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Effect of alternative site preparation treatments on soil chemistry, physical properties, climate and seedling growth on a mesic site in the northern interior of British Columbia Yole, D.

Abstract

The influence of four commonly used site preparation methods (disc trenching, pile-and-burn, broadcast burn, no treatment) on soil microclimate, soil nutrients, bulk density, and early survival and growth of hybrid interior spruce (Picea glauca [Moench] Voss x engelmannii Parry ex. Engelm.) and lodgepole pine (Pinus contorta Dougl. ex. Loud.) seedlings were examined in plots established in the Engelmann Spruce - Sub alpine Fir (ESSF) zone in the northwest interior of British Columbia. Soil moisture was monitored in 13 potentially plantable microsite types at weekly intervals over the first two growing seasons after site preparation. Although growing season soil moisture in 1994 was significantly effected by the microsite types under study, soil moisture was not believed limiting to seedling growth in any microsite studied and soils did not reach slightly to moderately dry conditions (> 2 bars tension) until late July, and only in three microsites, disc trench berm, disc trench hinge, and pile-and-burn-scalp (mineral soil exposed). Soil and air temperature were strongly affected by the four site preparation treatments and nine microsites studied, particularly in early spring periods between mid-May and mid-June. Soils (10-cm depth) warmed sooner, and for longer duration, in treatments which promoted soil drainage. Treatments which removed or incorporated insulating forest floor layers resulted in greater cumulative hours of soil temperature greater than 8°C in early spring periods, giving a distinct growth advantage over planting sites having intact forest floors. Untreated soils (slash left) were consistently colder for longer periods during the growing season. Broadcast burning decreased the frequency of frost events 20 cm above the ground surface during the 1994 growing season by 43 and 121%, relative to pile-and-burn and no treatment plots, respectively. Site preparation had strong effects on coarse fragment free bulk density of near surface (2-7 cm) and rooting zone (0-20 cm) layers one season after treatment. The coarse fragment free bulk density of the disc trench and hinge microsites 0-20 cm layer were 50 and 24% less, respectively, as compared to pre-treatment density. The disc trench berm and hinge microsites had significantly (p

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