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Kevin McGarigalBrad Compton
andScott Jackson
Critical Linkages
Assessing Local and Regional
Landscape Connectivity for
Transportation Planning in
Massachusetts
http://www.umasscaps.org
Conservation Assessment & Prioritization
System (CAPS)
Landscape Ecology Lab
Assessing ecological integrity and
supporting decision-making for
land conservation, habitat
management, project review &
permitting to protect biodiversity
Ecological Community
Approach
GIS data
Land cover
map
Integrity
metrics
Index of Ecological
Integrity
The CAPS Analysis
Integrated Index of
Ecological Integrity (IEI)
CAPS Critical Linkages ConceptsThe Three Faces of Connectivity
Dispersion
Connectedness
Conductance A B
Ecological Setting
…refers to the principal physical and chemical characteristics
at multiple scales that strongly influence the composition,
structure and function of a particular point in the landscape
over the long term and serve to describe and distinguish it
ecologically.
• Includes both local environmental conditions and
landscape context
• Relatively static at relevant ecological time frames
• Ecological conditions may vary in response to natural and
anthropogenic disturbances
Flo
w g
rad
ien
t
Hydroperiod
Ecological Setting
Flo
w g
rad
ien
t
Hydroperiod
Ecological Setting
Ponds
Forested Wetlands
Intermittent
Streams
Riverine
Marshes
Fringe Buttonbush Swamps
Aquatic Bed
Backwaters
Vernal Pools
Ecological Setting Variables
Temperature
• Growing season degree-days
• Minimum winter temperature
Solar energy
• Incident solar radiation
Moisture
• Wetness/Soil moisture
Hydrology
• Flow gradient
• Flow volume
•Tidal regime
Physical Disturbance
• Wind exposure
• Wave exposure
• Steep slopes
Chemical & physical substrate
• Soil pH
• Soil depth
• Soil texture
• Substrate mobility
• Water salinity
• Water CaCO3 content
Vegetation
• Vegetative structure
Development
• Developed
• Traffic rate
• Impervious
•Aquatic barriers
• Terrestrial barriers
Ecological Setting
Su
bstr
ate
Physical Disturbance
• Temperature
• Solar energy
• Substrate
• Physical disturbance
• Moisture
• Hydrology
• Vegetation
• Development
Similarity Matrix
(26 Variables)
Cell #1: ForestResistant Surface
Cell #2: ForestResistant Surface
Cell #3: Forested WetlandResistant Surface
Cell #4: RiverResistant Surface
Land Cover
Cell #1: ForestResistant Surface
Resistant Kernel
Cell #2: ForestResistant Surface
Resistant Kernel
Cell #3: Forested WetlandResistant Surface
Resistant Kernel
Cell #4: RiverResistant Surface
Resistant Kernel
Connectedness
Aquatic Connectedness
Critical LinkagesPhase I
Landscape Ecology ProgramDepartment of Environmental Conservation University of Massachusetts, Amherst
Critical Linkages Phase I
Beforecell 1
Aftercell 1
∆-Connectedness for Roads
Δ-Aquatic Connectedness
Critical Linkages Results: Crossings
Critical Linkages Results: Dams
Critical Linkages II
Assesses the effect of landscape changes on regional connectivity.
o Over a regional scale, concerned with connecting important conservation areas (“nodes”).
o Terrestrial connectedness only, because there are multiple choices when moving over land, but only one path when moving through stream network.
Definitions
NodeAn area of conservation interest (a.k.a. reserve). Critical Linkages II focuses on connections among nodes.
Contingent unitA specific place in the landscape that may change.
a. For road passage analysis, contingent units are sections of highway where road passage structures may be built.
b. For development analysis, contingent units are parcels of land that may be developed.
Node 1
Units
Node 2
A
B
C
Node 2
Random Low-Cost PathA possible route between a pair of nodes. Somewhere between the least-cost path (the single optimal route) and a random walk (which never really gets anywhere).
Node 1
Path distanceThe total length of a path in terms of functional distance: the sum of landscape resistance for each cell the path traverses.
Path distance may be assessed in terms of functional distance (resistance) or in terms of P(connect), given a bandwidth, based on dispersal ability.
distance = 8477P(connect) = 0.72
Node 2
Node 1
0 1
distance ÷ bandwidth
P
0
1
2 3 4
Mean functional distance = 9268 m
Mean P(connect) = 0.61
Internode distanceThe distance between a pair of nodes is simply the mean of all path distances between the nodes.
Node 2
Node 1
Probability of Connectivity (PC)Saura and Pascual-Hortal (2007)
A metric of the total landscape connectivity among nodes (each with a size or value) given P(connect) among nodes.
An unfragmented landscape consisting of a single giant node has PC = 1.
A landscape with few small, disconnected nodes approaches PC = 0.
∆PC
The change in probability of connectivity for a landscape after changing the size of nodes or P(connect) among nodes.
Changes that increase connectivity get a positive ∆PC.
Changes that decrease connectivity get a negative ∆PC.
Node 1
Node 2
C
A
B
Identify nodes and contingent units.
1. The Analysis
Calculate PC for the current landscape.
PC = 0.694
2.
Node 1
Node 2
C
A
B
Build lots of random low cost paths between each pair of nodes. Note which units are crossed by each path.
3.
Node 1
Node 2
Conductance Index
Sum of random low cost paths crossing through a particular cell gives the conductance index.
4.
Node 1
Node 2
C
A
BEvaluating links:
Select each unit, one at a time, and build a wildlife passage, thus changing the path distance for all paths that traverse the unit.
Recalculate PC and get ∆PC for the current unit.
5.
PC = 0.694 PC = 0.721
∆PC = 0.027
6.
Map the best single links across the landscape.
Nodes
• BioMap2 Candidate Forest Cores
• BioMap2 Candidate Wetland Cores
• Lentic portions of BioMap2 Aquatic Cores
• BioMap2 Vernal Pool Complexes
• Protected Open Space with IEI > 0.7
• Size threshold of 200 ha
Random Low-Cost Paths
Forest Forested Wetland Shrub Swamp Wetland
Random Low-Cost
Paths
Conductance index
Conductance Index
2k5k
10k
Conductance Index
Node Importance
Link Importance
Nodes
Conductance Index
Contingent Units
Contingent units: Road segments
(traffic ≥ 500 vehicles/day)
Critical Linkages
20 Most Important Linkages
20 Most Important Linkages
http://www.umasscaps.org
Funding and Other Support Provided by:
The Nature Conservancy
Federal Highway Administration
MA Department of Transportation
MA Department of Environmental Protection
MA Natural Heritage & Endangered Species Program
MA Office of Energy & Environmental Affairs
US Environmental Protection Agency
The Trustees of Reservations
Massachusetts Audubon Society
USDA’s Cooperative State Research, Education, and Extension Service (CSREES) is our federal partner, providing federal assistance and
program leadership for numerous research, education, and extension activities.
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