In the management of sustainable conifer plantations, the development of yield models allowing a proper planning of interventions within a low-input silvicultural system is of major interest. The fundamental hypothesis in most forest plantation yield studies assumes that individual tree growth is dependent upon the competitive influence of neighbouring trees. A critical synthesis of the best-known types of individual competition indices is presented, chiefly by discussing applicative differences between the ‘distance dependent’ (spatial) and the ‘distance independent’ (non-spatial) indices. Experimental preliminary trials show that non-spatial competition indices have a predictive ability no lower than the spatial ones, at least when used for conifer-plantation yield projection. The following simple index proved suitable: where Di is the diameter of the ith competitor and Dj is the diameter of the tree in question. Interactions between individual competition indices, predictive ability and stand attributes, such as density and fertility, have been observed.
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