DESCRIPTION

It follows a "sliding window" algorithm with overlapping windows. The amount of forest and its occurence as adjacent forest pixels within fixed- area "moving-windows" surrounding each forest pixel is measured. The window size is user-defined. The result is stored at the location of the center pixel. Thus, a pixel value in the derived map refers to "between-pixel" fragmentation around the corresponding forest location.

As input it requires a binary map with (1) forest and (0) non-forest. Obviously, one can replace forest any other land cover type. If one wants to exclude the influence of a specific land cover type, e.g., water bodies, it should be classified as no-data (NA) in the input map. See e.g., blog post.

Let Pf be the proportion of pixels in the window that are forested. Define Pff (strictly) as the proportion of all adjacent (cardinal directions only) pixel pairs that include at least one forest pixel, for which both pixels are forested. Pff thus (roughly) estimates the conditional probability that, given a pixel of forest, its neighbor is also forest. The classification model then identifies six fragmentation categories as:

interior:       Pf = 1.0
patch:          Pf < 0.4
transitional:   0.4 ≤ Pf < 0.6
edge:           Pf ≥ 0.6 and Pf - Pff < 0
perforated:     Pf ≥ 0.6 and Pf - Pff > 0
undetermined:   Pf ≥ 0.6 and Pf = Pff

NOTES

• The moving window size is user-defined (default=3) and must be an odd number. If an even number is given the function will stop with an error message.
• No-data cells are ignored. This means that statistics at the raster edges are based on fewer cells (smaller) moving windows. If this is a problem, the user can choose to have the output raster trimmed with a number of raster cells equal to 1/2 * the size of the moving window.
• The function respects the region. The user has however the option to set the region to match the input layer.

EXAMPLE

g.region raster=landclass96

r.mapcalc "forest = if(landclass96 == 5, 1, 0)"

r.forestfrag input=forest output=fragmentation window=7

Two forest fragmentation indices with window size 7 (left) and 11 (right) show how increasing window size increases the amount of edges.

SEE ALSO

The addon is based on the r.forestfrag.sh script, with as extra options user-defined moving window size, option to trim the region (by default it respects the region) and a better handling of no-data cells.

AUTHORS

• Emmanuel Sambale (original shell version)
• Stefan Sylla (original shell version)
• Paulo van Breugel (Python version, user-defined moving window size)
• Vaclav Petras (major code clean up)

REFERENCES

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