An IBI is somewhat similar to the economic indicators used to evaluate the condition of our economy. The value can be compared to reference values and help managers assess the relative health of individual wetlands. Although sampling methods and metrics are different for wetlands than for streams, the general IBI framework can be adapted for wetlands as well as lakes, estuaries, and terrestrial systems. The first step in creating an IBI is for researchers to classify wetlands and select reference sites. The goal is to group wetlands such that the diversity and composition of an assemblage within groups is minimized and the variation between groups is maximized.
Classification is an iterative process.
Researchers often start with one or more methods and then lump or split as needed to end up with an appropriate number of groups of biologically distinct wetlands. For example, when the Montana Department of Environmental Quality developed its IBI, the state used ecoregions as a first tier and then further separated wetlands by landscape position and other characteristics, such as acidity and salinity. The state later found that it could lump the wetlands of two ecoregions because of their biological similarity. After classifying wetlands, researchers select sampling sites across a gradient of human disturbance for each wetland group. Because no standard gradient of human disturbance yet exists, some projects have tried to quantify disturbance by using surrogates such as the percentage of impervious surfaces or agriculture in a watershed.