Using suitability analysis to select and prioritize naturalization efforts in legacy cities: An example from Flint,Michigan

Given the lack of market demand and the abundance of vacant lots in legacy cities, not all vacant lands can be redeveloped or even maintained in a highly manicured state. While many vacant lots are being creatively reused as community gardens and side lots, in areas where residents are few and vacancy is high, the best use for vacant lands may be in a naturalized state such as meadows or forests. The author argues that in legacy cities, the critical question is not whether to naturalize (i.e. to stop mowing lots and allow for succession), but rather how to determine which properties to naturalize, in what order, and how. Using the example of Flint, Michigan, the author proposes suitability analysis as a method for selecting and prioritizing naturalization. Every property in the city of Flint was assigned a naturalization score derived by calculating subscores on nine variables, weighing the subscores by their importance, and summing. The nine variables included were contiguous vacant land, prospective vacancy, public ownership, land use designation, parks adjacency, proximity to industry, waterway buffers, property values, and population change. The naturalization scores can be combined with the results of a prior study to create a vacant land use decision tree pre- and post-demolition. Ultimately, the purpose of the paper is to facilitate property selection for naturalization while encouraging public discourse around what should happen with vacant lots in legacy cities.     

Multiple ecosystem services of informal green spaces: A literature review

Informal green spaces (IGS) such as overgrown vacant lots and urban brownfields constitute a considerable amount of green resources in the city. Given that the increasingly competitive land use of the urban area, enhancing the potential ecosystem services (ES) of IGS through design and management practices is of critical importance. This literature review paper provides an overview of ES delivered by urban IGS: What types of IGS have been discussed? Which ES have been identified in IGS, what interrelationships among different types of ES have been identified, and how can the potential of IGS be enhanced by urban design practices? 112 scientific papers were analyzed for their 1) IGS terms applied, 2) ES studied, 3) current or potential ES discussed, 4) ES trade-offs, and 5) ES assessment methods. Through the review, we found that although different types of ES have been identified in IGS, most studies did not consider ES synergies and trade-offs. The few studies assessing trade-offs of ES in IGS mostly focused on large-scale IGS such as urban brownfields rather than on small-scale IGS such as vacant lands/lots. The literature review highlights two knowledge gaps for future research: the first one is to explore the design and management knowledge that integrate multiple ES in small-scale IGS based on the assessment of potential ES trade-offs and synergies; the second one is to develop the spatial assessment of ES trade-offs and synergies, which is the key to envision design and management interventions that optimize the benefits of IGS. The literature review promotes the acknowledgement of the term IGS through highlighting their value in ES provisioning and further outlines future research directions on small-scale IGS such as vacant lands/lots and patches of spontaneous vegetation.     

Greening potential of derelict and vacant lands in urban areas

This research proposes a more complete, easy and unique method to assess the greening potential of derelict and vacant urban lands in order to prioritize them for reclamation. Greening these lands can convert a problem into an opportunity, assuming that green spaces must fulfill multiple functions, being part of a green infrastructure. The evaluation cover a wide range of criteria that reflect the complexity of the city and consider environmental, ecological, social and economic aspects related to the local urban structure. The criteria were organized into three groups: ecology, stormwater, and community. For each criterion, there are quantitative or qualitative indicators, measured by continuous, binary or multi-categorical parameters converted into numerical values in order to create a ranking score from highest to lowest potential of greening. The city São Bernardo do Campo, in the Metropolitan region of São Paulo, Brazil, was chosen as the case study to apply this method. The city is experiencing a post-industrial process and has few urban green spaces accessible to the community, while there are several empty and abandoned areas. We identified and mapped sixty derelict and vacant lands, of which ten were chosen as samples to evaluate. The results revealed that 40% of evaluated lands have high potential to reclaim into green spaces, 40%, medium potential and 20%, low potential. Nature or vocation as green spaces was also evaluated: 50% of them have social importance, 20%, environmental, and 30% socio-environmental. The vocation is an important information since it identifies some areas that despite their medium-low potential, they should not be rejected due to their social value. The results can drive a preliminary environmental planning decision making, to be applied in any city that faces similar problems of land dereliction, offering support to professionals to prioritize the reclamation of new urban green spaces.     

Importance of urban street tree policies: A Comparison of neighbouring Southern California cities

Research points to numerous benefits provided by urban street trees including qualitative and quantitative public health, economic, and environmental advantages for a city and its residents. As with other key aspects of city management that help develop municipal success, urban forestry requires foresight, commitment and planning that lead to effective policies and strategies. Good street tree management based on effective policies can maximise street tree benefits. Poorly conceived policies or the absence of effective policies can lead to the opposite result. A case study of the neighbouring cities of Loma Linda and Redlands, California illustrates this difference. The urban tree care and protection policies in these two cities have evolved differently. The differences may be attributable to contrasting municipal commitments to preservation and to best-practice management principles. Based on a comparative analysis of street tree policies of the two cities, it can be concluded that a local culture favouring tree protection and reflective guidelines and policies can result in proactive and successful management of an urban forest. Such policies also include provision for gathering data essential for strategic tree planting, care and removal.     

Perception and preferred reuse of vegetated vacant lots along main streets in a shrinking city

Vacant land in cities is linked to generating insecurity and urban decline. However, vegetated vacant lots offer easy opportunities for reuse and have ecological, economic, and social potential. Four medium-sized vacant lots (0,7–1,5 ha) with spontaneous vegetation located along main streets in Ostrava (Czechia) have been purposefully selected for this study. Structured interviews (n = 383) were collected to assess the perception of passers-by and their reuse preferences for these lots. Structural equation models were then performed to test the effect of sociodemographic variables. This paper aims to evaluate whether vegetated vacant lots in a historic urban fabric are perceived as an asset or liability by visitors and to assess the prospects for a publicly-accepted reuse of such spaces in a shrinking Central European city. Results indicate that the selected lots are perceived ambivalently. Older visitors show a more positive perception of the vacant lots, while no significant gender differences were identified. Educated respondents visited the vegetated vacant lots less often and perceived them more negatively compared to their less educated counterparts. Policy implications are provided in the end.     

From borders to ecotones – Private-public co-management of urban woodland edges bordering private housing

This paper conceptualises and evaluates so-called co-management zones as an approach for user participation in urban forestry, specifically in the management of public woodland edges bordering residential areas. Co-management zones can metaphorically be viewed as ‘ecotone-like’ spaces, i.e. zones where overlapping interest – in this case residents’ and municipal authorities’ – can be used to create richness and meetings rather than boundaries. Building on the perspectives of ecotone thinking and governance arrangements, co-management zones in the Danish residential area of Sletten in Holstebro were evaluated. The presented case study combined interviews with residents and interviews with three key green space professionals who had led the planning, design, establishment and management of the woodland and the implementation of co-management. The resident participation in the co-management zone was also assessed and photo documented in a field survey, categorising individual households according to type and degree of physical signs of participation. Findings illustrate the potential of co-management zones to initiate collaboration between residents and public woodland managers in creating recreationally valuable and varied meetings between private gardens and urban woodlands. Challenges with establishing co-management zones were also highlighted, especially the need for clear guidelines and continuous communication between residents and the municipality. Perspectives and implications related to residents, managers and green space quality are discussed.     

Drivers of spontaneous and cultivated species diversity in the tropical city of Zhanjiang,China

Urban plant diversity influences the social functioning and well-being of urban dwellers. However, the patterns and drivers of plant diversity in tropical urban areas are still not entirely understood. In response to the knowledge deficiencies in this area, we investigated spontaneous and cultivated plant richness and their phylogenetic diversity and relatedness in 260 Urban Functional Units (UFUs), which represented nine different land use types according to anthropogenic function, in the tropical coastal city of Zhanjiang, China. Plant diversity was modelled as a function of UFU characteristics and human maintenance practices. Spontaneous species richness was highest in urban villages and vacant lands and lowest in transportation areas, while phylogenetic diversity was highest in utilities and lowest in parks. In comparison, cultivated species richness was highest in multi-family residential areas and lowest in vacant lands, while phylogenetic diversity of cultivated species was highest in commercial/industry areas and lowest in agriculture areas. The number of cultivated species and the degree of phylogenetic relatedness of spontaneous species were positively correlated with the human population density. The phylogenetic diversity of cultivated species within UFUs was generally higher than that of spontaneous species. Human maintenance of landscapes acted as an environmental filter for spontaneous species, but also promoted the number of cultivated plants. We conclude that appropriate investment in urban green areas may improve both plant species richness and phylogenetic diversity in urban environments.     

Adaptive planting design and management framework for urban climate change adaptation and mitigation

Implementing measures to adapt and mitigate climate change effects in cities has been considered increasingly urgent since the quality of life, health, and well-being of urban residents is threatened by this change. Novel communities of plant species that emerge and thrive in the harsh conditions of cities may represent a promising opportunity to address climate change adaptation and mitigation through the planting design and management of urban green spaces. The objective of this study is to develop an adaptive planting design and management framework. The proposed framework is grounded on previous adaptive approaches and focuses on the opportunities emerging from novel plant communities in urban conditions. The framework comprises three main steps (1 – Climate change assessment, 2 – Plant species database, and 3 – Planting design and management procedure). A proposal on how the framework could be tested was developed for the city of Porto, Portugal. Still, the application of the framework can also be adjusted to other urban contexts, offering a starting point for experimentation and assessment of plants’ adaptation and mitigation capacities through design and management. As lack of knowledge and uncertainty about climate change limits global capacity to implement robust adaptation and mitigation strategies, building knowledge in an adaptive way and context-specific locations will be of paramount interest to tackle climate change in cities.     

Branching out to residential lands: Missions and strategies of five tree distribution programs in the U.S

Residential lands constitute a major component of existing and possible tree canopy in many cities in the United States. To expand the urban forest on these lands, some municipalities and nonprofit organizations have launched residential yard tree distribution programs, also known as tree giveaway programs. This paper describes the operations of five tree distribution programs affiliated with the Urban Ecology Collaborative, a regional network for urban forestry professionals. We analyzed the programs’ missions, strategies, and challenges as reported through surveys and interviews conducted with program staff. The programs were led by nonprofit organizations and municipal departments in New York City, NY; Baltimore, MD; Philadelphia, PA; Providence, RI; and Worcester, MA. These organizations focused their tree distribution efforts on private residential lands in response to ambitious tree canopy or planting campaign goals. We assessed these programs through the framework of urban forests as social-ecological systems and discuss the programs’ biophysical, social and institutional contexts. Programs face principle-agent problems related to reliance on individual tree recipients to meet goals; their institutional strategies meant to ameliorate these problems varied. Differing organizational and partner resources influenced the programs’ abilities to perform outreach and follow-up on tree performance. Programs attempted to connect with diverse neighborhoods through free trees, targeting areas with low existing canopy, and forging partnerships with local community groups. Given tree recipients’ demand for smaller flowering or fruiting trees, as well as lack of resources for tree survival monitoring on private lands, program leaders appeared to have turned to social measures of success − spreading a positive message about trees and urban greening − as opposed to biophysical performance metrics. We conclude with suggestions for outcomes monitoring, whether those outcomes are social or biophysical, because monitoring is critical to the sustainability and adaptive management of residential tree programs.     

Exotic trees contribute to urban forest diversity and ecosystem services in inner-city Cleveland,OH

Vacant land, a product of population and economic decline resulting in abandonment of infrastructure, has increased substantially in shrinking cities around the world. In Cleveland, Ohio, vacant lots are minimally managed, concentrated within low-income neighborhoods, and support a large proportion of the city’s urban forest. We quantified abundance, richness, diversity, and size class of native and exotic tree species on inner-city vacant lots, inner-city residential lots, and suburban residential lots, and used i-Tree Eco to model the quantity and economic value of regulating ecosystem services provided by their respective forest assemblages. Inner-city vacant lots supported three times as many trees, more exotic than native trees, and greater tree diversity than inner-city and suburban residential lots, with the plurality of trees being naturally-regenerated saplings. The urban forest on inner-city vacant lots also had two times as much leaf area and leaf biomass, and more tree canopy cover. The quantity and monetary value of ecosystem services provided by the urban forest was greatest on inner-city vacant lots, with exotic species contributing most of that value, while native taxa provided more monetary value on residential lots. The predominately naturally-regenerated, minimally managed exotic species on vacant land provide valuable ecosystem services to inner-city neighborhoods of Cleveland, OH.     

Green space branding in Denmark in an era of neoliberal governance

City place branding, an entrepreneurial urban development scheme, aims to differentiate cities from their national and international competitors based on strengths and competitive advantage. One such strength is quality urban green space which has been shown to make cities more attractive and liveable places, drawing people and investments to urban centres. Applying a place branding approach, this paper presents the results of a survey of Danish municipalities and their place branding in terms of crafting green city, or environmentally sustainable, profiles. Based on survey responses from both municipal green space and communication staff, an overview is presented of the status of ‘green’ municipal place branding, with emphasis on branding through green spaces such as parks. Findings show that green concepts such as environmentally sustainable policies as well as biophysical assets such as green spaces are not in focus in municipal place branding campaigns. Moreover, survey results demonstrate that creative professionals and local citizens are the main focus of those municipalities that are branding. There is great potential to emphasize green spaces in municipal placing branding campaigns building on partnerships with the private sector and citizen volunteers.     

Envisioning the future—Creating sustainable,healthy and resilient BioCities

Numerous challenges – from population increase to climate change – threaten the sustainable development of cities and call for a fundamental change of urban development and green-blue resource management. Urban forests are vital in this transition, as they provide various ecosystem services and allow to re-shape and re-think cities. Based on a Europe-wide community effort with diverse experts centered around urban forests and urban greening, we propose five key research fields to generate the knowledge required to unlock fundamental changes in urban development and green-blue resource management: circular bioeconomy, climate resilience, governance, social and human environment, and biodiversity. To support the design of greener, cooler, more inclusive and resilient cities, all these research fields require inter- and transdisciplinary collaboration, engaging stakeholders in transforming urban engagement and functioning. We summarise main inter-, trans- und multi-disciplinary research paths for each field and the cross-cutting knowledge areas that can help to address the challenges many cities face (e.g., modelling and assessment of the urban microclimate). For transforming cities further knowledge is needed on e.g., urban innovation, transition, participation, and more. Finally, we address how the identified research gaps can be implemented (e.g., international coordinated research effort, interdisciplinary networks).     

Canadian urban tree canopy cover and carbon sequestration status and change 1990–2012

Urban trees provide numerous ecosystem goods and services by providing shade, habitat for wildlife, removal of air pollutants and the removal and storage of atmospheric CO₂. Carbon removal services provided by Canadian urban trees have previously been assessed using an IPCC 2006 guidelines approach based on the percentage of urban area covered by tree canopy (UTC) for the 2012 time period (Pasher et al., 2014). That work however provided only a single point in time assessment of the national scale UTC and carbon removal services. The research undertaken for this study was a continuation of this earlier work focusing on a 1990 national scale UTC assessment and carbon sequestration estimates for 1990. UTC estimates for 1990 were developed using a point sampling approach with circa 1990 air photos covering a large portion of Canadian urban areas. In total almost 179,000 points were sampled for the 1990 time period, reassessing 83% of the points used for the previous 2012 assessment. Based on the urban area boundary layers for 1991 and 2011, Canada’s urban areas grew by an estimated 6% for this time period. Most of this growth occurred through conversion of agricultural and forested lands to urban. At the national scale the UTC for 1990 was estimated to be 27.6%, as compared to the 2012 UTC estimate of 26.1%, the difference between estimates for the two time periods fell within the uncertainty range. Carbon removal estimates based on the UTC estimates were also very similar for the two dates with 660.2 kt C removed in 1990 and 662.8 kt C removed in 2012. It was noted that urban development in the Prairie regions resulted in an increase in tree cover as compared to the pre-conversion agricultural and natural landscapes and also that in most urban areas across the country UTC increases through time as tree cover matured in newly developed urban areas. These two assessments provide a time series of urban trees for 22 year time period, which will be useful for further studies and analysis.     

Values and beliefs about urban forests from diverse urban contexts and populations in the Greater Toronto area

Cities around the world are diverse. People’s perceptions of urban forests may vary according to urban contexts and people’s diverse identities. A better understanding of these diverse perceptions is critical to support stewardship initiatives, inform urban tree decisions, and guide community engagement, among other key management and governance processes in urban forestry. This study examines the values and beliefs that diverse people living in a variety of urban contexts associate with urban trees. Using an urban gradient approach, 2009 responses were collected through an online panel survey conducted in the Greater Toronto Area (GTA) to understand variations in values and beliefs of urban forests across municipal types (inner core, suburban, peri-urban, and regional cities). The GTA has an ethnoculturally diverse population, allowing us to also explore perceptions held by people with various identities. The study uses analytical techniques, such as means differences and linear regression models, to segment the diverse meanings people attribute to urban trees by municipal types and people’s identities. The results show that, while people value the urban forest very highly, people’s value orientations vary depending on their context and identities. For example, respondents who speak European or South Asian languages tend to hold value orientations related to cultural, social, and identity issues. Respondents living in inner municipal types tend to hold values related to identity issues, whereas respondents living in outer municipal types and regional cities tend to hold values related to natural issues. The results also show that people’s beliefs about urban forests are primarily positive. Urban forests managers and stewardship initiatives should recognize the diverse set of values and beliefs that people associate with urban forests, incorporating these perceptions into policy and programs. Additionally, since specific value and belief orientations may depend on personal identity and urban contexts, tailored messaging may also help generate support for policy or stewardship initiatives across different communities and in varied urban contexts.     

The public consultation is open: Insights from urban green infrastructure planning in Romania

Due to its potential to help mitigate current societal challenges and provide ecological, social, and economic benefits, urban green infrastructure (UGI) is an important investment for cities. However, its planning and implementation may be challenging due to the limited application of the conceptual foundations and the often-unknown character of the ways how the results of public consultations were integrated into the implemented UGI design. Using five Romanian urban areas as model system, we developed an evaluation protocol to assess 177 written comments submitted during the public consultation processes for 13 public UGI planning documents, along with the formal responses to these comments. Our results show critical comments towards the planning proposals (86.2 % of the comments) and a discussion of the shortcomings of the planning process (60.8 % of the comments). The analysis revealed that the UGI as it is developed and implemented currently in Romania has little public support as in 52.2 % of the comments none of UGI planning principles could be identified. Furthermore, we found a relatively low level of public comment consideration into the approved version of the planning documents as only 7.6 % of the comments were included, most of them being delegitimized by the responses of public officials/municipal administration. Thus, our results highlight that UGI consultation process is characterized by a lack of both genuine conceptual aspects and public participation substance.     

重金属污染土壤园林植物修复研究进展

我国土壤重金属污染形势严峻,直接威胁着人类健康,受到普遍关注,各种重金属污染土壤修复技术成为研究热点。植物修复技术因其安全、廉价,被认为是修复重金属污染土壤较好的措施之一,其中园林植物具有美化环境、不进入食物链及可带来环境效益等优势而成为植物修复领域的研究热点。该研究通过文献资料查阅,阐述了近年来关于园林植物对我国主要重金属污染土壤的修复效果,并从园林植物种类、富集特性、耐受性和环境效益几个方面进行了分析,最后,对进一步开发园林植物修复重金属污染土壤的研究方向进行了展望,为重金属污染土壤园林植物修复研究与应用提供参考。     

Urban greenspace delivery in Hong Kong: Spatial-institutional limitations and solutions

Hong Kong has developed an ultra-dense urban form dominated by buildings and roads with inadequate urban greenspace (UGS). Analyzing the fundamental constraints to UGS provision offers hints for improvements which are relevant to other compact cities. Twenty-five current issues regarding institutional and spatial limitations were evaluated with reference to three themes: open-space planning standards, urban-design guidelines and urban-greening governance. They were studied by interpreting relevant parts of government documents spanning the 1980s to 2015, map analysis, and field assessments. UGS standards of selected cities, and extensive research findings and practices reported in the literature specific to the respective constraints, have been enlisted for comparison and as the basis for formulating recommendations to improve delivery quantity and quality. The low local supply at merely 2.84 m²/person is tied down by outdated planning standards and policies which have remained unchanged for eight decades. UGS planning, design and management could be enhanced based on urban ecology and landscape ecology principles and best international practices, with suitable adjustments catering to local circumstances and the inordinately tight urban fabric. The package of suggested solutions in relation to the 25 institutional and spatial constraints could be considered for applications in other cities with compact precincts or undergoing densification to forestall problems and resolve difficulties.     

Adaptive governance of urban green spaces across Latin America – Insights amid COVID-19

Urban green spaces’ well documented role as a hub for physical and mental health was enhanced by restrictions to mobility issued worldwide as a response to COVID-19. In this context, managers of urban green spaces (UGS) were prompted to provide controlled access under impromptu safety protocols. This unprecedented challenge required planning and operational strengths reflecting flexibility, innovation and learning. These management features are essential for an adaptive governance – an underdeveloped research topic within the study of UGS. Using eighteen semi-structured interviews from six countries, we analyze adaptive governance as reflected by UGS managers’ responses across Latin America – a region where access to UGS is a matter of public health and of environmental justice. We document responses that can be categorized based on the governance arrangement in place. On one hand, both polycentric and dedicated-management governances have been able to learn through piloting ideas, adapting personnel roles and the function of UGS infrastructure, and adjusting their decision-making process. On the other hand, managers within municipal public services areas – the most prevalent governance arrangement across Latin America – report difficulty to adapt – likely due to their dependence on political will, limited autonomy, insufficient budgets, absence of formal paths to self-funding, shortage of technical know-how, and insufficient citizens’ involvement. We discuss implications of UGS adaptive governance in terms of capacity to deal with future public health, climate-related or other types of shocks.     

Contrasting natural regeneration and tree planting in fourteen North American cities

Field data from randomly located plots in 12 cities in the United States and Canada were used to estimate the proportion of the existing tree population that was planted or occurred via natural regeneration. In addition, two cities (Baltimore and Syracuse) were recently re-sampled to estimate the proportion of newly established trees that were planted. Results for the existing tree populations reveal that, on average, about 1 in 3 trees are planted in cities. Land uses and tree species with the highest proportion of trees planted were residential (74.8 percent of trees planted) and commercial/industrial (61.2 percent) lands, and Gleditsia triacanthos (95.1 percent) and Pinus nigra (91.8 percent). The percentage of the tree population planted is greater in cities developed in grassland areas as compared to cities developed in forests and tends to increase with increased population density and percent impervious cover in cities. New tree influx rates ranged from 4.0 trees/ha/yr in Baltimore to 8.6 trees/ha/yr in Syracuse. About 1 in 20 trees (Baltimore) and 1 in 12 trees (Syracuse) were planted in newly established tree populations. In Syracuse, the recent tree influx has been dominated by Rhamnus cathartica, an exotic invasive species. Without tree planting and management, the urban forest composition in some cities will likely shift to more pioneer or invasive tree species in the near term. As these species typically are smaller and have shorter life-spans, the ability of city systems to sustain more large, long-lived tree species may require human intervention through tree planting and maintenance. Data on tree regeneration and planting proportions and rates can be used to help determine tree planting rates necessary to attain desired tree cover and species composition goals.     

A municipal forest report card: Results for California,USA

This study integrates two existing computer programs, the Pest Vulnerability Matrix and i-Tree Streets, into a decision-support tool for assessing municipal forest stability and recommending strategies to mitigate risk of loss. A report card concept was developed to communicate levels of performance in terms that managers and the public easily understand. Grades were assigned to four aspects of a stable and resilient municipal forest: Species Dominance, Age Structure, Pest Threat and Potential Asset Loss. The data pool of 29 California municipal forest inventories contained information on 836,943 trees. Letter grades (A–F) were assigned to the four criteria and each city received customized recommendations for improving its grades. Three inventories received final grades of As, 18 received Bs, 6 Cs and 2 Ds. Twelve inventories received their highest grade for Species Dominance. Thirteen inventories received their lowest grade for Age Structure, largely because juvenile trees were underrepresented. Pest Threat received the lowest grade in 11 inventories and reduce Pest Threat was the top priority recommendation in 18 inventories. Four multi-host pests posed the greatest risk: Granulate ambrosia beetle, Asian longhorned beetle, Armillaria root rot and red palm weevil. Sycamore/plane was the most vulnerable taxon, followed by oaks, ash and eucalyptus. Eliminating or limiting the use of highly vulnerable tree species was recommended in nearly every city to reduce Pest Threat and improve Species Dominance. Increased planting of vacant sites with species not vulnerable to the most abundant and severe pests was a frequent recommendation for improving Age Structure. Another common recommendation to improve Age Structure was planned removal and replacement of overabundant mature and senescent taxa such as pear, eucalyptus, jacaranda and carrotwood.