Applying Gap Analysis to County Land Use Planning in Washington State
Matt Stevenson
Department of Fisheries and Wildlife, Utah State University, Logan
Introduction
The Washington Gap Analysis Project (WA-GAP) recently published the fifth and final volume of its final report and is now looking forward to continuing its efforts with the application of WA-GAP data to a variety of land and resource management problems. Last year I had the privilege of being involved in one of the first attempts at applying this information to land use planning in Spokane County, Washington.
When this work began in September 1997, Spokane County was updating its comprehensive plan as required by the Washington Growth Management Act (RCW 36.70A). The new county plan calls for the identification, improvement, and protection of fish and wildlife habitat. Additionally, the plan calls for the minimization of habitat fragmentation by protecting important fish and wildlife areas and open space and by interconnecting corridors to form a continuous network of fish and wildlife habitat and ecosystems. Furthermore, the county’s Critical Areas Ordinance (CAO) requires the protection of a variety of priority habitats, including wildlife corridors and landscape linkages. The county was interested in developing a method for locating and identifying these priority habitats and chose to enter into a pilot WA-GAP implementation project involving the Washington Department of Fish and Wildlife, the Inland Northwest Land Trust, and the Department of Urban Design and Planning and the Washington Cooperative Fish and Wildlife Research Unit, both at the University of Washington.
Methods
The protection of biodiversity was chosen as the design strategy for locating and delineating wildlife corridors and landscape linkages in Spokane County because we felt it would be the most effective way to achieve the CAO fish and wildlife goals. Furthermore, planning for biodiversity before species become endangered may help prevent imposition of governmental regulations as human activity continues to expand into previously undeveloped areas. The dual criteria of species representation and richness were chosen to capture biodiversity at the scale of the entire county. Species richness for Spokane County is depicted in Figure 1.
 Figure 1. Mammal species richness of Spokane County. |
Representation
The purpose of achieving species representation was to ensure that every species predicted to occur in the county is included at least once within any network of corridors and reserves created using WA-GAP data. Because we determined representation for mammals, birds, and reptiles and amphibians as individual taxonomic groups and then combined the results, we did not generate a minimum representative set. As a consequence, some species which were represented only once within the representative set for their respective group are represented more than once by the combination of the sets for mammals, birds, and reptiles and amphibians. This approach resulted in the map shown in Figure 2, the combination of the representative sets for all terrestrial vertebrates modeled by WA-GAP.
 Figure 2. Minimum area that includes at least one occurrence of each species mapped by GAP. |
Richness
Establishing increments of species richness by taxonomic group was necessary before areas of high species richness could be identified as potential locations for reserves. This process entailed the creation of a decision rule for which WA-GAP polygons should be selected, based upon the number of species predicted to be present in each. For this analysis, we arbitrarily set threshold levels at 75% of highest possible richness for mammals and birds and 50% of possible richness for reptiles and amphibians.
All polygons with high species richness as indicated by the use of this rule were initially considered for habitat reserves. The ideal polygons for potential habitat reserves were large, with high species richness, natural land cover, low internal and adjacent human development, and high levels of agreement with other wildlife distribution databases. Potential habitat reserves for all three groups are reflected in Figure 3.
 Figure 3. Potential vertebrate habitat reserves. |
Connections between potential habitat reserves and the suite of areas where all species are represented were made by identifying and selecting polygons with high species richness and natural land cover between the potential reserves and representative areas. Maps of species richness, representation, and potential connections between these areas were combined to produce Figure 4, the "raw material" from which a potential wildlife corridor and landscape linkage system might be created. Just over half of Spokane County is indicated in Figure 4 as being important for protecting biodiversity. This is a tremendous amount of land! In order to refine the areas indicated through the additive process described above, it was necessary to utilize additional sources of information providing a greater level of detail.
 Figure 4. Combined richness, representation, and connections. |
The additional information included a fine-grained (5-acre MMU) land cover map I created for the Interim Urban Growth Area (IUGA) surrounding the City of Spokane and its suburbs. A parcels coverage containing property boundaries was provided by the county and served as a proxy for the level of development outside of the IUGA. However, due to the sensitive nature of the information related to ownership and assessed valuation in the parcels coverage, the county provided only the boundaries and none of the attribute data. Additional county data sets used include roads, topography, wetlands and hydrology, land use and zoning, growth area boundaries for other cities, critical areas already recognized, governmental land holdings, and utility and railroad rights of way.
The final result of the additive process (determining representation, richness, and creating connections), plus the reductive process (refining the result from the additive process with additional higher-resolution information), is shown in Figure 5. This proposed system comprises approximately 30% of the county, a substantial reduction from the initial area indicated at the end of the additive process.
 Figure 5. Proposed system of wildlife corridors and habitat reserves. |
Results
If the system of wildlife corridors and habitat reserves shown in Figure 5 were implemented with no substantial modifications, all vegetation zones within the county would see a minimum 10% increase in protected area in addition to already protected land. Protection for the largest vegetation zone in the county, Ponderosa Pine, would increase by 26.5%. For vertebrate species, birds, mammals, and reptiles and amphibians would see median increases in protected areas of 38, 39, and 43%, respectively. (Once again, this is in addition to land already designated for the protection of biodiversity). These increases result in a combined median increase of 39% for all terrestrial vertebrates. It should be noted that this 39% increase occurs on only 30% of the county’s total land area.
Discussion
To implement the results, Spokane County (and any other municipalities interested in conducting similar analyses) will have to use a wide variety of land-use planning tools. There is no single mechanism by which the biologically important lands in Spokane County can be instantly protected. Rather, a combination of incentives, regulations, and acquisitions is the approach most likely to achieve the goals established in the CAO.
Presently, Spokane County is using the results to update their Comprehensive Plan and Critical Areas Ordinance. The Washington Department of Fish and Wildlife is using the information to analyze and evaluate properties proposed for acquisition under the state’s Conservation Futures program. The Inland Northwest Land Trust (INLT) is using the results as the centerpiece of their land protection work this year and intends to do so for the foreseeable future. According to Chris DeForest, Executive Director for the INLT, "Without this information, we would be operating by hunch and expert guess."
For more information about WA-GAP and land use planning, please contact Dr. Frank Westerlund in the Department of Urban Design and Planning at the University of Washington (206) 543-4190, or Dr. Christian Grue, WA-GAP Principal Investigator, at the Washington Cooperative Fish and Wildlife Research Unit, (206) 543-6475. Matt Stevenson can be contacted at Utah State University, Department of Fisheries and Wildlife, (435) 797-3892, mrs@nr.usu.edu.
This research was funded by the National Gap Analysis Program, USGS/BRD, the Washington Department of Fish and Wildlife, the Washington Cooperative Fish and Wildlife Research Unit, and the Department of Urban Design and Planning.