Forests, Lands and NR Operations

Responses of Hybrid White Spruce to Site Preparation in Wet and Very Wet Sub-Boreal Spruce subzones Over Three Decades  

TR109Author(s) or contact(s): L. Bedford, J.L. Heineman, J. McClarnon, R. A. Powelson, A. F. L. Nemec, T. Kaffanke, 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 2017. Hardcopy is available.


In 1984 and 1987, two experiments were initiated in wet and very wet Sub- Boreal Spruce biogeoclimatic units in north–central British Columbia to examine the effectiveness of different site preparation techniques in relieving constraints on hybrid white spruce (Picea engelmannii glauca) establishment.
The experiments were not replicates; however, mechanical mounding, patch scarification, and blade scarification treatments were included in both.

Responses were examined for bareroot spruce planting stock at the Upper Coalmine site in the Very Wet Cool Sub-Boreal Spruce subzone (SBSvk) and for container spruce planting stock at the Mackenzie site in the Finlay-Peace Wet Cool variant of the Sub-Boreal Spruce zone (SBSwk2). At the Mackenzie site, disc trenching and chemical site preparation treatments were also tested.

In both experiments, mounding was the only treatment that substantially improved survival and significantly increased spruce growth relative to the untreated controls. The other mechanical treatments (patch scarification, blade scarification, and disc trenching) that exposed mineral soil but did not
create raised microsites were ineffective, indicating that relieving cold, wet soil conditions was of primary importance at these sites. Due to its terrain, as well as to its lower meso-slope position, the Mackenzie site was also subject to frequent summer frosts; damage was highest in the chemical
site preparation treatment, probably because the herbicide completely eliminated overtopping vegetation that, in other treatments, is assumed to have provided some protection through the prevention of nighttime radiative heat loss. Damage from hares and white pine weevil was also common at the Mackenzie site; the former had the greatest effect in treatments that did not reduce vegetation abundance, and the latter predominantly affected trees in the mounding treatment that were least overtopped. The complexity of limiting factors observed in the Mackenzie experiment demonstrates the importance of correctly identifying the primary limiting factor to seedling establishment, as well as the difficulty in relieving multiple constraints that interact with each other.

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Updated October 26, 2007