Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

The indicator would report on the ecological integrity or health of riparian ecosystems, including both physical and biological factors.

The number and quality of streams and rivers and their associated riparian areas are a function of watershed conditions. Consequently, the condition of riparian areas may be useful as an indicator of ecological alterations of grassland and shrubland watersheds. For example, if land cover is altered, the stream flow may also be altered, changing the geomorphology of the river channel and influencing riparian dynamics. Regulation of rivers by dams and other flow-altering devices also influences downstream conditions, including streambank erosion and river meandering, sediment aggradation and seedbed development, and natural recruitment of riparian vegetation. Local land use within a floodplain, such as agriculture, grazing, and urbanization, may also greatly influence the condition of riparian ecosystems. In turn, riparian systems also influence hydrogeomorphic processes by trapping sediment and modifying flood flows and groundwater recharge.

The Data Gap

Several measures are being used nationally, but no “simple” index has received general acceptance among the research community. An appropriate “Index of Riparian Integrity” still needs to be fully developed. Several federal agencies use a combined qualitative metric called Proper Functioning Condition (PFC) when evaluating riparian systems (see Bureau of Land Management 1993). However, PFC is primarily hydrogeomorphic and includes little of the biological conditions such as species composition, age classes, understory condition, canopy condition, and successional processes. Another methodology developed in the past few years is the Hydrogeomorphic Methodology (HGM) (Brinson 1996, Smith et al. 1995). This methodology uses a complex of indices for hydrology, geomorphology, land use, biology, and other aspects to create a single index for the riparian system. It is complex, but a simplified version might be developed for broad-scale application. Yet another, simpler method is one that relies on satellite data (Iverson et al. 2001).

Aspects of the riparian condition that can be measured on a regional basis and that should be considered in any multi-metric index include hydrology (e.g., relationship to natural flow patterns), geomorphology (e.g., stream sediment transport), and biology (e.g., canopy cover condition; percentage of potential recruitment or successional measures; canopy diversity, or coverage of point bars). Many of these aspects either are being measured now or could be measured as part of a national riparian evaluation system.

Once an index is developed, it would be applied within a sampling design that would allow estimation of the conditions on all streams within a region. Thus, for example, such an approach might provide estimates of the number of miles of stream with “riparian condition index” that is “high,” “medium,” or “low,” each of these being within a selected numerical range of the index.

References

Brinson, M.M. 1996. Assessing wetland functions using HGM. National Wetlands Newsletter 18:10–16.

Bureau of Land Management.1993. Riparian area management: Process for assessing proper functioning condition. Technical Reference 1737-9. USDOI, BLM, Denver, CO. Revised 1995, 1998.

Iverson, L.R., D.L Szafoni, S.E. Baum, and E.A. Cook. 2001. Development of a riparian wildlife habitat evaluation scheme using GIS. Environmental Management 28(5):639–654.

Smith, R.D., A. Ammann, C. Bartoldus, and M.M. Brinson. 1995. An approach for assessing wetland functions using hydrogeomorphic classification, reference wetlands and functional indices. U.S. Army Corps of Engineers, Waterways Experiment Station. Vicksburg, MS. Tech. Rep. TR-WRP-DE-9