, T. 2001. Impacts of clearcut harvesting and wildfire on soil nutrient status in the Quebec boreal forest. Can. J. Soil Sci. 81: 229-237. 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. Les feux irréprimés ont toujours été la principale cause du renouvellement des peuplements dans la forêt boréale. Ce sont eux qui commandent la diversité des espèces, la succession de ces dernières et les fonctionnement de l'écosystème. La coupe à blanc pourrait ne pas avoir les mêmes conséquences sur les processus du sol et de la végétation, et on pourrait se assister à des changements à long terme au niveau de la productivité ou de la diversité biologique du peuplement. Les auteurs ont comparé les propriétés du sol de peuplements mésiques d'épinettes noires (Picea mariana) ravagés par le feu 2, 14 et 21 ans avant l'échantillonnage à celles du sol de peuplements coupés à blanc plus ou moins trois ans avant les feux de forêt et de peuplements témoins intacts. Les auteurs ont prélevé des échantillons volumétriques de la couverture morte (CM) et du sol minéral (de 0 à 10 cm), les ont séchés à l'a...

The nonvascular and vascular plant composition of the early regenerating vegetation present following wildfires and clear-cut logging has been compared separately in three areas of the black spruce (Picea mariana (Mill.) BSP) - feathermoss (Pleurozium schreberi (Brid.) Mitt.)) forest of western and central Quebec. In each area, a detrended correspondence analysis successfully differentiated the burned and logged stands along the first ordination axis. This separation mainly resulted from the greater abundance of pioneer species or lichens after fire and the greater abundance of residual species after clear-cutting. Spearman's correlation coefficients were calculated to relate variables characterizing physical disturbance of the forest floor and general site conditions to the two first differentiating axes. Variables characterizing forest floor disturbance severity were strongly associated with the first ordination axis in two of the study areas but not in the third one. The interpretation of compositional differences in the light of plant reproductive strategies led to the identification of regeneration patterns that illustrated the influence of disturbance type and severity on post-disturbance vegetation composition. These results suggest that certain forestry practices such as careful logging with the protection of regeneration and soil, scarification, and prescribed burning may differ in their capability to address sustainable forest management issues.

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