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White Spruce Responses to Mechanical Site Preparation, Chemical Site Preparation, and Post-planting Vegetation Control over Three Decades in the Boreal White and Black Spruce Zone of British Columbia

Author(s) or contact(s): R.A. Powelson, J.L. Heineman, L. Bedford, J. McClarnon, A. Nemec, and J.O. Boateng
Source: Forests, Lands, and NR Operations
Subject: Chemical Site Preparation, Mechanical Site Preparation, Prescribed Fire, Site Preparation, Vegetation Control
Series: Technical Report
Other details:  Published 2016. Hardcopy is available.


Site preparation is used to facilitate plantation establishment throughout the Boreal White and Black Spruce (BWBS) zone in northern British Columbia, where mechanical, burning, chemical, or manual techniques have been used on 88% of sites that were harvested and planted to white spruce between 1980 and 2014. Between 1984 and 1988, experiments to examine the Effectiveness of mechanical site preparation, chemical site preparation, and post-planting vegetation control for relieving constraints to the establishment and juvenile growth of white spruce (Picea glauca) were established on three Moist Warm Boreal White and Black Spruce (BWBSmw) sites that had well-developed backlog vegetation. In the Wonowon experiment, bareroot spruce was planted into site preparation treatments that had been applied through a well-developed layer of bluejoint-dominated (Calamagrostis canadensis) vegetation. The other two sites (Inga Lake and Iron Creek) also supported well-established plant communities, but vegetation was sheared prior to installation of the experimental treatments, and container rather than bareroot stock was planted. Following site preparation, dense vegetation again developed at these two sites; at Inga Lake, it was dominated by willow and green alder, with scattered patches of aspen, while at Iron Creek, it was dominated by aspen and balsam poplar. Mechanical site preparation treatments examined in the three experiments included mounding, plowing, mixing, trenching, and scarification. At each of the three sites, a glyphosate treatment to reduce vegetation abundance was also included; at Iron Creek, glyphosate was applied as chemical site preparation, while at Inga Lake and Wonowon, it was applied as a post-planting vegetation control treatment. Glyphosate efficacy was low at Inga Lake, and follow-up manual cutting treatments were conducted to approximate a high-efficacy glyphosate treatment. In this report, we present results to age 25 from the Inga Lake and Wonowon studies and to age 26 from the Iron Creek study. Stand-level results for the mounding and untreated control treatments at Wonowon extend to age 29.

The results from these long-term experiments are most applicable to situations where there is a need to establish white spruce on sites with well-developed vegetation communities; however, these are now relatively rare in northern British Columbia because most of the backlog area has been rehabilitated. Nonetheless, the results from these long-term experiments are of interest because they examine a broader range of techniques than are currently in use. We anticipate that the data will be useful for calibrating growth and yield modelling tools as their sophistication increases to include the ability to model spruce growth in overtopped and mixedwood stands.

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Updated June 23, 2017