Dr. J. Wu: Lecture Notes in Landscape Ecology

Landscape Ecology - Lecture Notes

Some Basic Concepts in Landscape Ecology

Landscape Elements

Landscape elements are spatial units that comprise a landscape (mosaic). But landscapes can also be conceptualized as systems with continuously changing gradients.
Three types of landscape elements are commonly recognized (The Patch-Corridor-Matrix Model; Forman and Godron 1986 and Forman 1995)

Patch : "A relatively homogeneous nonlinear area that differs from its surroundings" (Forman 1995)

Corridor : A strip of a particular type that differs from the adjacent land on both sides (as a conduit, barrier, or habitat)

Matrix : The background ecosystem or land-use type in a mosaic, characterized by extensive cover, high connectivity, and/or major control over dynamics

[Click to zoom in.]

Pattern and Process

Pattern usually refers to the composition and configuration of a system.
Processes refer to actions or activities that create, modify, or maintain spatial patterns.
Both pattern and process are scale-dependent.
"Pattern and process are related to each other" - the cliche; but is it always true?

Pattern and process may be interactive, but when?
Pattern may constrain process, but when?
Does process always affect pattern?
They may not be related to each other?

Disturbance

"Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment" (Pickett & White 1985)

Contrast

The degree of difference among spatial elements, in particular, among patches, and between patches and underlying matrix

Spatial Heterogeneity

Spatial variation composed of patchiness (discrete changes) and gradients (gradual changes). Spatial heterogeneity is, therefore, a more general term than patchiness.

Scale

The spatial or temporal dimension of an object or process, characterized by both grain and extent

Grain

The coarseness in texture of an area, as determined by the size of patches recognized (i.e., fine grained landscapes have mostly small patches, while coarse grain has mainly large patches)

The finest level of spatial resolution (or the finest level of temporal resolution) possible with a given data set; e.g., pixel size for raster data

(Figure from Turner et al. 2001)

Extent

The size of the study area or the duration of time under consideration

Cartographic scale

- The degree of spatial reduction indicating the length used to represent a larger unit of measure; ratio of distance on a map to distance on the earth surface represented by the map, usually expressed in terms such as 1:10,000

Resolution

- Precision of measurement: spatial or temporal grain size

Absolute scale

- The actual spatial or temporal dimension

Relative scale

- A transformation of absolute scale to a scale that describes the relative spatial or temporal dimension

Fine scale vs coarse scale

Fine scale usually refers to the pattern of a small area, where the difference between map size and actual size is relatively small.
Coarse scale refers to the pattern of a large area, where the difference between map size and actual size is great.

A comprehensive conceptualization of scale
(Wu, J. and H. Li. 2006. Concepts of scale and scaling. Pages 3-15 in J. Wu, K. B. Jones, H. Li, and O. L. Loucks, editors. Scaling and Uncertainty Analysis in Ecology: Methods and Applications. Springer, Dordrecht.)

Hierarchy Theory (see Wu 2013 for details)

What is a hierarchy or a hierarchical system?

What is hierarchy theory?
How has it been applied in landscape ecology?

A simple definition of hierarchy is a partially ordered set of objects.

As a theory of complex systems, hierarchy theory was developed in the framework of general systems theory, mathematics, and philosophy in the 1960s and 1970s.

A hierarchically organized system can be seen as a system in which levels corresponding with progressively slower behavior are at the top, while those reflecting successively faster behavior are seen as lower levels in the hierarchy. Higher levels impose constraints on lower levels, and thus can be expressed as constants. On the other hand, the dynamics of the lower levels can be so fast that their signals are smoothed out at higher levels, and often can be treated as averages.

A central property of hierarchy theory in ecology is that many complex systems have a structure that is hierarchical and thus "decomposable," implying that both the analysis and understanding of these systems can be enhanced by organizing their numerous components into fewer discrete, interactive units at different levels based on differences in process rates.

Process rates (expressed by, for example, cycle time, response time, or occurrence frequency) are fundamental characteristics of most systems, and thus may serve as a common criterion for decomposing. - Other features, such as tangible boundaries and structural components, also can be used.

From the theory, discontinuities in hierarchies for organizational, spatial, and temporal scales (e.g., breaks in vegetation pattern, distribution of organism abundance, distribution of animal body mass, frequency domain of disturbance) are expected to be a common feature of ecological systems.

A main contribution of hierarchy theory to landscape ecology has been its role in promoting the study of scale and scaling.

References:

Wu, J. 2013. Hierarchy theory: An overview. Pages 281-302 in: R. Rozzi, S.T.A. Pickett, C. Palmer, J.J. Armesto, and J.B. Callicott, (eds). Linking Ecology and Ethics for a Changing World: Values, Philosophy, and Action. Springer, New York
Wu, J. 1999. Hierarchy and scaling. Canadian Journal of Remote Sensing 25(4): 367-380.

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