CWHR American Marten species distribution, California

The following information describes, and should always accompany, the California Department of Fish and Game's California Wildlife Habitat Relationship System (CWHR) species distribution data.

The data is organized into four folders according to the four major taxonomic groups in CWHR: amphibians, reptiles, birds and mammals. Each species is represented by a single shapefile and is named according to its 4 digit alpha-numeric CWHR ID code. The file lookup.xls contains a record for each species including its CWHR ID, scientific name, common name, and range map revision history.

Each layer contains two attributes: a season code and a SHAPE_NAME or CWHR ID code. Season codes include S for summer-only, W for winter-only, and Y for yearlong. A few species have a migration-only stopover location mapped and represented with an "M". The CWHR System software contains species predictions for migration-only locations, yet most of these are not mapped.

The CWHR species range maps are continually being reviewed and updated as new animal occurrence data becomes available, especially in digital format. While the original maps were digitized from 1:5,000,000 scale depictions of range, a major revision effort started in 1995 to have maps reviewed and delineated by species-level experts at a scale of 1:1,000,000. Maps dated later than 1995 are therefore much more detailed and precise in their representation of a species' range.
Increasingly, species-level experts and CWHR staff have made every effort, where justified by the distribution of known species observations or known habitat associations, to represent a species' range with standard polygons of major geographic features in California such as mountain ranges, valleys, buffered river corridors, and ecological subsections of California. The smallest units of the "Ecological subregions of California: section and subsection descriptions" (Miles and Goudy, 1997. USDA Forest Service Report No. R5-EM-TP-005) capture areas with very similar soils, vegetation, precipitation, geology, climate, and geography.

In cases where a population of a species is known to be isolated, its point location is buffered to a minimum radius of 2 miles.

Vector datasets of CWHR range maps are one component of California Wildlife Habitat Relationships (CWHR), a comprehensive information system and predictive model for California's wildlife. The CWHR System was developed to support habitat conservation and management, land use planning, impact assessment, education, and research involving terrestrial vertebrates in California. CWHR contains information on life history, management status, geographic distribution, and habitat relationships for 694 species of amphibians, reptiles, birds, and mammals known to occur regularly in the state. Range maps represent the maximum, current geographic extent of each species within California. They were originally delineated at a scale of 1:5,000,000 by species-level experts and have gradually been revised at a scale of 1:1,000,000.

Range maps were digitized as GIS layers to support the predictions of the CWHR System software, which allows users to query for wildlife species meeting a set of location and habitat conditions. Presently, they are used to help generate a tabular location database for the system software. Outside the system software, the GIS layers are used to support species richness assessments for statewide conservation planning.