When Is a Landscape Perspective Important?

Concepts of Landscape Scale

http://www.fhsu.edu/biology/ranpers/ert/landscape.htm

• Grain = spatial resolution of a study or data set, e.g., m², ha, km² .
• Resolving power = ability to distinguish small objects
• Smaller grain = smaller objects resolvable.
• Extent = refers to size of study area being considered

Note: no fixed scale, either grain or extent defines landscape ecology.

Satellite data:

• 70s satellites = grain size about 90 x 90m (Landsat Multispectral Scanner)
• 80s satellites = about 30 x 30m (Landsat Thematic Mapper), a.k.a. TM
• French SPOT, 10 x 10m

And Spectral Resolution = also higher on newer satellites

How are Patterns Measured on Landscapes?

GIS used to digitize, store, and analyze landscape data

• Raster v. Vector format Idrisi v. Arcinfo, polygons v. pixels
• Raster is more common in landscape ecology, because most satellite data is in raster format.

Three Main Types of Data

• Aerial photography available back to the 30s. B&W, Color, IR. Get from FSA.
• Digital Remote Sensing widely used and available (e.g., Landsat and SPOT)
• Airborne imaging scanners fine resolution for locales

Published data and censuses good for older surveys

Questions Asked by Landscape Ecologists:

1. How does spatial patterns affect species abundance?

• Patch = relatively homogenous nonlinear area that differs from its surroundings
• Effect of patch size - small patches have greater perimeter, large patches have greater interior

• Effect of habitat arrangement - how patches are arranged relative to each other, e.g., corridors
• Identifying suitable habitat e.g., species reintroductions
• Habitat connectivity - percolation theory used to describe critical thresholds of connectivity. Threshold refers to a point at which habitats either become connected or disconnected. Depends on ability of organism to disperse and spatial characteristics of landscape.

When Is a Landscape Perspective Important?

http://www.fhsu.edu/biology/ranpers/ert/fahrigessay.htm

Lenore Fahrig
Ottawa-Carleton Institute of Biology
Carleton University
Ottawa, Canada K1S 5B6

lfahrig@ccs.carleton.ca

When is a Landscape Perspective Necessary?

From the preceding it should be clear that a landscape perspective is necessary whenever landscape structure can be expected to have a significant effect on the response variable (abundance/distribution/local process) of interest. This leads to the somewhat frustrating Catch-22 that, in order to determine whether a landscape perspective is necessary, one must conduct a landscape-scale study. Practically speaking, this implies that a landscape perspective is always necessary.

However, we expect there must be some, if not many, situations in which landscape structure does not have a large effect on the response variable of interest which, in retrospect, tells us that a landscape perspective was not necessary for that problem. Avoiding a landscape-scale study when one is not necessary will be time- and money-saving. Can we delineate some circumstances in which a landscape perspective is not necessary?

When is a Landscape Perspective Not Necessary?

Probably the most straightforward situation in which a landscape perspective is not necessary is when a sufficient proportion of variation in the response variable can be explained with local variables only. The definition of "sufficient" will of course depend on the purposes of the study. One might argue that the rarity of landscape-scale studies (as defined above) in the ecological literature suggests that the proportion of variation explained by local variables is high in most cases. However, we know this is not the case. Reasons for the lack of landscape-scale studies are discussed in the following section.

In addition to an arbitrary cut-off of explained variation, it may be possible to identify certain classes of circumstances in which at least certain components of a landscape perspective can be ignored. For example, landscape configurational information may be unnecessary for certain types of organisms or when the amount of habitat is below or above certain threshold amounts.

Impediments to Landscape-scale Studies

The impact of landscape structure has been ignored, largely because of the perceived difficulty of conducting such large-scale studies. This constraint is disappearing with the increasing availability of remotely-sensed data, allowing much easier measurement of landscape structural variables.

The main constraints that must now be overcome are cultural constraints within the discipline of ecology. For example, many ecologists view a "landscape-scale" study as simply a study that covers a large area. If a study including several patches of forest is "large" to that researcher (s)he may call it a landscape-scale study. As I argue above, a landscape-scale study is one that examines the effect of landscape context on a response variable. It answers the question, "does the structure of the landscape in which this observation is imbedded affect its value?" This can only be answered by comparing the response variable across several landscapes with different structures.

Probably a greater hindrance to true landscape-scale studies is the current emphasis in ecology on experimental studies. By definition, landscape ecological studies look at the effect of a pattern (landscape structure) on a response. Judicious choice of landscapes with contrasting structures can result in a pseudo-experimental design. However, manipulative experimentation at a landscape scale (i.e, multiple experimental landsapes) is generally not possible. Where landscape-scale studies have been conducted, large effects of landscape structure (especially landscape composition) have been found. Inability to apply "in vogue" experimental methods to landscape ecological studies is no reason to ignore these effects or avoid the landscape perspective.