EXECUTIVE
SUMMARY
THE
CALIFORNIA GAP ANALYSIS PROJECT
Report
Date: 30 June 1998
CA-GAP Database Development
Assessment of the Management Status of Biodiversity
Conservation Priorities
CA-GAP Database Uses and Availability
The California
Gap Analysis Project (CA-GAP) was initiated in 1990 as a cooperative
effort between the U.S. Fish and Wildlife Service and researchers
at the University of California, Santa Barbara. Dozens of public and
private organizations also provided invaluable support. The objectives
of the project were to 1) develop new geographic information system
(GIS) databases of land-cover, wildlife habitats, predicted distributions
of native wildlife species, and land stewardship and management; 2)
identify land-cover types and wildlife species that are inadequately
represented in existing biodiversity management areas (i.e., the "gaps");
and 3) make all CA-GAP information available to users to encourage
and facilitate its use so that resource managers may be more effective
stewards of California's biological heritage.
CA-GAP Database Development
Land Cover
CA-GAP compiled the first new medium-resolution map of actual land-cover
of California since 1980. This land-cover map was produced using
summer 1990 Landsat Thematic Mapper satellite imagery, 1990 high
altitude color infra-red photography, the Vegetation Type Maps based
on field surveys conducted between 1928 and 1940, miscellaneous
recent vegetation maps, and ground surveys. Initial landscape boundaries
were drawn by manual photointerpretation of the satellite imagery.
The minimum mapping unit for upland land-cover was 100 ha and 40
ha for wetlands. Median map unit size is 528 ha. The final land-cover
map includes distribution information on 194 natural plant community
types and 27 land use classes, plus 96 dominant species of trees
and 237 shrub species. A formal accuracy assessment of this map
has not been conducted, but initial comparisons indicate that the
map is in close agreement with other, recent vegetation maps.
Vertebrates
Distributions of 455 native vertebrate species were predicted by
GIS modeling. Species’ range limits and habitat suitability ratings
came from the California Wildlife Habitat Relationships System,
while the distribution of habitat types was derived from the CA-GAP
land-cover map. The predicted distribution database rates each mapped
landscape polygon on the basis of the suitability of the individual
habitat types it contains and their relative abundance. Thus a highly
rated polygon would have >50% of its area in high suitability
habitat. The maps, therefore, categorize the habitat of all map
units on a scale from 0-5 rather than dividing the state into suitable
and unsuitable habitat. Accuracy assessment on the predicted vertebrate
distributions are underway but were not completed at the date of
this report.
Land Ownership and Management
To determine how well species and plant communities are currently
protected, CA-GAP enhanced the 1:100,000 scale land ownership map
maintained by the California Teale Data Center by adding boundaries
of special managed areas not in the original ownership map, incorporating
recent acquisitions, and classifying all lands by management status.
This classification uses a scale from 1 to 4 to denote the relative
degree of management for biodiversity, with "1" being the highest,
most permanent level and "4" being the least secure. The status
level was assigned based on the management intent of the land steward
as expressed in general policies or legislation. Generally all private
lands were assigned to status level 4 because long-term management
of individual tracts is unknown.
Roughly 15% of California is currently managed as status 1, with
an additional 3% in status 2. Just over half of the state is in
status 4 management, most of which is privately owned. The remaining
30% is other public lands managed by agencies such as the U.S. Forest
Service and the Bureau of Land Management and not otherwise designated
for biodiversity management. Most of the 741 status 1 and 2 managed
areas are quite small, with a median size of only around 800 ha.
Although the proportion of protected area in California is relatively
high compared to other regions, the distribution is highly biased
towards certain geographic and topographic locations. The majority
of status 1 and 2 lands are in the southern Sierra Nevada and in
the Mojave and Sonoran Desert regions (especially following passage
of the California Desert Protection Act of 1994). Low elevations,
particularly along the coast and in the Great Central Valley are
strikingly under-represented.
Figure 1. Management status of lands in California.
Assessment of
the Management Status of Biodiversity
Land Cover
Of the entire state, 13% has been converted to agricultural uses,
nearly 5% to urbanization, 3% is unvegetated, and 79% remains vegetated
with natural communities. As there is no concensus on a definition
of "adequate representation," a pratical solution is to
report the percentages of each community type in status 1 and 2
areas and allow the user to determine which types they believe need
additional conservation. Of the 194 community types mapped by CA-GAP,
73 have less than 10% representation, 46 types have between 10 and
20%, 44 have between 20 and 50%, and 31 have more than 50%. The
types with less than 10% representation generally fall within several
categories: coastal scrub, Great Basin scrub, prairie grasslands,
hardwood woodlands, and a few conifer forests. The types that are
best represented are communities characteristic of Mojave Desert
scrub or subalpine conifer and alpine communities (Figure 2).
Figure 2. Plant communities that are least- and
best-represented in managed areas in California.
Coastal scrub types are of great concern both because they are
often prime land for urbanization along California's coastal plains
and large proportions of their historical extent has already been
converted. As a result, they harbor a large percentage of the state's
threatened and endangered plant and animal species. Native grasslands
have been similarly affected through conversion to agriculture,
invasion by exotic Old World annual plants, and change in fire regime,
so that all are considered highly threatened. Most hardwood types
occur principally on private lands and are subject to a number of
impacts such as grazing, fuelwood cutting, clearing for pasture
or cultivation, and fire suppression. Several oak species, notably
Valley oak (Quercus lobata), Blue oak (Q. douglasii),
and Engelmann oak (Q. engelmannii), have exhibited low rates
of recruitment in recent decades, adding to the concern about the
long-term viability of these ecosystems. The under-represented conifer
types tend to contain the most commercially valuable timber species
such as redwoods, ponderosa pine, and douglas-fir. Even though these
types have not been extensively converted to other uses, they have
been heavily altered in composition or structure either by selective
removal of favored species (e.g., sugar pine) and/or great reduction
in the extent of late successional stands.
Forty-six types were found to have between 10-20% representation
in GAP status 1 and 2. Many of these are chaparral types which in
general were assigned low levels of threat in the NHD rankings.
These tend to occur in steep terrain with few resource conflicts.
The primary issue in preserving chaparral is fire management.
Also in the 10-20% group are some of the riparian forest types,
most of which are considered threatened or very threatened in the
NHD rankings. Several of the saltbush or sink scrub communities
also are in this category. All are considered threatened by NHD
due to past losses from irrigated agriculture and the accidental
flooding of the Salton Basin at the beginning of the century.
Forty-four cover types have 20-50% representation in GAP status
1 and 2. Most of these types are from the deserts, marshes, and
the upper conifer forest zone. Included here are the creosote scrub
communities of both the Sonoran and Mojave deserts, Alkali Playas,
Desert Dry Wash Woodland, Desert Sink Scrub, and Mojavean Pinyon
and Juniper Woodland. The montane types include communities such
as Big Tree, Jeffrey Pine and Red Fir Forests, Huckleberry Oak Chaparral,
Canyon Live Oak Forest, and meadows. Most of these types are not
considered threatened in the NHD rankings, but there are several
notable exceptions such as Desert Sink Scrub, Valley Needlegrass
Grassland, Sitka Spruce-Grand Fir Forest, Beach Pine and Bishop
Pine Forests, Siskiyou Enriched Coniferous Forest, and the wetland
types.
Thirty-one types out of the 194 that were mapped have over half
of their distribution in status 1 or 2 managed areas. Of these,
8 were mapped over less than 25 km². Two types (Northern Coastal
Bluff Scrub and Santa Lucia Fir Forest) occur entirely within protected
areas. The majority of types in this category are Mojave Desert
scrub or subalpine conifer forests and alpine communities, corresponding
to the areas where protected areas are most concentrated. The remaining
types tend to be rather rare or highly localized and often the focus
of conservation action. Examples of this are the Salmon-Scott Enriched
Coniferous Forest, Port Orford Cedar, and Valley Sacaton Grassland.
The latter is ranked as very threatened by the Natural Heritage
Division (NHD) of the California Department of Fish and Game and
has suffered extensive reductions from agricultural land uses. Some
of the few remaining stands have been recently acquired by the California
Department of Parks and Recreation, but additional management action
may still be required to preserve this type.
Vertebrates
For this gap analysis, we limited the predicted distributions of
terrestrial vertebrates to habitats within each species’ range that
were rated as 4 or 5, i.e., most of the land-cover/habitat polygon
was classified as moderate to high suitability. Several species
have very low levels of representation (<5 %) in managed areas.
These species fall into four general groupings:
- adapted to human-dominated habitats
(little or no action
needed)
Inca dove
Bronzed cowbird
Black phoebe
Western kingbird
American crow
Red-winged blackbird
Hooded oriole
American goldfinch
Woodhouse’s toad
Black- and Yellow-billed magpies (commonly feed in agricultural
habitats but also depend on riparian or oak woodland habitat for
breeding and cover)
- very limited ranges
(very narrowly endemic species are best
evaluated in a "fine-filter" approach to complement
the "coarse-filter" gap analysis)
Townsend’s pocket gopher (subspecies found in California is restricted
to the Honey Lake area in Lassen County)
White-footed vole
Fresno (or San Joaquin) kangaroo rat
Tiger salamander
Redbelly newt
Siskiyou Mountains salamander
Shasta salamander
Spotted frog (may, in fact, have never occurred in California;
may be misidentified specimens)
Grasshopper sparrow (wider range than these other species, but
its abundance is erratic from year-to-year)
- marginal to the state
(should be re-assessed in ecoregional
gap analyses over their entire range)
Gila woodpecker
Cordilleran flycatcher
Cedar waxwing
Northern pocket gopher
Pronghorn
Short-horned lizard (most widely distributed lizard in North America
but in California only occurs in the Modoc Plateau region at the
margin of its range)
- diminishing or degraded habitats
(generally the most vulnerable
group of species)
Swainson’s hawk
Black-chinned hummingbird
California kangaroo rat
Western spadefoot
Of all native
vertebrates, the largest group has 10-20 % of their predicted distributions
in managed areas, with about equal numbers with <10 and 20-50
% (Table 1). Very few species have >50 % protection and these
tend to be species with very small ranges, such as the Alpine chipmuck
(Tamias amoenus), which was predicted over only 444 km²,
or <0.1% of California’s land area, in the rocky habitats above
2800 m in the High Sierra.
Table
1. Summary of species at different levels of biodiversity management.
|
# (%) with < 10% Status 1/2 |
# (%) with 10-20% Status 1/2 |
# (%) with 20-50% Status 1/2 |
# (%) with > 50% Status 1/2 |
Total # of species |
Land Birds |
72
(35%) |
83
(41%) |
44
(22%) |
5
(2%) |
204 |
Mammals |
30
(23%) |
52
(39%) |
40
(30%) |
11
(8%) |
133 |
Amphibians |
18
(44%) |
14
(34%) |
7
(17%) |
2
(5%) |
41 |
Reptiles |
10
(14%) |
21
(30%) |
35
(49%) |
5
(7%) |
71 |
All Native Vertebrates |
130
(29%) |
170
(38%) |
126
(28%) |
23
(5%) |
449 |
As a group, reptiles appear to be the best protected according
to their management status. More than half of the 71 reptiles have
>20 % status 1 and 2 habitats. Only 10 reptiles have <10 %
in managed areas. This high level of protection for this group is
explained not so much because conservation action has focused on
them but rather by an extensive set of parks and wilderness areas
designated in the California deserts where most of the reptiles
reside. Amphibians are the least well-represented group in managed
areas. The largest category of amphibians has <10 % status 1
and 2. Only 9 amphibians (22 %) have >20 % protection.
CA-GAP predicted species distributions on the basis of range boundaries
and the suitability of habitat types with the range. It does not
guarantee that a species will occur at all locations that are modeled
as suitable habitat. For some species, there are additional habitat
elements that further control their distribution. Elements such
as the presence of snags, proximity to surface water, or the adjacency
of different critical habitat types, for example, are site-specific
features that can not be detected at a regional scale with remotely
sensed data. Habitat structure is also a crucial factor in determining
habitat suitability for many species. Structure would characterize
the height of the canopy, the density of canopy cover, and the number
of layers in the canopy in multi-storied, uneven-aged habitats.
Those species that are dependent on either these key habitat elements
or on specific seral stages are likely to be grossly overestimated
by our modeling methods. Species such as the California spotted
owl and the fisher require mature stands of dense forest. This level
of detail was also not compiled for CA-GAP, so suitability was based
only on the type of habitat, not its structure.
Conservation
Priorities
Priority Community Types
Within the set of plant communities, we distinguished seven categories
(Table 2). The first two categories include all those rated as rare
by the NHD (S1 or S2). Of these, the highest priority (Group A)
is for rare communities with less than 20% level of status 1 and
2 management, while the second priority types have more than 20%
(Group B).
Priority Group |
Rarity |
% Status 1 and 2 |
Threat Index |
Weight |
A |
Rare |
<
20 |
|
1.0 |
B |
Rare |
>20 |
|
0.75 |
C |
Common |
|
high |
0.75 |
D |
Common |
<10 |
low |
0.5 |
E |
Common |
10-20 |
low |
0.3 |
F |
Common |
20-50 |
low |
0.1 |
G |
Common |
>50 |
low |
0.0 |
H
(non-vegetated) |
|
|
|
0.0 |
Table 2. Vulnerability
groups of plant communities from the statewide gap analysis based
on a combination of current protection and threat and the weights
used for scoring sites.
For widespread
community types, priorities were set based on a combination of two
factors: percentage of status 1 and 2 lands and an index of threat.
The threat index was based on a combination of roadedness and projected
population growth. The first group (Group C) of common communities
was characterized by a high threat index, indicating a relatively
high degree of either past disturbance or future loss. Note that
this threshold level was selected as a natural break in the set
of plant communities, not on any a priori or theoretical
basis. It had the further advantage of allowing us to divide communities
into approximately equal-sized groups. Virtually all Group C community
types were also relatively under-represented (< 20% status 1
and 2). The remaining four groups all appear relatively less threatened
by roads or future development (low threat index) and were categorized
based on their level of protection into roughly equal numbers of
types in each group. We used the same break points, i.e., 10%, 20%,
and 50%, in decreasing order of priority. Five exceptions were made
to these general rules. Four types that were rated as rare by NHD
were mapped over extensive areas by CA-GAP, perhaps due to differences
in interpretation. We therefore chose to assign Mojave Mixed Steppe,
Upland Redwood Forest, Westside Ponderosa Pine Forest, and Eastside
Ponderosa Pine Forest to groups G, E, E, and D respectively, as
if they were not rare types. Also, we assigned Tamarisk Scrub to
group G because it is not a native community type and in fact is
generally considered a pest species. The remaining urban, agricultural,
and non-vegetated land cover types were assigned to group H that
has no conservation priority for its vegetation values. There may
still be important habitats and other ecosystem values, however,
in the non-vegetated types (e.g., water bodies, sand dunes, rock
outcrops, etc.).
Of the 194 natural
community types, we have ranked 41 as highest priority for conservation
(Class A) based on their rarity and lack of protection. Another
20 community types are also rare but have greater than 20% protection.
All of these rare types need to be examined in greater detail to
determine more their true extent, which was only coarsely estimated
by CA-GAP methods, and the actual threats they face. Some of the
common types include rare subtypes. Coast Range Ponderosa Pine Forest,
for instance, includes a maritime subtype that is restricted to
sterile marine sand deposits in Santa Cruz County that may need
additional management. These caveats underscore the need to complement
the coarse-filter of gap analysis with a fine filter approach to
catch these special cases.
The common types
were divided into roughly equal-sized priority groups, with between
23 and 31 types in each. Twenty-four types were ranked as Group
C, with low protection and relatively high level of threat. Group
C types include the coastal scrub, chaparral, and woodland types
of southern California where population growth pressures are the
greatest. Group D contains communities that are not well-represented
in biodiversity management areas but face less threat than Group
C according to our simple index. These communities include Great
Basin scrub, non-native grassland, oak woodlands, and mixed conifer
types, although they all face other forms of threat that our index
does not address. Group E is the types with relatively low threat
and greater than 10% in status 1 and 2 management areas. This group
includes many of the common chaparral types, forests of the coastal
mountains, and some Great Basin communities. Types with low threat
and moderate protection are in Group F, which consists of many of
the desert communities and montane shrub and forest types. Group
G has the most well-represented communities, which therefore have
the lowest levels of threat. These communities generally are from
the desert and subalpine areas, which are the best protected in
California.
A few plant
community types deserve special mention where the CA-GAP is insufficient
to evaluate them adequately. One group of communities that need
to be highlighted are those that could not be mapped reliably at
the resolution of GAP. Most important of these are the wetland types,
such as marshes, vernal pools, riparian scrub, and other aquatic
habitats. Joshua Tree Woodland is another example. It was not mapped
as a specific plant community in the land-cover database of the
Mojave Desert region where it is most common. The presence of Joshua
Tree was only recorded as present where known. Frequently the density
of Yucca brevifolia is so low (or unknown) that the community
was classified as a scrub type. Many of these locations may actually
be Joshua Tree Woodland, but our analysis is unable to evaluate
its current management status reliably at this time.
Priority Places
Gap analysis is designed to identify conservation priorities among
the set of ecosystems or plant communities, but it does not automatically
imply to a distinct set of priority places. Many techniques have
been proposed in the conservation literature for meeting various
conservation goals. There is no consensus about the best approach,
however. Here we use a simplified scoring approach to rank 7.5 minute
quadrangles in California and identify some locations that appear
worthy of further investigation. Quadrangles are obviously not ecologically
defined land units nor are they useful as potential managed area
boundaries. Nevertheless, they provide a set of equal sized planning
units that are of a scale appropriate to regional conservation planning.
We ranked plant communities by their conservation importance based
on the coarse-filter of gap analysis as follows:
- Assign weights
to the vulnerability categories described in Table 2
- Calculate
the area in a quadrangle of each category in status 3 and 4 lands
- Multiply
the area in a category by its weight
- Sum weighted
area for all categories in the quadrangle
Figure
3. Site scoring by quadrangle for plant communities weighted by
their priority category.
The map of site
scores is shown in Figure 3. The highest scoring quadrangles tend
to occur in a ring around the Great Central Valley, particularly
in western Kern County, and in Glenn, Colusa, and Tehama counties.
Western Santa Barbara County and Solano County contain other particularly
high scoring clusters of quadrangles. Other relatively high scoring
areas include the Sierra Nevada foothills, much of the Central Western
region, parts of Shasta County, undeveloped areas throughout the
Southwestern California region, and a small area along the border
with Nevada in Lassen County. Low scoring sites occur throughout
the Great Central Valley, Los Angeles Basin, and the Imperial Valley
near the Mexican border where agriculture or urbanization have eliminated
most of the native vegetation. Other low scoring areas occur in
the higher elevations of the southern Sierra Nevada and the majority
of the Mojave and Sonoran Desert regions where the plant communities
are well-represented in managed areas and thus tend to have low
priority. Readers should note that a quadrangle could have a low
score and yet contain a rare community type that only occurs at
that site.
CA-GAP Database Uses and Availability
The CA-GAP database provides researchers, resource managers, educators,
and those interested in California's biodiversity with an unprecedented
opportunity for study and conservation planning. Toward that end,
the database and our final assessment are being published on compact
disk in a user-friendly format with all software necessary to run
it. The CD-ROM will be distributed through the California Department
of Fish and Game, which is also assuming long-term responsibility
for management and distribution of the data. The contents of the
full report will also be available on the World Wide Web at http://www.biogeog.ucsb.edu/projects/gap/gap_home.html.
Check this web site also for assistance with accessing to the database
and ordering the CD-ROM.
The database will also be distributed on a CD-ROM. The CD-ROM disk
will contain this report, GIS coverages (except see note below)
and TM image mosaics, all metadata, an interactive atlas version
with a customized graphical user interface to run ARCVIEW software
to make routine queries of the database that are relevant to gap
analysis.
Note: At the time of this report, access to the 1:100,000 scale
land stewardship/management layer compiled for CA-GAP is restricted
to subscribers of the state's Teale Data Center. Therefore it will
not be distributed either through GAP or California Department of
Fish and Game. Those interested in acquiring the coverage for a
fee are directed to the Teale Data Center GIS Solutions Group, http://www.gislab.teale.ca.gov/
or (916) 263-1767, for details. Check the CA-GAP or the Fish and
Game web sites, however, for the current status for this layer.
As an alternative, CA-GAP has compiled a 1:2,000,000 scale version
from unrestricted public-domain data. This lower resolution version
is being distributed without restriction. Check the CA-GAP web site
listed above for access.
Appropriate Uses: The following is a general list of applications:
- Statewide
biodiversity planning
- Regional
(Councils of Government) planning
- Regional
habitat conservation planning
- County comprehensive
planning
- Large area
resource management planning
- Coarse-filter
evaluation of potential impacts or benefits of major projects
or plan initiatives on biodiversity, such as utility or transportation
corridors, wilderness proposals, regional open space and recreation
proposals, etc.
- Determining
relative amounts of management responsibility for specific biological
resources among land stewards to facilitate cooperative management
and planning.
- Basic research
on regional distributions of plants and animals and to help target
both specific species and geographic areas for needed research.
- Environmental
impact assessment for large projects or military activities.
- Estimation
of potential economic impacts from loss of biological resource
based activities.
- Education
at all levels and for both students and citizens.
Inappropriate
Uses: It is far easier to identify appropriate uses than inappropriate
ones, however, there is a "fuzzy line" that is eventually crossed
when the differences in resolution of the data, size of geographic
area being analyzed, and precision of the answer required for the
question are no longer compatible. Examples include:
- Use of the
data to map small areas (less than thousands of hectares) typically
requiring mapping resolution at 1:24,000 scale and using aerial
photographs or ground surveys.
- Combining
GAP data with other data finer than 1:100,000 scale to produce
new hybrid maps or answer queries.
- Generating
specific areal measurements from the data finer than the nearest
thousand hectares (minimum mapping unit size and accuracy affect
this precision).
- Establishing
exact boundaries for regulation or acquisition.
- Establishing
definite occurrence or non-occurrence of any feature for an exact
geographic area (for land cover, the percent accuracy will provide
a measure of probability).
- Determining
abundance, health, or condition of any feature.
- Establishing
a measure of accuracy of any other data by comparison with GAP
data.
- Altering
the data in any way and redistributing them as a GAP data product.
- Using the
data without acquiring and reviewing the metadata and this report.
The California
Department of Fish and Game will be the long-term custodian of the
CA-GAP database, both for its distribution and its maintenance.
Ultimately it is anticipated they will establish a web site for
users to download the data. Check the CA-GAP web site at:
http://www.biogeog.ucsb.edu/projects/gap/gap_data.html
for information
on how to contact the Department of Fish and Game.