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The urban heat island (UHI) is a problem that is likely to be exacerbated by ongoing climate change, but it is often claimed that urban trees can mitigate it and hence adapt our cities to climate change. Many researchers have attempted to quantify the cooling effects of trees using modelling approaches. However, the major disadvantage of most of the models is that they consider all vegetation to act as a single saturated layer and that their effect is merely proportional to its surface cover. Therefore, they fail to take into account potential differences between tree species and the effect of different environmental and growing conditions. To address this issue four different studies were conducted in Manchester, UK from February, 2010 to December, 2012. The studies compared the growth and cooling abilities of several commonly planted urban tree species, and investigated a single species planted in a range of growing conditions: investigating the effect of urban soil compaction and aeration and also the effect of urbanization and simulated climate change in the rooting zone. Overall, our studies showed that species selection and growing conditions can substantially alter the evapotranspirational cooling provided by urban trees. Fast growing species such as Pyrus calleryana, with their dense and wide canopy can provide cooling up to 2.2 kW tree-1, 3-4 times that of Sorbus arnoldiana, which have a thinner and narrower canopy and a moderate growth rate. P. calleryana was also investigated under three contrasting growth conditions: in cut-out pits in pavements; in grass verges; and in pits filled with Amsterdam soil. Trees in the less compacted Amsterdam soil had grown almost twice as fast as those in pavements and also had better leaf physiological performance. Together with a longer growing season, and better uptake of soil nutrients and moisture, trees grown in Amsterdam soil provided evapotranspirational cooling of up to 7kW, 5 times higher than those grown in pavements. Another experiment in which P. calleryana trees were planted in 3 standard planting techniques with non-compacted load bearing soils and with or without permeable slabs showed that optimum cooling is not only dependent on preventing soil compaction but also on ensuring that the covering materials are permeable to oxygen. Trees in the open pits provided up-to 1 kW of cooling, compared to around 350 and 650 W by the small and large covered pits respectively. Our final experiment showed that urbanization can increase tree growth by 20-30%; however, despite being under more water stressed conditions trees grown in simulated climate change plots had 40% higher sap flux density, and hence cooling potential. The study suggested that at least with P. calleryana, transpirational cooling benefit might be enhanced in places like Manchester with increased soil temperature in future, but potentially at the expense of photosynthesis and carbon gain. Together these studies show that evaporative cooling of trees depends strongly on both species and growing conditions. If incorporated into regional and local energy exchange models our results can help us to quantify the magnitude and effectiveness of greenspaces in the city in adapting them to climate change.

The process of urbanization dramatically alters the landscape which can have negative effects on the environment, and thereby, places the inhabitants and the city itself at risk. The development of an urban heat island can have severe health implications for city inhabitants during prolonged heat waves. Urbanisation also alters hydrological processes, which can place urban areas at a greater threat of surface flooding during heavy rainfall. As cities are continuing to expand, and as climate change proceeds, these problems are only likely to be exacerbated and there is a need to find ways to reduce these negative effects.This thesis builds upon previous modelling work on the effect of greenspace on the climate and hydrology of Manchester, U.K. The aims were to test the predictions of this model by investigating the effect of trees and grass in reducing surface temperatures and rainfall runoff, and further investigate their effects on air and globe temperatures. Surface, globe, and air temperatures were measured on grass and concrete areas in full sun and tree shade, both under large tree canopies, and below those of a range of street tree species. The rainfall runoff from experimental plots covered in asphalt, asphalt plus a tree and grass, was also investigated. Grass reduced surface temperatures in full sun by up to 24°C, in good agreement with previous models, but permanent tree shade reduced concrete temperatures by almost as much, up to 19°C. Tree shade also reduced globe temperatures by up to 7°C, a reduction which can improve human comfort on hot day. These results indicate that both forms of vegetation will act regionally, reducing the urban heat island effect, but that trees can dramatically improve the local environmental conditions. Street trees reduced surface and globe temperatures by rather less, 12°C and 4°C respectively, though trees with a higher leaf area index provided greater cooling. Because of advection neither trees nor small areas of grass had an effect on local air temperatures.Grass was most effective vegetation type at preventing rainfall runoff, reducing runoff coefficients of the plots from around 60% on asphalt to near zero. However, tree units also reduced the runoff coefficient to around 25%, despite having a canopy that covered only a small proportion of the plot, suggesting that much of the rainfall must have infiltrated into the planting hole. These reductions are higher than predicted by previous modelling, highlighting the importance of greenspace on the hydrology of the urban environment.The results suggest that trees and grass provide complementary environmental benefits in cities, and that the benefits of trees strongly depend on species and planting conditions

The distribution of trees across urban areas of the UK has been shown to be uneven, with lower density residential areas containing many more trees and much higher tree cover than areas of higher density housing. However, in Greater Manchester, tree number within high density housing areas also varies substantially. This thesis sought to explore the reasons for this variation in tree cover, whether tree cover should be increased and if so, how. The research investigated a potential cause for the variation in number of trees and tree cover within high density housing areas – housing type – for the study area of western Greater Manchester. Eleven different types of high density housing were categorised and all high density housing within the study area was classified as one of these types. Within these housing types, the amount of tree cover was determined, along with the proportions of other surface types. The land uses where the trees were growing were also determined. Finally, the potential increases in tree cover were also calculated for each housing type by a simulated planting technique. Maximum surface temperatures and rainfall runoff were calculated using computer models, for both existing and potential tree cover in each housing type. It was found that urban tree cover varies from 1.6% in pre 1919 terraced housing that opens directly onto the road to 14.8% in 1960s walkway-style housing. Tree cover could theoretically be increased by at least 5% in all housing types, reducing maximum surface temperatures by at least 1°C. In housing types with less than 4% existing tree cover, maximum surface temperatures could be reduced by up to 4.5°C. The views of residents were determined using a postal questionnaire about urban trees sent to residents of 4 different types of street environment. Residents of all street types surveyed were very positive about urban trees; their attitudes were not affected by whether there are trees in their street or not. The vast majority of respondents considered trees important to their quality of life, and that cost to the council should not prevent tree planting. The views and practices around urban trees and greening by practitioners were determined by running a workshop and their recommendations to increase tree cover are presented. These include changes in funding to include money for tree maintenance after planting, the importance of a full tree inventory and innovative ways to raise funding for trees. The effectiveness of a community greening scheme at increasing tree cover was compared with two regeneration schemes. The community tree planting scheme was found to deliver tree planting much closer to the potential than regeneration schemes.

Tree plantings are often proposed as a solution to a variety of urban problems. The purpose of this project is to investigate the historical formation of urban tree cover in Gallup, New Mexico, and the extent to which urban tree plantings can benefit areas with inequitable urban tree distribution. To do this, I employ a mixed methods approach that includes correlation analysis, historical analysis, and analysis of urban tree canopy change from 1972-2005. The findings from this study indicate that Gallup’s history of tree plantings is heavily influenced by its history of economic development. Additionally, the findings demonstrate that if the economic dimensions of urban trees are not identified and addressed, equitable distribution of urban tree cover cannot be achieved. This project serves not solely as a criticism of tree planting programs, but also as a review of the assumptions made during urban forestry prioritization and decision-making processes.

Local residential streets that can support the growth of significant shade trees are critical for mitigating urban heat - an increasing public health risk in Western Sydney; and for increasing total urban canopy. In the state of New South Wales, regional and district plans for the rapidly developing suburbs of Western Sydney include a planning priority to increase urban canopy. However, planning controls that encourage increased density, combined with development models that continue to favour single-family, detached dwellings, result in decreased lot sizes with insufficient space to support canopy trees around homes or in the streetscape. Using a qualitative methodology, the research undertook a comparative analysis of local residential streets in two areas of the Camden Local Government Area in the metropolitan region of Western Sydney - one that was developed in the mid-1990s and the other constructed within the past three years. The investigation sought to reveal the spatial factors that contribute to the realisation of tree-lined streets. A tree-focussed reading of the urban planning and development controls, codes, guidelines and specifications that specifically apply to local streets was carried out to assess how these documents impact on the implementation of tree-lined streets. Council officers involved in the planning, design, certification and maintenance of streets were first interviewed individually and later participated together in a focus group discussion. Findings indicate that although there is political will to implement tree-lined local streets, codes and specifications for other infrastructure impact on the space available for trees. The research concludes that unless trees are accepted as a critical component of the streetscape, urban canopy will not increase and the potential for street trees to mitigate urban heat will not be realised. The discussion suggests actions for policy and for codes and practices that impact on trees. If implemented these actions would result in more tree-lined streets in Western Sydney. The actions could also be replicated in other jurisdictions.

Tree species composition and health are key attributes for rural and urban forest biodiversity, and ecosystem services preservation. Remote sensing has facilitated extraordinary advances in estimating and mapping tree species composition and health. Yet previous sensors and algorithms were largely unable to resolve individual tree crowns and discriminate tree species or health classes at this essential spatial scale due to the low image spectral and spatial resolution. However, current available very high spatial resolution (VHR) remote sensing data can begin to resolve individual tree crowns and measure their spectral and structural qualities with unprecedented precision. Moreover, various machine learning algorithms are now available to apply these new data sources toward the discrimination and the mapping of tree species and health classes. The dissertation includes an introductory chapter, three stand-alone manuscripts, and a concluding chapter, each of which support the overarching theme of mapping tree species composition and health using remote sensing images. The first manuscript, now published in the International Journal of Remote Sensing, confirms the utility of combining VHR multi-temporal satellite data with LiDAR datasets for tree species classification using machine learning classifiers at the crown level in a rural forest the Fernow Experimental Forest, West Virginia. This research also evaluates the contribution of each type of spectral, phenological and structural feature for discriminating four tree species: red oak (Quercus rubra), sugar maple (Acer saccharum), tulip poplar (Liriodendron tulipifera), and black cherry (Prunus serotina). The second manuscript investigates the performance of tree species classification in urban settings with three contributions: 1) 12 very high resolution WorldView-3 images (WV-3), whose image acquisition date covering the growing season from April to November; 2) a large forest inventory providing sufficient calibration/validation datasets in Washington D.C.; 3) object-based tree species classification using the RandomForest machine learning algorithm. This manuscript identifies the incremental losses in classification accuracy caused by iteratively expanding the classification to 19 species and 10 genera. It also identifies the optimum pheno-phases and spectral bands for discriminating trees species in urban settings. Building on these promising results from the second manuscript, the third manuscript detect a signal of statistical difference among individual tree health conditions using WorldView-3 images from June 11th, July 30th and August 30th , 2017 in Washington D.C.. It examines six vegetation indices calculated from WorldView-3 images to describe three health condition levels in good, fair and poor, and discusses the effects of green-down phenology for tree health analysis. Overall, this dissertation research contributes to remote sensing research by combining data from both active and passive sensors to discriminate tree species in rural forest. For the species-rich urban settings, this dissertation illustrates the importance of phenology for tree species classification at crown level using VHR remote sensing images. Finally, this dissertation provides important insights on detecting statistical differences among tree health conditions at individual crown-level in the urban environment using VHR remote sensing images.

Bioretention is a green infrastructure practice commonly implemented to manage urban stormwater worldwide. While studies have described the many benefits trees provide to urban areas, including improved air quality, wildlife habitat creation, and heat island mitigation, knowledge of their contributions to stormwater management in bioretention is limited. There is a need to characterize tree health in bioretention and the performance benefits they provide to inform appropriate plant selection and maximize the functionality of these systems. In response, several studies were implemented to investigate the role of trees in bioretention practices.The health of trees in existing bioretention practices was compared to urban trees in the southeastern United States. Using crown condition to measure overall tree health, health differences were linked to dissimilarities between bioretention conditions and species-specific site preferences. The environmental factors influencing tree health in bioretention were investigated using random forest models, which identified parameters relating to media composition and chemistry, along with species selection and planting location. Results indicated that tree health may be improved in bioretention if species selection is guided by media analysis and species compatibility with bioretention growing conditions is considered.The contributions of various tree species in bioretention were investigated in a mesocosm-scale study. Differences in pollutant uptake between species were not significant, indicating the role of bioretention media in pollutant removal. Evapotranspiration from treed mesocosms was significantly higher than nonvegetated mesocosms, highlighting the role of transpiration in the systems. Results suggested that trees contribute to bioretention hydrology and that significant differences among species, which were attributed to growth rate, exist.Two bioretention suspended pavement systems were installed and monitored over 27-months. Significant runoff volume reductions were observed at both practices. Influent suspended solids were significantly reduced at the underdrained practice, though other influent pollutant removal was not significant. Tree transpiration from the systems increased with greater water availability. Regression models indicated that transpiration was influenced by vapor pressure deficit and that stomatal regulation of water losses were occurring in water-limited conditions. Findings demonstrated the viability of suspended pavement systems in stormwater management applications and illustrated how design parameters influence transpiration within these practices.

Short duration intense rainfall causes an increase in rainfall derived infiltration and inflow (RDII) in aging sewer networks, which leads to Sanitary Sewer Overflows (SSOs). This, in turn, causes various detrimental impacts, both on human health and the environment. This research aims to quantify the benefits of Water Sensitive Urban Design (WSUD) approaches to mitigate the negative impacts of rainfall induced SSOs. In this context, this research develops a generalised framework for assessing and mitigating the impacts of intense rainfall on the performance of the sanitary sewer network. The first part of the developed framework involves detailed hydraulic modelling to evaluate the performance of the sewer network. The second part deals with the development of SSO mitigation strategies based on popular WSUD approaches. This study also demonstrates the application of the developed framework for a case study catchment in Melbourne, Australia. A detailed hydraulic modelling to analyse the performance of the case study sewer network during a wet (2010) and a dry year (2008) has been presented. The hydraulic performance analysis found that the system experienced 23 ML of sewer overflow volume in 2010 as compared to 3.42 ML in 2008. Towards mitigating the negative impacts of SSOs, this study has implemented two commonly used WSUD approaches, namely rainwater tanks and rain gardens for the case study sewer network. A detailed hydraulic modelling has been undertaken with rainwater tanks and rain gardens (individually and in combination) for the wet year 2010. It was observed that rainwater tanks (individually) could lead to a maximum reduction in SSO volume by 33% when compared to the base case overflow volume of 23 ML. A higher reduction in SSO volume up to a maximum of 45% was observed when rain gardens were implemented in conjunction with rainwater tanks. Such an analysis will benefit the urban water authorities to develop sustainable WSUD based mitigation strategies for controlling SSOs in their sewer system. Thus, the study will be beneficial for the community and the environment.

Plants provide invaluable ecosystem services to urban centers. Yet, these services cannot be decoupled from the cost to maintain landscaping plants. Costs are particularly difficult to quantify in urban ecosystems, like Los Angeles, where a combination of mild climate and a legacy of landscape design driven by social and economic factors has produced unprecedented species diversity. As these plants subsist entirely on irrigation water, the resulting ‘global common garden’ is ideally suited for testing anatomical and physiological scaling hypotheses across many diverse species to inform generalized predictive models for other species and ecosystems. My dissertation seeks to uncover relationships between leaf anatomy and function to build models estimating water use and drought tolerance in Los Angeles.I first analyzed allometric slopes describing relationships between the dimensions of leaf cells and tissues and found cell sizes, cell wall thickness and leaf thickness scale together across tissues and species. I then created a mathematically explicit model that predicted leaf mass per area (LMA) from its constitutive anatomy and composition with unprecedented explanatory power. Cell size, the number of mesophyll cell layers, and cell mass density principally drove species differences in LMA and had strong impacts on the Leaf Economics Spectrum. I linked leaf structure with physiology by resurrecting a classic method for quantifying loss of rehydration capacity in dehydrating leaves, placed associated thresholds in the sequence of drought response (e.g. stomatal closure, turgor loss), and tested their relationship with structure and composition. I found leaves to be considerably more vulnerable than previously believed. This prompted a study in which I tested canopy stomatal conductance across minor shifts in vapor pressure deficit (VPD) modeled from plant traits against empirical sap flux and leaf area data collected in urban trees. Finally, I found enormous variation in functional traits across Los Angeles species, influenced by climates of origin, growth forms, leaf habit and canopy position (i.e., sun versus shade leaves). The vast trait diversity in Los Angeles urban trees demonstrates the need for integration of species information into predictive models in urban ecosystems and highlights Los Angeles as an invaluable resource for future ecophysiological study.

As the process of urbanization advances across the country, so does the importance of urban forests, which include both trees and the soils in which they grow. Soil microbial biomass, which plays a critical role in nutrient transformation in urban ecosystems, is affected by factors such as soil type and the availability of water, carbon, and nitrogen. However, the microbial dynamics of urban forest soils remain largely unknown. A key mechanistic link between plant species diversity and ecosystem function is heterotrophic microbial communities that inhabit the soil and mediate principal processes that control ecosystem carbon (C) and nitrogen (N) cycling. The aim of this study was to characterize residual forest patches and open fields in residential areas in the City of Knoxville. A field study was conducted along an urban-to-rural gradient in order to address the three objectives: 1.The first objective was to investigate tree species diversity and soil characteristics along an urban-to-rural gradient in residual forest patches and open fields. 2. The second objective was to investigate spatial and temporal differences in chemical, physical and biological soil characteristics along urban-to-rural gradient in residual forest patches and open fields. 3. The third objective was to utilize the chemical, physical and biological soil characteristics and tree diversity in study plots to predict residual forest patches or open field based on urban or rural location. Determining tree species diversity and soil composition along an urban-to-rural gradient in residual forest patches and open fields it was found that tree diversity did not differ significantly for residential urban and rural plots in Knoxville, Tennessee. Biologically, there was no indication that soils were affected by tree diversity, in terms of soil microbial biomass C/N along an urban-to-rural gradient in Knoxville residential plots. Rural soils did differ physically from urban soils, cation exchange capacity (CEC) and soil moisture content (GSM). Similarly, physical soil properties such as bulk density, both urban and rural sites were negatively correlated with tree diversity. Results indicate that although the urban-rural gradient is subject to urban environmental stressors, the urban ecosystem is resilient in maintaining the ecosystem functions of more natural systems.

As urban land expands across the globe and impervious surfaces continue to be used for constructing urban infrastructure, stormwater treatment costs and environmental damage from untreated stormwater will rise. Well designed urban landscapes can employ trees and soils to reduce stormwater runoff flowing to streams and treatment facilities. Typical urban soil, however, is compacted and restricts tree growth via high soil strength and inadequate gas exchange. A site preparation method that deeply incorporates compost and includes trees for long term carbon input and pore development was evaluated in the urban setting of Arlington, Virginia. Three species were used in that study of 25 streetside plantings. The site preparation affected soil at 15 30 cm by lowering soil bulk density by 13.3%, and increasing macro-aggregate-associated carbon by 151% compared to control plots, and resulted in 77% greater tree growth during the first year after transplant. In a second experiment, rainfall simulations were used to evaluate common landscape mulch materials for their ability to prevent compaction from traffic as well their affect on surface runoff before and after traffic. When plots were subjected to heavy rainfall, (>97 mm/h) mulches were found to reduce sediment loss 82% and 73% before and after traffic, respectively. Runoff rates from wood chips were only 0.19 ml/s faster after traffic while rates from bare soil and marble gravel with geotextile increased 2.28 and 2.56 ml/s, respectively. Management of soils, trees and landscapes for stormwater benefit could reduce cost of wastewater treatment for municipalities and can prevent environmental degradation.

Urban nutrient sustainability faces challenges of both too much and too little: Excess nutrient loading to the environment can degrade ecosystem functions and impact human health, while at the same time depleting nonrenewable nutrient sources and moving nutrients into unrecoverable pools. Most studies and efforts to date have focused on source reduction, identifying and reducing the largest drivers of carbon (C), nitrogen (N), and phosphorus (P) consumption. However, this addresses only one aspect of urban nutrient cycling; processes that transport, transform, or retain nutrients also determine their eventual fate as pollution, inert storage, or recycling. The first chapter examined C, N, and P output fluxes from ~2,700 households in the Twin Cities metropolitan area (Minneapolis-Saint Paul, Minnesota, USA), and tracked these fluxes through various transformations in the waste streams to their eventual fates. We found few opportunities to redirect pollutant fluxes to either inert storage or recycling; reducing household nutrient pollution must rely primarily on reducing consumption. High pollution fluxes were driven not only by household nutrient outputs, but also by waste-management practices (e.g. septic vs. sewer) and spatial considerations. In contrast, we found substantial opportunities to increase household N and P recycling by ten-fold, which could potentially exceed household inputs of N and P in food. To complement this study of opportunities for improving nutrient waste management, the second and third chapters examined opportunities to manage the biophysical environment - specifically, the urban forest - to reduce nutrient pollution. We focused on the role of urban trees driving N and P movement from land to water, both leaching to groundwater and loading to stormwater. In the second chapter, we compared nutrient leaching under 33 trees of 14 species, as well as open turfgrass areas, and explored correlations with soil nutrient pools and plant functional traits. Trees had similar or lower N leaching than turfgrass in 2012 but higher N leaching in 2013; trees reduced P leaching compared with turfgrass in both 2012 and 2013, deciduous trees more than evergreens. Scaling up our measurements to the Capitol Region Watershed (~17,400 ha), we estimated that trees reduced P leaching to groundwater by 533 kg in 2012 and 1201 kg in 2013. Removing the same amounts of P with stormwater infrastructure would cost $2.2 million and $5.0 million per year, respectively. In the third chapter, we measured tree litter nutrient inputs to street gutters, which can ultimately contribute to stormwater loading, under four species of boulevard trees. Differences among tree species in the total amount of nutrients in the street gutters were driven primarily by interspecific differences in the mass of litter dropped, which were much greater than differences in litter chemistry. In developing management recommendations, we found that tree phenology is a more important consideration than litter chemistry. Cleaning up spring and autumn pulses of tree litter shortly after they fall has substantial potential to reduce nutrient inputs to stormwater; for autumn litterfall, we estimated that doing so could remove 219.0-274.4 kg N km-2 and 14.2-20.6 kg P km-2. Because of the wide variation in species' litterfall timing, achieving this goal is likely to require adjusting both boulevard tree selection and litter cleanup strategies.

Urban areas are known to have different climatic conditions than their rural counterparts including higher temperatures, greater wind speeds, and increased precipitation otherwise known as urban heat islands, urban wind, and urban precipitation. These phenomena are all caused by the design and form of the city. Large amounts of impervious surface area, obtrusive buildings, and a lack of vegetation in the urban landscape all contribute to these problems. Landscape architects have the potential to mitigate urban heat islands, urban wind, and urban precipitation by understanding what causes these phenomena and knowing a few key principles by which to mitigate them. Parking lots can cover up to half of the land area in cities and offer a great opportunity to correct urban climate problems. This thesis looks at current United States parking lot ordinances to determine if and how well principles of designing with climate have been incorporated. Guidelines are then given to help in the construction of a parking lot ordinance that aims to ameliorate the city's mesoclimate. A design is then created that shows how these parking lot guidelines could be incorporated into a functional, aesthetically pleasing parking lot.