Subproject Summary

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Introduction:

In response to the need for long-term information on the impact of brushing activities, the Mackay River herbicide trial (SX85702C) was selected for remeasurement. Field surveys during the summer of 1994 and the spring of 1995 suggested that although it had been approximately 9 years since treatment and technically the trial had been abandoned, the trial plots had not been compromised and were intact.

Objectives:

• Original objective: To compare the effectiveness of 2,4-D amine (Forestamine®), 2,4-D ester (For-ester®), glyphosate (Roundup®), and a manual brushing treatment for reducing vegetation competition and releasing crop trees.
• Remeasurement in 1995: To determine the long-term treatment impacts (9 years post-treatment) on spruce seedling growth and vigor, stocking levels, and the cover and height of non-crop vegetation.

Treatments:

Layout:

• The trial used an incomplete block design (IBD consisting of five treatments replicated three times for a total of 15 treatment plots
• Plots were situated across the entire cutblock grouped into three blocks with an additional single plot (O) on its own
• Two of the 2,4-D amine treatment plots were found in one block but were absent in the other two blocks
• Treatment plots were 0.3 ha (60 m X 50 m), and included a 5-m herbicide-free buffer zone inside the perimeter
• During 1986 and 1987, 20 seedling-centered subplots were established within each plot to assess the size and vigour of spruce seedlings and the height and condition of four target species: Lonicera involucrata (black twinberry), Alnus viridis (Sitka alder), Sambucus racemosa (elderberry), and Epilobium angustifolium (fireweed)
• Herbicides were applied by backpack sprayer on August 7, 1986
• Manual cutting with brush saws took place on August 19, 1986

Sites:

1. SX 85702 - C Mackay River Site

Major Findings:

Early reported results (Newsome 1987, 1988) showed that the glyphosate treatment had reduced vegetation cover significantly; however, significant seedling damage was also incurred, resulting in a net decrease in seedling height and root collar diameter in comparison to the control. Glyphosate seedling damage may be an indication that the treatment was applied prior to cessation of spruce bud activity.

In 1995, the surviving spruce seedlings from the glyphosate treatment plots were larger overall than seedlings from any other treatment (Table 1.). Between 1989 and 1995, 2-year spruce height growth was significantly greater in the glyphosate treatment seedlings than similar height growth from any of the other treatments (Figure 1.).

On the basis of the 1995 assessment, it can be concluded that the 1986 glyphosate treatment resulted in a statistically significant improvement in seedling growth over all the other treatments.

It is important to note that the interpretation of results from a single study are applicable to that site only and that repeated studies located at different sites are necessary to increase the confidence in generalizing results. Continued monitoring and research into crop tree and vegetation response to operational treatments across a variety of sites is essential to improving our understanding of the long-term effects of forest vegetation management practices.

References and Publications (Click on the Highlighted Reference to Obtain an Electronic Copy in PDF Form):

Harper, G.J. 1997. Mackay river herbicide trial: conifer response to 9 years post-treatment. Research Report #11. B.C. Min. For., Research Branch, Victoria.

Newsome, G. 1987. Establishment report for Mackay Herbicide Trial - SX Trial No. 85702c. B.C. Min. For., Cariboo Forest Region, Horsefly Forest District (Unpub. rep.)

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Last Updated: May 29, 1998.