A case study in profitability and greenhouse gas emissions for the city of Berlin

Autumn tree leaves collect as waste on many city streets every year. In the city of Berlin, they are usually collected and transported for composting as their final treatment, which emits greenhouse gases (GHG) into the atmosphere. This study assesses alternative end uses of autumn tree leaves in order explore the potential of reducing GHG emissions while producing electric energy from residual biomass. It uses a combination of partial life-cycle assessments and net present value (NPV) to explore the different net GHG emissions and economic benefits of using autumn tree leaves for the following scenarios: anaerobic digestion (biogas), gasification, and co-firing. Assuming the use of 36,000 tonnes of leaves per year, co-firing in existing power plants shows the highest NPV, of between 10.3 million and 12.1 million euros for a 10-year lifetime, in line with the phase-out of coal combustion in Germany. It also results in the lowest net GHG emissions, with savings of between 252,000 and 144,000 tonnes of CO2eq. Gasification in new plants resulted in similar NPVs, estimated at between 9.80 and 9.86 million euros over a 20-year investment horizon, but lower emissions savings of 178,000 to 127,000 tonnes of CO2eq. Biogas production showed high emissions savings of 204,000 to 203,000 tonnes of CO2eq, but a much lower NPV of between 2.3 and 2.5 million euros. Composting was the only scenario with positive net GHG emissions. The amount of energy retrieved from the conversion technologies and the electrical tariff applied were the main drivers of these results. Other aspects that can shape the results include the availability of infrastructure and transport distances. The results are highly sensitive in both cases to the dryness of the leaves, while electricity tariffs influenced the economic performance considerably.