The Diversity Index

Diversity or richness is one of the most used and abused indexes in ecology. The precise meaning of diversity has its roots in information theory, in the probability of finding in a sampled collection of objects new objects at every step.

The diversity index applied to the mosaic describes the typologies of the patches, their variety according to some pre-established patterns.

When we measure the diversity of a vegetation mosaic, we can use categories like old growth forest, regeneration forest, secondary forest, logging, etc. These characters are selected according to our purposes and must be calibrated according to the focal organisms or process under investigation. In some cases the diversity is simply the number of pixel types inside an area determined for our purposes.

Diversity in remote sensing is used to evaluate the complexity of the neighboring area and to relate such complexity (in this case equal to diversity) to processes like presence-absence of species, abundance of a focal species, and distance from diverse sites.

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Fig. 7.4 Example of distribution of patch types in two matrixes. Matrix A is characterized by the maximal diversity (H') and evenness (J') possible. Matrix B has a low diversity and also a very lower evenness. Where H' = -£ pi log pi, J = H'/Hmax, Hmax = log S, S = Number of categories

The use of this index in remote sensing is particularly useful, especially when the information on the land is partial and when for instance, multispectral images are not available (Fig. 7.4).

Diversity of pixels is strictly connected with the scale of observation, namely the amount of area in which the diversity has been computerized.

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