Diversity, Floristic Richness, and Species Evenness During a Secondary (Post‐Fire) Succession

Diversity, species richness, and species evenness were analyzed in II boreal forest areas that had been burned from 0 to 44 years previously. The values of the information measure of diversity, H'. and Hurlbert's probability of interspecific encounter. Delta_1, obtained here are highly correlated. Both show a long—term declining successional trend, but exhibit relatively high values for the period 4 to 11 years after burning. Fluctuations in both appear to be attributable to variations in richness rather than evenness, supporting Pielou and Hurlbert's contentions that the two components of diversity should be analyzed separately. Delta_1 is preferred to H' because, if used in conjunction with a knowledge of spatial heterogeneity, it can provide information about the levels of competition in a community. The results indicate a slight increase in the amount of intraspecific competition during the course of succession, contrary to what might be expected as the outcome of evolution. It is argued that the species present are adapted to the occurrence of frequent catastrophes, particularly fires, so that prevailing evolutionary pressures and their outcome differ from those in more stable environments.