Drone remote sensing in urban forest management: A case study

We applied drone remote sensing to identify relationships between key forest health indicators collected in the field and four Vegetative Indices (VI) to improve conservation management of urban forests. Key indicators of urban forest health revealed several areas of conservation concern including a majority of overstory trees in moderate to severe decline, canopy gaps, anthropogenic dumping, vines overtaking the forest canopy, and invasion by non-native plant species. We found plot-level vegetation index (VI) values of NDVI, NDRE, GNDVI, and GRVI calculated from drone imagery are significantly related to the impact of several of these ecological concerns as well as metrics of forest composition and equitability. Despite the small number of plots, too few to provide a general predictive framework, these findings indicate a substantial potential for drone remote sensing as a low-cost, efficient tool for urban forest management. We discuss how our findings can advance urban forest management and discuss challenges and opportunities for future drone VI research in urban natural areas.     

Review on urban tree modelling in CFD simulations: Aerodynamic,deposition and thermal effects

This paper reviews current parameterizations developed and implemented within Computational Fluid Dynamics models for the study of the effects linking vegetation, mainly trees, to urban air quality and thermal conditions. In the literature, passive mitigation via deposition is parametrized as a volumetric sink term in the transport equation of pollutants, while a volumetric source term is used for particle resuspension. The aerodynamics effects are modelled via source and sink terms of momentum, turbulent kinetic energy and turbulent dissipation rate. A volumetric cooling power is finally considered to account for the thermal (transpirational cooling) effects of vegetation. The most recent applications are also summarized with a focus on the relative importance of both aerodynamic and deposition effects, together with recent studies evaluating thermal effects. Those studies have shown that the aerodynamic effects of trees are stronger than the positive effects of deposition, however locally the pollutant concentration increases or decreases depending on the complex inter-relation between local factors such as vegetation type and density, meteorological conditions, street geometry, pollutant characteristics and emission rates. Unlike aerodynamic and deposition effects on pollutant dispersion which were also found in street far from trees, the thermal effects were in general locally restricted to the close vicinity of the vegetation and to the street canyon itself. Future requirements in CFD modelling include more in depth investigation of resuspension and thermal effects, as well as of the VOCs emissions and chemical reactions. The overall objective of this review is to provide the scientific community with a comprehensive summary on the current parameterizations of urban vegetation in CFD modelling and constitutes the starting point for the development of new parametrizations in CFD as well as in mesoscale models.     

Effects of local background climate on urban vegetation cooling and humidification: Variations and thresholds

Vegetation plays a critical role in climate regulation by cooling and humidifying urban regions. The climate regulation capacity of vegetation varies in different seasons, and its association with the coupling of temperature and humidity remains poorly understood. Here, we investigated the climate regulation potential of vegetation by establishing a set of indices, namely, cooling intensity (CI), cooling efficiency (CE), humidifying intensity (HI), and humidifying efficiency (HE), using continuous decadal field measurements (2013–2022) of temperature and humidity in vegetation and built-up areas in Beijing, China. Additionally, we examined the coupling effect and threshold of cooling and humidification using these indices. Climate regulation by vegetation was insignificant at night. However, the daytime results were as follows: (1) the maximum CI and CE were similar in four seasons, and their ratio was 2:3:2:1 in spring, summer, autumn, and winter, respectively; (2) the ratio of maximum HI was 4:10:7:3, whereas that of the maximum HE was 7:8:7:2 in spring, summer, autumn, and winter, respectively; and (3) the coupling of ambient temperature and humidity affected the climate regulation of vegetation. The CE and HE of vegetation increased significantly when the ambient temperature exceeded 15.1 °C and 8.5 °C, respectively. The CI and HI decreased with increasing humidity and were highest in a high temperature and low humidity ambient environment. Our study presents scientific insights into vegetation cooling and humidifying effects under different climate backgrounds and provides an enhanced understanding of the coping ability of vegetation in a severe heat island environment.     

The routes to fruit: Governance of urban food trees in Canada

Interest in planting urban food trees (UFTs) in public spaces is growing in popularity as a form of urban greening and a potential food source. Currently there is minimal research on the governance and policy aspects of integrating food trees into cities. To fill this gap, we investigated the characteristics of UFT site governance and how it compares to current urban forest governance. Semi-structured interviews were conducted with relevant municipal officials in Calgary, Edmonton, Toronto and Victoria about their perspectives and involvement with UFT sites in their city. A scan of policy documents was completed to supplement the interviews. The interviews were analyzed using a deductive coding framework based on the Policy Arrangement Approach. We found that key actors at the UFT sites were local organizations and site champions, with minimal municipal engagement. Most site resources provided by municipalities were in-kind. There are also basic knowledge gaps about how to care for UFTs. Currently municipal by-laws prohibit the harvesting and removal of plant material, and are at odds with the purpose of UFT sites, with few municipalities fully integrating UFTs in policies. The primary discussion around UFTs centre concerns for public health and safety, management, and use of public space with limited discussions of benefits. This research demonstrates the value of co-governance models to support UFTs, while a shift in focus from risks to benefits could encourage additional resources and policy integration. Further, including UFTs into policy would also support foraging and food tree maintenance in public spaces, and more fully reflect the plurality of urban forest engagement.     

A general grass growth model for urban green spaces management in tropical regions: A case study with bahiagrass in southeastern Brazil

Urban green spaces (UGS) positively impact the population, providing essential ecosystem services and improving public health. Urban vegetation management needs to optimize mowing process costs and reducing impacts on the natural ecosystem. Thus, we implemented a general grass growth model suitable for UGS management in tropical areas, focused on lawns, public parks and squares, roadsides, and around waterways. The model incorporates local edaphoclimatic conditions to simulates the daily dynamics of leaf area index (LAI), biomass, evapotranspiration, and soil water content, going under mowing processes or not, with spatialization capability which might be integrated within geographic information system (GIS) environments. A case study assessing bahiagrass (Paspalum notatum Flüggé) vegetation species in São Carlos, southeastern Brazil, is presented, considering two scenarios to demonstrate the spatial capabilities of the model: (i) UGS as a single area, and (ii) several areas independently. For model validation, vegetation indices calculated based on data from an unmanned aerial vehicle (UAV) and CubeSat imagery (PlanetScope) were used to retrieve LAI time series, calibrated with spectral signatures from leaf ground sampling. For performance analysis, LAI time series from the model and LAI retrieved from both sensors were compared via determination coefficient (R²⁾ and root mean square error (RMSE). Our findings suggest that the proposed model is accurate, and due to its spatialization capability and integration with a GIS, its application may help government administrations to optimize UGS mowing processes.     

Barriers to the effective planning and management of residential encroachment within urban forest edges: A Southern Ontario,Canada case study

Studies document degradation and loss of publicly owned urban woodland area following adjacent residential development due to residential encroachment. Residential encroachment is the negative impacts of housing land uses within both rural and urban green infrastructure networks. Prevailing planning, design and management approaches in Southern Ontario municipalities in Canada indicate planning and management tools have been developed to remove and impede encroachment impacts; however, many are infrequently implemented. This lack of implementation contributes to a high prevalence and spatial area of encroachment within Southern Ontario municipal woodland edges with adjacent housing. Long interviews were conducted with the planners, landscape architects, woodland managers and bylaw enforcement staff of six Southern Ontario municipalities to determine the barriers to implementation of municipal encroachment tools. Results indicate key barriers to policy implementation that reflect a lack of awareness of, and priority placed on addressing, residential encroachment impacts, and impacts following the point of development in general. Barriers include: (1) insufficient community and municipal access to information regarding residential encroachment and their significance relative to other development impacts; (2) lack of clarity of goals by municipalities and between departments; (3) insufficient municipal leadership and commitment to limiting encroachment; (4) lack of sufficient means within municipal departments to prevent and address encroachment; and (5) ineffectual dynamics of enforcement. Recommendations for overcoming barriers to the development and implementation of effective approaches for addressing encroachment are provided.     

Decision making in urban forestry by using approval voting and multicriteria approval method (case study: Zvezdarska forest,Belgrade, Serbia)

This paper deals with a common urban forestry problem: selecting the most appropriate management policy for a forest situated within a city zone. In the presented case study, we analyzed this problem within the Zvezdarska forest in Belgrade, Serbia. The decision makers that took part in the decision making process represented the two main stakeholder groups – the public and the experts. The public group is divided into three different subgroups: local residents, tourists and environmentalists. The experts group is represented by local authorities and academic experts. The procedure implemented for evaluating and selecting the most desired management policy for the case study area combines approval voting and the multicriteria approval method, two social choice theory methods suitable for decision-making in forestry. The main reason for combining these techniques is to be sure that the selected policy will be accepted as the most desired option by both the public and the experts. The results and discussions with involved decision makers clearly show that the applied procedure possesses sufficient analyticity and full transparency in the decision-making process; hence it is applicable to problems in urban forest management as well as to natural resources in general.     

A comparative perspective of urban forestry in Belgrade,Serbia and Freiburg,Germany

As in many countries after periods of political unrest and with unstable economical conditions, urban woodland and green spaces are becoming prioritized in the last decade in Serbia. This stands in stark contrast to countries like Germany, where there is a long history of integrating urban green space in urban development.Looking through the lens of urban forestry, this paper compares the status, planning and management of urban woodland in the Serbian capital of Belgrade with the German city of Freiburg. Holding up the difficult situation in Belgrade to the good-practice case of Freiburg allows the identification of status, problems and potentials for development. Both cases of urban forestry were analysed by a series of methods, including expert interviews, on-site observations, and analysis of documents, literature and maps.Results indicate that in Belgrade institutions and policies of urban woodland management have being much less developed than in Freiburg. Furthermore, Belgrade faces various problems that need to be solved, e.g. in terms of developing the policy framework for urban forestry and the need to promote political awareness about its importance. Important lessons can be learnt from the experiences of cities like Freiburg.     

Assessing above-ground biomass of open-grown urban trees: A comparison between existing models and a volume-based approach

Assessment of the amount of carbon sequestered and the value of ecosystem services provided by urban trees requires reliable data. Predicting the proportions and allometric relationships of individual urban trees with models developed for trees in rural forests may result in significant errors in biomass calculations. To better understand the differences in biomass accumulation and allocation between urban and rural trees, two existing biomass models for silver birch (Betula pendula Roth) were tested for their performance in assessing the above-ground biomass (AGB) of 12 urban trees. In addition, the performance of a volume-based method utilizing accurate terrestrial laser scanning (TLS) data and stem density was evaluated in assessing urban tree AGB. Both tested models underestimated the total AGB of single trees, which was mainly due to a substantial underestimation of branch biomass. The volume-based method produced the most accurate estimates of stem biomass. The results suggest that biomass models originally based on sample trees from rural forests should not be used for urban, open-grown trees, and that volume-based methods utilizing TLS data are a promising alternative for non-destructive assessment of urban tree AGB.     

Informal urban greenspace: A typology and trilingual systematic review of its role for urban residents and trends in the literature

Urban greenspace is vital in fulfilling people's nature needs. Informal urban greenspace (IGS) such as vacant lots, street or railway verges and riverbanks is an often-overlooked part of the natural urban landscape. We lack a formal definition of IGS and a comprehensive review of knowledge about IGS and its role for urban residents. This paper advances a formal definition and typology of IGS that can be applied globally. Based on this definition, a total of 65 peer-reviewed papers in English (57), Japanese (7) and German (1) were reviewed. We analyzed this literature for its temporal trends, spatial patterns, studied IGS types, methods used and key authors, and summarized the individual research papers’ findings concerning IGS. Results show IGS plays an important role for urban residents, but also highlight limitations and problems in realizing IGS’ full potential. Research papers focused on perception, preferences, value and uses of IGS. Residents could distinguish between formal and informal greenspace. They preferred a medium level of human influence in IGS. The analysis of patterns in the literature reveals: a marked increase in publications in the last 20 years; a strong geographical bias towards the USA; and a lack of multi-type IGS studies including all IGS types. Publications outside of scholarly research papers also make valuable contributions to our understanding of IGS. Our results suggest IGS is emerging as an important sub-discipline of urban greening research.     

Community gardens:An investment in social cohesion,public health,economic sustainability,and the urban environment

This study utilizes survey and interview data collected in 2018 and 2019 in the United States to examine a range of social, health, economic, and environmental benefits community gardens yield, as well as the political factors that enable and impede the success of community gardens. The results indicate there are a multitude of individual-level benefits that accrue to garden participants, as well as community-level benefits. The findings also suggest municipal governments can best aid gardens by providing long-term secure land access, affordable water access, administrative support, and plot fee structures that are inclusive to people of all socio-economic backgrounds.     

Variations of urban greenness across urban structural units in Beijing,China

Urban structural units (USUs) are work (or similar) units in urbanized areas. In this study, USUs based on urban land use and land cover were used to explain and compare urban ecological conditions within Beijing. This study focused on the spatial pattern of land use for different USUs in urban areas. The results showed that 453 USUs belong to 12 primary USUs and to 38 different secondary USUs. The percentage of built-up area was highest in those regions with hotels, and lowest in areas with cemeteries. The percentage of woodland area was highest in primary and middle schools, and the lowest in entertainment plazas. The percentage of grassland area was highest in farmland or orchards, and lowest in Siheyuan (courtyards). The percentage of green space is highest in lands dedicated to middle and primary schools, and lowest in areas with museums. There is no significant linear relationship between construction period and green space percentage in Colleges/Universities (R = 0.045, p = 0.806 > 0.05) and Parks (R = 0.13, p = 0.43 > 0.05). However, there was an inverted-U curve relationship with the relevant housing price in the residential area, a relationship that can be described by the equation: f = 17736.45 + 348.21x ? 4.15 x², p = 0.0022 < 0.05. This relationship implied that the socio-economic factors like housing prices may be a factor in determining the green space pattern of urban ecosystems in Beijing.     

A method for locating potential tree-planting sites in urban areas: A case study of Los Angeles, USA

A GIS-based method for locating potential tree-planting sites based on land cover data is introduced. Criteria were developed to identify locations that are spatially available for potential tree planting based on land cover, sufficient distance from impervious surfaces, a minimum amount of pervious surface, and no crown overlap with other trees. In an ArcGIS environment, a computer program was developed to iteratively search, test, and locate potential tree-planting sites by virtually planting large, medium and small trees on plantable areas, with large trees given priority as more benefits are expected to accrue to them. A study in Los Angeles, USA found 2.2 million potential planting sites, approximately 109.3 km² of potential tree canopy cover.     

Conserving rare plants in locally-protected urban forest fragments: A case study from Miami-Dade County,Florida

We consider Miami-Dade County’s Environmentally Endangered Lands (EEL) network of preserves as a means to conserve rare plant species in urban and suburban forest fragments. In this rapidly urbanizing landscape, upland forests are at particularly high risk of development. We examined the number of rare plant species present in preserves based on the site area, ecosystem type and management practices using the EEL database maintained by the county and a database of plant species inventories collected by the Institute for Regional Conservation. About 99% of the area of the EEL system is located in southern Miami-Dade. Pine rockland forests are primarily in the outer suburbs of the county where fire can be used most effectively for management. Hardwood hammock forests are distributed throughout the county including within the urban core. All 56 EEL forested sites under study contained at least one rare plant species. Small sites often contained high numbers of rare species per unit area, but presumably at lower population sizes. The type of upland forest was not related to the mean richness of rare or state-listed plant species. Public access was not related to the mean richness of rare plants, but was negatively associated with the richness of state-listed plant species.     

Life cycle assessment of utilizing freshly cut urban wood: A case study

Large amounts of urban wood resources are generated through tree removals in urban areas. Therefore, there is a growing interest to improve the environmental performance of the urban wood supply chain by quantifying the environmental impacts of creating high-value products from urban tree removals to enhance its utilization. By surveying existing urban wood utilization operations for primary data in two major cities: Baltimore, Maryland, and Milwaukee, Wisconsin, a new life cycle inventory (LCI) dataset per m³ of dry urban hardwood lumber and live edge slabs was created. Incorporating the new LCI data into life cycle assessment method, the total global warming (GW) impact of converting urban trees to kiln-dried lumber was estimated to be 122 kg CO₂ eq and 336 kg CO₂eq per m³ of lumber produced for Baltimore and Milwaukee, respectively. In both cases, the total environmental impact of the product was dominated by the conversion of urban trees to kiln dried lumber at the sawmill processing stage. Using scenario analysis for the source of heat generation used in kiln (force) drying wood, substituting wood fuel from coproducts for natural gas in a boiler for Milwaukee resulted in a substantial reduction in fossil-derived GW impact. Urban and traditional hardwood lumber production follow similar GW impact trajectories over their life-cycle stages with the lumber processing stage having the highest environmental impacts for both. Increasing the overall lumber yield and decreasing kiln (force) drying would substantially improve the environmental performance of urban hardwood lumber and help make it comparable to traditional lumber.     

Understanding the relationship between small urban parks and mental health: A case study in Shanghai,China

The literature to date has mainly explored the impact on public mental health of green spaces around residential areas, large urban parks, family gardens, blue spaces, national parks, etc., while few studies have examined the association of Small Urban Green Spaces (SUGS) with public mental health. The role, function, and service radius of SUGS in urban people’s lives are quite different from those of general green spaces, and the relationship and mechanism linking general green spaces to mental health cannot be fully applied to small parks. This work was conducted to: 1) investigate the relationship between SUGS and mental health; 2) understand what factors affect mental health; 3) determine what kind of SUGS is more conducive to improving mental health. SUGS’ designs and physical characteristics were evaluated with the Natural Environment Scoring Tool (NEST) and user information for 10 SUGS (1–5 ha) in Shanghai in 2021 was collected via a questionnaire. We developed a multilevel model for exploring the factors affecting mental health from two aspects: the individual level and the park level. This study found that SUGS and mental health were positively associated. In addition to individual–level variables like income, marital status, social cohesion, and use frequency, park–level variables such as usability, aesthetics–natural features, and civilized environment are also conducive to improving mental health, while entertainment facilities in SUGS have a negative association with mental health. There was no evidence that visit frequency, stay time, social cohesion, or physical exercise act as a mediator between park features and mental health. This study provides empirical evidence for the positive correlation between SUGS and mental health and presents a means of promoting public mental health with efficient SUGS planning and management.     

Microhabitat preferences of butterflies in urban parks: Both vegetation structure and resources are decisive

Urban parks comprise diverse microhabitats, such as vegetation units of lawn and arbour forests, with differing biodiversity potentials. However, the influences of microhabitats on butterfly diversity and the mechanisms involved remain unclear. This study used butterfly survey data from 112 plots in 27 urban parks in the central metropolitan area of Beijing, China, from June to September 2020. Based on the growth form of larval host plants, recorded butterfly species were classified into three functional groups: woody plant-feeding taxa (WF), herb-feeding taxa (HF), and feeding on multiple plant growth forms taxa (MF). We analysed the effects of 11 variables among three facets, namely, vegetation composition, vegetation structure, and human activity, on the butterfly diversity (species richness and abundance) of the whole community, three functional groups using generalised linear mixed models. Twenty-five butterfly species observed mainly feed on herbs rather than on woody plants. Our results demonstrated that vegetation community characteristics explain up to 24% and 43% variation in butterfly species richness and abundance, respectively. Of this, vegetation structure facets crucially affected butterfly species richness, and vegetation composition facets had the most significant influence on the abundance of the whole butterfly community. However, the impact of human activity factors was minimal. Light availability and herb height belonging to vegetation structure factors and nectar plant species richness and nectar abundance which belonged to vegetation composition factors showed the most important and positive effects on butterfly diversity. The positive impact of the above significant factors was found especially on herb-feeding butterfly diversity. In contrast, the diversity of butterflies feeding on woody plants was most positively influenced by herb height. We thus suggest that it is necessary to guarantee the presence of a well-developed herb layer, which provides abundant nectar sources and maintain specific open spaces to ensure light availability. In conclusion, our findings imply that the critical role of the spatial structure of vegetation community is conspicuous in the formation of suitable microhabitats for butterflies, and managers could combine vegetation management practices with the needs of specific functional groups.     

The effect of urban leaf area on summertime urban surface kinetic temperatures: A Terre Haute case study

The urban heat island effect (UHIE) has been documented in many temperate region cities. One cause of the UHIE is the replacement of green spaces with impervious materials as urbanization commences and the city builds up and fills in. During the summer, elevated urban temperatures result in increased electricity usage, higher pollution levels, and greater resident discomfort. Through evapotranspiration and the interception of solar radiation, increasing urban tree canopy cover can help mitigate the UHIE. While this is universally accepted, the exact statistical relationship between urban leaf area (as measured by leaf area index, LAI) and urban temperatures has not been extensively studied. In a case study conducted in urban/suburban Terre Haute, Indiana, USA, simple linear regression was employed to quantify the relationship between in situ ceptometer LAI measurements and surface kinetic temperatures (SKTs) measured using thermal satellite imagery acquired at 1100 local time. For the 143 sample sites located in the study area, LAI accounted for 62% of the variation in surface temperature. For every unit increase in LAI, surface temperature decreased by 1.2 °C.     

Exploring the use and perceptions of inner-city small urban parks: A case study of Budapest,Hungary

Globally, accelerating urbanization has led to a severe shortage of urban green spaces. This scarcity is particularly acute in inner cities with high population densities and ratios of built-up areas. To explore park visitors’ usage and perceptions, we present the results of a survey of 681 individuals from different socioeconomic groups conducted in four small urban parks in Budapest, Hungary’s capital. The survey results found that people living near the block parks were their primary users, but many people from distant areas also visited the parks due to their good accessibility. In addition, findings show that the green components of the parks were generally more satisfactory to users than other amenities, indicating higher quality expectations for cultural ecosystem services in small urban green spaces. However, perceptions of park safety varied across socioeconomic groups, suggesting that views of safety did not necessarily reflect actual park security. Finally, while most respondents stated they would not want to contribute to park maintenance, young people, particularly neighborhood newcomers, showed greater willingness to volunteer for such work.