HSI models can be constructed by various techniques. The following steps describe an approach that may be useful in a workshop setting for determining variables in a model. The assumed use of the model is for planning a restoration project, but the steps can be adjusted for other purposes. Several options exist for the format of a variable. One format is illustrated here, where the name of the variable is "Percent cover of overstory," referring to the canopy coverage of overstory trees in a forest. The characteristics of the variable are described for the range of possible conditions, 0-100%. A Suitability Index (SI) relates the condition of the overstory to the habitat needs of the species being modeled.
The model subject can be a species, subspecies, species life stage, cover type, or community. The steps below are sequential in general but may be altered, for example, if some of the work is done ahead of time.
Before the Workshop
1. Contact individuals with knowledge of the subject in the area that the model will be applied.
2. Develop an agenda that allows at least four hours of working time. (The time needed for this process will depend on the participants' knowledge of the process, the complexity of the model, adequacy of preparation for the workshop, and the ability of the workshop leader. The estimated minimum time would be four hours and the maximum 16 hours.)
3. In introductory material, describe the purpose and application for which the model is being constructed, why the model subject was selected, and other information to bring the participants to a state of common understanding.
At the Workshop
1. Ask participants to introduce themselves and describe the expertise they contribute. Describe the after-workshop report so participants will appreciate the need for documenting what they say and decide.
2. Identify and clearly describe the subject to be modeled and the area of applicability. Include the land cover classes used by the subject.
3. From the objectives of the restoration, identify the desired model endpoints, e.g., suitability of nesting habitat, maintenance of the community.
4. List and describe as clearly as possible the habitat requirements of the model subject. Provide quantification at least as an estimate or range, e.g., acres of a particular cover class, diameter of nest trees, size class of substrate material, etc.
5. Identify the limiting factors present in the project area relative to the model endpoints and habitat requirements.
6. Identify any special features known to be used by the subject, e.g., travel lanes, vines.
7. Determine the life requisites that will be modeled. Choices include often include habitat for feeding, reproduction, movement, or protection.
8. Define the variables for each life requisite. Desirable characteristics of variables are listed here Refine the list of variables, combining, adding, or deleting as appropriate. Verbally describe and record how each variable relates to each other and reduce the list to as few as possible. Remove redundant and adjust or remove conflicting variables. Examples of variables are vegetation height for ground-nesting birds, water depth for dabbling ducks, and space for movement of an amphibian.
9. Revisit steps 6-8 and evaluate against decisions in steps 2-5 to assure that you are on track.
10. For each variable, define optimum and unacceptable conditions and place them on a graph as upper and lower endpoints (1.0 and 0). The optimum and unacceptable conditions are derived from thresholds, i.e., points at which the subject of the model will begin to respond or stop responding. Examples are minimum vegetation height tolerated by ground-nesting birds, maximum depth of water for feeding by a dabbling duck, and width of unshaded open space that an amphibian can successfully cross.
11. Draw a curve or points that describe the relationship between optimum and unacceptable conditions. The default, pending any knowledge of intermediate conditions, is a straight line. Browse a few of the existing HSI models for examples of relationships that others have established.
Additional work is necessary to complete a model, but the steps above will provide a good basis. The following items are suggested for after the workshop.
After the Workshop
1. Write and distribute minutes of the workshop. In addition to the results, include:
the participants
the agenda
the process followed
assumptions made during the process
decisions made
follow-up items with responsible parties and agreed-upon dates.
2. Begin writing the model itself, with adequate documentation of the group's thinking so that others can follow the line of reasoning used.