Effects of soil compaction and chipped aspen residue on aspen regeneration and soil nutrients

The effects of soil compaction and depth of chipped aspen residue on aspen regeneration, plant community development, decomposition, and nutrient cycling were tested on an Orthic Gray Luvisol in the Lower Foothills of Alberta. Twenty-seven 100-m × 15-m plots were established in 1992. Three depths of chipped aspen residue (0, 1–5 cm and >10 cm) and three levels of compaction (no compaction, 6 and 16 skidder passes) were applied following whole-tree harvesting in 1993. Sixteen skidder passes and chip residue depths >10 cm resulted in reduced plant cover and aspen sucker densities for at least 2 yr following treatment. Nutrient concentrations of the chip residue and surface organic horizon (LFH) were similar for the three compaction treatments. The initial total nitrogen (N) concentration of the chipped aspen residue was 3.6 g kg−1. Ammonium (NH4+-N) concentrations in the LFH of the chip residue treatments, particularly at the >10-cm residue depth, were lower compared with the no-residue treatment. However, adequate N apparently was available to the aspen suckers and understory vegetation as the NH4+-N concentration remained higher than in the LFH before harvesting. Compaction and woody residue applications had only short-term (3 yr) effects on soil properties, plant community development and aspen suckering at this site when clear-cut harvesting was done in the fall with low soil moisture content. Key words: Ammonium, aspen regeneration, wood residue, compaction