Effects of competitor spacing in individual-tree indices of competition

All indices of competition represent effects of distance between competing trees. However, the functional forms of these distance relations differ, because distance interacts with tree size in the many of the indices. In particular, some of the newer indices use vertical angles and crown geometry to define the effect of separation implicitly. Graphical displays showing effects of distance between subject tree and a competitor in published distance-dependent indices of competition are presented to permit visual comparisons of the indices. Nine pairs of subject and competitor crown classes are included for each index. Relation of these distance functions to the function implicit in distance-independent (stand-level) variables included in the growth prediction model is discussed.