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While many practitioners and experts understand the risks associated with low urban tree diversity, they often lack the ability to rectify issues they encounter on their own. The current system of tree production and procurement is complex – shaped by market pressures, nursery and site constraints, local governance, and differing professional objectives among those who grow, specify, and plant trees. To understand this complexity as well as constraints to- and opportunities for increasing urban tree diversity, we conducted a series of focus groups comprised of nursery growers, landscape architects, and urban foresters. Our results highlight a significant list of considerations and constraints to diversity (both shared among green industries and some specific to growers or purchasers). More importantly, in discussing our findings we outline actionable strategies for increasing urban tree diversity.

Urban forest ecosystems are the collections of trees and other woody plants such as bushes and shrubs in urban areas, as well as the non-living (sidewalks, buildings, soil) and living (people, insects, wildlife) things that interact with them. Most humans throughout the world (56%) live in urban forest ecosystems, so it is important that these environments are safe, healthy, and sustainable. This article will point out the urban forests in your life. It will also explain the environmental, health, and societal benefits that urban forests create.

Trees make our cities and urban areas more livable. Trees provide many benefits, known as ecosystem services, to residents. Cities often make management plans and care for their trees to increase the benefits provided by their urban forests. These plans often include goals to increase tree cover. This study assessed tree cover in 300 Florida (U.S.A.) cities. Each city’s urban tree canopy coverage (a percentage of how much of a city is covered by the leafy tops of trees) was analyzed. The goal was to assess the effects of hurricanes, past land cover, and local laws on total tree cover. The study found that hurricanes can decrease tree canopy coverage. It also found that the type of land cover present before a city was built can predict present canopy coverage. Results also found that some local laws can protect or enhance urban tree canopy, even in the face of city development and natural disasters.

Despite the abundance of tree diversity in the natural world, and generally high tree species richness in urban areas, urban forests continue to be dominated by a limited number of species. As socio-ecological systems, urban forests are shaped by historical and current management efforts and decision-making of a wide range of human actors. Drawing on past research, we offer a conceptual framework for describing the complex interactions among tree producers and consumers as trees are selected, grown, specified, and planted in private and public urban areas. We illustrate how multiple layers of selection criteria filter down the entirety of potential local tree diversity to a handful of commonly used and accepted tree species. We detail the actors and decision makers who impact tree composition and diversity across several land types. Finally, we identify research, education and outreach needs as they relate to creating more diverse and resilient urban forest ecosystems.

Urban stormwater managers have traditionally used pipes, ditches, ponds and other gray infrastructure elements to quickly divert runoff away from its main sources—buildings and roadways. In contrast, proponents of green infrastructure attempt to manage stormwater near its origin, utilizing natural drainage pathways and best management practices (BMPs) to reduce runoff and increase infiltration. In doing so, stormwater is retained where it is needed to support urban vegetation. This vegetation, in turn, helps reduce future runoff, while producing a whole range of environmental, economic, and social/human health-related benefits. Despite the many advantages of green infrastructure, retrofitting the infrastructure of a city is a costly process that requires careful planning. The transition from gray to green infrastructure requires communication between managers from different disciplines and a willingness to stray from management strategies that have defined stormwater management for centuries. The Gray to Green (G2G) green infrastructure planning tool is designed to facilitate these conversations—showing both technical and non-technical users how green infrastructure BMPs can work within the urban forest to manage stormwater on existing or proposed development sites. This paper details the data sources and research at the core of G2G—documenting all methods, equations, and assumptions used in its creation to provide users with a fully-transparent and peer-reviewed planning tool. The paper concludes with descriptions and user insights from two case studies from Tampa, Florida (United States) and Milwaukee, Wisconsin, (United States).

This new 13-page article combines canopy coverage data from all of Florida's metropolitan and micropolitan areas with ecological models developed by the USDA Forest Service to calculate several key benefits of urban trees and an approximation of their monetary value. Benefits of urban trees include carbon sequestration/storage, air pollution filtration, and stormwater mitigation. Written by Drew C. McLean, Andrew K. Koeser, Deborah R. Hilbert, Shawn Landry, Amr Abd-Elrahman, Katie Britt, Mary Lusk, Michael G. Andreu, and Robert J. Northrop, and published by the UF/IFAS Environmental Horticulture Department.https://edis.ifas.ufl.edu/ep595

Urban tree diversity is important when attempting to create a healthy, beneficial, and resilient urban forest. Having a variety of trees can increase the aesthetic value for residents and create habitats for plants and animals. Some common street trees currently in the landscape are not site-appropriate and create infrastructure damage. By planting different types of trees in these locations, maintenance costs and infrastructure damage can be reduced and tree longevity increased. This new 4-page fact sheet is intended to provide urban foresters, arborists, landscape designers, and others in charge of tree planting with a process for introducing new species into the urban environment. Written by Deborah R. Hilbert, Andrew K. Koeser, and Robert J. Northrop, and published by the UF/IFAS Environmental Horticulture Department.https://edis.ifas.ufl.edu/ep589

As urban development increases in density, the space to grow urban trees becomes more constrained. In heavily developed areas, small stature trees can be planted to reduce both above- and below-ground conflicts with infrastructure elements. However, even these species can interfere with pavement when placed in extremely confining conditions. In this study, we build on past work to determine the minimum planting space widths of small stature urban trees. Species, stem diameter, and the height at which stem diameter measurements occurred were all strong predictors of trunk flare (i.e., the interface region between large structural roots and the trunk) diameter (adjusted R2 of 0.843). Additionally, we modelled the relationship between planting space and the presence or absence of pavement conflicts using the predictions derived from this effort to project the potential cost savings in two United States cities. Study results provide a guideline to create sufficient space for urban trees and minimize infrastructure damage and associated cost savings.

While often considered “open grown,” urban trees are often found in relatively close proximity to neighboring trees, buildings, and other elements of urban infrastructure. These spatial arrangements may provide wind protection during severe weather events such as hurricanes. Beyond this very local scale, urban tree abundance and condition are often influenced by the greater sociodemographic context of the neighborhood or community where they are found. In an effort to assess the impact of these external factors on wind firmness after Hurricane Irma impacted Florida in 2017, we revisited three urban areas that had previously been inventoried using sample plots prior to the storm. At each plot we assessed storm damage and characterized surrounding protective elements (i.e., buildings and other trees) using a combination of ground-based and aerial approaches. This was then paired with block group level sociodemographic data derived from the United States Census. Logistic regression results confirmed previous research, showing that partial and whole tree failure were significantly more likely with a larger stem diameter (p = 0.001) and perceived/previously documented lower wind firmness (p = 0.004). However, our results disagreed with previous studies linking species diversity and resilience, showing tree failure was significantly more likely with higher Shannon Diversity Index (p = 0.008). A comparative geographically weighted logistic regression model also found that the higher proportions of African American residents and Hispanic residents, and the median age of residents were significant predictors of less likely tree failure in 30 %, 36 %, and 20 % of plots, respectively. However, this evidence was weak, compared to that of tree- and plot-level effects. Despite being a key predictor of interest, we did not see any significant protective effect from neighboring trees or structures.

Many cities actively manage their urban trees in an effort to increase canopy coverage, manipulate species and size distributions, and maximize associated environmental and social benefits. As development is one of the most significant factors limiting tree abundance and health, many local governments have enacted policies or ordinances which attempt to reduce tree loss during construction activities through preservation or replacement requirements. Recently, the state of Florida passed a state statute which significantly limits local government oversight of trees on private residential properties – a land use type which can often account for the majority of a municipality’s urban forest. In this study, we accessed ordinance databases to assess the potential impact of this law on urban forest governance in Florida’s 300 largest cities (by population). We also surveyed urban tree managers in the largest 150 cities to assess the range of strategies being developed to function under this new political normal. Ordinances that regulate the removal of urban trees were the most likely to be impacted by the new state legislature and were in place in 46% of the communities assessed. Despite this, very few responding cities had changed their ordinances to comply with the new statute – though several indicated such changes were in progress. Other changes in policies and ordinances ranged from maintaining business as usual to actually investing more into urban forest management through increased inventory and management plan activities.

Tree roots often come in conflict with elements of the built environment, particularly when planted in limited soil locations. For street trees located between roadways and sidewalks, minimum planting width requirements can be calculated to prevent large supporting roots from lifting or growing over paved surfaces. In this study, we used diameter at breast height (DBH) to predict trunk flare diameter for common shade tree species from four different communities in the United States (Milwaukee, Minneapolis, Saint Paul, and Tampa). These predictive models were then used to calculate minimum width requirements to reduce infrastructure damage given the maximum expected DBH measurements for each species based on existing urban forest inventory data in the communities studied. For all ten taxa tested, DBH was a significant predictor of trunk flare diameter (minimum R2 = 0.81), indicating that this commonly used urban forestry measurement can be used to design minimum growing space based on selected species to potentially prevent root and infrastructure conflicts. The methods employed in this paper can be easily replicated by other researchers in order to create guidelines for species and environments not captured in our data set. Alternatively, broader functions for estimating trunk flare based on DBH are provided for species based on natural habitat type (i.e., upland, wetland, variable).

A study of the vascular plants of the Palm Hammock Nature Area, a designated natural area on the west side of the Eckerd College campus in Pinellas County, Florida, was carried out between January 2012 and January 2013. The site is situated entirely on dredged fill soil, rendering it an intriguing site on which to study natural succession. This floristic inventory provides baseline data on the species composition at the site for use in future studies of the Palm Hammock and other forested dredge and fill sites. A total of 157 vascular species were collected from the 4.6 ha site, including 155 angiosperms. Of these, 99 species are native to North America, and 58 species are not native. Of the nonnative species, 20 are considered invasive. The most frequently represented families included Asteraceae (18), Fabaceae (18), Poaceae (14), and Cyperaceae (11). The Palm Hammock Nature Area, which comprises small patches of cabbage palm/oak hammock, cabbage palm stands, and grasslands similar to coastal s...

Many cities around the world have set ambitious urban tree canopy cover goals, with the expectation that urban forests will provide ecosystem services as functional green infrastructure. Numerous studies have examined intra-city spatial patterns in urban tree canopy (UTC) and found that UTC relates to socioeconomic indicators and urban form. Additionally, a few studies have shown local regulations can be linked to increased tree cover. However, the relationship between UTC and governance across different cities has not been well-explored. To address this gap, we compared the management practices enacted by 43 municipalities in Florida (United States) to investigate their potential impact on tree canopy coverage. UTC was assessed through visual interpretation of aerial images. We used multiple linear regression to predict inter-city variation in UTC based on 1) municipal forestry management practices, including whether the municipality had an arborist, tree ordinances, a municipal tree inventory, and a canopy cover goal, and 2) community sociodemographic data. UTC ranged between 17.6% and 63.3% among the municipalities assessed, with an average UTC of 33.7%. Two factors significantly predicted canopy coverage. Housing density had a negative relationship with tree canopy (P-value = 0.0116). In contrast, municipalities with heritage tree protections had 6.7% more canopy coverage (P-value = 0.0476). Future research should continue to consider the potential impacts of governance structures on the spatiotemporal dynamics of inter- and intra-city UTC patterns.

Urban tree planting initiatives can experience high levels of mortality during establishment years. Mortality tied to the stresses of transplanting can be partially negated or exacerbated depending on the species selected, nursery materials used, site conditions present, and management practices employed. Past research has quantified post-planting survival, health, and growth. However, varying climates, species, land use types, and management practices warrant additional region-specific research. The purpose of this study is to assess the success of plantings along Florida highways and identify species, site, and management factors related to tree and palm health and establishment. Results show high establishment survival (98.5%) across 21 planting projects ranging from 9 to 58 months after installation (n = 2711). For transplanted palms, the presence of on-site irrigation significantly improved establishment from 96.2% to 99.4%. No establishment differences were detected with regard to irrigation treatment for small-stature trees, shade trees, and conifers. Additionally, there were significant differences in tree health response among tree groups given species, management, and site factors.