Measuring biological heterogeneity of forest vegetation types: avalanche index as an estimate of biological diversity

Ideally, the estimates of biological diversity of a community of species in a habitat should refer to the biological variation among the species and n ot merely to their numbers and frequencies. However, the current estimates of biodiversity incorporate only the latter two components but not the biol ogical differences among the species. Ganeshaiah et al. [(1997) Current Sci ence 73: 128-133] have proposed an estimate called the Avalanche Index (AI) that can incorporate the biological heterogeneity among the species in a h abitat. This estimate, besides being methodologically simple, can incorpora te any quantifiable differences among the species, information on species r ichness and their frequencies in the habitat. In this paper we have estimat ed AI for tree vegetation in 14 forest types across different ecosystems of the world and have compared these estimates with other indices being curre ntly used. Through this we have attempted to analyse the relative utility o f AI in discriminating the habitats based on their biological heterogeneity by capturing their intra-community biological variation. We discuss the me rits and demerits of the AI as a comprehensive estimate of biological diver sity.