Mounding in the Sub-boreal Spruce Zone of west-central British Columbia: 8-year results

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Results are presented from two site preparation trials involving mounding on a moist to wet site with a medium soil nutrient regime (5–6/C) located in a lower slope to toe of slope position and on a near-level area upslope from the first site with medium soil moisture and nutrient regimes (4/C). Both trials compared the performance of long-rooted hybrid white spruce (Picea glauca × P. engelmannii [Parry ex Engelm.]) (Sxw) container stock (PSB 323) to that of a standard-sized stock (PSB 313) planted in inverted mounds and untreated spots. The trial on the first site also tested the effectiveness of two mound capping depths and of planting the 313 stock to two different depths in mounded spots. After eight seasons, there were no significant differences between 313s and 323s in terms of height growth or proportions of free growing trees. Although diameter growth was significantly greater among 323s in mounds compared to 313s this relatively small difference is unlikely to justify the higher cost of the larger stock. Height and diameter growth among 313s were 17 and 22% greater, respectively, for trees planted in mounds with 20 cm of capping compared to 12 cm of capping. Deep-planting in mounds consistently resulted in slight increases in height growth and survival relative to planting to the standard depth, though differences were not statistically significant Rates of growth were substantially greater among trees planted in mounds compared with those in untreated spots.The greatest relative differences were noted on the first site where height growth among 313s was 43 to 74% greater in mounded treatments depending on planting depth and capping thickness, with similar improvements in diameter growth. Key words: Site preparation, mounding