Growth
Rocky Mountain Douglas-fir grows more slowly than coast Douglas-fir and is also much more cold tolerant. Tolerance of different environmental conditions varies among populations of Rocky Mountain Douglas-fir, especially among populations from the northern and southern Rockies. However, even nearby populations can differ in cold hardiness.
Root morphology is variable, but when unimpeded, a taproot forms within several years. "Platelike" root morphologies occur where growth is impeded. The most prominent lateral roots begin in the 1st or 2nd year of growth. Most roots in surface soil are "long ropelike laterals of secondary and tertiary origin". Fine-root production is episodic in response to changing environmental conditions; the average lifespan of fine roots is usually between several days and several weeks.
Rocky Mountain Douglas-fir reaches reproductive maturity at 12–15 years. It has winged seeds that are dispersed primarily by wind and gravity. In western Montana clearcuts, seeds were dispersed up to 250 m (800 feet) uphill from their source, but seedfall between 180–250 m (600–800 feet) was only 7% of that found in uncut stands. Other studies determined that seedfall in clearcuts beyond 80 m (265 feet) from seed trees was about 3% of seedfall in uncut stands where seed trees are close together. Well-stocked stands have resulted from seedfall from sources 1–2 km (0.6–1.2 miles) distant, but most Douglas-fir seeds fall within 100 m (330 feet) of their source. Small amounts of seed are dispersed by mice, chipmunks, and squirrels. Rocky Mountain Douglas-fir seeds are disseminated about twice as far as seeds of Ponderosa pine.
Read more about this topic: Pseudotsuga Menziesii Var. glauca
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