The Simpson index is used to emphasize the evenness of species (Nagendra 2002). Producing values from 0 to 1, Simpson’s index defines the probability that two equal-sized pekarangan, selected at random, belong to different pekarangan areas. The D also represents the uniformity of individual quantities of various species, which means the more species, the higher the uniformity and the value of D (Hong et al. 2012). The index is thus
where ni = number of individuals of species i and N is the total number of organisms of all species found.
22.214.171.124 Species Similarity (Sprensen Index)
The S0rensen index is used to measure similarity of vegetation types in a pekarangan. The index is thus
A + B
where A and B are the number of species in samples A and B, respectively, and C is the number of species shared by the two samples. This expression is easily extended to abundance instead of presence/absence of species. An A value approaching 1.0 indicates high similarity in species present in the two landscapes (Miller and Winer 1984).
17.3.2 Data Performance
The heterogeneity of plants in pekarangan is calculated by biodiversity indices. The statistical analysis was conducted using statistical software (PASW). All data were analyzed statistically into three levels of consideration: (1) orientation level, southern areas (SAs) and northern areas (NAs); (2) stream level, the level of altitude inside each watershed [there are three stream levels, upper-stream (UP), middle – stream (MD), and down-stream (DW)]; and (3) group level, the group criteria for size classification of pekarangan plot. There are four groups: G1, G2, G3, and G4.