Marina Alberti

Complexity of Coupled Human and Natural Systems

Integrated studies of coupled human and natural systems reveal new and complex patterns and processes not evident when studied by social or natural scientists separately. Synthesis of six case studies from around the world shows that couplings between human and natural systems vary across space, time, and organizational units. They also exhibit nonlinear dynamics with thresholds, reciprocal feedback loops, time lags, resilience, heterogeneity, and surprises. Furthermore, past couplings have legacy effects on present conditions and future possibilities.

Integrating Humans into Ecology: Opportunities and Challenges for Studying Urban Ecosystems

Abstract Our central paradigm for urban ecology is that cities are emergent phenomena of local-scale, dynamic interactions among socioeconomic and biophysical forces. These complex interactions give rise to a distinctive ecology and to distinctive ecological forcing functions. Separately, both the natural and the social sciences have adopted complex system theory to study emergent phenomena, but attempts to integrate the natural and social sciences to understand human-dominated systems remain reductionist—these disciplines generally study humans and ecological processes as separate phenomena. Here we argue that if the natural and social sciences remain within their separate domains, they cannot explain how human-dominated ecosystems emerge from interactions between humans and ecological processes. We propose an integrated framework to test formal hypotheses about how human-dominated ecosystems evolve from those interactions.

The Effects of Urban Patterns on Ecosystem Function

Urban ecological systems are characterized by complex interactions among social, economic, institutional, and environmental variables. These interactions generate complex human-dominated landscapes, which significantly influence the functioning of local and global earth ecosystems and the services they provide to humans and other life on earth. Urban development fragments, isolates, and degrades natural habitats; simplifies and homogenizes species composition; disrupts hydrological systems; and modifies energy flow and nutrient cycling. Urban areas also appropriate a large share of earth’s carrying capacity from other regions in terms of resource input and waste sinks. Change in ecological conditions that result from human actions in urban areas ultimately affect human health and well-being. In this article, the author reviews the empirical evidence on the effects that patterns of urban development have on ecosystem function. Urban development affects the spatial heterogeneity of the landscape (i.e., pattern of variation in land cover) and spread of disturbance (i.e., invasive species). The author proposes that alternative urban patterns generate differential ecological effects. The review reveals that the interactions between urban development patterns and ecosystem dynamics are still poorly understood. The author draws on an empirical study of the Puget Sound metropolitan region currently developed at the University of Washington to propose directions for future empirical research that can inform strategies to minimize urban impacts on ecosystems.

Coupled Human and Natural Systems

Abstract Humans have continuously interacted with natural systems, resulting in the formation and development of coupled human and natural systems (CHANS). Recent studies reveal the complexity of organizational, spatial, and temporal couplings of CHANS. These couplings have evolved from direct to more indirect interactions, from adjacent to more distant linkages, from local to global scales, and from simple to complex patterns and processes. Untangling complexities, such as reciprocal effects and emergent properties, can lead to novel scientific discoveries and is essential to developing effective policies for ecological and socioeconomic sustainability. Opportunities for truly integrating various disciplines are emerging to address fundamental questions about CHANS and meet societys unprecedented challenges.

Ecological resilience in urban ecosystems: Linking urban patterns to human and ecological functions

Urban ecosystems evolve over time and space as the outcome of dynamic interactions between socio-economic and biophysical processes operating over multiple scales. The ecological resilience of urban ecosystems—the degree to which they tolerate alteration before reorganizing around a new set of structures and processes—is influenced by these interactions. In cities and urbanizing areas fragmentation of natural habitats, simplification and homogenization of species composition, disruption of hydrological systems, and alteration of energy flow and nutrient cycling reduce cross-scale resilience, leaving systems increasingly vulnerable to shifts in system control and structure. Because varied urban development patterns affect the amount and interspersion of built and natural land cover, as well as the human demands on ecosystems differently, we argue that alternative urban patterns (i.e., urban form, land use distribution, and connectivity) generate varied effects on ecosystem dynamics and their ecological resilience. We build on urban economics, landscape ecology, population dynamics, and complex system science to propose a conceptual model and a set of hypotheses that explicitly link urban pattern to human and ecosystem functions in urban ecosystems. Drawing on preliminary results from an empirical study of the relationships between urban pattern and bird and aquatic macroinvertebrate diversity in the Puget Sound region, we propose that resilience in urban ecosystems is a function of the patterns of human activities and natural habitats that control and are controlled by both socio-economic and biophysical processes operating at various scales. We discuss the implications of this conceptual model for urban planning and design.

An integrated urban development and ecological simulation model

This paper develops an integrated strategy to model the urban development and ecological dynamics in the Central Puget Sound Region. This effort is part of the Puget Sound Regional Integrated Synthesis model (PRISM) – an interdisciplinary initiative at the University of Washington aiming to develop a dynamic and integrated understanding of the environmental and human systems in the Puget Sound. We describe a model that predicts the environmental stresses associated with urban development and related changes in land use and human activities under alternative demographic, economic, environmental, and policy scenarios. We build on UrbanSim, an existing urban simulation model developed by Waddell [42]. The principal urban actors, represented in the model as objects corresponding to businesses, households, developers, and governments, make choices about location of activities and land development. We extend the object properties and methods now implemented in the UrbanSim model to predict three types of human-induced environmental stressors: land conversion, resource use, and emissions. The core location model in UrbanSim will be revised from its current aggregate structure to one based on microsimulation, and from a zone description of space to one based on a high-resolution grid structure. We will use a spatially explicit process-based landscape modeling approach to replicate ecosystem processes and represent land use–cover interactions at the regional scale. The output of the urban ecological model will serve as the input to several biophysical models for hydrology, hillslope stability, water quality, atmosphere, and ecosystems. Ecological changes will feed back on the choices of both households and business locations, and availability of land and resources.

Urban Patterns and Environmental Performance: What Do We Know?

This paper reviews the empirical evidence on the relationships between urban patterns and various dimensions of environmental quality and performance. I first examine approaches to measuring urban environmental perfomance, drawing on the concepts of carrying capacity, ecological footprint, environmental space, and appropriated ecosystem area. Since cities affect and are affected by ecological systems far beyond their physical boundaries, I propose including interactions at the local, regional, and global scales in the definition of environmental performance. I then systematcally review the current literature on the reltionship between four structural variables typically used to describe urban patternform, density, grain, and connectivity and four dimensions of environmental perfomance sources, sinks, ecological support systems, and human well-being. I conclude that what we measure and the scale of analysis affect the direction of observable urban ipacts. We must consider these factors as we select measures of urban environmental peformance.

Eco-evolutionary dynamics in an urbanizing planet.

A great challenge for ecology in the coming decades is to understand the role humans play in eco-evolutionary dynamics. If, as emerging evidence shows, rapid evolutionary change affects ecosystem functioning and stability, current rapid environmental change and its evolutionary effects might have significant implications for ecological and human wellbeing on a relatively short time scale. Humans are major selective agents with potential for unprecedented evolutionary consequences for Earths ecosystems, especially as cities expand rapidly. In this review, I identify emerging hypotheses on how urbanization drives eco-evolutionary dynamics. Studying how human-driven micro-evolutionary changes interact with ecological processes offers us the chance to advance our understanding of eco-evolutionary feedbacks and will provide new insights for maintaining biodiversity and ecosystem function over the long term.

Urban Land-Cover Change Analysis in Central Puget Sound

A methodology was developed to interpret and assess land cover change between 1991 and 1999 in Central Puget Sound, Washington at several scales (landscape, sub-basins, and 90 m grid window) relevant to regional and local decision makers. Land cover data are derived from USGS Landsat (Thematic Mapper and Enhanced Thematic Mapper � ) images of Central Puget Sound. Landsat data were registered, intercalibrated, and corrected for atmosphere and topography to ensure accuracy of land cover change assessment. We apply a hybrid classification method to each image to address the spectral heterogeneity of urbanizing regions. The method combines a supervised classification approach with a spectral unmixing approach to produce seven classes: � 75 percent impervious, 15 to 75 percent impervious, forest, grass, clear cut, bare soil, and water. Land cover change is identified using the direct spatial comparison of classified images derived independently for each time period. We assess that the overall accuracy of each classified image was 91 percent for 1991 and 88 percent for 1999 respectively, which produces an accuracy of 85 percent for the change analysis. Our results show that urban growth over the last decade has produced an overall 6.7 percent increase in paved area.

Quantifying the urban gradient: Linking urban planning and ecology

Ecologists have suggested that ecological conditions in urbanizing landscapes can be described by a complex urban-to-rural gradient (McDonnell and Pickett 1990). The gradient paradigm offers a useful framework to test hypotheses on the impacts of urban development on ecological processes. These studies, however, tend to simplify the actual urban structure into monocentric agglomerations characterized by concentric rings of development surrounding a dense core. The assumption of gradient analysis is that the overall urban exposure changes predictably with distance from the urban core. Due to such simplification, current gradient studies fail to capture the effects of alternative urban development patterns on ecological processes. In this paper we argue that urban-to-rural gradients cannot be represented by the distance from the urban core. Rather they can best be described using a series of pattern metrics that link urban development to ecological conditions. Based on an analysis of land-use and land-cover patterns in the Seattle metropolitan area we propose a strategy to quantify urban patterns. We examine the behavior of various pattern metrics and propose a set of metrics useful to test formal hypotheses on the relationships between urban patterns and ecological disturbances. Finally, we discuss the implications of this empirical study for gradient analysis of metropolitan areas and for future urban ecological research.