South Coast Missing Linkages Project Executive Summary
Habitat loss and fragmentation are the leading threats
to biodiversity, both globally and in southern California. Efforts to
combat these threats must
focus on conserving well-connected networks of large wildland areas where
natural ecological and evolutionary processes can continue operating
over large spatial and temporal scales--such as top-down regulation by
large predators,
and natural patterns of gene flow, pollination, dispersal, energy flow,
nutrient cycling, inter-specific competition, and mutualism. Adequate landscape
connections
will thereby allow these ecosystems to respond appropriately to natural
and unnatural environmental perturbations, such as fire, flood, climate
change,
and invasions by alien species.
The tension between fragmentation and conservation is particularly acute
in California, because our state is one of the 25 most important hotspots
of biological diversity on Earth. And nowhere is the threat to connectivity
more severe than in southern California--our nation's largest urban area,
and still one of its fastest urbanizing areas. But despite a half-century
of rapid habitat conversion, southern California retains some large and
valuable wildlands, and opportunities remain to conserve and restore
a functional
wildland network here.
Although embedded in one of the world's largest metropolitan areas, Southern
California's archipelago of conserved wildlands is fundamentally one
interconnected ecological system, and the goal of South Coast Missing
Linkages is to keep
it so. South Coast Missing Linkages is a collaborative effort among a
dozen governmental and non-governmental organizations. Our aim is to
develop Linkage
Designs for 15 major landscape linkages to ensure a functioning wildland
network for the South Coast Ecoregion, along with connections to neighboring
ecoregions. The Tehachapi Connection is perhaps our most important linkage
in that it is the sole wildland connection between two major mountain
systems--the Sierra Nevada and the Sierra Madre.
On September 30, 2002, 90 participants representing over 40 agencies,
academic institutions, land managers, land planners, conservation organizations,
and
community groups met to establish biological foundations for planning
landscape linkages in the Tehachapi region. They identified 34 focal
species that are
sensitive to habitat loss and fragmentation here, including 9 plants,
7 insects, 1 amphibian, 5 reptiles, 4 birds and 8 mammals. These focal
species cover
a broad range of habitat and movement requirements: some are widespread
but require huge tracts of land to support viable populations (e.g.,
mountain
lion, badger, California spotted owl); others are endemic species, narrowly
restricted within the linkage planning area (e.g., yellow-blotched salamander).
Many are habitat specialists (e.g., pond turtle in riparian habitat,
or acorn woodpecker in oak woodlands) and others require specific configurations
of
habitat elements (e.g. California quail or western toad). Together, these
34 species cover a wide array of habitats and movement needs in the region,
so that planning adequate linkages for them is expected to cover connectivity
needs for the ecosystems they represent.
To identify potential routes between existing protected areas we conducted
landscape permeability analyses for 9 focal species for which appropriate
data were available. Permeability analyses model the relative cost for
a species to move between protected core habitat or population areas.
We defined
a least-cost corridor--or best potential route--for each species, and
then combined these into a Linkage Union covering all 9 species. We then
analyzed
the size and configuration of suitable habitat patches within this Linkage
Union for all 34 focal species to verify that the final Linkage Design
would suit the live-in or move-through habitat needs of all. Where the
Linkage
Union omitted areas essential to the needs of a particular species, we
expanded the Linkage Design to accommodate that species' particular requirements
to
produce a final Linkage Design (Figure ES-1).
We also visited priority areas in the field to identify and evaluate
barriers to movement for our focal species. In this plan we suggest restoration
strategies
to mitigate those barriers, with special emphasis on opportunities to
reduce the adverse effects of Interstate-5, State Route 58, and the California
Aqueduct.
The ecological, educational, recreational, and spiritual values of protected
wildlands in the South Coast Ecoregion are immense. Our Linkage Design
for the Tehachapi Connection represents an opportunity to protect a truly
functional
landscape-level connection--and an ecological jewel at the remarkable
juncture of several major ecoregions. The cost of implementing this vision
will be
substantial--but the cost is small compared with the benefits. If implemented,
our plan would not only permit movement of individuals and genes between
the Sierra Nevada and the Sierra Madre, but should also conserve large-scale
ecosystem processes that are essential to the continued integrity of
existing conservation investments throughout the region. We hope that
our biologically
based and repeatable procedure will be applied in other parts of California
and elsewhere to ensure continued ecosystem integrity in perpetuity.
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