Root development in planted Douglas-fir under varying competitive stress

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Abstract
Roots of 5-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) on three Oregon sites were excavated with explosives and analyzed for the effects of competition on root biomass and for planting-induced root deformities. The plantations were in Nelder designs with graduated spacing from 300 to 15 250 cm2 per tree. Competition treatments consisted of weed-free intraspecific competition, grass cover seeded after 1 year of seedling growth, and red alder (Alnusrubra Bong.) interplanted 1:1 among the Douglas-fir. All plantations were kept at low water stress in year 1. The ratio of standing aboveground to belowground biomass was the same for each competitor type. Shoot:root ratios averaged about 4:1, except in severely suppressed trees, where ratios dropped toward 1:1 in those near death. Neither shoot:root ratio nor tree size was affected by planting-induced root deformities such as J- or L-rooting. It appears that after 5 years all root systems have fully compensated for planting deformities and future growth and stability have not been jeopardized.

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