Urban Ecology最新文献

Finding useful generalizations about urban forest structures for a nation can assist in developing urban forest science and urban forestry planning and management. This process entails adopting commonly understood definitions of urban forest structure and urban boundaries. Urban forest structure is determined by three broad factors: urban morphology, which creates the spaces available for vegetation; natural factors, which influence the amount and types of biomass likely to be found within cities; and human management systems, which account for intraurban variations in biomass configurations according to land use distributions. Together these factors provide an explanation for urban forest structure and enhance our ability to predict structures from limited information.

Forested residual open spaces are a unique resource that contribute to the diversity of urban ecosystems. Five forested sites located along the Palisades escarpment in New Jersey were selected for a study of tree species distribution, abundance and diversity. Significant correlations existed between these parameters and a number of selected environmental characteristics, including site size and distance from nearest roadway, soil lead and sodium concentrations and surrounding population density. A number of planning and management strategies and considerations for these sites are discussed.

Principles from Campbell's Experimenting Society are transferred from program evaluation to habitat design. Diverging meanings of the concept of experiment are contrasted to show how scientific methods can be used by designers and social scientists for addressing problems of both practice and knowledge. As integrating the concerns of the two groups is an immense task, islands of theory should be constructed as an initial step for organizing the efforts of those involved in the proposed marriage of the two professions. The islands of theory discussed here explore the problem of how much habitat structure should be designed by professionals and how much should be left to the initiatives of residents. As behavioral constraint is both a by-product and a requirement of habitat design, upper and lower limits of structure are inspected to elucidate conditions when habitats are oppressive or anomic (i.e., allowing either too few choices or too many choices of their respective residents to foster community development). A theoretical framework and methodology is discussed for inspecting this topic; a research agenda is also proposed.

The recent literature of urban social ecology has produced an emergent body of theory and methodology together with empirical verification. Yet, the entire conception is dependent upon cross-sectional analyses or international comparisons, with little attention directed to processes of change. This paper focuses explicitly on system change by comparing cross sections over time and by the direct decomposition of change data. The first approach, which has been extensively utilized, should provide evidence consistent with existing theory. The second approach, which is less well understood, should provide an alternative set of perspectives.

Empirical content is provided by analyzing a consistent 43 variable set for the census tracts of Detroit both for 1960 and 1970. In addition, the same variable set is constructed to represent change over the decade and then analyzed for the identification of change dimensions. For both time periods theoretically expected dimensions emerge. However, the substantive simplicity of the 1960 structure is far more complex a decade later. Much of the additional complexity involves the separation of family status related variables from a unidimensional concept to an increasingly multidimensional representation. It is suggested that these findings are not unique and they may represent the emergence of post-industrial patterns. Although cross-sectional findings and change dimensions derived from change variables are related, they are not the same. These two approaches provide differing perspectives on the nature of urban system modification.