These metrics usually are best considered as representing landscape configuration, In addition to these primary metrics, FRAGSTATS also summarizes the. There is a wide variety of landscape metrics that have been developed and applied for many years. These metrics help us to quantify physical characteristics on. every patch is counted; FRAGSTATS does not sample patches from the . For a categorized list of FRAGSTATS output metrics see the FRAGSTATS Metrics.
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In a real landscape, the meyrics of patch sizes may be highly irregular. In the study of forest fragmentation, therefore, it is important to know how much of the target patch type habitat exists within the landscape. For example, a mean patch size of 10 ha could represent a class with 5 ha patches or a class with 2- 3- 5-,and ha patches, and this difference could be important ecologically.
It is important to keep in mind that both standard deviation and coefficient of variation assume a normal distribution about the mean. Edge metrics usually are best considered as representing landscape configuration, even though they are not spatially explicit at all.
Number of patches NP or patch density PD of a particular habitat type may affect metics variety of ecological processes, depending on the landscape context. Go to the Fragstats webpage. The minimum value of LSI is always equal to 1 when either the class is maximally compact at the class level or the landscape consists of a single patch at the landscape level. These summary measures provide a way to characterize the distribution of area among patches at the class or landscape level.
There is also a stand alone version that can be downloaded. However, the maximum value of LSI varies at the class level with class area.
This index measures the perimeter-to-area ratio for the landscape as a whole. Thus, a landscape with a smaller mean patch size for the target patch type than another landscape might be considered more fragmented. However, the size of a patch may not be as important as the extensiveness of the patch for some organisms and processes.
Specifically, the former landscape has greatly varying fragstays smaller patch sizes, while the latter has more uniformly-sized and larger patches. In contrast, patch density is a function of total landscape area.
Total edge TE is an absolute measure of total edge length of a particular patch type class level or of all patch types landscape level. Radius of gyration GYRATE is a measure of patch extent; that is, how far across the landscape a patch extends its reach.
In addition to these primary metrics, FRAGSTATS also summarizes the distribution of patch area and extent radius of gyration across all patches at the class and landscape levels. This index is similar to the habitat diversity index proposed by Pattonexcept that we apply the index at the class level as well. In this case, the interpretations of landscape structure could be very different, even though the coefficient of variation is the same.
The number or density of patches in a landscape mosaic pooled across patch types can have the same ecological applicability, but more often serves as a general index of spatial heterogeneity of the entire landscape mosaic.
At the class and landscape levels, edge can be quantified in other ways. Nevertheless, patch size coefficient of variation also can be misleading with regards to landscape structure in the absence of information on the number of patches or patch density and other structural characteristics.
For example, northern spotted owls have minimum area requirements for late-seral forest that varies geographically; yet, individual spotted owls use late-seral forest that may be distributed among many patches Forsman et al.
All other things equal, the larger the patch, the larger the radius of gyration. For these reasons, mean patch size is probably best interpreted in conjunction with total class area, patch density or number of patchesand patch size variability.
In addition, although many vertebrate species that specialize on a particular habitat have minimum area requirements e. For example, two landscapes may have the same patch size coefficient of variation, e. Using a moving window focal function, values were assigned to each pixel tabulating the percent of forested pixels within 1 km circle around that pixel.
Frabstats, mean patch size can serve as a habitat fragmentation index, although the limitations discussed below may reduce its utility in this respect.
Fragstats and Landscape Metrics | GEOG Conservation GIS
A landscape with a greater number or density of patches has a finer grain; that is, the spatial heterogeneity occurs at a finer resolution. Graphic helps fragsttats illustrate how landscape metrics can be used to understand environmental condition and establish thresholds of change. However, when comparing classes or landscapes of identical size, total edge and edge density are completely redundant. Variation in patch size may convey more useful information.
The image on the bottom depicts one way to assess landscape cohesion. Similarly, metrixs area constant, the more extensive the patch metrisc.
Images show examples of how landscape metrics can be used to quantify condition on land surfaces. In many ecological applications, second-order statistics, such as the variation in patch size, may convey more useful information than first-order statistics, such as mean patch size.
An excellent source for information on landscape metrics are the Fragstats webpages and their associated documentation.
Fragstats and Landscape Metrics
Alternatively, two landscapes could have the same number of patches and total landscape area and thus have the same patch density; yet, if class area differed, mean patch size could fragsyats very different between landscapes.
For example, two landscapes could have the same number and size distribution of patches for a given class and thus have the same mean patch metris yet, if total landscape area differed, patch density could be very different between landscapes. Greater variability indicates less uniformity in pattern either at the class level or landscape level and may reflect differences in underlying processes affecting the landscapes.