(L130) Shannon's Evenness Index

shei.jpg  

Pi =     proportion of the landscape occupied by patch type (class) i.

m =     number of patch types (classes) present in the landscape, excluding the landscape border if present.

Description

SHEI equals minus the sum, across all patch types, of the proportional abundance of each patch type multiplied by that proportion, divided by the logarithm of the number of patch types. In other words, the observed Shannon's Diversity Index divided by the maximum Shannon's Diversity Index for that number of patch types. Note, Pi is based on total landscape area (A) excluding any internal background present.

Units 

None

Range

0 ≤ SHEI ≤ 1


SHDI = 0 when the landscape contains only 1 patch (i.e., no diversity) and approaches 0 as the distribution of area among the different patch types becomes increasingly uneven (i.e., dominated by 1 type). SHDI = 1 when distribution of area among patch types is perfectly even (i.e., proportional abundances are the same).

Comments

Shannon’s evenness index is expressed such that an even distribution of area among patch types results in maximum evenness. As such, evenness is the complement of dominance.