. Seven-year response of 35-year-old Douglas-fir to nitrogen fertilizer. Trees Growth; Forest soils Fertilization; Nitrogen fertilizers. the response surface (p < ). Thus the 420-pound-N treatment was not large enough to determine the dosage of N at which d. growth would have leveled off. Growth of Larger Trees Particularly Stimulated by Nitrogen In all plots, diameter growth of surviving trees was significantly related to initial tree size; largest trees grew most in Fertilizing enhanced this relation- ship. Additions of 280 and 420 pounds of nitrogen per acre signif
. Seven-year response of 35-year-old Douglas-fir to nitrogen fertilizer. Trees Growth; Forest soils Fertilization; Nitrogen fertilizers. the response surface (p < ). Thus the 420-pound-N treatment was not large enough to determine the dosage of N at which d. growth would have leveled off. Growth of Larger Trees Particularly Stimulated by Nitrogen In all plots, diameter growth of surviving trees was significantly related to initial tree size; largest trees grew most in Fertilizing enhanced this relation- ship. Additions of 280 and 420 pounds of nitrogen per acre significantly increased growth of larger trees more than that of smaller trees (fig. 3). The 140-N dosage also differentially increased the growth of larger trees but to a lesser extent than higher dosages. Because higher fertilizer dosages resulted in greater mortality, the increase in growth of larger trees following the 280- and 420-N treatments is explained in part by release as well as by improved nutrient status. The antici- pated effects of this fertilization on future stand structure are increased average diameter and range, also continued advantage of large trees over small trees. 5 _ 4 _. 0 2 4 6 8 10 12 INITIAL (INCHES) Figure 3.—Average growth of trees of varying initial and treatment. 5. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Miller, Richard E. cn; Pienaar, Leon V. (Leon Visser), 1936-; Pacific Northwest Forest and Range Experiment Station (Portland, Or. ). Portland, Or. : Pacific Northwest Forest and Range Experiment Station, U. S. Dept. of Agriculture, Forest Service
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