Wildfire has historically been the major cause of stand initiation in the boreal forest, shaping species diversity, successional and ecosystem processes. Clearcut harvesting may differ from fire in its effects on soil and vegetation processes and thus may cause long-term changes in stand productivity or biodiversity. This study compared the soil properties of mesic black spruce (Picea mariana) stands burned 2, 14, 21 yr prior to sampling, with stands clearcut within ±3 yr of each wildfire and recently undisturbed control stands. The forest floor (FH) and mineral soil (0-10 cm) were sampled volumetrically, air dried and analysed for pH, organic carbon content, available P, Ca, Mg, and K, mineralizable N and nitrification. Forest floors were also digested and analysed for total N, P, K, Ca and Mg. Significant differences between disturbed and control stands were observed in all study areas, with disturbance effects generally decreasing with time since disturbance. Burned stands generally had forest floors with thinner humus layers, lower mass of organic carbon, higher pH, and higher concentrations of total and available nutrients than in either clearcut or control stands. Significant losses in the total mass of N and K in the forest floor were observed in the youngest burned stands as well as a pulse of extractable P that was at least four times higher than cut or control stands in any other treatment or study area. The forest floor of cut stands had greater mass of organic matter and total nutrients, and higher levels of potentially mineralizable N than either fire or control stands. No significant nutrient loss was observed following clearcut harvesting in any study area. Overall, this study suggested that clearcut harvesting can result in changes to the status of soil nutrients that are different from those produced by wildfire. Further study is necessary to determine whether these differences have significant effects on the long-term productivity or biodiversity of the boreal forest. Key words: Fire, clearcutting, boreal forest, nutrients, Quebec
Structural dynamics at boreal forest edges created by a spruce budworm outbreak