Colorado Gap Analysis Project

Overview of the Gap Analysis Project: (Much of the following was taken verbatim from Scott et al. 1997)
Gap analysis is a scientific method for identifying the degree to which native animal species and natural communities are represented in our present-day mix of conservation lands. Those species and communities not adequately represented in the existing network of conservation lands constitute conservation "gaps." The purpose of the Gap Analysis Program (GAP) is to provide broad geographic information on the status of ordinary species (those not threatened with extinction or naturally rare) and their habitats in order to provide land managers, planners, scientists, and policy makers with the information they need to make better-informed decisions.

The Colorado Gap Analysis Project (CO-GAP) was initiated in 1991 as a cooperative effort, led by the Colorado Division of Wildlife in collaboration with the Natural Resource Ecology Center (NERC/USFWS), and state, federal, and private natural resources groups in Colorado.

Objectives of the Study
There are five major objectives of a GAP Project:

  1. Map actual land cover as closely as possible to the Alliance level (Jennings 1993)
  2. Map the predicted distribution of those animals for which adequate distributional habitats, associations, and mapped habitat variables are available
  3. Document the occurrence of natural land cover types that are inadequately represented (gaps) in special management areas
  4. Document the occurrence of animal species that are inadequately represented (gaps) in special management areas
  5. Make all GAP Project information available to users in a readily accessible format.
There are three major objectives of the Colorado Gap Analysis Project:
  1. Develop geographic information system (GIS) based databases describing the state's vegetation/land cover, terrestrial vertebrate wildlife distributions, and land management status at a scale of 1:100000, interpreted to identify land stewardship categories consistent with those described in the Wildlife Monograph, entitled Gap Analysis: A Geographic Approach to Protection of Biological Diversity (Scott et al., 1993).
  2. Identify land cover types and terrestrial vertebrate species that are either not represented, or are under-represented in areas managed for long-term maintenance of biological diversity.
  3. Facilitate cooperative development and use of information so that institutions, agencies, and private land owners may be more effective stewards of Colorado's natural resources.

Land cover mapping
With funding from National Gap offices, 12 scenes of Landsat imagery were acquired to augment 4 Division of Wildlife scenes; providing a complete, in-house, statewide coverage with which a statewide baseline map of vegetation/land cover was developed at sufficient detail to model vertebrate wildlife distributions based upon habitat relationships. Following methodology developed for Wyoming Gap (WY-GAP), attributes were assigned to each polygon describing primary, secondary, and other land cover; crown closure for forested primary types; and the types of wetlands and/or disturbance found in the polygon, if any. Polygon attributes were assigned using image interpretation, existing maps, field reconnaissance, digital reference layers from Federal land management agencies, and literature sources. Formal state-wide validation of the land cover map is being performed as a separate task in conjunction with the Wyoming Gap Analysis project.

Species distribution mapping
Individual distributions for 597 vertebrate species were predicted using habitat associations linked to the vegetation/land cover base-layer, constrained by data on elevation ranges and confinements to the east or west side of the Continental Divide from known occurrences of individual species in Colorado. Point localities, and thematic distribution maps were used to evaluate preliminary distribution maps, and later as a guide in developing the county-level distribution masks used to constrain occupancy to likely areas of predicted habitat. County-level masks were developed by cross-reference to locational databases providing field/museum records of species localities. After synthesizing this information for modeling efforts, the modeled maps, predicting species range based on habitats were reviewed by local experts. A special submodel was developed to account for riparian species distribution, given the importance of this habitat and the minor extent to which it was observable based solely on the Landsat imagery.

Land Stewardship mapping
The Gap Analysis Program (GAP) uses a scale of 1 through 4 to denote the relative degree of management for biodiversity maintenance for a particular tract of land, where "1" represent the highest, most permanent and comprehensive level of maintenance, and "4" represents the lowest, or unknown status. Status codes were assigned to public lands with state and federal agency input based on legal and intended management, using a key developed by the New Mexico Gap Analysis Project (NM-GAP). Most private lands were assigned status 3 or 4 depending on the availability of information on their intended long-term management. Land Stewardship is derived from land ownership (Click on land ownership to view a map of Colorado Land Ownership.).


The final output
After land stewardship was modeled using the land status base layer, the derived layer was overlain on the vertebrate species habitat/distributions to provide the tabular output essential to a Gap Analysis of Colorado biodiversity. These tables provide listings to show the distribution of species habitats, across the major land ownership categories, and are further partitioned by hectares (and %) of the species habitat distributed by the land stewardship categories. Land cover types, and vertebrate species were generally considered under-represented in areas managed for biological diversity if less than 1%, or less than 50,000 hectares of available cover type, or occupied habitat was found within status 1 and 2 lands.

For more information on:

Read "A Description of the National Gap Analysis Program" by Scott et al. 1997

Products of the Colorado Gap Analysis

Spatial Data
Display/Print Species Models 
Display/Print Land cover Maps 
Download CO-GAP Report
Download 100k block datasets
Download Habitat Affinities Modules
Land Cover Accuracy Assessment
Manual to Accompany the Gap Analysis Land Cover Map of Colorado
Download Species Grids

National GAP

Page last updated Wednesday July 18, 2001
By Colorado Division of Wildlife