Summary

Mathematical indices, formed by combining several primary measures, can help researchers summarize, interpret and display results from plant competition experi-ments. This essay compiles and discusses more than 50 indices that have been used in studies of plant competition. 2 Indices allow researchers to quantify and express several attributes of plant com-petition, including competition intensity and importance, competitive effects and responses, and the outcome of competition. 3 Several qualities should be considered when selecting a competition index for use. These include specificity and clarity of meaning, mathematical and statistical pro-perties, density dependence, versatility and freedom from size bias. 4 Many indices are based on comparisons of plant performance in mixtures compared with pure stands or control plots. Additional measures of competition are also available from yield-density functions, size distributions and neighbourhood analysis. 5 Indices reflect the consequences of competition. In order to appreciate competitive processes, indices have to be used in conjunction with studies of the chronology, circum-stances and composition of plant associations. Key-word