Development of the Structural Root System of Sitka Spruce

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Abstract
Growth ring analysis was carried out on root systems of Sitka spruce trees which had been planted 8 and 34 years previously. Retrospective measurements were made on root extension, and on cross-sectional area increment near the root base. The extension of main lateral roots started slowly, then increased, and they achieved a mean length of 4.4 m in 8 years. Differentiation into roots of widely different radial growth rates took place during the first 6 years, resulting in 3 to 11 ‘major’ woody roots and a large number of small ‘minor’ ones, with some of intermediate vigour, radiating from the stump. The major roots established during the first few years constituted the main structural root system at 34 years. Many of the minor roots stopped growing in diameter after a few years, but were still alive and extending at 34 years. The differentiation into major and minor roots is discussed with reference to their origin on the root system, primary xylem diameter and the local environment.