In a quadrat sample with 20 equally abundant tree species, the Shannon's index is approximately:
For S equally abundant species, every relative abundance is 1/S and Shannon entropy simplifies to ln(S). With twenty species, ln(20) is about 2.996, which rounds to approximately 3 using natural logarithms. Diversity has separable richness and evenness components. Shannon entropy rises when species number increases or abundances become more equal, while Pielou evenness scales Shannon entropy against the maximum possible value for that richness. Simpson measures emphasize the probability that sampled individuals belong to the same or different species, depending on convention. Every calculation
Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation