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Introduction:

During 1994 and 1995, several vegetation management trials were evaluated (>5 years post-treatment) for the possibility of remeasurement to obtain long-term conifer response data. Candidate research trials were screened using published and unpublished reports, experimental design, field surveys, and communications with operational and research staff. Of those candidate trials, the Stewart Lake project in the Dawson Creek Forest District was chosen for remeasurement.

Objectives:

• To document and compare spruce seedling response to the three 1983 site preparation treatments 12 years after planting (Valpar® gridballs and winter-shearing, Roundup® and winter-shearing, and winter-shearing alone).
• To compare the number of stems per hectare of conifer and broadleaf species and of well-spaced and free-growing spruce seedlings (B.C. Ministry of Forests 1990) 12 years after three site preparation treatments (Velpar® gridballs and winter-shearing, Roundup® and winter-shearing, and winter-shearing alone).
• To document and compare vegetation development, species diversity, and forage use on the three site preparation treatment areas during the 1996 growing season.

Treatments:

Layout:

• Untreated buffer strips between the herbicide treatment areas were established (a minimum of 30 m wide)
• A three blocks (hexazinone, glyphosate, and the untreated control) were winter sheared (cleared) during the first week of December 1983 with D-7 and D-65 (Komatsu) crawlers equipped with angled dozer blades.
• The blades effectively sheared off vegetation and piled the debris without excessive soil disturbance because of the frozen soil conditions.
• Picea glauca (white spruce) seedlings (2 + 0 PSB 415) from seedlot no. 3962 were planted the following spring (May 1984).
• Two large demonstration plots for the hexazinone gridball treatment were separated by an untreated and unsheared buffer.
• A single control and a single glyphosate treatment area were also established.
• The hexazinone treatment area consisted of two plots of 100 X 150 m divided by a buffer of approximately 70 m.
• The glyphosate treatment area was approximately 100 X 250 m separated by an unsprayed and uncleared buffer 70 m wide.
• The uncleared buffers and other areas surrounding the plots were not planted.
• Figure 1. Enlargement of 1994 aerial photo of trial site (BCC 94011#178) (88k jpg).

Sites:

1. Stewart Lake Research Area

Major Findings:

Statistical analysis suggests that the spruce seedlings from the hexazinone and glyphosate treatments were not significantly different in height during the time period of 1985 to 1995 (Figure 2. (37k jpg)). The spruce seedlings from the herbicide treatments were clearly taller than the control treatment seedlings.

Figure 3. Representative photos of control, hexazinone, and glyphosate treatment areas on August 14, 1996. (74k, 64k, and 83k jpg)

Twelve years post-treatment, spruce height growth in the herbicide-treated areas continues to be significantly greater than in the control area. Similar long-term response of white spruce to weed control treatments has been reported by Sutton (1995) where "initial weed control was still exerting highly significant effects on performance of white spruce" after 28 years.

The spruce height:diameter ratio is significantly larger in the control area than in the herbicide treatment areas (Table 1. (63k jpg))

The glyphosate treatment has resulted in a significantly reduced broadleaf cover, with willow and birch the only broadleaf species present. Repeated ungulate browsing of the willow and birch has kept these species in dwarf form.

The hexazinone treatment has promoted the establishment of alder in clumps and patches. The alder has established in microsites where the clearing and hexazinone treatment created mineral soil or good seedbed conditions.

Bluejoint grass has the largest cover of all herbaceous species present (Figure 4.). Even within the understory of the control area, cover of this species was more than 35%, although it was significantly reduced from that found in the open hexazinone-treated area. No discernible differences in vegetation vigour and distribution were found.

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

Harper, G.J., L.J. Herring, and W.J. Hays-Byl. 1997. Conifer and Vegetation Response in the BWBSmw1 12 years after Mechanical and Herbicide Site Preparation Res. Br., B.C. Min. For., Victoria, B.C. Work Pap. 29/1997.

Herring, L.J. 1988. Performance of white spruce following an early glyphosate brushing and weeding treatment. Expert Committee on Weeds Research Report, Western Canada Section Meeting Nov. 29, 30 and Dec. 1, 1988. Winnipeg, Man. Vol. 3, p205.

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Last Updated: May 29, 1998.