Altered resources, disturbance, and heterogeneity: A framework for comparing urban and non-urban soils

We propose a framework of key concepts useful in understanding how urban soils can contribute to general ecological theory. The major factors that can cause urban soils to be different from soils in non-urban ecosystems are identified and related to the familiar state factor approach. We evaluate directly altered resource availability, and the role of stress in mediating resource availability in urban ecosystems. Modified groundwater and stream flow, and atmospheric deposition of nitrogen and base cations are particularly important resource fluxes to soils in urban ecosystems. Disturbance can be conceptualized in the same way in urban as in non-urban ecosystems. However, in addition to biophysical disturbances familiar to ecologists studying wild lands, demographically and socially mediated changes in ecosystem structure must also be considered. These changes include human migration and population structure, institutional shifts, and the effects of human health. Finally, spatial heterogeneity, including fragmentation and differential connectivity, integrates the effects of resources and disturbance, and has an effect on subsequent resource availability and susceptibility to disturbance. Layers of heterogeneity include not only the geomorphic template, but urban climate, biotic composition, buildings and infrastructure, and demographic-social patterns. The complex layering of natural and social factors that constitute urban heterogeneity permit the continuation of important ecological processes, as well as modify ecological fluxes involving soils. We present a modification of the state factor approach as an expanded framework for the study of urban soils. The understanding of urban soils can contribute to general ecological theory by testing the generality of important ecosystem drivers and their linkage with social processes in an under investigated ecosystem type that is increasing in extent and impact worldwide.     

A conceptual framework for the study of human ecosystems in urban areas

The need for integrated concepts, capable of satisfying natural and social scientists and supporting integrated research, motivates a conceptual framework for understanding the role of humans in ecosystems. The question is how to add humans to the ecological models used to understand urban ecosystems. The ecosystem concept can serve as the basis, but specific social attributes of humans and their institutions must be added. Learning and feedback between the human and natural components of urban ecosystems are key attributes of the integrated model. Parallels with familiar ecological approaches can help in understanding the ecology of urban ecosystems. These include the role of spatial heterogeneity and organizational hierarchies in both the social and natural components of urban ecosystems. Although urban watersheds are commonly highly altered, the watershed approach can serve as a spatial basis for organizing comparative studies of ecosystems exhibiting differing degrees of urbanization. The watershed concept can also spatially organize the hierarchically scaled linkages by which the integrated human ecosystem model can be applied. The study of urban ecosystems is a relatively new field, and the questions suggested by the integrated framework can be used to frame ecosystem research in and associated with urban and metropolitan areas.     

A social ecology approach and applications of urban ecosystem and landscape analyses: a case study of Baltimore,Maryland

The early interactions between plant, animal, and human ecology in the 1920s in the United States provide an initial basis for understanding and directing an integrated ecosystem approach to the study of sociocultural and biophysical patterns and processes of present day cities. However, whereas the human ecology approach of the 1920s and 30s was interested in metaphorical similarities with plant and animal ecologists, we propose a more integrated approach to human ecosystem observation and analysis. A critical feature to an integrated, urban ecosystem approach is the ability of researchers to address the spatial heterogeneity of urban ecosystems; i.e. the development and dynamics of spatial heterogeneity and the influences of spatial patterns on cycles and fluxes of critical resources (e.g. energy, materials, nutrients, genetic and nongenetic information, population, labor, and capital). An important question in this context is how differential access to and control over critical resources affect the structure and function of urban ecosystems.To address this heterogeneity, we illustrate a human ecosystem and landscape approach and how the concept of social differentiation can be applied spatially at different scales with a case study from our research in Baltimore, Maryland. Further, we identify different methods, tools, and techniques that can be used for an integrated, urban ecosystem approach.     

Remembering our roots: A possible connection between loss of ecological memory,alien invasions and ecological restoration

When a community or ecosystem is lost, some of its properties may remain, leaving behind an ecological memory. The soil properties, spores, seeds, stem fragments, mycorrhizae, species, populations and other remnants of the previous inhabitants contribute to shaping the replacement community and building a new ecosystem. The loss of ecological memory for the natural stability domain of a site reduces ecosystem resilience and enables alien invasive species to become established more easily. These invasives may eventually create a new ecosystem with its own ecological memory and resilience. These new ecosystems are described here as novel ecosystems and are placed in the context of adaptive cycles. Ecological restoration of urban ecosystems requires removing the ecological legacy of invasive alien species. To be successful, invasive species control must address both internal within patch memory of invasives and external between patch memory. The restoration of Garry oak ecosystems (Quercus garryana), by students of the Restoration of Natural Systems Program at the University of Victoria, British Columbia, and a number of other examples are presented here that highlight why ecological memory is especially important in urban ecosystems.     

Approaches to the study of urban ecosystems: The case of Central Arizona—Phoenix

CAP LTER focuses on an arid-land ecosystem profoundly influenced, even defined, by the presence and activities of humans and is one of only two LTER sites that specifically studies the ecology of an urban system. In this large-scale project, biological, physical, and social scientists are working together to study the structure and function of the urban ecosystem, to assess the effects of urban development on surrounding agricultural and desert lands, and to study the relationship and feedbacks between human decisions and ecological processes.Our interdisciplinary investigations into the relationship between land-use decisions and ecological consequences in the rapidly growing urban environment of Phoenix are of broad relevance for the study of social ecological systems and cites in particular. Refinements in our conceptual model of social ecological systems focuses our attention on recognizing the scales and periodicities of ecological and human phenomena, understanding the means and impacts of human control of variability in space and time, and finally an evaluation of the resilience of various aspects of socio-ecological systems especially their vulnerabilities and their potential for adaptive learning.     

Urbanization impacts on the structure and function of forested wetlands

The exponential increase in population has fueled a significant demographic shift: 60% of the Earth's population will live in urban areas by 2030. While this population growth is significant in its magnitude, the ecological footprint of natural resource consumption and use required to sustain urban populations is even greater. The land use and cover changes accompanying urbanization (increasing human habitation coupled with resource consumption and extensive landscape modification) impacts natural ecosystems at multiple spatial scales. Because they generally occupy lower landscape positions and are linked to other ecosystems through hydrologic connections, the cascading effects of habitat alteration on watershed hydrology and nutrient cycling are particularly detrimental to wetland ecosystems. I reviewed literature relevant to these effects of urbanization on the structure and function of forested wetlands. Hydrologic changes caused by habitat fragmentation generally reduce species richness and abundance of plants, macroinvertebrates, amphibians, and birds with greater numbers of invasives and exotics. Reduction in soil saturation and lowered water tables result in greater nitrogen mineralization and nitrification in urban wetlands with higher probability of NO^– ₃ export from the watershed. Depressional forested wetlands in urban areas can function as important sinks for sediments, nutrients, and metals. As urban ecosystems become the predominant human condition, there is a critical need for data specific to urban forested wetlands in order to better understand the role of these ecosystems on the landscape.     

Methods for spatial and temporal land use and land cover assessment for urban ecosystems and application in the greater Baltimore-Chesapeake region

Understanding contemporary urban landscapes requires multiple sets of spatially and temporally compatible data that can integrate historical land use patterns and disturbances to land cover. This paper presents three principal methods: (1) core analysis; (2) historic mapping; and (3) gradient analysis, to link spatial and temporal data for urban ecosystems and applies their use in the Baltimore-Chesapeake region. Paleoecological evidence derived from the geochronology of sediment cores provides data on long-term as well as recent changes in vegetative land cover. This information, combined with contemporary vegetation maps, provides a baseline for conducting trend analyses to evaluate urbanization of the landscape. A 200-year historical land use database created from historical maps, census data, and remotely sensed data provides a spatial framework for investigating human impacts on the region. A geographic information system (GIS) integrates core analyses with historic data on land use change to yield a comprehensive land use and land cover framework and rates of change. These data resources establish the regional foundation for investigating the ecological components of an urban ecosystem. Urban-rural gradient analyses and patch analyses are proposed as the most appropriate methods for studying the urban ecosystem as they link ecological and social patterns and processes for varying degrees of urbanization.     

Ecological integrity in urban forests

Ecological integrity has been an umbrella concept guiding ecosystem management for several decades. Though plenty of definitions of ecological integrity exist, the concept is best understood through related concepts, chiefly, ecosystem health, biodiversity, native species, stressors, resilience and self-maintenance. Discussions on how ecological integrity may be relevant to complex human-nature ecosystems, besides those set aside for conservation, are growing in number. In the case of urban forests, no significant effort has yet been made to address the holistic concept of ecological integrity for the urban forest system. Preliminary connections between goals such as increasing tree health, maintaining canopy cover, and reducing anthropogenic stressors and the general notion of integrity exist. However, other related concepts, such as increasing biodiversity, the planting of native species, and the full meaning of ecosystem health beyond merely tree health have not been addressed profoundly as contributors to urban forest integrity. Meanwhile, other concepts such as resilience to change and self-maintenance are not addressed explicitly. In this paper we reveal two camps of interpretation of ecological integrity for urban forests that in turn rely on a particular definition of the urban forest ecosystem and a set of urban forest values. Convergence and integration of these values is necessary to bring a constructive frame of interpretation of ecological integrity to guide urban forest management into the future.     

Is there a need for a theory of urban ecology?

Although urban ecosystems are governed by the same ecological laws as rural ecosystems, the relative importance of certain ecological patterns and processes differs between the two types of ecosystems. For instance, as compared to rural areas, urban habitats are usually more islandlike, more often represent early successional stages, and more easily invaded by alien species. All these features are results of the intense human influence on urban landscapes. The question then arises whether a distinct theory of urban ecology is needed for understanding ecological patterns and processes in the urban setting. The answer is no, because urban ecosystems can be successfully studied using existing ecological theories, such as the metapopulation theory. However, due to the intense human presence approaches that include the human aspect are useful in studying urban systems. For instance, the human ecosystem model, which emphasizes human impact by identifying social components with connections to ecology, is a useful approach in urban studies. This model, combined with the urban–rural gradient approach, forms an effective tool for studying key ecological features of urban ecosystems. Better understanding of these features would increase our ability to predict changes that land use causes in urban ecosystems, and would help to integrate ecology better into urban planning.     

Social dimensions of gradients in urban ecosystems

Urban ecosystems are complex mosaics in which the biophysical characteristics are transformed over time by a concentrated, diverse set of human activities. Understanding their complexity requires the continuing development of interdisciplinary approaches. The use of gradient approaches has pointed towards the need to examine in greater detail the roles of human influences. In this paper, I propose the addition of three social dimensions to characteristics defining urban gradients: landuse, land management effort, and historical context. These dimensions correspond with major types of social activities that modify the physical environment. They are intended to augment research by explicitly elaborating on the social factors contributing to the variation along the complex, indirect gradients that typify urban areas.The diversity of urban landuses has numerous influences, obvious and subtle, on the complex urban land gradients. Incorporating new information on historical and spatial characteristics of management practices supports more direct fine-scale analyses of the impact of human activities on the environment. This path of inquiry also requires engaging in more detailed research on historical dimensions of urban development in conjunction with biophysical analyses. Examples from Columbia, South Carolina, illustrate the ways that social and historical processes contribute to urban ecology.     

Residential landscapes as social-ecological systems: a synthesis of multi-scalar interactions between people and their home environment

Residential landscapes are a common setting of human-environment interactions. These ubiquitous ecosystems provide social and ecological services, and yard maintenance leads to intended and unintended ecological outcomes. The ecological characteristics of residential landscapes and the human drivers of landscape management have been the focus of disciplinary studies, often at a single scale of analysis. However, an interdisciplinary examination of residential landscapes is needed to understand the feedbacks and tradeoffs of these complex adaptive social-ecological systems as a whole. Our aim is to synthesize the diversity of perspectives, scales of analysis, and findings from the literature in order to 1) contribute to an interdisciplinary understanding of residential landscapes and 2) identify research needs while providing a robust conceptual approach for future studies. We synthesize 256 studies from the literature and develop an interdisciplinary, multi-scalar framework on residential landscape dynamics. Complex human drivers (attitudinal, structural, and institutional factors) at multiple scales influence management practices and the feedbacks with biophysical characteristics of residential landscapes. However, gaps exist in our interdisciplinary understanding of residential landscapes within four key but understudied areas: 1) the link between social drivers and ecological outcomes of management decisions, 2) the ecosystem services provided by these landscapes to residents, 3) the interactions of social drivers and ecological characteristics across scales, and 4) generalizations of patterns and processes across cities. Our systems perspective will help to guide future interdisciplinary collaborations to integrate theories and research methods across geographic locations and spatial scales.     

Learning about restoration of urban ecosystems: a case study integrating public participation,stormwater management,and ecological research

Restoration of ecosystem functions in urban environments is made challenging by 1) a public that often lacks understanding of ecological principles, 2) inadequate evidence of the effectiveness of restoration practices, and 3) difficulty integrating social and biophysical factors in studies of urban ecosystems. This paper describes a case study in which potential solutions to these challenges were explored. We facilitated collaborative learning through public participation in the design and implementation of an urban riparian buffer along a headwater stream in a neighborhood park, a process that was informed by ecological research. Learning outcomes were evaluated using surveys and qualitative assessment of discussion. Results indicated that participants’ knowledge about water quality problems associated with urbanization, stormwater, and nonpoint-source pollution increased, familiarity with stormwater management practices increased, and perceptions about the importance of stream ecosystem functions changed. In-stream monitoring of sediment delivery, as well as direct measurements of buffer infiltration capacity, provided early evidence of buffer effectiveness in prevention of sediment inputs to the stream and absorption of runoff from surrounding surfaces. This study provides a useful model for integration of collaborative learning through participation, ecological restoration, and ecological research in an urban setting. Elements deemed essential to success of this model included an opportunity for dialog focused on a specific natural feature, sustained interaction between participants and researchers, opportunities for hands-on participation by urban residents, and flexibility in restoration practice installation.     

From feedbacks to coproduction: toward an integrated conceptual framework for urban ecosystems

Research in urban ecology depends on frameworks that meaningfully integrate our understanding of biophysical and social change. Although the coupled nature of urban ecosystems is widely accepted, the core mechanisms we use to integrate the social and biophysical aspects of urban ecosystems – their social-ecological feedbacks – are poorly understood. This paper considers how feedbacks are used to conceptualize social-ecological change, noting their utility and their limitations. In so doing, we suggest that coproduction provides a meaningful alternative to feedbacks, one that captures not only the structure-function relationships usually assumed in studies of biophysical landscape change, but also the structure-agency relationships that facilitate our most comprehensive understanding of social change. By addressing both the stepwise forms of transformation that a feedback approach captures and the simultaneous forms of transformation captured by a coproduction approach, a more comprehensive assessment of the ways that social and ecological change take place is afforded. We contend that thinking in terms of coproduction is essential for moving beyond the interdisciplinary approach that usually guides urban ecology models, toward a more integrated, trans-disciplinary approach.

     

Fengshui theory in urban landscape planning

The spatial configuration of urban landscapes results from cumulative interactions between human activities and the physical environment. Traditional philosophies and cultural legacies have had important influences on urban development and planning in East Asia. In Seoul, traditional land use practices based on ‘Fengshui’ have significantly contributed to human-mediated patterns of landscape changes, in addition to the role of the socio-economic background (development) and other human activities. The concept of Fengshui was originally founded upon people’s empirical cognition of natural landscape patterns. Recently, however, advanced economic development, westernization and urbanization have been rapidly altering the old traditions of the holistic landscape systems through changing urban planning practices. Since the type, scale, frequency, distribution and spreading pattern of environmental and human disturbances have been changed, a new paradigm for urban landscape planning is necessary to maintain the ecological and cultural integrity of landscapes in Korea. In this paper, we discuss recent concepts and methods of landscape ecology and urban planning from the viewpoint of Fengshui, the traditional land use patterns in Seoul, whose application has so far been restricted only to traditional land evaluation. We conclude that, to maintain the sustainability of the urban landscape, it is necessary to develop a new urban planning framework for the region that is based on the integration between landscape ecology principles with the traditional concepts of Fengshui.     

Habitat structure: A fundamental concept and framework for urban soil ecology

Habitat structure is defined as the composition and arrangement of physical matter at a location. Although habitat structure is the physical template underlying ecological patterns and processes, the concept is relatively unappreciated and underdeveloped in ecology. However, it provides a fundamental concept for urban ecology because human activities in urban ecosystems are often targeted toward management of habitat structure. In addition, the concept emphasizes the fine-scale, on-the-ground perspective needed in the study of urban soil ecology. To illustrate this, urban soil ecology research is summarized from the perspective of habitat structure effects. Among the key conclusions emerging from the literature review are: (1) habitat structure provides a unifying theme for multivariate research about urban soil ecology; (2) heterogeneous urban habitat structures influence soil ecological variables in different ways; (3) more research is needed to understand relationships among sociological variables, habitat structure patterns and urban soil ecology. To stimulate urban soil ecology research, a conceptual framework is presented to show the direct and indirect relationships among habitat structure and ecological variables. Because habitat structure serves as a physical link between sociocultural and ecological systems, it can be used as a focus for interdisciplinary and applied research (e.g., pest management) about the multiple, interactive effects of urbanization on the ecology of soils.     

Impact of urban structure on avian diversity along the Truckee River, USA

Urban riparian habitats are potentially important resources for native birds in arid ecosystems. Most studies have assessed the value of urban riparian habitat in terms of vegetation and natural resources; however, the surrounding land use and infrastructure may determine the viability of urban habitat. We studied the impact of urban structure, the combination of land use, infrastructure and vegetation variables that work together to shape the urban environment, on avian riparian habitat in the Truckee Meadows, Nevada, USA. Land use and infrastructure explained avian species richness and abundance better than local vegetation alone, but community resemblance was more strongly correlated to vegetation. Avian species guilds responded differentially to surrounding land use, suggesting there may be a functional difference between land use types. The best models for bird diversity used urban structure (both land use and vegetation) to describe potential habitat. Urban structure describes urban habitat in ways that vegetation variables alone cannot. Studies that ignore land use and infrastructure and other socioeconomic variables are likely missing key functional differences within urban ecosystems, and may miss the potential for compatible development that encourages both biodiversity and urban growth.     

Socio-economic variables as indicators of pond conservation value in an urban landscape

Despite their designation as nationally important habitats in the UK, ponds are among the least well studied of urban habitats. Ponds, as well as existing in a physical landscape, are part of human socio-economic landscapes, especially those in towns and cities. Socio-economic, ecological and land cover data were collected from thirty seven ponds in the urban area of Halton, northwest England over a 3?year period. Significant variation was observed in the CCI Scores for ponds in different Output Area Classifications. Within postcode districts there was a significantly negative correlation between increasing house prices and decreasing BMWP scores. This research offers insights into the impact of urban development on pond ecology, and suggests the potential impacts of future developments and how these may be ameliorated. The research contributes towards the understanding of freshwater systems in the urban context and the relationship between the human and natural elements of urban green and blue spaces.     

A comparative gradient approach as a tool for understanding and managing urban ecosystems

To meet the grand challenges of the urban century??such as climate change, biodiversity loss, and persistent poverty??urban and ecological theory must contribute to integrated frameworks that treat social and ecological dynamics as interdependent. A socio-ecological framework that encapsulates theory from the social and ecological sciences will improve understanding of metropolitan dynamics and generate science for improved, sustainable management of urban ecosystems. To date, most urban ecological research has focused on single cities. A comparative approach that uses gradients within and between cities is a useful tool for building urban ecological theory. We offer five hypotheses that are testable using a comparative, gradient approach: (i) the current size, configuration, and function of larger metropolitan ecosystems predicts the potential trajectory of smaller urban areas; (ii) timing of growth explains the greatest variance in urban ecosystem structure and function; (iii) form and function of urban ecosystems are converging over time; (iv) urban ecosystems become more segregated and fragmented as populations increase; and (v) larger cities are more innovative than smaller cities in managing urban ecosystems.     

Habitat origins and microhabitat preferences of urban plant species

Urban vegetation is commonly described as dominated by weedy species that are adapted to human disturbance. In this study, we determined the original (pre-agriculture) habitats of urban plant species sampled quantitatively in the spontaneous vegetation of a university campus in Halifax, Nova Scotia (eastern Canada). We sampled 11 distinct patch types corresponding to different built forms. Differences in vegetation among patch types were related in part to environmental variables such as soil moisture and light availability. The urban vegetation was dominated by species from rocky habitats such as cliffs and talus slopes, with lesser representation from grassland and floodplain habitats. When compared to a null model of species origins based on the global area and species richness of different original habitats, species from rock outcrops and grassland habitats were overrepresented in the urban vegetation. These results contrast with the received view that cities represented highly “unnatural” ecosystems: built form appears to replicate the habitat templates required by rock outcrop species. Urban ecological theory should incorporate the replication of habitat analogs by built forms in addition to the creation of ecologically novel habitats.     

Diversity patterns of alien and native plant species in Trieste port area: exploring the role of urban habitats in biodiversity conservation

Nowadays, urban areas play a crucial role in biodiversity conservation and habitat protection despite the constant pressures on which these habitats are subjected. They may even host relatively new plant communities due to the peculiar ecosystem where they vegetate. The port of Trieste (NE Italy) is characterized by a mixed mosaic of intensely human impacted areas (where commercial activities are still ongoing) flanked by abandoned areas where vegetation persists or has spontaneously recovered. In this study, we sampled the whole port area through a stratified random sampling by placing multiscalar nested plots in four different habitats (strata) previously identified by photo-interpretation. Plant species richness and abundance were assessed in each plot. Each species was then classified as native or alien and patterns of species richness and complementarity were compared among habitats. Results show that there is a significant difference in species richness patterns among habitats, while observed patterns are likely to vary at different spatial scales. As expected, urban plots account for most of the alien species in the sampling, while wooded plots cope better with invasion, accounting for a lower alien/native ratio. These results highlight how habitat diversity enhances biodiversity in urban areas and how it could provide an effective filtering effect able to reduce the spread of alien species. In addition, we provide further evidence for the use of multi-scale approaches in order to study the complex relationships between spatial heterogeneity and plant species richness.