. Development over 25 years of Douglas-fir, western hemlock, and western redcedar planted at various spacings on a very good site in British Columbia. Douglas fir British Columbia; Western hemlock British Columbia; Western redcedar British Columbia; Tree planting British Columbia. Basal area per hectare —For all three species, the wider the spacing the less the basal area per hectare. Differences among spacings widened initially but for the four wider spacings, are now generally stabilized (fig. 14). The superiority of the spacing di- minished as competition pressure reduced growth rates
. Development over 25 years of Douglas-fir, western hemlock, and western redcedar planted at various spacings on a very good site in British Columbia. Douglas fir British Columbia; Western hemlock British Columbia; Western redcedar British Columbia; Tree planting British Columbia. Basal area per hectare —For all three species, the wider the spacing the less the basal area per hectare. Differences among spacings widened initially but for the four wider spacings, are now generally stabilized (fig. 14). The superiority of the spacing di- minished as competition pressure reduced growth rates and increased mortality. Net growth at the spacing slowed markedly, while that at wide spacings apparently accelerated. All per-hectare yield values (number of trees, basal area, total-stem volume, and mer- chantable volume) were strongly influenced by survival as well as by diameter; survival and diameter trends are presented together in figure 15. Diameters were influenced to a much lesser extent by variations in survival. A look at survival percentages reveals the reasons for irregularities in other stand parameters. Because some variation in survival was the result of factors unrelated to spacing and occurred irregularly over time, one must be careful in interpreting differences in basal area and volumes among species and plots. The slowdown in net basal area growth of Douglas-fir after age 17 at the spacing in the 49-tree-plot trial was associated with a slight increase in rate of mortality (number per hectare) and a slight decrease in the rate of diameter growth. The lower level of basal area at age 18 at the spacing in the trial was associated with about one-half the number of trees per hectare present in the 49-tree-plot trial. Differences between the 49-tree-plot and the trials for other spacings were associated mostly with differences in preestablishment mortality, and to a lesser extent with differen- ces in postestablishm
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Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, bookleafnumber31
