A research trial was established in 1986 in the southern interior of British Columbia to study the effectiveness of glyphosate applied at 3 L/ha (1.07 kg ai/ha), glyphosate applied at 6 L/ha (2.14 kg ai/ha), and manual cutting to release naturally regenerated lodge pole pine seedlings and suppress the Dry Alder Complex. Pine seedlings and two target species (Sitka alder and fireweed) were assessed for the first 3 years, and again in the ninth year following treatment.
Within 2 years of treatment, stem diameter of seedlings in all treatments had increased significantly compared to the control, and this difference was maintained through year 9. There were no significant differences in height until 1995, by which time seedlings in all treatments were taller than in the control. There were no significant differences in seedling response among the three release treatments.
Manual cutting had the greatest effect on height and cover of Sitka alder for the duration of the study, the did not produce significantly larger lodgepole pine seedlings than the other treatments. That Sitka alder height reductions had no effect on pine growth suggests that competition for light was less important on this site than competition for soil resources (water and nutrients). Seedlings in plots treated with glyphosate at 6 L/ha tended to have the largest height and stem diameter in 1995, while growing among 15% cover of Sitka alder. This is consistent with earlier findings by Simard (1990), that a cover of Sitka alder (as much as 35%) may be beneficial to lodgepole pine seedlings instead of suppressing them.
None of these treatments were very effective at reducing fireweed height and cover, although the glyphosate treatments had a slight effect for 1-2 years.
FRDA Research Report 259 (1985 KB)
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Updated July 24, 2015