Municipal Tree Research Articles

Expectations of i-Tree Eco as a tool for urban tree management in Nordic cities

While urban forests are recognized as imperative toward climate adaptation in cities and provide health and recreational benefits to citizens, municipal tree officers often struggle to find successful governance arrangements and budget support toward long-lasting investment and implementation in new planting schemes and protection of existing trees. Since its release in 2006, i-Tree Eco has helped urban tree officers worldwide to find tangible leverage in the means of quantitative mapping, numeric measures, and economic values of ecosystem services. This may in turn help ease gridlocks and potentially support constructive dialogues across sectors, with decision-makers and public engagement. With the release of i-Tree Eco v. 6 in Europe 2018, 13 Nordic cities were engaged in a larger research project with ambitions to use i-Tree Eco for the purpose of retrieving numeric and monetary data of the biophysical structures and ecosystem services of the urban forest. Based on questionnaires and semi-structured interviews, we present the results from the Nordic i-Tree project with a focus on expectations, opportunities, and potential barriers experienced in using i-Tree Eco in urban forest management. The most prominent expectation and foreseeing opportunities were recognized toward using numeric information on trees to change policies and support cross-sectoral collaboration while reaching politicians and the public. Identified barriers involved how limited resources are spent on public outreach and how information about the project to relevant stakeholders were not distributed from the beginning which may have implications on the dissemination of results. As some important ecosystem services, e.g., cultural services, are not captured by i-Tree Eco, presenting the partial value of urban trees may pose also potential risks to cross-sectoral collaboration. Other findings conclude that although numeric information on ecosystem services is seen as beneficial in terms of communicating with different stakeholders, a deeper understanding toward the criteria used in the valuation process and the potential risks of numeric approaches may provide more context-specific applications.

Progressing towards Estimates of Local Emissions from Trees in Cities: A Transdisciplinary Framework Integrating Available Municipal Data, AI, and Citizen Science

Urban tree cadastres, crucial for climate adaptation and urban planning, face challenges in maintaining accuracy and completeness. A transdisciplinary approach in Kaiserslautern, Germany, complements existing incomplete tree data with additional precise GPS locations of urban trees. Deep learning models using aerial imagery identify trees, while other applications employ street view imagery and LIDAR data to collect additional attributes, such as height and crown width. A web application encourages citizen participation in adding features like species and improving datasets for further model training. The initiative aims to minimize resource-intensive maintenance conducted by local administrations, integrate additional features, and improve data quality. Its primary goal is to create transferable AI models utilizing aerial imagery and LIDAR data that can be applied in regions with similar tree populations. The approach includes tree clusters and private trees, which are essential for assessing allergy and ozone potential but are usually not recorded in municipal tree cadastres. The paper highlights the potential of improving tree cadastres for effective urban planning in a transdisciplinary approach, taking into account climate change, health, and public engagement.

Analysis Options for Urban Green Spaces Based on Unified Urban Masks: Selected Results for European Cities

At a time of rising urbanisation and climate change, urban green spaces (UGSs) are an essential element to help adapt to extreme weather events. Especially in urban core areas, heat and drought are regarded as human stress factors. The delineation of such areas constitutes an important reference geometry in topographic geodata (urban mask). This article deals with possibilities for investigating UGSs in European cities—based on unified urban masks—by applying city-wide metrics to Copernicus data (Urban Atlas including the Street Tree Layer). Both public and tree-covered urban green spaces are examined in detail. Selected results are presented for 30 European cities that display a wide range of urban structures. The spatial reference to uniformly delineated urban masks places the analytical focus of city-wide metrics onto corresponding core areas. In general, the values of UGS metrics vary considerably between cities, indicating the strong influence of city-specific factors on urban structures in Europe. For the comparative analysis of tree-covered urban areas, the Urban Green Raster Germany and a municipal tree register are used to provide additional data sources. The regular updating of the Copernicus dataset means that green spaces in European cities can be monitored, also using urban masks.

Emotional geographies of an urban forest: Insights from an email‐a‐tree initiative

AbstractInternational and national policies are being used to prioritise increases in urban forest coverage and diversity, support equitable access to urban greenspaces, and advance sound environmental governance outcomes. Yet, the relationship between people’s feelings about urban trees and public policy remains under‐examined. Drawing on a unique dataset from an email‐a‐tree initiative, the objectives of this study were to identify how concern and connection for urban trees is expressed and determine how insights from the initiative might inform urban forest governance. We examined emails sent to trees using a mixed‐methods approach that included qualitative coding, VADER sentiment analysis, and statistical and spatial analyses. We identified and considered three themes based on emails sent by members of the public and municipal tree inventory data. Those themes were location, age and loss, and type. In accord with other studies, overall sentiment for urban trees was positive and underscored people’s strong connections with trees, often based on routine and repeated engagements. However, people noticed and were concerned about a limited range of trees and tree types in urban settings. Based in Melbourne, Australia, our case study shows how examining feelings for trees helps residents and researchers understand urban tree relationships and gauge how those designing public engagement programs might learn from such an initiative to create meaningful opportunities for active participation in governance.

The ecosystem disservices of trees on sidewalks: A study based on a municipality urban tree inventory in Central Italy

Urban green infrastructure, including street trees, plays a key role in providing ecosystem services to urban residents. However, to fully understand the effective role of trees in the urban context, it is also necessary to evaluate the disservices that they can produce in the development of their functions if not managed in an adequate and integrated way. This contribution aims to demonstrate an approach to assess three disservices (pavement damage, aesthetic damage, likelihood of tree failure) of street trees at the municipal level, starting from the existing municipal tree inventory. In this case study, from the street tree population, a sample of approximately 5% of the trees was drawn by stratified random sampling, where the strata were composed of groups of tree species. In particular, a sampling scheme is adapted in which the probability to select a tree in the sample is greater for bigger trees, under the assumption that the bigger the trees the greater are the disservices caused. In this way, a greater precision of the estimates of the considered disservices for the population of urban trees is expected. The results show a high variability of disservices provision among species groups. The results also confirmed a positive correlation between the considered disservices and tree diameter at breast height, while other tree attributes such as total height and crown diameter were found to be positively related only to pavement damages. Finally, severe pruning can lead to a high level of the aesthetic and functional disservices even for shorter and younger street trees.

Value ‘generalisation’ in ecosystem accounting - using Bayesian networks to infer the asset value of regulating services for urban trees in Oslo

In this paper, we demonstrate value generalisation from a sample of ecosystem assets – municipally managed trees - to all tree assets within an urban ecosystem accounting area. A Bayesian network model is used to machine-learn non-parametric correlation patterns between biophysical site condition variables and output variables of an ecosystem service model – here iTree Eco for modelling the regulating services of urban forests. The paper also demonstrates the use of spatial Bayesian network modelling to quantify the reliability of value generalisation for accounting purposes. Value generalisation entails inferring ecosystem service values for all locations in an ecosystem accounting area, where the accounting practitioner has less information about the asset and its context, than in an available sample of managed sites within the accounting area. The modelling is carried out as a “proof-of-principle” of potential value generalisation and uncertainty analysis methods for ecosystem accounting. It does not cover all regulating ecosystem services of urban forests, nor cultural services. While noting that wide confidence intervals for generalised values pose challenges for using monetary accounts for the accounting purpose of change detection, we find that tree-specific asset valuation is possible in an urban accounting setting. Our findings serve the purpose of raising awareness about asset values of urban green infrastructure, to bring them more on a par with grey infrastructure in urban planning. We also argue that the reliability of the asset value of individual trees is also good enough to be used for non-accounting purposes, such as municipal tree damage assessments.

Expanding Urban Tree Species Diversity in Florida (USA): Challenges and Opportunities for Practitioners

While many practitioners and scholars understand the risks associated with low urban tree diversity, they often lack the ability to rectify this challenge on their own. The complex system of tree production and procurement is shaped by market pressures, nursery and site constraints, local governance, and differing professional objectives among those who grow, specify, and plant trees. To understand constraints to and opportunities for increasing urban tree diversity, we conducted a series of focus groups comprised of nursery growers, landscape architects, and municipal tree managers. Our results highlight a significant list of considerations and constraints to diversity, with some issues shared among green industries and some specific to growers or purchasers. In light of our findings, we outline actionable strategies for increasing urban tree diversity.

The impact of pruning and mortality on urban tree canopy volume

Urban trees provide a wide range of ecosystem services for city residents, with tall, mature trees with wide crowns generally regarded as preferable. The tree biomass which is responsible for shading, pollution removal, rain runoff retention etc. gets periodically reduced by the municipal tree management practice of pruning. This is a necessary activity, which reduces the risk of infrastructure damage and falling branches, but many estimates of ecosystem service provision in cities do not consider its impact explicitly. Tree mortality is also higher in cities, preventing trees from attaining and remaining at large sizes. This study used extensive field measurements of tree structure to estimate the impact of pruning on 8 tree species in two Italian cities: Taranto and Florence. Crown widths were reduced by 1.6 m on average, however there is large variation between species variation with branches more often being removed for thinning crowns resulting in larger gap fractions, which increased by 15% on average. No significant differences were observed for crown widths or gap fraction between trees pruned 3 and 4 years previously, suggesting that tree crowns structurally recover from pruning after 3 years. A deterministic model revealed that current urban forest pruning rates (every 6 years) and mortality (1%) may create a situation in which a city dominated by the species studied benefits from 93.5% of the maximum ecosystem services possible. This work will allow more nuanced estimates of urban forest services to be calculated.

Municipal Employees’ Perceptions of Tree Risk and Liability in Alabama

Abstract Research about the broad range of ecological, social, and economic benefits urban forests provide communities trees has expanded significantly and helped provide justification for protecting and enhancing urban forests. However, an empirical understanding of risks and liabilities is limited despite an abundance of risk research in other disciplines. Employing Alabama as a case study, this research examined municipal employees’ perceptions of factors, including legal liability, influencing actions towards urban tree risk mitigation. Qualitative interviews revealed attitudes and practices regarding municipal responsibility towards public tree management. Cities were unlikely to implement risk assessments to provide a foundation for tree maintenance. As a result, there was limited adaptive and integrative governance to handle risk in the community forest. Results are implicated in the broader narrative of community sustainability and resilience, particularly management of complexity, uncertainty, and ambiguity of urban forest risk and benefits. Study Implications: Large-population cities were equipped to address tree maintenance, implement best management practices, and focus on preventative risk management. However, all cities were limited in capacity to conduct comprehensive tree risk assessments and communicate with residents about proper tree selection and care to reduce risk of failure. Whereas this has negative implications for community resilience, a number of small and medium-sized communities demonstrated opportunities to address urban forest health such as harnessing employee champions, local sources of expertise, and encouraging volunteerism. Municipal tree programs should not overlook community assets and culture in the goal to reduce risk while maximizing tree benefits.

Potential impacts of the invasive Agrilus planipennis on various demographics in Winnipeg, Canada

The hardiness of Fraxinus spp. (ash) makes them a common municipal tree in adverse growing conditions. In Winnipeg, Manitoba, the impacts of Dutch elm disease resulted in increased reliance on Fraxinus, resulting in a monoculture of Fraxinus across the city. Emerald ash borer (EAB) (Agrilus planipennis) poses substantial risk to Winnipeg's urban forest, forecasted to result in the total loss of Fraxinus in Winnipeg. With a lens of distributional equity, this study examines associations between Fraxinus abundance and distribution and human population demographics at the Dissemination Area and Census Tract levels. There are positive correlations with Fraxinus abundance and distribution and median household income and proportion of the population that self-identifies as a visible minority. Population density was positively associated with Fraxinus abundance and distribution at the Census Tract level. These results underscore the importance of assessing the distribution of vulnerable trees as a component of green equity. Using information on urban forest management in response to EAB, potential issues and possible opportunities are discussed.

Historical Urban Tree Canopy Cover Change in Two Post-Industrial Cities.

Present-day spatial patterns of urban tree canopy (UTC) are created by complex interactions between various human and biophysical drivers; thus, urban forests represent legacies of past processes. Understanding these legacies can inform municipal tree planting and canopy cover goals while also addressing urban sustainability and inequity. We examined historical UTC cover patterns and the processes that formed them in the cities of Chelsea and Holyoke, Massachusetts using a mixed methods approach. Combining assessments of delineated UTC from aerial photos with historical archival data, we show how biophysical factors and cycles of governance and urban development and decay have influenced the spatiotemporal dynamics of UTC. The spatially explicit UTC layers generated from this research track historical geographic tree distribution and dynamic change over a 62-year period (1952-2014). An inverse relationship was found between UTC and economic prosperity: while canopy gains occurred in depressed economic periods, canopy losses occurred in strong economic periods. A sustainable increase of UTC is needed to offset ongoing losses and overcome historical legacies that have suppressed UTC across decades. These findings will inform future research on residential canopy formation and stability, but most importantly, they reveal how historical drivers can be used to inform multi-decadal UTC assessments and the creation of targeted, feasible UTC goals at neighborhood and city scales. Such analyses can help urban natural resource managers to better understand how to protect and expand their cities' UTC over time for the benefit of all who live in and among the shade of urban forests.

Volunteer engagement in urban forestry in the United States: reviewing the literature

ABSTRACT This article presents the results of a literature review related to volunteerism in urban forestry in the United States. Themes explored were inductively emergent from the research reviewed and included ‘volunteer demographics’, ‘motivations of volunteers’, ‘benefits of volunteering’, ‘volunteer engagement and barriers’, ‘value of volunteering’, and ‘volunteer recruitment and retention’. Urban forestry volunteers are often motivated by personal, social, and environmental considerations. Volunteers in urban forestry may not be representative of a cross-section of the communities that they are serving, rather they are often middle-aged, well-educated white women. Further research is required both to ascertain barriers to volunteerism and to enhance future volunteer recruitment and retainment efforts. Volunteers in the United States account for 5% of municipal tree care in urban forests – accounting for an estimated $35 million USD in value. Volunteers perform critical urban forestry-related tasks that aim to increase urban tree canopy cover through tree selection and planting efforts. Volunteers encourage urban tree survival by advocating for, as well as performing, important maintenance-related duties including the administration of supplemental watering and urban tree pruning. With proper training and support, volunteers may accurately perform important data collection efforts that may inform management decisions and urban tree care maintenance programmes.

Urban Planning Insights from Tree Inventories and Their Regulating Ecosystem Services Assessment

With the uncertainties that our societies are living with (the COVID-19 pandemic and climate change), it becomes essential to provide urban planners and decision-makers with state-of-the-art and user-friendly methodologies to incorporate ecosystem service considerations into their designs for resilient cities. In this regard, urban forests play a crucial role. The quantification of the ecosystem services is geo-specific and needs studies in different urban contexts. At this scope, we evaluated the urban forest of a neighborhood of a densely built-up Italian city (Perugia) with a low level of urban greenery management and with a tree inventory still in progress. Furthermore, we defined a tool helpful in tree-planting decisions and management. This paper involves citizens in field research for trees inventory. Then, it uses i-Tree Eco to evaluate four ecosystem services (carbon storage and sequestration, pollution removal, and runoff avoided) provided by 373 inventoried urban trees belonging to 57 species. Our results show that Italian Municipal tree inventories do not adequately represent their urban forest and that citizens’ participation provides a cost-effective method for integrating field data. Finally, the paper develops an easy tool helping local administrations enhance the ecosystem services provisions in urban green design.

Is Street Tree Diversity Increasing in New York State, USA?

Diversity in tree populations is viewed as essential for protecting the public investment in urban trees and for preserving the environmental, social, and economic benefits that these trees provide. It is therefore crucial for officials responsible for the management of municipal trees to know the diversity of their municipal tree populations and whether their efforts to increase diversity have been effective or should be modified. We assessed street tree diversity in New York State, USA by analyzing municipal street tree inventory data from two data sets, the first comprised of 75 inventories collated from municipalities, and the second comprised of 32 sets of inventories conducted at multiple points in time. This analysis builds on two previous papers containing similar assessments by analyzing more current data and by calculating diversity index statistics and relative abundance percentages for prevalent street tree species and genera. Findings indicate that there has been substantial progress to increase street tree diversity in New York State. This progress is correlated with reductions in the dominance of Norway maple (Acer platanoides), the state’s most prevalent street tree species (17% of street trees statewide), and in the dominance of maple (Acer), the state’s most prevalent street tree genus (35% of street trees statewide). Work remains to be done to further increase species and genus diversity so as to meet the challenges posed to municipal street tree populations by invasive pests and climate change. Strategies are proposed for accomplishing this.

Tracking Changes to Urban Trees over 100 Years in Ithaca, NY, USA

Municipally managed urban trees provide environmental, social, and economic benefits. Continued provision of these benefits depends on the health and sustainability of these trees, which depends in turn on tree managers having the type of information usually found in a tree inventory. The city of Ithaca, New York, USA possesses 7 inventories of its street and park trees dating back to 1902. This paper uses the data contained in these inventories to assess the health and sustainability of the city’s street and park tree populations. Attention is given to the structure of these populations with emphasis placed on species and genera diversity and DBH size class distributions. Prior to 1987, the city’s municipal tree population was dominated by a few species, such as Norway maple (Acer platanoides), and genera such as maples (Acer) and elms (Ulmus), and the DBH size class distribution was skewed unsustainably towards older trees. From 1987 onwards, new plantings have significantly increased species and genera diversity, and the DBH size class distribution suggests sufficient younger trees to account for tree mortality and removals. These changes did not occur quickly due to the persistent legacy effect of past planting preferences and practices, but required a consistent effort by municipal tree managers over many years. As a result, based on an analysis of the most recent tree inventory conducted in 2019, the city’s street and park trees and the benefits they provide look to be on a more sustainable footing, although challenges still remain.

Increasing functional diversity of the urban canopy for climate resilience: Potential tradeoffs with ecosystem services?

Cities are home to an increasing number of people who depend on urban forests to provide ecosystem services such as temperature regulation, air quality improvement and storm water abatement. Climate change may challenge the capacity of urban forests to provide these services. Intensification of heat waves, droughts and strengthening storms could lead to tree die-offs. In Quebec City, work has suggested that the urban canopy is vulnerable to future projected climates, i.e. hotter and drier summers. Compounding this threat, the exotic emerald ash borer is expected to kill 11 % of municipal trees over the next decade. Together these pressures could lead to a significant loss of canopy cover and ecosystem service provisioning in the near-term.We test whether replanting strategies for lost ash, which shift the forest community towards a more climate-tolerant canopy using a functional trait-based approach, can help to mitigate or improve ecosystem service provisioning in the near-term. Using a municipal database of urban trees, we simulate canopy growth and replacement over 20-years for three different replanting scenarios: i) ‘business-as-usual’, ii) ‘stratified’ or iii) ‘conifer-focused’ replanting strategy, and compare their delivery of ecosystem services.Results from the simulations find clear trade-offs in ecosystem service provisioning within and between replanting approaches. The ‘conifer-focused’ scenario provides the highest level of air quality improvement, storm water abatement and reduced energy demands in winter, however there are limitations on where coniferous trees can be planted in cities. In contrast, the ‘business-as-usual’ scenario achieved greater canopy cover, carbon sequestration, and high summertime cooling, but remains vulnerable to climate change. Stratifying replanting across tree functional groups results in the greatest increase to canopy diversity, intermediate levels of ecosystem service provisioning and important reduction in vulnerability to future pests . We suggest that a replanting approach focused on increasing the functional trait diversity of the urban canopy will likely confer the greatest ecosystem service benefits to the urban population and improve the resilience of the urban canopy to pests and climate pressures in the future.

Tree preservation during construction: An evaluation of a comprehensive municipal tree ordinance

In the United States, urban forests represent 35 % of all urban land cover, and deliver benefits to nearly two-thirds of the population. As global urban populations continue to rise, however, redevelopment is continually reported as a major factor in reduced canopy cover. While urban trees provide us with measurable benefits when adequately maintained, their costs when not cared for remains poorly understood. In order to safeguard the benefits that urban forests provide, municipalities have begun to introduce ordinances with the intention to protect and manage trees within their community. The aim of this study was to better understand the condition and survival outcomes of residential trees intended to be preserved through a municipal tree preservation ordinance. The results of this study found that a comprehensive tree preservation ordinance can successfully protect tree and soil health during and after residential development occurs. This is evident through an overall preservation rate of nearly 75 %, having found no correlation between proximity to newly developed foundation and observed tree condition or mortality, and the discovery of healthy soil compaction levels within tree protection areas and the critical root zones of preserved trees. Collaborative research as demonstrated by this project can help both academics and professionals gain a better understanding of how to best manage their own urban forests.

The potential of geospatial analysis and Bayesian networks to enable i-Tree Eco assessment of existing tree inventories

Valuing the ecosystem services of urban trees is important for gaining public and political support for urban tree conservation and maintenance. The i-Tree Eco software application can be used to estimate regulating ecosystem services provided by urban forests. However, existing municipal tree inventories may not contain data necessary for running i-Tree Eco and manual field surveys are costly and time consuming. Using a tree inventory of Oslo, Norway, as an example, we demonstrate the potential of geospatial and machine learning methods to supplement missing and incomplete i-Tree Eco attributes in existing municipal inventories for the purpose of rapid low-cost urban ecosystem accounting. We correlate manually surveyed stem diameter and crown dimensions derived from airborne laser scanning imagery to complete most structural attributes. We then use auxiliary spatial datasets to derive missing attributes of trees’ spatial context and include differentiation of air pollution levels. The integration of Oslo’s tree inventory with available spatial data increases the proportion of records suitable for i-Tree Eco analysis from 19 % to 54 %. Furthermore, we illustrate how machine learning with Bayesian networks can be used to extrapolate i-Tree Eco outputs and infer the value of the entire municipal inventory. We find the expected total asset value of municipal trees in Oslo to be 38.5–43.4 million USD, depending on different modelling assumptions. We argue that there is a potential for greater use of geospatial methods in compiling information for valuation of urban tree inventories, especially when assessing location-specific tree characteristics, and for more spatially sensitive scaling methods for determining asset values of urban forests for the purpose of awareness-raising. However, given the available data in our case, we question the accuracy of values inferred by Bayesian networks in relation to the purposes of ecosystem accounting and tree compensation valuation.

Mobile Terrestrial Photogrammetry for Street Tree Mapping and Measurements

Urban forests are often heavily populated by street trees along right-of-ways (ROW), and monitoring efforts can enhance municipal tree management. Terrestrial photogrammetric techniques have been used to measure tree biometry, but have typically used images from various angles around individual trees or forest plots to capture the entire stem while also utilizing local coordinate systems (i.e., non-georeferenced data). We proposed the mobile collection of georeferenced imagery along 100 m sections of urban roadway to create photogrammetric point cloud datasets suitable for measuring stem diameters and attaining positional x and y coordinates of street trees. In a comparison between stationary and mobile photogrammetry, diameter measurements of urban street trees (N = 88) showed a slightly lower error (RMSE = 8.02%) relative to non-mobile stem measurements (RMSE = 10.37%). Tree Y-coordinates throughout urban sites for mobile photogrammetric data showed a lower standard deviation of 1.70 m relative to 2.38 m for a handheld GPS, which was similar for X-coordinates where photogrammetry and handheld GPS coordinates showed standard deviations of 1.59 m and the handheld GPS 2.36 m, respectively—suggesting higher precision for the mobile photogrammetric models. The mobile photogrammetric system used in this study to create georeferenced models for measuring stem diameters and mapping tree positions can also be potentially expanded for more wide-scale applications related to tree inventory and monitoring of roadside infrastructure.

Protecting the urban forest: Variations in standards and sustainability dimensions of municipal tree preservation ordinances

Trees help create sustainable urban systems by providing important functions aligned with the three dimensions of sustainability, i.e., environment, economy, and society. Yet urban forest loss remains a problem in expanding metropolitan regions. To accrue urban forest services, municipalities have enacted tree preservation ordinances (TPO) to regulate tree removal. These ordinances describe not only how cities manage their urban forests but also what urban forest services they value. The goals of this research are to locate cities with TPOs in Texas, compare the scope and intent of these ordinances, and assess the extent to which they reference the sustainability dimensions of urban forest services. We documented the parameters, extent, and conditions of tree protection found in TPOs via descriptive statistics and examined their statements of purpose for references to urban forest services through a quantitative content analysis (QCA). We found 60 municipalities possess TPOs, and most are in rapidly growing metropolitan areas. Our results indicate variations occur in their scope and intent. The majority of TPOs protect trees on private property but many also contain exemptions that potentially limit their effectiveness. Over half of TPOs contained a statement of purpose with references to one or more of the sustainability dimensions of urban forest services. Communities across metropolitan areas place more emphasis on the environment and society dimensions of sustainability. Overall, our results suggest that more communities should enact TPOs with less exemptions, and the sustainability dimensions of urban forests should be explored with equal vigor and stated more clearly so that all stakeholders are equipped with a better argument of not only why to write TPOs but why to enforce them.