Using spot treatments to regenerate an intimate mixture of trembling aspen and white spruce in Alberta: Results at age 15

Abstract

Mixedwood stands, dominated by trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss), are an important fibre source in Canada’s boreal forest and provide a range of ecological services. We present results from a study established in 2002 to test a strategy for growing intimate, single cohort mixtures of these two species involving controlling woody and herbaceous vegetation within 2-m radius spots centered on the spruce planted at 5-m spacing. After 15 growing seasons spruce survival was high (74–90%) in the radial treatments with spruce DBH and height being intermediate between untreated spruce growing under a dense aspen canopy and spruce growing without aspen in the broadcast complete control treatment. Repeated browsing by snowshoe hare, associated with reduced height of spruce, lead to severe reductions in spruce survival and size in the untreated stand, which had an average of 24 500 stems/hectare of aspen at age 15. While spot treatment alone did not significantly affect aspen height or diameter at age 15, thinning of the aspen matrix at age 10 in spot treated stands resulted in increases in diameter growth of both aspen and spruce. Results indicate that radial spot herbicide treatments can effectively improve early survival and growth of white spruce through control of aspen, shrubs, herbs, and grasses and that adding precommercial thinning leads to additional increases in growth of both trembling aspen and white spruce.

Aspen and Spruce Densities Affect Tree Size, Future Stand Volume, and Aboveground Carbon Following Precommercial Thinning

“…Differentiation amongst treatments increased with measurement age for all variables. Reductions in aspen DBH with increasing aspen density and increases in DBH following thinning are consistent with results from many other studies [9,11,[23][24][25][26][27][32][33][34][35].…”

“…As observed in this study, other studies also demonstrate increases in spruce height and DBH following reductions in aspen density [9,11,26,27,35]. However, increases in spruce height growth may be delayed for a few years following thinning.…”