Illinois Natural History Survey - University of Illinois


Inventory of Resource Rich Areas in Illinois:
An Evaluation of Ecological Resources

The identification and characterization of areas rich in biological resources, or Resource Rich Areas (RRA), used an analysis of natural resource data utilizing GIS technology that was guided by scientists with extensive knowledge of ecosystem concepts and Illinois biota. The process of identification of RRAs was begun by meeting with scientists at the Illinois Natural History Survey to develop a list of ecological characteristics and functions of large ecological reserves, and to develop criteria to be applied in identification and evaluation of RRAs.

A landscape level approach envisions the existence of a system of areas that would protect, maintain, and enhance the living natural resources of Illinois. From an ecological perspective these areas need to be large enough to provide habitat for area-sensitive species and to allow management practices to reasonably simulate natural forces (e.g. fire). Further, the areas need to be distributed in a way that the various ecotypes in Illinois are adequately represented. The specific ecological roles of sites were determined to be the following:

  1. provide areas large enough to allow for the natural dynamic nature of eco systems and to allow management to simulate natural forces to meet the needs of various communities and species.
  2. protect, restore, and enhance areas to provide the ecological requirements for animals and plants that need large areas.
  3. include representative examples of the natural communities of Illinois.
  4. protect areas with significant habitat and species diversity.
  5. protect habitat types that are diminishing at an alarming rate, such as wetlands, forests, prairies, and biologically significant streams.

Watersheds, as identified by the Illinois Environmental Protection Agency (IEPA), were used as the geographic unit for evaluation and analysis. These watersheds have the advantage of being an ecologically identifiable unit and are important administratively within the state. They have the disadvantage of being irregular in shape and variously sized. The average area covered by an IEPA watershed, of which there are 816, is 69 square miles (44,000 acres). RRA boundaries are derived directly from watershed boundaries.

Criteria for the evaluation and characterization of RRAs were selected because they (1) emphasized ecologically important characteristics; (2) were available as digital statewide databases; and (3) were suitable for analysis using IEPA watersheds. The criteria, analysis, maps, and summaries in this report are based upon ecological characteristics; economics, recreational interests, and other considerations were not explicitly accounted for in this effort. Watersheds were evaluated using the follow ing variables:

  1. Forest - percent of the watershed
  2. Wetlands - percent of the watershed
  3. Illinois Natural Areas Inventory - total area
  4. Biologically Significant Streams - total length

The sources of data for the four variables are discussed later in this section.

Time limitations made it impossible to acquire new field data and required that decisions be based upon the best data available for the entire state. The Illinois Natural Areas Inventory and Biologically Significant Streams digital datasets were updated and enhanced for use in the analysis. Other datasets, including boundaries of state and federally owned land in Illinois, were created or improved to provide supplemental information.

The four variables were given equal weight in the analysis. Each watershed was ranked against all other watersheds for each variable. Watersheds were placed into 10% quantiles for each variable and given a score of 10 points if they were in the top quantile, 9 points in the 81-90 % quantile, 8 points in the 71-80 % quantile, etc. Watersheds in which a variable did not occur were given a 0 score for that variable. The scores for each variable in each watershed were summed; the maximum possible cumulative score was 40. Watersheds were defined as resource rich if their cumulative score ranked in the top 10%. This qualification resulted in inclusion of watersheds having a score of 26 or greater (actually the top 12% of all watersheds due to tie scores).

Spatially adjacent watersheds were grouped to form RRAs. All watersheds with scores of 26 or above were included in the RRAs and none were excluded. Review of the selections and additional information and advice regarding inclusion of additional adjacent watersheds and determination of boundaries was provided by an advisory group of four INHS scientists. Some RRAs were modified by the addition of adjacent water sheds with cumulative scores of less than 26 in order to accommodate (1) contiguous landcover; (2) watersheds of the three current IDNR project areas (i.e. Rock River, Cache River and Prairie Parklands; and (3) important natural features that were known by INHS scientists (Figure 14). Boundaries of RRAs with shared borders were determined based on consideration of such factors as natural divisions and drainage basins. RRAs were named for the predominant natural feature, usually the major stream. They are ordered by geographic location from north to south in the tables of this report.

RRAs were collectively and individually described by the occurrence and composition of several characteristics. These include information about landcover classes, Natural Areas, and Biologically Significant Streams, which were used in the screening process. Supplemental data about Natural Heritage communities, state and federally owned land, Illinois Nature Preserves, and natural divisions are also reported. These datasets are described below.

Landcover information was derived from the Critical Trends Assessment Project Landcover Database produced by the Illinois Natural History Survey from satellite imagery acquired from 1991 to 1995. Seven landcover classes were utilized in this projectupland forest, bottomland forest, nonforested wetland, grassland, cropland, urban or built-up, and water. For the screening process, forests were defined as the combination of upland forest and bottomland forest landcover classes, and wetlands as nonforested wetland and bottomland forest classes. Upland forests consists of any wooded, nonbottomland area; these may be relatively small and the term "forest" is applied loosely. The grassland class was not used in the screening because "natural" grassland habitats such as prairies and savannas are not distinguished from grassland impacted by farming and other human uses. The grassland category includes pastures, hay, idle fields, rural road and railroad rights-of-way, and prairie remnants. The landcover data has a ground resolution of 93.5 feet (28.5 meters) on a side. Each pixel covers 0.2 acres although a filter with a threshold of up to 5 pixels (1 acre) was applied to the database for this analysis. Area calculations reflect the use of the Universal Transverse Mercator (UTM) projection, zone 16, North American datum of 1927.

The Illinois Natural Areas Inventory is a dynamic listing of approximately 1,200 sites known to possess important natural qualities within the state. The INAI data base includes sites based on the presence of (a) high quality natural communities, (b) habitats for endangered species, (c) habitats for relict species, (d) outstanding geologic features, (e) natural community restoration and endangered species relocations, approved natural areas and restoration sites, (f) unique natural features, and (g) outstanding streams and rivers (McFall, pers. comm; White 1978). Outstanding streams and rivers were included in the analysis under this category if they were not included under Biologically Significant Streams. The INAI data are maintained by the Division of Natural Heritage of IDNR (DNH-IDNR). The digital database was created and is maintained at INHS and was updated through November 1995.

Biologically Significant Stream designation is based on a comprehensive evaluation of the state's aquatic resources. BSS designation indicates the presence of high quality aquatic systems (Page, et al. 1991). The criteria included fish populations, water quality, macroinvertebrates, endangered and threatened species, and mussel diversity. The database is maintained at INHS and was current as of November 1995.

The Natural Heritage database provided information about significant communities, endangered and threatened species locations, geological features, and nesting bird colonies. INHS maintains this DNH-IDNR database in its digital form and was updated in November 1995.

Because information about state and federally owned land may be important in planning management strategies, a comprehensive GIS database of these resources was developed for this project. IDNR owns the largest acreages of state-owned land in Illinois. The state owned lands database consists of State Parks, Forests, Conservation Areas, and Fish and Wildlife Areas.

Illinois Nature Preserves are areas that retain a high degree of their presettlement character or have significant ecological, geological, or archaeological features (McFall and Karnes 1995). They are dedicated by law to being maintained in their natural state. The digital database at INHS was current as of November 1995 with 236 Nature Preserves (from data provided by IDNR).

Natural Divisions is a classification of the natural environments in Illinois based on topography, soils, bedrock, glacial history, and distribution of plants and animals (Schwegman 1973). Fourteen natural divisions are defined in Illinois.

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