functioning rather than ecosystem goods and services, ecological condition is used. These terms are defined in the next section.

This chapter is organized into five sections to summarize the interaction between roads and ecological conditions. After this introduction, terms and concepts are defined in the second section. A short summary of effects on ecological goods and services is provided in the third section. The fourth section summarizes published, mostly refereed literature and is organized according to two dimensions: the first is the ecological process of interest (many of which are listed in Table 3-1) and includes the effects of each process on the different levels of ecological organization (for example, abiotic, population, species, and ecosystem), and the second is the scale of the effect. Many of the effects of roads on the environment are caused by other forms of human activity and land use. Impacts of agriculture, urbanization, forest practices, and manufacturing are in many ways similar and sometimes interrelated with the impacts of roads. Information gaps are discussed in the fifth section.


Ecological condition is a general term that describes the structure and functioning of ecosystems. It may refer to the status of the ecological environment at a particular time or to dynamic changes in its components and processes over time. The dynamic aspects of these condition measurements are discussed later in the chapter where both spatial and temporal dimensions are addressed. Ecosystems encompass all living organisms (biotic components) plus the nonliving environments (abiotic components) with which they interact. The abiotic components consist of hydrological and geomorphological processes, chemicals, and such disturbances as landslides, climate and weather. Levels of organization of biotic components used in this report are genetics, species and population (plants and animals), and ecosystem. Each level of biotic components has attributes of composition, structure, and functioning, and together constitute biological diversity (often called “biodiversity”).

Composition refers to the identity and variety of elements in each of the biodiversity components. Structure refers to the physical organization or pattern of the elements. Ecological (or ecosystem) functioning refers to the ecological and evolutionary processes acting among the elements, or how the ecosystem works.

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