A competition index for predicting the vigour of planted Douglas-fir in southwestern British Columbia

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Abstract
To provide a method of quantifying brush competition in coastal Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantations, data from 124 planted trees, 1–5 years old, were used to derive a competition index for predicting changes in tree vigour measured as a relative production rate. The index, including measures of brush proximity, relative height, and percent ground cover, appears to act as a measure of light interception around the tree crown. Tree vigour was found to be largely a function of the age of the tree from planting and the competition index (r2 = 0.71). Foliage-based measures of growth vigour were more strongly related to the index than basal area or height measures. The index has potential for assessing interspecific competition problems in young Douglas-fir plantations.