Results of the delay in the application of mechanical release in white and black spruce plantations in an early reforestation scenario

Vegetation management is required so that plantations present expected yields, but its impacts depend on the time of application. Our objective was to evaluate the effect, after 15-20 years, of delaying the application of a mechanical release treatment in Picea glauca and Picea mariana plantations, relative to the timing prescribed based on operational guidelines in Quebec (Canada). We used three experimental sites established following an early planting scenario that comprised the following treatments: i) control, no release; ii) mechanical release applied during the required year with motor-manual brushsaws; iii) mechanical release applied one year after the required year; and, iv) mechanical release two years after the required year. Our results show that, under an early planting scenario that includes a cleaning treatment at the sapling stage, there is no significant impact on plantation growth to delay the mechanical release for up to two years compared to the required year. This operational window should be used to ensure that vegetation management treatments are performed; omitting release treatments at the seedling stage has a marked negative effect on tree and stand productivity. Mechanical release indeed increased tree height, diameter, and stand total basal area.