Abstract
The results from various studies with Sitka spruce ( Picea sitchensis (Bong.) Carr.) in Scotland and Northern England were analysed to determine the effect of initial planting stock size on early field growth. In most cases (21 of 22), the taller stock at planting was also taller after 6 years of field growth. For example when stock 30 cm tall was planted instead of stock 20 cm tall, the average height differential after 6 years had increased to approximately 27 cm. On sites of average fertility (where the 6-year height of 20 cm trees would be 160 cm), this would equate to a 17 per cent gain in height at year 6. The gains in height at 10 years were similar to those found at 6 years. These results suggest that most of the height gains were achieved during the first 6 years of establishment. Even when seemingly small differences in average size exist at time of planting, researchers evaluating early growth responses due to various treatments (e.g. stock type, genetics, physiology, fertilization) should account for these differences in their analyses.

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