Epicormic branching in Rocky Mountain Douglas-fir

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Abstract
The origin and morphology of epicormic branches in Rocky Mountain Dougas-fir (Pseudotsugamenziesii var. glauca (Beissn.) Franco) was studied by dissecting pole-sized trees. Epicormic shoots arose from buds on first-order branches, not as first-order axes buried in the bark of the trunk. The buds are suppressed 9–14 years before elongating. Epicormic shoots often produced buds at basal positions which elongated to form epicormic clusters.Intermediate trees tended to have more epicormics in the lower crown than dominants and codominants. Epicormics were significantly more frequent at higher elevations. The effects of aspect and slope were not significant.Douglas-fir stands in California and Idaho had substantially fewer trees with epicormics than stands in Utah, Wyoming, or Montana. Frequency of epicormics appears to be under genetic control. The appearance of epicormics does not require outside catastrophic influence, but is a routine event that occurs as shaded limbs decine in vigor. This habit appears to occur in several other coniferous genera.

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