Using GIS to Determine the Effects of Development on Wildlife in Oak Woodlands

Over half of California’s terrestrial vertebrate species find at least part of their life requisites in oak woodland—more than any other major habitat type in the state. However, little information is available on how species of oak woodland wildlife respond to residential development, the leading cause of loss of oak woodlands. To assist assessment of the impacts of development in oak woodland a prototype GIS software product called DEWOW, an acronym for Development Effects on Wildlife in Oak Woodland, was prepared.

DEWOW was developed and operates under the premise that development impacts habitat components—food, water, cover—required by wildlife.

Figure 1: DEWOW takes information from wildlife experts and the literature, processes it, and displays the results.

Wildlife populations will usually respond spatially and numerically to habitat changes that result from development. Some species are capable of adjusting their home range to fulfill their requirements but this option is generally limited by occupancy of adjacent habitat by the same species or limited habitat quality.

The DEWOW system is interactive. The user selects the species of interest (models are available for 22 species from a range of taxonomic groups) and the level of development. The GIS then creates a habitat map of tree density (canopy cover) and slope and determines whether the species will increase, decrease, or stay the same in number based on user input. The output map displays where the species will exhibit these changes, if any, and calculates area statistics for each category.

DEWOW Structure

Levels of Development

Three density levels of development are used in DEWOW and are typical of those found in county General Plans. High Density—parcel size is 2 ha or less. The number of dwellings ranges from one to many units. DEWOW assumes that at this level of development, the oak-woodland habitat has been greatly altered due to removal of most vegetation, land grading, construction of buildings and roads, landscaping, and disturbances associated with occupancy. Medium Density—parcel size is 2-16 ha. Typically, one to several buildings are constructed and land alterations occur over a small portion of the parcel when compared to a subdivision. Most environmental disturbance is adjacent to residences or other development. Low Density—parcel size is greater than 16 ha. Residential development is limited typically to one or two residences and a few agricultural buildings. DEWOW assumes little habitat alteration.

Wildlife Habitat Preferences

For each species in the DEWOW prototype, habitat suitability is identified as either "preferred" or "secondary". These categories were derived from the California Wildlife Habitat Relationships System (CWHR) and other sources of wildlife habitat relationship information including available scientific literature, expert opinion, and workshop proceedings. Vegetation cover type classification and habitat preference information were used to develop expert system rules for DEWOW. These rules were often constrained by information in the GIS database and by the availability of information to describe development and wildlife habitat elements in oak woodlands. Important habitat relationship information such as presence or absence of an understory, downed woody material, snags and other elements are not currently available in GIS formats for many areas but will make significant future improvements to the predictive capability of DEWOW.


DEWOW uses the ArcMacro Language (AML) tools within ArcInfo to construct the user interface and complete the data analysis. The results of a DEWOW session produce both area statistics of the changes to the habitat of a species and a map of the spatial distribution of those changes.


Figure 2: Structure of the DEWOW software.


Figure 3: An example of a habitat suitability map produced by DEWOW for the gray squirrel.

By downloading the DEWOW tool, the user agrees to the following terms and conditions. The State of California and the Department of Forestry and Fire Protection make no representations or warranties regarding the methods, procedures, or results of tools. The user will not seek to hold the State or the Department liable under any circumstances for any damages with respect to any claim by the user or any third party on account of or arising from the use of the tool. There are no restrictions on distribution of the tool by users. However, users are encouraged to refer others to the Department of Forestry and Fire Protection to acquire the tool, in case an updated tool becomes available.


Tietje, B., L. Myers, W. Bremer, D. Elliott, and C. Rogers. 1994. Development effects on wildlife in oak woodlands. A report submitted to the California Department of Forestry and Fire Protection. Fire and Resource Assessment Program. Sacramento, CA 130p.

Tietje, W. W. Bremer, T. Craig, and C. M. Gallagher. 1995. Use of GIS in determining development effects on wildlife in oak woodlands. Transactions of the Western Section of The Wildlife Society 31:7-11.

Last edited: August, 2000