Releasing conifers from the competition effects of aspen (Populus tremuloides Michx.) is a key focus of plantation management in sub-boreal and boreal forests, often at considerable cost. However, other factors affect early plantation performance. This study investigates the relative influence of aspen competition and soil factors on the performance of planted lodgepole pine (Pinus contorta Dougl. ex Loud.) and hybrid white spruce (Picea glauca [Moench] Voss ×
engelmannii Parry ex Engelm.) in north-central British Columbia. Plots were established across a gradient of natural aspen competition levels that resulted from a test of aspen control treatments at one site. Within these plots, 240 of each of the target conifer species were measured and their immediate soil and vegetative environment quantified. Regression trees and regression analysis were used to examine the importance of aspen competition relative to other factors in determining target conifer size. Soil factors generally provided the best partitioning of height growth differences for lodgepole pine and hybrid white spruce, whereas a mix of vegetation competition and soil factors provided the best partitioning of diameter growth differences. Regression models accounted for 19-28% of spruce size and 24-33% of lodgepole pine size. The single variable explaining the most variability in lodgepole pine size was aspen competition, whereas it was humus depth for hybrid white spruce. Practices should be altered to alleviate soil-induced growth reductions, particularly for hybrid white spruce.
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Updated March 06, 2007