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The composition, structure,
and function of habitat in a network will determine which species can
use it. A coarse-scale assessment of the biodiversity in a given
region where a conservation network is planned should reveal the locations
of the most suitable habitat for target species. In general, areas with
intact native vegetation will serve as anchors sites for the network.
Areas where natural disturbances (like fires, floods, landslides) can
occur without disrupting human activities are especially valuable. Finer
scale assessments may be used to locate unique habitat features (caves,
large trees suitable for cavity nesters, vernal pools, etc.) and locations
where at-risk species may be found.
In highly modified regions, a conservation network may be composed partially
of areas that are currently not in the best ecological condition and that
are suitable for restoration. Ecological restoration, a relatively new
science may involve removing invasive species, replanting native ones,
and restoring some hydrologic function. Working farms and forests may
also be incorporated into the network, provided that they are managed
in a manner that is consistent with the surrounding natural lands.
In addition to identifying priority habitat areas by analyzing the composition
and ecological elements across the landscape, spatial considerations of
those habitat patches and the overall network should also be taken into
account to ensure that the network supports biodiversity and meets ecological
needs and goals of the overall conservation plan. These conservation network
design principles are described below.
Size
Large patches are typically considered more important than smaller ones
because they tend to include more viable populations of native plants
and animals, including species dependent on interior habitat. They are
also more likely to sustain ecological processes and disturbance regimes.
However, small patches can also be important conservation targets because
they may contain unique or rare habitat types or species or may act as
stepping stones. Small patches may also provide sufficient habitat for
species that don't have large area requirements.
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Size: Habitat fragmentation
As the human footprint continues to spread across the landscape, it is
essential to protect large blocks of habitat before they are lost or fragmented.
Fragmenting a large parcel into smaller parcels creates additional edge
habitat and eliminates interior habitat. Habitat fragmentation typically
results in an increase in edge species, which are common across a landscape,
and the loss of interior species, which are less common and often of conservation
importance.
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Size:
Interior and Edge Habitat
Larger patches have more interior habitat, while smaller patches have
less or no interior habitat.
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Size:
Population Stability
Populations are typically more stable and sustainable and less susceptible
to local extinction in large patches than small patches.
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Size:
Diversity
A large patch often contains greater habitat and species diversity than
a small patch. More importantly, large patches are more likely to maintain
native species in good quality habitat, whether or not greater diversity
naturally occurs or not. Large patches are also more insulated from surrounding
disturbance than small patches and contain more interior habitat.
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Matrix
Lands between mostly natural patches of wildlife habitat are sometimes
called matrix lands. Many of these areas are semi-natural lands that are
usually managed primarily for farming, timber, recreation or other human
purposes, but provide some important benefits. Semi-natural matrix lands
provide habitat for some species and buffer core habitat areas from outside
threats and disturbance. (See Land
Management Rating Scale.) On the other hand, matrix lands that have
been developed or are in poor condition may have adverse effects for species
populations, inhibiting movement among patches and hindering overall population
viability.
Proximity
Patches located close enough to allow species movement will enhance the
persistence of the overall population.
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Connectivity
Species movement among habitat patches can be facilitated through the
protection of discrete spatial features such as stepping stones and linkages
or through surrounding matrix lands that allow movement among patches.
Proximity and location of patches and the specific behavior and life histories
of the target species are also factors in determining species movement
among habitat patches. Connectivity could potentially facilitate some
adverse affects, such as spreading invasive species, disease, and wildfire.
Connectivity to habitat patches in conservation networks in neighboring
study areas should also be taken into consideration.
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Connectivity:
Isolation
Small patches that are connected to other patches generally are more ecologically
viable than isolated patches. Species within an isolated habitat patch
are highly susceptible to disturbance and degradation from surrounding
land uses because species movement (to and from the patch) is limited.
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Connectivity:
Interconnectedness
Interconnectedness is an important feature of networks, as it facilitates
species movement among patches. Small interconnected patches provide cover,
resting, and foraging habitats for animals en route to larger habitat
patches. However, a network that is designed for connectivity but ignores
other principles may have too much linear habitat and edge.
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Shape
Irregularly shaped parcels have more edge habitat and edge species and
less interior habitat and interior species than round shaped parcels.
Also, irregularly shaped patches have greater interaction with the surrounding
habitat matrix, increasing chances for negative interactions such as habitat
degradation from adjacent land use or other disturbances.
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Shape:
Linear vs. Blocks
Linear shaped patches, including corridors and riparian buffers, contains
little or no interior habitat, while blocks of habitat in a rounder shape
has more interior habitat.
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Integrating
Terrestrial and Aquatic Components - Portland Metro
Many conservation network designs have focused either on terrestrial species
or aquatic species. A conservation network to be effective should include
both elements since the quality and integrity of each is dependent on
the other. An example of this type of design is the Portland Metro fish
and wildlife habitat mapping effort, which incorporated riparian and terrestrial
elements into its final design. Before integrating the two components,
Metro designed two separate conservation networks- one focused on wildlife
habitat and the other focused on riparian elements. Both are shown below.
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Portland Metro - Terrestrial
An example of the Portland Metro wildlife habitat mapping effort.
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Portland Metro - Aquatic
An example of the Portland Metro riparian habitat mapping effort.
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Integrating Terrestrial
and Aquatic Components - Massachusetts Division of Fisheries and Wildlife
The Massachusetts Division of Fisheries and Wildlife developed an aquatic
biodiversity project, called Massachusetts'
Living Waters, to compliment its existing BioMap,
which is primarily focused on terrestrial resources.
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Massachussets BioMap - Terrestrial
BioMap focuses on the protection of terrestrial and wetland species.
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Massachussets Living Waters
- Aquatic
Living Waters focuses on the protection of freshwater biodiversity.
For more information on this aspect of network design, refer to
The Nature Conservancy's integration of marine and terrestrial
elements
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