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