independent of the rangeland's use and how it is managed, recognizing that if its health is preserved, the rangeland could accommodate a variety of uses (including livestock production and recreation, for example). As does the NRC report on soil and water quality, the rangeland report emphasizes that measures of condition would not be sufficient to guide decisions about uses and management practices, and it notes the need for other data and for aggregate assessments of rangeland health at the national level.
The committee recommended three criteria for making a determination of the state of rangeland health: the degree of soil stability and watershed function, which is critical to the prevention of soil degradation; nutrient cycling and energy flow; and the ability of the rangeland to adapt to change, which is necessary to maintain or move toward a healthy state and might be indicated by increases in vegetative cover or changes in plant age-class distributions.
Although it is not specific about how to quantify and combine indicators relevant to each criterion, the report does present an evaluation matrix that relates indicators to categories of ecosystem health. For example, the distribution and incorporation of plant litter in the soil could be used to assess the degree of nutrient cycling. Declines in production of plant matter and consequent reduction in the incorporation of plant litter into the soil may occur because of overgrazing by livestock. Such outcomes would indicate a diminution of the total volume of nutrients in the rangeland ecosystem.
Even this cursory review of the findings of recent NRC reports on soil quality and rangeland health is sufficient to confirm the relatively undeveloped state of quantitative measures of environmental condition and performance for agriculture. That is not to say the lack of good measures should constrain immediate efforts to improve the environmental sensitivity of management practices. To the contrary, both reports address the current possibilities at length. However, both also call, with some degree of urgency, for intensification of efforts to understand the functioning of managed farm and ranch ecosystems. The selection both of indicators of condition and of performance standards is hampered by ignorance of the causal mechanisms that link farming and ranching practices with resource degradation. Although the general pathways are recognized—the action of heavy machinery in compacting soil, for example—it is usually less clear exactly what the practice contributes to the degradation of the resource. For instance, to continue the example, how much compaction can be tolerated before the soil loses its capacity to absorb rainfall or nutrients?
The question of the adequacy of condition and performance measures is not simply academic. The reauthorization of the Clean Water Act focuses on nonpoint-source pollution. Agriculture is the nation's largest remaining unregulated