tors, such as soil nutrient content, size of stream buffers, and distribution of nonnative pest organisms (plants and animals).

To date, attributes of road networks are not often considered in lists of ecological indicators, but road density and the spatial arrangement of new roads or roads that are removed strongly influence the ecological implications of road networks.


In evaluating ecological effects of roads, two areas of integration were identified. The first involves integration across scales and complexities of ecological systems. The second involves integration across multiple societal goals associated with roads.

Ecological systems cover wide ranges of spatial and temporal scales. The cross-scale structure and dynamics are not always amenable to simple scaling approaches and are the source of unexpected behavior. Some road effects confine the scale of ecological effects, and other effects can increase or decrease the spatial or temporal extent of ecological processes.

The complexity and cross-scale interactions in ecological systems generate problems for assessment and planning. Multiple assessments must be developed, each at different spatial and temporal scales to address key ecosystem processes and structures. Ecological concerns should be included early in the assessment and planning processes, which are context sensitive. Some components of the environment are incompatible with the existence of roads. Although great progress has been made in understanding and mitigating road effects, much more is needed. The development of a broader set of robust ecological indicators and learning-based institutions will help to facilitate understanding of the complexities in ecological systems.

Complexities that arise in the dynamics of social structures used to assess, plan, construct, and manage road systems must be addressed. Better integration of the social institutions will probably require the development of new relationships among the existing institutions. Transportation agencies have an opportunity to play a key role in meshing and integrating planning and management of environmental issues. New types of institutions are needed to address the mix of socioeconomic and ecological concerns. Enhanced collaboration can be generated by new kinds of rules and groups for interactions among agencies and stakeholders.

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