Root system development of 12-year-old white spruce ( Picea glauca (Moench) Voss) on a mounded subhygric-mesic site in northern interior British Columbia

Abstract

On a silt-loam soil in the boreal white and black spruce (BWBS) zone in northern interior B.C., 50 root systems of 12-year-old planted white spruce ( Picea glauca (Moench) Voss) seedlings were excavated; 25 from mounds (14 cm of mineral soil over inverted organic matter) and 25 from untreated ground. Diameter, depth, and substrate of main structural roots were assessed at 10 cm intervals from the stem. The total number of roots and the aggregate cross-sectional root area (CSA) exiting the mound or a 50-cm control radius in untreated ground were also determined. Seedlings on mounds had well-developed root systems that were equally as symmetric as those in untreated ground. Roots extended well beyond the mound, excepting those few that were surrounded by saturated soil conditions. Mound seedlings had more, and thicker, main lateral roots than seedlings in untreated ground. CSA of mound seedlings was approximately five times greater than for seedlings in untreated ground, and the total number of roots was 2.5 times greater. Beyond the mound, depth and substrate of main lateral roots was similar to that of seedlings in untreated ground. It was concluded that the potential for long-term mechanical stability of white spruce on such mounds would be no less than that of seedlings planted without site preparation.