Ecological Indicators: Taking the Pulse of Ecosystem Health

Illinois is uniquely situated at America's ecological crossroads. Five distinct eco-regions or "biomes" come together within our state. They include the eastern deciduous forest,western great plain, northern boreal forest, Ozark uplift, and southern coastal plain. This patchwork of biomes is a melting pot for an extremely diverse range of flora and fauna. As host to more than 54,000 species of native organisms, Illinois contains  some of the richest natural areas in the entire Midwest.  Given the abundance and variety of species throughout Illinois, using an inventory approach to track ecosystem health is both timeconsuming and expensive. Instead, scientists have devised a set of key ecological indicators to measure ecological trends and biodiversity. Indicators include native and non-native species known to reflect the condition of biotic integrity. Certain physical parameters describing habitat structure are also examined. Select species can be usedas indicators

themselves or as components of composite indices, which provide a snapshot of ecosystem health. Changes in the abundance or distribution of indicator organisms also reflect underlying changes in ecological factors influencing biodiversity. Ecological indicators offer many advantages over other methods of measuring ecosystem health. They tend to be highly sensitive to small changes in ecosystem quality and allow conditions over a wide area to be assessed in a short period of time. Moreover, indicator-based monitoring methods are widely recognized and accepted among the scientific community, and are easily adapted for use by Citizen Scientists.Five major taxanomic groups have been selected from which the primary CTAP/EcoWatch ecological indicators will be developed: vascular plants, birds, terrestrial insects, fishes, and aquatic macroinvertebrates. Vascular plants are being monitored in forest, wetland, and grassland habitats

to detect changes in biotic integrity. Encroachment by invasive and/or exotic species, disease, or altered fire regimes can lead to changes in community structure, the loss of sensitive native plant species, and the homogenization of historically diverse plant communities. Plant community indicators include the presence of "disturbance sensitive" native species, the diversity of native plant species, and the percent cover of exotic versus native plants. Other indicators are also being investigated. Long-term monitoring will reveal patterns of change within plant communities. Bird populations are also being monitored in forests, wetlands, and grasslands. Indicators include, but are not limited to: the abundance and diversity of habitat specialists (for example, species that can only survive in wetlands); threatened and endangered species; species sensitive to fragmentation and other forms of habitat alteration; and the ratio of cowbirds (brood parasites) to host species. Because birds are highly mobile, these indicators

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