Equations to estimate net basal area response of Douglas-fir to nitrogen fertilization in terms of initial stand attributes were developed, based on remeasurement data over a period of 9 years from 176 plots (0.05- 0.10 ha in size) of the British Columbia Forest Productivity Committee study. The data suggest that, in the slightly dry, nutrient-poor to medium sites in the CWHxm1 subzone on Vancouver Island, fertilizing immature Douglas-fir stands has several effects:
On the average, it results in a stand net basal area cumulative response of about 5% (2.0 m2/ha) in the unthinned stands, and about 7% (3.2 m2 /ha) in the thinned stands, after 9 years with a single application of 225 kg N/ha.
Doubling the fertilizer dosage from 225 kg N/ha to 450 kg N/ha on the average increased stand net basal area relative response 1.5-fold to about 11% in the thinned stands, but had no effect on the unthinned-stand response, after 9 years.
Net basal area annual response dissipates within 9 years in the unthinned stands, but persists after 9 years (probably as indirect response) in the thinned stands. The relationship of stand response to initial stand attributes could not be detected or was confounded by the association between the initial stand attributes. Note, however, that the range of site and stand conditions in the data was relatively small. The average values of the initial stand attributes were: total age (37 years), basal area (40 m2/ha), and site index (26 m at 50 years total age).
FRDA Research Report 097 (591 KB)
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Updated July 24, 2015