Competition Indices: What have we learned, where should we use then and what additional research is required?

Competition indices are an attempt to quantify in a simple expression, the effects of neighboring plants on the growth of an individual tree. Many such indices have been proposed, and although few have reached operational use, this research has provided insights into tree growth and competition. Competition indices offer little utility for yield forecasting in "typical" stands. Few indices provide better forecasts than stand basal area and other simple measures of stand density and tree rank, which are easier to estimate. "Silvicultural" growth models designed to investigate management options must employ competition indices to provide reliable predictions under extreme silviculture. The need for the model to respond sensibly to extremes of thinning and pruning suggest that indices based on light interception (i.e. both crown area and sky view) have greatest potential. Even relatively simple models based on these principles may prove useful.