Exploring the characteristics of successful volunteer-led urban forest tree committees in Massachusetts

Citizen engagement through urban forest tree committee volunteer service may aid in providing essential experience, ideas, and skills that support municipal tree management. Using semi-structured, research interviews with tree committee (TC) representatives from across the Commonwealth of Massachusetts, this study addresses current knowledge gaps concerning the general composition, processes, and relationships of volunteer-led urban forest tree committees. Our findings indicate that TC representatives are typically motivated, passionate volunteers who generally desire to work cooperatively with the many associations, organizations, and agencies that comprise the local socio-political landscape. Our findings also indicate it is important that TC representatives make a sustained, concerted effort to work collaboratively with their local tree warden to advance the care of their community’s urban trees. Furthermore, it is also essential that municipal managers and decision-makers attempt to provide TC volunteers with appropriate training opportunities, resources, as well as demonstrate appreciation, to further encourage and solidify volunteer-engagement in urban forestry at the local level.     

Public satisfaction with urban trees and their management in Australia: The roles of values,beliefs, knowledge,and trust

The success of urban forest management strategies is dependent on public support for and engagement with urban trees. Satisfaction with urban trees and their management, and the level of trust people have in urban tree managers, are useful for understanding public opinions. Yet these concepts, and the mechanisms leading to the formation of public opinions remain poorly explored in the literature. Here we explore how satisfaction with urban trees and with urban tree management, and trust in the agencies responsible for urban tree management, are explained by cognitive factors (values, beliefs, and knowledge) and socio-ecological contextual factors (tree presence/canopy cover, cultural diversity, and socioeconomic status) using an online survey of 16 local government areas in south-eastern Australia. Analyses of 2367 responses revealed that people’s opinions about trees in general (values and beliefs) were overwhelmingly positive, while their opinions about more contextualised measures such as satisfaction and trust were more mixed. Two distinct pathways that influence satisfaction were identified: one linked to beliefs about having trees in cities, and another one linked to trust in urban tree management. At the local government level, satisfaction was negatively associated with a measure of cultural diversity and very low levels of tree canopy cover, but not with socioeconomic disadvantage. Satisfaction with local trees could be improved by increasing the quality of ecological function of trees, such as habitat provision and tree diversity. Community engagement could also improve satisfaction and trust, particularly perceived procedural fairness of decision-making, reinforce positive beliefs about the outcomes of having trees in cities, and dispel negative beliefs. Engagement processes should recognise that people hold complex and diverse opinions about urban trees, and by incorporating these opinions into decision-making we can meet the increasingly complex and diverse expectations being placed on urban forests.     

Attitudes towards tree protections,development, and urban forest incentives among Florida (United States) residents

Tree ordinances can be an effective means of preserving urban forests in the face of development pressures. Despite this, they also have the potential to be divisive among the public - especially when applied to privately-owned land. In this study we surveyed 1716 Florida urban residents to understand how they value regulation and management of the urban forest. Specifically, we asked about: tree protection ordinances, incentive programs to manage or plant trees, justification for tree removal, and development. Most respondents supported tree protections, even when applied to trees on their own property or when they had the potential to limit development activities. Additionally, there was limited support for removing healthy trees for development. Respondents supported the use of funds for urban forestry efforts – particularly at the local or state level.     

Comparing street tree assemblages and associated stormwater benefits among communities in metropolitan Cincinnati,Ohio, USA

Green infrastructure approaches leverage vegetation and soil to improve environmental quality. Municipal street trees are crucial components of urban green infrastructure because they provide stormwater interception benefits and other ecosystem services. Thus, it is important to understand the patterns and drivers of structural heterogeneity in urban street tree assemblages. In this study, we compared the forest structure of street trees across nine communities along both geographic and demographic gradients in metropolitan Cincinnati, Ohio, USA. Specifically, we used a two-part statistical model to compare both the proportion of sampled street segments containing zero trees, and basal area magnitude for street segments with trees. We made community-scale comparisons based on street tree management, socioeconomics, and geographic setting. Then, using modeled stormwater interception estimates from i-Tree Streets, we investigated the implications of heterogeneity in street tree assemblages for stormwater interception benefits. The forest structure of street trees varied across communities in relation to management practices, namely participation in the Tree City USA program. As a consequence of this structural difference, we observed a stark discrepancy in estimated stormwater interception between Tree City USA participants (128.7 m³/km street length) and non-participants (59.2 m³/km street length). While street tree assemblages did not vary by community poverty status, we did find differences according to community racial composition. In contrast to previous research, basal area was greater in predominantly black (i.e., African American) and racially mixed communities than in predominantly white communities. We did not observe structural differences across geographic strata. This research underscores the importance of proactive management practices for increasing the forest structure of street trees. Our findings regarding socioeconomics and geographic setting contrast previous studies, suggesting the need for continued research into the drivers of structural heterogeneity in street tree assemblages.     

Future climate risk and urban tree inventories in Australian cities: Pitfalls,possibilities and practical considerations

Urban tree inventories are useful tools to assess the environmental and socio-economic services provided by urban forests. These inventories enable the evaluation of the climate change risk to urban forests, and governments rely on such inventories for urban planning and management. Here, we assessed the future climate risk of Australia and the state of urban tree inventories across 116 local government areas (LGAs), representing 21 % of the country’s LGAs and encompassing 55 % of the national human population. We evaluated projected changes in temperature and precipitation by 2050 for each LGA and conducted a survey to obtain information on the extent and types of data available in existing urban tree inventories. Additionally, we compiled demographic, socio-economic, and geographical data for all LGAs to explore correlates with tree inventory status. Temperature increases in 2050 were predicted in all LGAs, with higher latitude and smaller LGAs identified to undergo greater increases in temperature compared to larger and lower latitude LGAs. Decreases in seasonal precipitation were predicted for 97 LGAs. Seventy-six (66 %) of surveyed LGAs had urban tree inventories, which most commonly included trees along streets and in parks. Sixty-one LGAs record information on tree mortality, while 31 LGAs dynamically update their inventories. The presence of an inventory and the area it covered were positively associated with human population density. More than 30 years ago, in 1988, John Gray wrote that “insufficient statistics were available in Australia to provide an accurate picture of the urban forest estate”. Our research shows there has not been a significant advance in the adoption and use of urban forest inventories over the past three decades. Long-term, dynamically updated inventories are crucial for urban forest management to inform planting choices to support sustainable and resilient cities.     

Structural diversity and height growth models in urban forest plantations: A case-study in northern Italy

Current knowledge on the growth models of urban forest plantations several years after their establishment still remains poor and fragmentary. Furthermore few studies have assessed the growth of urban plantations on reclaimed land, such as brownfield sites.This paper assesses urban forest plantations in terms of tree height growth, crown width and vertical structural using as a case study tree inventory-data collected in an urban forest plantation (Parco Nord Milano, PNM northern Italy). In this research tree inventory-data was used to achieve the following objectives: (i) to develop a series of tree height-growth models and tree crown-width models for the main taxonomic units in the study-area; (ii) to analyse the temporal pattern of current increments of tree height; (iii) to assess the vertical stratification of tree crowns using a method developed by Latham et al. (1998).The results suggest that during the earlier stage after planting, trees reach high levels of growth (tree height and crown width) regardless of the taxonomic unit. Evidence is found to support a high level of spatial competition between individual trees of different taxonomic units in as little as 15–18 years. Competition between trees appears to be mainly affected by diametrical differentiation rather than hypsometric variation: trees grow more in diameter than in height. Furthermore a decrease in longitudinal growth was observed for most tree species while the radial growth tends to be constant over time. The research at PNM shows that in temperate climates this can be achieved in less than 30 years. We believe that these analyses could provide important data supporting the planning of new urban forest plantations on reclaimed land and inter alia provide some answers to the questions around plantations growth evaluation and management.     

Private trees contribute uniquely to urban forest diversity,structure and service-based traits

The urban forest provides our communities with a host of benefits through the delivery of ecosystem services. To properly quantify and sustain these benefits, we require a strong baseline understanding of forest structure and diversity. To date, fine-scale work considering urban forest diversity and ecosystem services has often been limited to trees on public land, considering only one or two green space types. However, the governance of urban green spaces means tree species composition is influenced by management decisions at various levels, including by institutions, municipalities, and individual landowners responsible for their care. Using a mixed-method approach combining a traditional field-inventory and community science project, we inventoried urban trees in the residential neighbourhood of Notre-Dame-de-Grȃce, Montreal. We assessed how tree diversity, composition and structure varies across multiple green space types in the public and private domain (parks, institutions, street rights of way and private yards) at multiple scales. We assessed how service-based traits – traits capturing aspects of plant form and functions that urban residents find beneficial – differed across green space types, with implications for the distribution of ecosystem services across the urban landscape. Green space types displayed meaningful differences in tree diversity, structure, and service-based traits. For example, the inclusion of private trees contributed an additional 52 species (>30% of total species) not found in the local public tree inventory. Trees on private land also tended to be smaller than those in the public domain. Beyond patterns of tree richness, size, and abundance we also observed differences in the composition of tree species and service-based traits at site-scales, particularly between street rights-of way and private yards. While species composition varied considerably across street blocks, blocks were very similar to one another in terms of mean service-based traits. Contrastingly, while species composition was similar from yard to yard, yards differed significantly in mean service-based trait values. Our work emphasises that public tree inventories are unlikely to be fully representative of urban forest composition, structure, and benefits, with implications for urban forest management at larger spatial scales.     

Twelve-year change in tree diversity and spatial segregation in the Mediterranean city of Santiago,Chile

Tree diversity is one of the most important components of urban ecosystems, because it provides multiple ecological benefits and contributes to human well-being. However, the distribution of urban trees may be spatially segregated and change over time. To provide insights for a better distribution of tree diversity in a socially segregated city, we evaluated spatial segregation in the abundance and diversity of trees by socioeconomic group and their change over a 12-year period in Santiago, Chile. Two hundred vegetation plots were sampled across Santiago in 2002 and 2014. We found that overall abundance and diversity of urban trees for the entire city were stable over 12 years, whereas species richness and abundance of native tree species increased. There was segregation in tree species richness and abundance by socioeconomic group, with wealthier areas having more species and greater abundance of trees (for all tree species and native species) than poorer ones. Tree community composition and structure varied with socioeconomic group, but we found no evidence of increased homogenization of the urban forest in that 12 years. Our findings revealed that although tree diversity and abundance for the entire city did not change in our 12-year period, there were important inequities in abundance and diversity of urban trees by socioeconomic group. Given that 43% of homes in Santiago are in the lower socioeconomic areas, our study highlights the importance of targeting tree planting, maintenance and educational programs in these areas to reduce inequalities in the distribution of trees.     

Soil water stress at young urban street-tree sites in response to meteorology and site parameters

Growth conditions at urban street-tree sites are unfavorable and tree vitality is increasingly threatened by water scarcity due to changing climate. Developing adaption and management strategies to ensure early stage and long-term tree- and root growth requires thorough knowledge about root zone soil-water dynamics at young urban street-tree sites. Therefore, we established a soil water potential (SWP) monitoring at 17 young urban street-tree sites in the city of Hamburg, Germany. Over four years (2016–2019) we measured and quantified critical soil water availability in the root ball, planting pit, and surrounding urban soil using a threshold value (SWP < −1200 hPa) and assessed the tree sites sensitivity towards meteorological variables, tree- and site characteristics using a data driven random forest model. During 2018 and 2019, average critical soil water availability in the root ball and planting pit occurred between three to five months per year, and the trees were exposed to prolonged periods of critical soil-water availability for two consecutive years. After planting, critical soil water availability increasingly shifted year wise from the root ball into the entire planting pit as a consequence of root development and increasing water demand of the trees. Considering less usable water within the surrounding sandy soils, soil water in the planting pit may be depleted earlier and more rapidly with tree aging. The random forest model successfully predicted critical soil water availability and identified tree age as an important predictor. Long-term (10-day) rainfall was the most important variable predicting the occurrence of critical soil water availability, suggesting a further extension of periods with critical soil water availability as rainy summer days are projected to decrease with climate change. Additionally we identified soil temperature as a more important predictor than air temperature as it reflects site specific characteristics affecting water- an energy balance. This study underlines the urgency to adapt the growing conditions of young urban street-trees in terms of sufficient water storage, and provides an approach for future application in tree site soil water management, to maintain their vitality under urbanization pressure and climate change.     

Tree species-rich open oak woodlands within scattered urban landscapes promote biodiversity

It is becoming increasingly evident that cities are important places for biodiversity. Biodiverse urban forests are vital green areas within cities and have favorable impacts on the citizens, including their health. We focused on the effect of the urban forest environment on biodiversity in Prague, the capital of the Czech Republic. We used a multi-taxon approach with five taxa of different ecological demands: butterflies, bees and wasps, vascular plants, mosses, and lichens. We modeled their responses to the various urban forest attributes at four hierarchical levels – plot, permeability, forest, and landscape. Our results revealed that temporally continuous forests dominated by native oaks with open canopies, a high number of admixed and interspersed tree species and shrubs, together with scattered trees in the surrounding landscape, were optimal biodiverse forest environments. The most influential parameter that positively influenced bees and wasps, plants, and lichens at the plot level was canopy openness. We found that the permeability was suitable mainly on 20 m surroundings and increasing coverage of native oaks and tree species richness were the most important parameters. Continuity was the only found parameter that influenced mosses at the forest level. Scattered tree vegetation was the most important landscape parameter and positively drove the species richness of bees and wasps. Forest management methods can relatively easily solve the improvement of the scattered light gap structure within urban forests. Applying traditional forest management (pasture management, controlled burning and/or coppicing) is also an option but requires sensitive communication with the public. The canopy cover has been used as an indicator of urban forest health conditions, now indicating that artificial disturbances could be important issues for urban forest management and planning in the future. Therefore, active forest management is an essential method for biodiversity maintenance. We conclude that urban forests have a high potential for increasing native biodiversity. The response of the studied groups in urban forests was complementary. The resulting biodiverse stages of urban forests are akin to the established idea of the open temperate deciduous woodlands.     

Changes in public requests to remove significant urban trees after severe bushfires in Canberra, Australia

Trees on leased land provide an important contribution to Canberra's urban forest and consequently the Australian Capital Territory (ACT) Government introduced legislation to protect urban trees on leased land from unwarranted removal under the Tree Protection (Interim Scheme) Act 2001. This tree protection legislation applies to significant trees, classified using size-based criteria, on leased land for urban and other non-rural purposes. Responsibility resides with the ACT Government to preserve and protect significant trees on leased land in Canberra, until such time as removal is warranted and prudent. On Saturday 18 January 2003, 2 years after the introduction of the tree protection legislation, Canberra experienced a state of emergency when major bushfires swept through the bush–urban interface and penetrated into the western urban area subsequently destroying or damaging over 500 houses. There was a substantial increase in requests lodged under the Act immediately after the fires, but by February 2004 the number of requests returned to February 2002 levels which suggests leaseholder response to the fire declines relatively quickly. The percentage of requests approved (88%) remained relatively constant which indicates that the increased number of applications were for reasons that were considered valid under the Act although it is unlikely that these concerns only became valid during the month proceeding the fire. Dominant genera removed each February from 2002 to 2004 were similar; however, Eucalyptus species have shown a small but significant relative increase although there are insufficient data to conclude this increase indicates an increased aversion to this genus. Future management needs to consider the community perception of trees and temporal reaction to major events.     

Mapping the urban forest in detail: From LiDAR point clouds to 3D tree models

Trees are an integral component of the urban environment and important for human well-being, adaption measures to climate change and sustainable urban transformation. Understanding the small-scale impacts of urban trees and strategically managing the ecosystem services they provide requires high-resolution information on urban forest structure, which is still scarce. In contrast, there is an abundance of data portraying urban areas and an associated trend towards smart cities and digital twins as analysis platforms. A GIS workflow is presented in this paper that may close this data gap by classifying the urban forest from LiDAR point clouds, detecting and reconstructing individual crowns, and enabling a tree representation within semantic 3D city models. The workflow is designed to provide robust results for point clouds with a density of at least 4 pts/m² that are widely available. Evaluation was conducted by mapping the urban forest of Dresden (Germany) using a point cloud with 4 pts/m². An object-based data fusion approach is implemented for the classification of the urban forest. A classification accuracy of 95 % for different urban settings is achieved by combining LiDAR with multispectral imagery and a 3D building model. Individual trees are detected by local maxima filtering and crowns are segmented using marker-controlled watershed segmentation. Evaluation highlights the influences of both urban and forest structure on individual tree detection. Substantial differences in detection accuracies are evident between trees along streets (72 %) and structurally more complex tree stands in green areas (31 %), as well as dependencies on tree height and crown diameter. Furthermore, an approach for parameterized reconstruction of tree crowns is presented, which enables efficient and realistic city-wide modeling. The suitability of LiDAR to measure individual tree metrics is illustrated as well as a framework for modeling individual tree crowns via geometric primitives.     

Spatial patterns of a subtropical,coastal urban forest: Implications for land tenure,hurricanes, and invasives

Spatial patterns of tree structure and composition were studied to assess the effects of land tenure, management regimes, and the environment on a coastal, subtropical urban forest. A total of 229 plots in remnant natural areas, private residential, public non-residential, and private non-residential land tenures were analyzed in a 1273 km² study area encompassing the urbanized portion of Miami-Dade County, USA. Statistical mixed models of structure, composition, location, and land tenure data were used to analyze spatial patterns across the study area. A total of 1200 trees were measured of which 593 trees (49%) were located in residential areas, 67 (6%) in public non-residential areas, 135 trees (11%) in private non-residential areas, and 405 (34%) in remnant, natural areas. A total of 107 different tree species belonging to 90 genera were sampled. Basal area in residential land tenures increased towards the coast while private residential land tenures and natural areas had higher species diversity than non-residential areas. Tree height, crown light exposure, and crown area might indicate the effects of past hurricane impacts on urban forest structure. Land tenure, soil types, and urban morphology influenced composition and structure. Broadleaf evergreen trees are the most common growth form, followed by broadleaf deciduous, palms, and conifers. Exotic tree species originated mainly from Asia and 15% of all trees measured were considered exotic-highly invasive species. We discuss the use of these results as an ecological basis for management and resilience towards hurricane damage and identifying occurrence of invasive, exotic trees.     

Tree establishment practice in towns and cities – Results from a European survey

A working group within the European Union funded COST Action E12, “Urban Forests and Trees”, carried out a survey between 1999 and 2001 to study current tree establishment practice in European towns and cities. An extensive questionnaire requesting information on the urban area, selection of tree species, establishment and aftercare practices and the main damaging factors was sent to tree professionals in urban areas in each of 17 countries.Indicators such as the relationship between the urban population and the number of street trees were used to compare urban areas. While most central European cities have a ratio of 50–80 street trees per 1000 inhabitants, the tree density was as low as 20 street trees per 1000 inhabitants for Nice. Often only a few species are planted and this may give cause for concern, since species diversity is considered an important factor in increasing the resilience of the urban tree population to abiotic and biotic stresses.The planting of larger street trees of 20–30 cm circumference, usually with hessian-wrapped rootballs, is becoming increasingly common practice. However, some countries report the use of mostly bare-rooted stock of much smaller trees (less than 12 cm circumference). Establishment costs for street trees range from less than 200 Euro to over 1500 Euro each. Poor site conditions, and impacts such as utility trenching are considered to be major restrictions to healthy tree life. Vandalism affects up to 30%of newly planted street trees in some towns and cities.Overall, the survey reveals large differences in tree establishment and management practices among European cities. There is a need to provide urban tree managers with guidance on good practice for tree selection and establishment based on empirical information. The survey was a first step towards collecting the necessary urban forest information from across Europe.     

Diversity and structure in California’s urban forest: What over six million data points tell us about one of the world's largest urban forests

Urban street trees provide many benefits to surrounding communities, but our ability to assess such benefits relies on the availability of high-quality urban tree data. While these data are numerous, they are not available in an easily accessible, centralized place. To fill this gap, we aggregated public and private data into a single, comprehensive inventory of urban trees in California called the California Urban Forest (CUF) Inventory. These data are offered to the public (aggregated to ZIP code) via an online data portal, which at the time of publication contained over 6.6 million urban tree records. In this study, we first describe the assembly and utility of the inventory. Then, we conduct the most comprehensive assessment of the diversity and structure of California’s urban forest to date at statewide, regional, and local spatial scales. These analyses demonstrate that California’s urban forests are highly diverse and among the most diverse urban forests in the world. We present a new and intuitive metric of species diversity, the top diversity or TD-50 index, which represents the cumulative number of species accounting for the top 50 % abundance of trees in an urban forest. We used species abundance data from 81 well-inventoried cities to demonstrate that the TD-50 index was a robust metric of diversity and a good predictor of comprehensive metrics like the Shannon Index. We also found that small-statured trees, such as crape myrtles (Lagerstroemia cv.) dominate California’s urban forests. This aggregated inventory of one of the world's largest urban forests provides the data necessary to assess the structure, diversity, and value of California’s urban forests at multiple spatial scales. The inventory’s presentation to the public and the information that can be gained from its analysis can be a model for urban forest management worldwide.     

Changes over time in tree cavity availability across urban habitats

In urban ecosystems, tree cavities provide critical habitat for a variety of wildlife, and their occurrence is influenced by tree health, management, and cavity excavators. Changes over time in vegetative structure, human use patterns, and built environment affect the formation and persistence of tree cavities, and these changes may differ in various urban habitats. Trees with some decay are often associated with tree cavities, however, parks and residential habitats which are highly managed often lack highly-decayed trees, and large trees which are dead and damaged are likely to be removed and replaced with saplings. We surveyed changes over seven years (in 2013 and 2020) in the abundance of both excavated woodpecker cavities and decay cavities, in three urban habitats (forest, park, and residential) in the Chicago region, IL, USA. We observed greater stability of cavity abundance in managed park and residential habitats over time. Low numbers of highly-decayed trees in park and residential habitats were associated with reduced excavated cavity presence compared to forests. As expected, in both 2013 and 2020, the probability of cavity presence for both excavated and decay cavities was increased with greater tree size and higher levels of tree decay, though the patterns of this association varied between habitat types and years. The continued replacement and maintenance of existing trees means that managed park and residential habitats were more stable than unmanaged forest remnants, which are vulnerable to large changes in tree characteristics which could foster unpredictable booms or busts in cavity supply. A stable inventory of tree-cavities depends on preserving large trees, and decay of urban trees benefits habitat quality for cavity-nesters. Pruning of branches or removal of dead trees curtails the life-cycle of tree cavities in decayed branches, so that more highly managed habitats contain fewer cavities than the number of trees could potentially support. Cavity abundance could be improved in stable habitats through reduced intervention where safe, allowing cavity development to occur in situ.     

Homeowner perceptions,knowledge, and decision making regarding residential trees and natural areas in a Midwestern U.S. suburb

Residential properties in the United States represent a considerable amount of land area and contain substantial tree cover. Homeowners are important decision makers in the management of city trees because they influence the structure of urban forests, and ultimately, ecosystem service potential. To better understand the perceptions, knowledge, and practices of homeowners regarding residential tree preservation, we surveyed owners of newer versus older homes in a midwestern suburb in the United States. We found that newer homeowners were younger, wealthier, and less knowledgeable about the natural aspects of their property. During the redevelopment process, they relied on professionals to make major decisions regarding tree preservation. In contrast, owners of older homes often identified as retirees and gardeners, had more knowledge of the natural aspects of their property, and were more likely to hire an arborist. Regardless of these differences, both homeowner groups expressed equal appreciation for nature, planted, pruned, and mulched their trees, experienced tree loss, hired landscaping and tree care professionals, and communicated with the City’s Forestry Section. The results of our study further clarify the role that homeowners play in decision-making during development and highlight the important relationships that exist between homeowners and urban forest professionals.     

The impacts of historical land-use and landscape variables on hollow-bearing trees along an urbanisation gradient

Hollow-bearing trees provide habitat for diverse taxonomic groups and as such they are recognised for their importance globally. There is, however scant reference to this resource relative within urban forest patches. The functional ecology of habitat remnants along an urbanisation gradient plays an important ecological, social and economic role within urban landscapes. Here we quantify the impacts of urbanisation, landscape, environmental, disturbance (past and present) and stand variables on hollow-bearing tree density within urban forest patches. This was undertaken by surveying 45 forest patches on the Gold Coast, south-east Queensland, Australia. Sites were categorised as; urban, peri-urban or rural along an urbanisation gradient, with an additional five control sites. Historical logging practices were found to be the driving factor influencing hollow-bearing tree density along the urbanisation gradient; while the impacts of urbanisation itself are not as yet discernible. These findings highlight the significance of incorporating historical land use practise into current and future urban planning, as these will have continuing impacts on remaining urban biodiversity values. These findings, will benefit natural resource managers and urban planners when making decisions about where and how best to manage for hollow-bearing trees along urbanisation gradients.     

Relationships between urbanization,tree morphology,and carbon density: An integration of remote sensing,allometric models,and field survey

Urban trees store and sequester large amounts of carbon and are a vital component of natural climate solutions. Despite the well-recognized carbon benefits of urban trees, there is limited effort to examine how spatial distribution of carbon density varies across distinctive social, demographic, and built dimensions of urban landscapes. Moreover, it is unclear whether specific aspects of landscape structure and design could help increase carbon densities in urban trees. Here, we produced a fine-resolution carbon density map of urban trees in New York City (NYC) by integrating high-resolution land cover map, LiDAR-derived tree metrics, i-Tree Eco, and field survey data. We then explored spatial variations of carbon density across the gradients of urban development intensity, social deprivation index, and neighborhood age, and we examined the relationships between carbon density, and fragmentation, aggregation, size, and shape of tree canopy cover. We find that carbon stored in urban trees in NYC is estimated as 1078 Gg, with an average density of 13.8 Mg/ha. This large amount of carbon is unevenly distributed, with carbon densities being highest in Bronx and in open parks and street trees. Furthermore, carbon densities are negatively associated with urban development intensity and the social gradient of deprivation. Regarding the impacts of tree morphology on carbon density, our results show that while the amount of tree cover is the most influential factor in determining carbon density, small-sized forest patches and moderate levels of forest edges are also conductive to increasing carbon densities of urban trees. To incorporate urban forestry into developing innovative, effective, and equitable climate mitigation strategies, planners and decision makers need to identify the optimal spatial configuration of urban forests and invest in tree planting programs in marginalized communities.     

Detecting,quantifying, and mapping urban trees' structural defects using infrared thermography: Implications for tree risk assessment and management

Urban trees are a fundamental and key component of urban green areas, however, they are subject to several stresses which can compromise their mechanical integrity through the development of defects such as wood decay. In this study, we evaluated the structural health state of trees in four urban parks in the city of Mytilene, Greece, using structural traits of the trees, their trunk surface temperature distribution as recorded using infrared thermography, and spatial statistics both at single tree and at park level. We developed thermal indices by analyzing data from 334 trees belonging to three main species (Robinia pseudoacacia, Morus alba and Melia azedarach). We estimated temperature spatial dependence across each tree trunk using Moran's I index, while statistically significant spatial clusters were assessed using local spatial autocorrelation statistics. Relationships between tree traits, thermal, and spatial indices were established using linear and logistic regression models. Finally, we used the Getis-Ord Gi* statistic for the identification of risky tree hotspots and we applied the kriging geostatistical procedure for mapping of such hotspots. Our results have shown that the thermal and spatial indices can sufficiently predict different types of structural defect, and to identify hotspots of risky trees and their spatial extent. This approach can successfully contribute to tree risk assessment for a more effective urban park management.