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Incorporating Protection of Biodiversity into County Land Use Planning: A Gap Analysis Pilot Project in Pierce County, Washington

A Report on GAP Research
Project #1434-HQ-97-RU-01583


Washington Cooperative Fish and Wildlife Research Unit, School of
Fisheries, University of Washington, Seattle, Washington


Department of Urban Design and Planning, University of Washington,
Seattle, Washington


Department of Urban Design and Planning, University of Washington,
Seattle, Washington


Department of Urban Design and Planning, University of Washington,
Seattle, Washington


Department of Urban Design and Planning, University of Washington,
Seattle, Washington


Gap analysis is a process by which lands of high conservation pri-
ority are identified. The process uses land cover, wildlife/habitat
relationship models, and other data to predict the distribution of
wildlife species in a given geographic area. By overlaying land
cover and vertebrate distributions onto land ownership, cover types
and vertebrate species with poor representation on protected lands
are identified. Gap analysis is designed to be a proactive approach
to conservation, identifying important wildlife habitats or species
before they become threatened by habitat degradation or loss.

A gap analysis of Washington State was recently completed by the
Washington Gap Analysis Project (WA-GAP) (Cassidy et al. 1997).
However, additional work is needed to make this process an effec-
tive tool for local land use planning. Although the data from WA-
GAP have been summarized and analyzed at a statewide level, the
analysis was conducted using ecoregions and vegetation zones,
which are not easily applied to local land use planning and habitat
conservation. Data must be significantly manipulated, analyzed,
and reinterpreted before they can be applied to the local land use
planning process.

The Department of Urban Design and Planning (UDP) at the Uni-
versity of Washington (through its Remote Sensing Applications
Laboratory), in cooperation with WA-GAP, is conducting an ongo-
ing program to develop procedures and materials supporting the
application of WA-GAP data and methodology to local land use
planning in Washington State. The intent of this work is to give
local planners, elected officials, and the public the tools they need
to incorporate biodiversity protection into their planning programs.
The initial pilot project of the program took place in Spokane County
in eastern Washington during 1997 and 1998 (Stevenson 1998, 1999;
Westerlund 1998). UDP and WA-GAP identified Pierce County as
an excellent location for a westside pilot project because of the
county’s broad range of habitat types and development densities,
current conservation issues, and existing planning and GIS infra-
structure. Funding and support for this project were provided by
Pierce County, Washington State Department of Fish and Wildlife
(WDFW), U.S. Fish and Wildlife Service, the USGS Biological
Resources Division (National Gap Analysis Program and Coopera-
tive Research Units), and the Rocky Mountain Elk Foundation.

Our Pierce County pilot project was conducted in collaboration with
Pierce County and WDFW and was executed in two phases. The
primary objective of Phase 1 (January - May 1999) was to review,
validate, and augment the county’s Open Space Implementation
Committee’s draft Open Space and Greenbelt Corridor Map by in-
corporating terrestrial biodiversity and salmonid habitat issues. The
analysis and products of this phase were broad in scale and appro-
priate for policy-level decision making. The objectives of Phase 2
(May - December 1999) were to develop the open space and
greenbelt system recommendations to a higher level of detail, present
a methodology for establishing and implementing a priority system
for habitat conservation and restoration, and prepare project docu-
mentation in both hard copy and digital formats.

The project team consisted of the authors and Kelly Cassidy and
Karen Dvornich (WA-GAP and NatureMapping), Katherine Rose,
Grant Griffin, Karen Trueman (Pierce County), and Michelle Tirhi

WA-GAP Conservation Priorities for Pierce County

The Puget Trough and Southwest Cascades ecoregions comprise
the majority of Pierce County. The lowland vegetation zones of the
Puget Trough ecoregion (Puget Sound Douglas Fir, Woodland/Prai-

rie Mosaic, Willamette Valley, and Cowlitz River) were identified
as among those with the highest priority for conservation in the
state. These areas have been heavily converted to both agriculture
and development. The remaining forests are now a patchwork of
hardwood, mixed, and early-seral conifer forest. There are only a
few small areas of moderate richness of at-risk species, because
most at-risk species have been extirpated from these zones. A ma-
jor priority of these zones is management of the handful of verte-
brate species or subspecies that cannot “retreat” into less-impacted,
higher-elevation vegetation zones.

The mid-elevation Western Hemlock vegetation zone (also found
in both the Puget Trough and Southwest Cascades ecoregions) was
identified as a moderately high priority for conservation. This zone
has not been as severely impacted by development and agriculture
as the lower elevation zones but has a low protection status and has
seen extensive logging. Areas of high amphibian and mammal rich-
ness occur here, and the remaining mid- to late-seral forests sup-
port large numbers of at-risk amphibian, mammal, and bird spe-
cies. Less than 10% of the zone remains in late-seral forest; an
additional 20% is estimated to be mid-seral. This statewide per-
spective provided a framework for applying the WA-GAP data and
methodology to local land use planning issues in Pierce County.

The Pierce County Project

Phase I - The objectives of Phase I were to: 1) update the WA-GAP
land cover classification to a 1998 base line, 2) generate predicted
species distributions for all breeding native vertebrates based on
this classification, 3) identify lands in Pierce County of high con-
servation priority, and 4) develop a biodiversity network that in-
cluded the lands identified in 3) and that complemented the Pierce
County Open Space and Greenbelt Corridor Map. The study area
for the pilot project included all of Pierce County plus adjacent
lands within the watersheds partially contained in the county.

The original WA-GAP land cover map for the study area (based on
1991 Landsat TM imagery) was updated in a three-tier process.
On-screen interpretation of unclassified 1998 Landsat TM data was
used to determine large-scale land conversions resulting from hu-
man activities: new development, clearcut forests, and regenerated
clearcuts. Existing county coverages facilitated interpretation.
National Wetlands Inventory digital data were used to identify
smaller wetlands missed during the original interpretation. The
original WA-GAP classification scheme, which assigned primary,
secondary, and tertiary land cover, was simplified to a single (“pri-
mary”) classification. This process resulted in disaggregation of
some large land cover units. The nominal minimum mapping unit
for the updated classification was 40 hectares.

The predicted species distribution models (a series of AMLs devel-
oped by WA-GAP) overlaid species ranges on the land cover clas-
sification data and compared each within-range habitat polygon with
the appropriate habitat matrix. The results were compiled in a data
set indicating presence or absence for each species in the four taxo-
nomic groups considered (mammals, birds, amphibians, and rep
Presence was confined to habitat rated as “primary, core, and good quality”
(Cassidy et al. 1997). This resulted in a conservative prediction of
presence appropriate to the resolution available from the 30-meter resolution Landsat TM.

A value for richness for each taxonomic group (number of native
species predicted to occur) was calculated for each habitat poly-
gon. Habitat polygons with a richness value greater than one stan-
dard deviation above the mean for a taxonomic group were consid-
ered “rich” in subsequent analyses. An example of species distri-
bution richness (in this case, mammals) is presented in Figure 1.

Figure 1. Predicted mammal species richness with study area.

The identification of lands important for biodiversity protection
coupled the concept of richness described above with “representa-
tion.” Our goal was to ensure that each species predicted to occur in
the study area would be represented in a minimal set of habitat
polygons. The minimal set of habitat polygons was selected through
an interactive process (run as an AML) beginning with the richest
land cover units and most frequently occurring species. Each itera-
tion added a unique set of habitat polygons that provided habitat
suitable for a unique set of species (e.g., mammals in Figure 2). As
this process was conducted independently for each taxon, redun-
dancy was anticipated to provide for more than the minimum selec-
tion for most species.

GapBulletin846-00.jpg 468x522

Figure 2: Core areas for mammal biodiversity protection.

This representative set was examined, and areas excessively frag-
mented or isolated were trimmed from the set (where possible with-
out compromising representation). The resultant set of land cover

units depicted the “core areas” whose preservation as functional
habitat was considered essential to biodiversity protection within
the study area for each taxon. Figure 3 depicts the resultant
Biodiversity Management Areas (BMAs) for mammals. BMAs—
the basic component of the proposed biodiversity management net-
work—were generated by applying a 0.4 km buffer to the core ar-
eas. This buffer (based on recommendations from WDFW) was
intended to isolate the core areas from adjacent land uses and pos-
sible impacts. Characterizations of the BMAs were compiled that
identified the species predicted to occur (highlighting species iden-
tified by WA-GAP as being “at-risk”) and the land cover types
present. These characterizations were used in Phase II and will be
used in future work by the county to develop land management
plans and regulatory guidelines that will balance appropriate use
of the areas and preservation of the essential habitat qualities.

The BMAs were integrated into a contiguous network using “con-
nections” to provide movement corridors for large and/or migra-
tory species and to avoid population isolation. Where possible,
these connections were routed through areas of high richness. Ar-
eas of intense development (as interpreted from road and parcel
data) were avoided. WDFW Priority Habitat and Species (PHS)
data and the distributions of threatened salmon species were also
considered (the final network contains 59% of the PHS observa-
tion points within the county). The connections were delineated
independently for each taxon and then adjusted to take advantage
of redundant alignments.
GapBulletin846-01.jpg 453x512
Figure 3. BMAs and connections for mammals. 
GapBulletin847-00.jpg 452x507

The final BMA network and connections (Figure 4) were reviewed
by biologists (assembled by WDFW) familiar with the study area.
This group verified the network and suggested additional areas for
inclusion—habitats not considered by WA-GAP (e.g., critical win-
tering areas for some bird species) or dependent on features smaller
than the resolution of the land cover data (e.g., snags for eagle nests).
The additional areas were incorporated into the network as con-

GapBulletin847-01.jpg 433x503

Figure 4. Biodiversity management network for Pierce County.

The network composed of Biodiversity Management Areas and
connections was presented to the county as a recommendation for
expansion of the proposed Open Space and Greenbelt Corridor Map
under review. Forty-five percent of the network overlapped with
the county’s proposed map. The portion of the network within the
county boundaries contains an area equal to 29% of the county.
The network captured 60% of the remaining natural cover of the
Woodland/Prairie Mosaic, rated as “highest conservation priority”
by WA-GAP. Land stewardship status within the network is Status
1 and 2 (most protected) - 28%, Status 3 (extractive uses permitted)
- 13%, and Status 4 (least protected) - 59%. In October 1999, the
County Council adopted the revised Open Space and Greenbelt
Corridor Map.

Phase 2 - In this phase of the project, we characterized the BMAs
in terms of the species predicted to occur, conducted a preliminary
species-viability analysis, examined opportunities to protect/en-
hance habitat on Status 4 (primarily private lands) using existing
state and county regulations, and refined the boundaries of the BMAs
within four case study areas representing varying amounts of ur-
banization and agriculture.

Characterizations (lists of species including salmonids and their
status) were developed for each BMA to guide future specialized
wildlife surveys to confirm species/habitat presence. Of particular
interest were “trigger” species, the predicted presence of which
governed the selection of a particular BMA during the representa-
tive set analysis (Phase 1). In addition, profiles (habitat needs and
management considerations) were developed for each “at risk” wild-
life and salmonid species predicted to occur within the BMAs.

The preliminary species-viability analysis was based on the acre-
age predicted to be available within the BMA network (excluding
corridors) for each of the terrestrial vertebrates included in the pilot
project. Following review by WDFW, University of Washington,
and Project personnel, 11 species were identified as potentially not
having sufficient acreage to maintain populations. Several of these
species were identified as having only “peripheral” (as opposed to
“core”; Cassidy et al. 1997) habitat in Pierce County, limited habi-
tat remaining in the county (e.g., Woodland/Prairie Mosaic), being
restricted to remote, highly protected areas outside the BMAs (e.g.,
Wolverine [ Gulo gulo ]), or species associated with aquatic habitats
not adequately surveyed by WA-GAP or the state (e.g., River Otter 
Redefining Status 4 lands was important to the county, as nearly
60% of the BMA network was in private or military ownership.
Our new classification divided Status 4 lands into 4-a (most highly
protected), 4-b (moderately protected), 4-c (slightly protected), and
Inconsequential (little or no effective protection provided) based
on existing state and county regulations (Iolavera 1999). We then
evaluated the existing state and county policies and regulations for
habitat protection as they pertained to the redefinition of Status 4
lands. These included provisions of the Washington Growth Man-
agement Act, Shoreline Management Act, and State Environmental
Policy Act; elements of the Pierce County Comprehensive Plan re-
lated to open space, shorelines, wetlands, and wildlife conservation
areas; and local regulatory and incentive tools including zoning,
impact fees, conservation easements, and vegetation protection or-
dinances. Recommendations were made for revisions and addi-
tions to these policies and regulations to enhance biodiversity pro-
tection (Iolavera 1999).

The last component of Phase 2 was to demonstrate to the county
how one could refine BMA boundaries based on a higher-resolu-
tion analysis of land cover within portions of four BMAs. This is
an important step in moving toward acquisition of lands for open
space or the implementation of open-space designation mechanisms.
We used 1991 orthorectified photographs, a 1998 high-resolution
land cover classification, a restricted zoning overlay, and WDFW
PHS data to primarily eliminate areas along the original boundaries
of the BMAs where urban development or other land uses not com-
patible with habitat existed that were not visible at the resolution
used in Phase 1. Similar land uses within the BMA study areas
were not removed if they were surrounded by largely high-quality,
unfragmented vegetative cover. These refinements resulted in re-
ductions of 3, 14, 19, and 61% of the original size of the four BMAs
within the study areas (see Figure 5). In the case of the 61% reduc-
tion between Phase 1 and 2, the area removed largely represented
the 0.4 km buffer that was drawn around the core habitat in the
most highly developed BMA. This suggests that, in some cases,
attempts to designate buffers may require more educational out-
reach to private landowners than actual open space acquisition.

GapBulletin848-00.jpg 473x499

Figure 5. Phase 2 refinement of boundaries of BMA within Tanwax
study area.

Copies of the Pierce County report and CD are available for pur-
chase from the Washington Cooperative Fish and Wildlife Research
Unit (206-543-6475).

Literature Cited
Cassidy, K.M., C.E. Grue, M.R. Smith, and K.M. Dvornich, editors.

1997. Washington State Gap Analysis - Final Report. Washing-
ton Cooperative Fish and Wildlife Research Unit, University of
Washington, Seattle, Washington. Volumes 1-5 (1,450 pp.).

Iolavera, P.R. 1999. Pierce County, Washington, GAP application
pilot project: Expanding the GAP land stewardship categoriza-
tion for use at the county planning level. M.S. thesis, Department
of Urban Design and Planning, University of Washington, Seattle,
Washington. 103 pp.

Stevenson, M. 1998. Applying Gap Analysis to county land use
planning in Washington State.
Gap Analysis Bulletin 7:30-32.

Stevenson, M. 1999. A different look at the land. Planning (Ameri-
can Planning Association magazine) 7:65-68.

UDP. 2000. Pierce County GAP application project: A biodiversity
plan for Pierce County, Washington. Department of Urban De-
sign and Planning, University of Washington, Seattle, WA. 196

Westerlund, F. 1998. Wildlife corridors and landscape linkages: An
approach to biodiversity planning for Spokane County, Washing-
ton. Department of Urban Design and Planning, University of
Washington, Seattle, Washington. 91 pp.

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