Assessing components of competition indices for young boreal plantations

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Abstract
Important components of interspecific competition affecting apical and cambial growth in young plantations of black spruce (Piceamariana (Mill.) B.S.P.) and jack pine (Pinusbanksiana Lamb.) in northern Ontario were identified. The relative importance of competition, initial seedling status, and some soil factors was also assessed. Measures of perennial competition were calculated using hemispherical photographs, stand maps, and mensurational data from 360 seedling-centred plots (1.4 m radius) for each of the two species. Fractal geometry was used to quantify the textures of the competing canopies. Reliable competition indices should include horizontal and vertical dimensions and express the amount of competition relative to the size of the seedling. The total canopy fraction on the photographs and some simple field measurements of competition correlated significantly with seedling growth. Complex expressions of competition were unjustified, and measures of dispersion and canopy texture correlated weakly with growth. The consistently good correlations between growth and some components of competition revealed that an index applicable to all species, stock types, and growth responses could be developed.