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.

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.

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.

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.

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 ????

Defining a Patch

Digitizing: Using remotely-sensed data, one can subjectively delineate polygons (patches) using visual determination of boundaries.

Aerial Photo Vector Coverage

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.

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.

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

Corridors and Edges

Corridor = narrow, linear elements of a type that differs from that on either side.

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)

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

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

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

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

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.

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.

The Landscape Continuum Model

Habitat Destroyed

Intact Variegated Fragmented Relictual

Decreasing connectivity, increasing edge effects