Effects of timing of cleaning and residual density on regeneration of juvenile aspen stands

In the absence of chemical vegetative management tools, young regenerating trembling aspen (Populus tremuloides) is typically removed mechanically from sites intended for white spruce (Picea glauca) regeneration. In many cases the aspen vigorously re-suckers and re-sprouts after cutting all the stems. A field study was established to test whether the regeneration of aspen can be reduced by maintaining residual saplings and/or by the timing of cleaning. It was further tested how these treatments affect root carbohydrate reserves. Nine healthy, 10-year-old aspen stands were manually cleaned to three residual aspen densities (0, 500, and 1500 stems per hectare) at three times of the year (late summer, winter, and spring). Retaining residual aspen reduced regeneration by 23–39% relative to complete removal; however, the amount of regeneration was not affected by season. Height growth and leaf area was reduced in spring cleanings compared to late summer and winter and in both residual trees treatments compared to the complete removal. The vast majority of regeneration was from stump sprouting. Generally, as the residual density increased, regeneration decreased; however, regeneration after the first growing season was still too abundant for these treatments to be a viable option for density management of aspen. Maintaining residual stems reduced the root carbohydrate reserves in root associated with regeneration compared to reserves in roots associated with residual saplings or in the control plot. Only in the complete removal treatment did root reserves recover to control levels within one growing season.