AI (landscape level)

Aggregation index (Aggregation metric)

Usage

lsm_l_ai(landscape, directions = 8)

Arguments

landscape: A categorical raster object: SpatRaster; Raster* Layer, Stack, Brick; stars or a list of SpatRasters
directions: The number of directions in which patches should be connected: 4 (rook's case) or 8 (queen's case).

Value

tibble

Details

$$AI = \Bigg[\sum\limits_{i=1}^m \Big( \frac{g_{ii}}{max-g_{ii}} \Big) P_{i} \Bigg](100) $$

where $g_{ii}$ is the number of like adjacencies based on the single-count method and $max-g_{ii}$ is the classwise maximum number of like adjacencies of class i and $P_{i}$ the proportion of landscape compromised of class i.

AI is an 'Aggregation metric'. It equals the number of like adjacencies divided by the theoretical maximum possible number of like adjacencies for that class summed over each class for the entire landscape. The metric is based on the adjacency matrix and the single-count method.

Units

Percent

Range

0 <= AI <= 100

Behaviour

Equals 0 for maximally disaggregated and 100 for maximally aggregated classes.

References

McGarigal K., SA Cushman, and E Ene. 2023. FRAGSTATS v4: Spatial Pattern Analysis Program for Categorical Maps. Computer software program produced by the authors; available at the following web site: https://www.fragstats.org

He, H. S., DeZonia, B. E., & Mladenoff, D. J. 2000. An aggregation index (AI) to quantify spatial patterns of landscapes. Landscape ecology, 15(7), 591-601.

Examples

landscape <- terra::rast(landscapemetrics::landscape)
lsm_l_ai(landscape)
#> # A tibble: 1 × 6
#>   layer level     class    id metric value
#>   <int> <chr>     <int> <int> <chr>  <dbl>
#> 1     1 landscape    NA    NA ai      82.5