Instructions
Before using the Index of Ecological Condition (IEC) Calculator Tool, read these instructions.
1 Download the IEC calculator
To help you understand the spreadsheet, here are what the tabs mean:
- Instructions: instructions on how to use the IEC calculator and metadata
- CalcQ: calculator for estimating an IEC score for a group of sites or management area using frequency data
- CalcPA: calculator for estimating an IEC score for a single site using presence/absence data
- SppCodes: list of species 4-letter alpha codes, common names, and scientific names
- BirdBR: list of biotic response (BR) function parameters (mean (M), SD (standard deviation), and H (height)), which use a normal distribution function, for the 38 indicator bird species
For tabs CalcPA and CalcQ, only cells highlighted in blue (Observed data) may be changed by entering collected bird data. Cells under gray highlighted column headers contain parameters for all bird BR functions needed for IEC calculation. These have been previously determined by Gnass (2012) and should not be altered. If you wish to add species or use different BR functions, please contact us for guidance.
2 Identify reference gradients
Identify one or more "reference" gradients of environmental condition (Cenv), scaled from maximally stressed (Cenv = 0) to minimally stressed (Cenv = 10). These gradients help us identify bird species that are sensitive to environmental stressors and, to a limited extent, tell us what the indicator species actually indicate. We have used a gradient of human disturbance based on geographic information system (GIS) variables, such as land cover (e.g., percent developed lands), habitat fragmentation metrics (e.g., edge density), and other publicly-available variables that characterize the “human footprint” on the landscape (e.g., housing density; Gnass 2012).
3 Determine species sensitivity
Next, determine sensitivity of species to environmental stress. We use a modified normal distribution function (Bluman 2008) to model bird species’ responses to the environmental condition gradient. Bird data for this process were collected previously from sites (n = 917) located in a variety of landscapes ranging from high environmental stress (i.e., relatively poor condition) to low stress (i.e., relatively pristine condition) in Wisconsin and Michigan (Gnass 2012). The best-fit curve is described by three parameters (μ, σ, h) determined by computer iteration. These species’ curves are called biotic response (BR) functions.
In the diagrams to the right (Figure 1), the shape of each curve can vary widely given that some species are more sensitive to disturbance than others (Howe et al. 2007a,b). For example, a fairly tolerant species such as European Starling (Sturnus vulgaris) would be more likely observed in highly degraded forests, where environmental condition values are close to 0 (Figure 1; Gnass 2012). An intolerant, more sensitive species like Ovenbird (Seiurus aurocapilla) would more likely occur in minimally degraded forests with condition values near 10 (Figure 1; Gnass 2012).
Figure 1. Biotic response (BR) functions of European Starling and Ovenbird (Gnass 2012). The y-axis represents probabilities of detecting species across values of condition (Cenv). The x-axis represents the reference gradient of environmental condition (Cenv) that ranges from highly degraded (Cenv = 0) to minimally degraded forests (Cenv = 10).
Following the methods of Howe et al. (2007b), we then select an assemblage of bird species for estimating the bird-based ecological condition (or IEC score) of new sites. We chose 38 breeding bird species (Table 1) that were sensitive (positively or negatively) to the environmental reference gradient and were representative of northern mesic forests in the western Great Lakes region. In order to distinguish heavily disturbed sites from healthy forested areas, however, we included a few species that are not characteristic of northern mesic forests in this region, including invasive species (e.g., European Starling) and species associated with human-disturbed landscapes (e.g., Common Grackle [Quiscalus quiscula]; Guth 1978).
4Install the MS Excel Solver Add-in
The MS Excel Solver helps you determine the value of one cell when you change other cells. For the purpose of our project, (how can it help?)
5 Enter Data
Enter collected bird point count data (including flyovers) in the Observed column for species listed in the first column (e.g., AMCR, AMRE, etc.). A key to 4-letter species codes is given in the SppCodes tab. Observations of species not listed are ignored.
Two options are available for entering bird data and calculating the IEC:
- If your data have been collected from a single count at a single site, use the CalcPA tab. Enter the number of individuals, or simply input 1 (=present) or 0 (=absent) for each species in the Observed column.
- If your data consist of multiple point counts at a site or multiple counts in an area of interest, use the CalcQ tab. Enter the proportion of point counts for which each species was observed (i.e., frequency = # of counts a species was observed / total # of counts) in the Observed column.
6 Set an initial “guess” for the numeric IEC score to 5
For both the CalcQ and CalcPA tabs, the IEC core will be in cell 04.
7Calculate the IEC score
Open Solver (located in the upper right hand corner of the page), then click "Solve" in the Solver Parameters window. The steps are identical for both CalcPA and CalcQ tabs. Click "OK" in the Solver Results window.
IEC scores close to zero describe forested areas that are highly disturbed, fragmented, or associated with a heavy “human footprint”; whereas IEC scores close to 10 describe forested areas that are very healthy based on the birds found there. Results are more than just re-statements of the original reference gradient, since birds that are sensitive to the measured “human footprint” are also likely to be sensitive to other environmental stressors that we have not identified and quantified.
8 Record newly calculated IEC score
The IEC score (0-10) will now appear in cell 04 in either tab. If you're calculating scores for multiple sites or landscapes, record the result and repeat steps 3-5 for a new site or group of sites.
Breeding Bird Species List
38 indicator breeding bird species selected for use in the Index of Ecological Condition (IEC) model for northern mesic forests in northern Wisconsin (Gnass 2012). Click on the common name of a species to view its biotic response (BR) function.
Ask an Expert
Meet Erin Giese, Associate Director of the Cofrin Center for Biodiversity. She champions student experience and truly enjoys training the next generation of scientists. If you have questions about the Forest Health Tool, including how to become involved as a student, Erin can help.