defining landscapes forman and godron (1986): a heterogeneous land area composed of a cluster of...
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Defining Landscapes
Forman and Godron (1986): A heterogeneous land area composed of a cluster of interacting ecosystems that is repeated in similar form throughout.
Turner at al. (2001): An area that is spatially heterogeneous in at least one factor of interest.
Both stress the presence of patches or elements and interactions between systems.
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Defining Landscapes
4m2
16m2 plots
1km2
100s of km2
• A landscape has no absolute size; size may differ among organisms depending on the question or problem.
• Functional landscapes occur at multiple spatial scales that may not correspond to human perceptions of the environment.
• Therefore, the manager or investigator must define the landscape appropriately.
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Patches: definitions
Vector Data = polygons. In ArcGIS, these are shape files.
Grid Cells = homogenous rectangles, typically squares. Also called lattice data, pixels. In ArcGIS, these are grids files.
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Models of Landscape Cover
Patch-Corridor-Matrixmodel:
The extent, shape, andconfiguration of landscape elements defines landscapepattern.
Landscape continuum model:
Rather than solely patches and corridors, landscapes are composed of a gradient of vegetative (or habitat) cover.
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Defining a Patch
Patch = relatively discrete areas or periods of relatively homogeneous environmental conditions, with boundaries distinguishable or relevant to the object of interest.
Humans Environmental /Natural Disturbance
Fragments Introduced ????
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Defining a Patch
Digitizing: Using remotely-sensed data, one can subjectively delineate polygons (patches) using visual determination of boundaries.
Aerial Photo Vector Coverage
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Defining a Patch
Simple aggregation: Combine all adjacent areas that have the same (or similar) value for the attribute of interest, usually in a GIS.
Moving/split window:
Local variance methods – variance is computed within a moving window; boundaries have high local variance.
Local rate-of-change methods –calculate a local regression and examine the slope; steep slopesindicate boundaries.
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Defining a Patch
Global zonation: Hierarchical, divisive partitioning based on the ratio of between- to within-patch variance.
Spatially-constrained clustering:multivariate clustering that joins groups only if they are spatially adjacent.
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Patch Characteristics
AREA- sensitive to your unit of measurement
PERIMETER- actual length dependent upon the smallest distance unit
SHAPE COMPLEXITY- many methods available for measurement
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Corridors and Edges
Corridor = narrow, linear elements of a type that differs from that on either side.
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Defining Corridors and Edges
Structural attributes: • Length and Width of corridor • Shape or Curvilinearity• Contrast from the matrix or other
patches• Is there an environmental gradient
included across the corridor? If so, is it an edge?
• Presence of separate internal conditions?
• Connectivity or presence of gaps along the corridor
Corridor definition can be defined on structural attributes
Patch type B
Patch type A
Patch type B
Patch type A
Patch type
A
Corridor
Corridor
Matrix(Patch type C)
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Defining Corridors and Edges
Habitat corridors: Increase connectivity by providing breeding habitat that facilitates gene flow across the landscape.
Facilitated movement corridors:Increase connectivity by facilitating movement during dispersal, migrations, and/or range shifts.
Corridor definitions based on functional attributes
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Facilitated Organism Movement Corridors
Selectivity – Degree to which an organism can discriminate between habitat patches so as to maximize its likelihood of successful dispersal.
Resistance – Survival costs per unit of time spent in a given corridor.
Velocity – Average rate of organism movement in a given corridor.
NOTES:Corridors may/may not facilitate movement and alleviate a loss of connectivity in the matrix.
Ultimate test of corridors: does the rate of immigration increase? Migration of more than desirable species may be enhanced!
May include:
• Roads and powerlines• Woody strips, windbreaks, and
hedgerows• Riparian corridors
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Defining Corridors and Edges
Barrier or filter corridors:Prohibit or differentially impede (filter) the movement of organisms across the landscape.
Modifying corridors:Alter the abiotic or biotic connection between patches or matrix.
Corridor definitions based on functional attributes
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Barrier and Filter Corridors
May include:
• Roads and powerlines• Rivers and streams
Corridor/Edge may function to prevent or filter movement of organisms across landscapes, thereby decreasing connectivity, depending on:
• Corridor width
• Frequency of human or other disruptive activities in the corridor
• Mobility and behavior of the species
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The MatrixMatrix = the most common or connected landscape element type that
generally plays the dominant role in landscape function.
• The matrix is defined based on the object of interest
• The matrix is dynamic and a function of time and space
• The definition of a matrix will influence the interpretation of landscapes as well as landscape metrics - because of its large extent, the matrix may dominate certain metrics.
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The Landscape Continuum Model
• In many landscapes, patches and corridors are too difficult to define, at least from a human perspective.
• Small or isolated elements may not serve as habitat alone, but may do so collectively, such that they should not be considered part of the background matrix.
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The Landscape Continuum Model
Habitat Destroyed
Intact Variegated Fragmented Relictual
Decreasing connectivity, increasing edge effects