Black spruce (Picea mariana (Mill.) B.S.P.)-feathermoss forests are a common subtype of the northern boreal forests. These forests are associated with large accumulations of mor humus, which is regarded as an important source of nutrients, contributor to soil structure, moisture retention and vital to the long-term sustainability of these forests. Harvesting with protection of advance regeneration (CPRS) is currently used in northwestern Quebec as the method for sustainable management, which reduces soil compaction and protects advance regeneration, and genetic diversity. We examined the effects of CPRS on organic matter and advance regeneration 6 years after harvesting. During the summer of 2002, a humus classification based on observable field characteristics was developed and applied to six CPRS sites in the northern Abitibi claybelt region of Quebec. At each site 75 humus profiles were surveyed and classified by order and thickness of horizons present. Humus horizons were easily observed using morphological features, and master horizon classes were distinguished by their nutritional and biochemical attributes with differences occurring as a result of the natural process of decomposition. Individual humus horizon and total profile thickness was the variable that most affected profile nutrient mass. High forest floor disturbance was associated with shallow profile depth, resulting in low humus profile nutrient mass and low density advance regeneration. Lower forest floor disturbance resulted in deeper profiles associated with higher available nutrients in humus profiles and higher density of advance regeneration. These results suggest that disturbance caused by harvesting may reduce overall stand productivity in the short term due to the effect of low tree density and possibly in the long-term due to loss of nutrients.

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The effect of species, parent material, and stand age on nitrogen mineralization were examined during aerobic lab and field incubations. The experimental design consisted of 3 tree species (birch (Betula papyrifera Marsh.); poplar (Populus tremuloides Michx.); and conifers (Abies balsamea (L.) Mill. and Picea glauca (Moench) Voss.)); two parent materials (lacustrine clay and glacial till); and three stand ages (50, 75, and 124 years of age). The strongest determinant of nitrogen mineralization potential was species. The effects of parent material and stand age were variable. Total nitrogen, pH, and soil moisture also affected N mineralization. Nitrogen mineralization dynamics may be largely affected by annual changes in quality of organic matter or climate. Available nitrogen inherent in forest stands must be taken into consideration when replacing hardwood stands with softwoods, because eliminating stages of boreal mixedwood succession could have detrimental effects on available nitrogen and forest productivity in the long-term.

A comparison of the soil fertility and relationships between soil fertility and early regenerating vegetation were examined following clearcut harvesting and wildfire in the black spruce-feathermoss zone of west-central Quebec. During the summer of 1997, sampling was conducted in wildfires burnt 2, 14, and 21 years ago, stands clearcut within +/-3 years of each fire, and undisturbed control stands. At each site an estimation of vegetative cover of each species present and a volumetric sample of the forest floor (FH), and mineral soil (0--10 cm) were collected from at least 8 fire and cut sites and at least 4 control sites in each study area. The comparison between the soil fertility of stands clearcut and burnt suggested that important differences exist following these two disturbance types in the boreal forest. The forest floor of clearcut sites had greater dry mass, mass of total nutrients and mineralized N than fire or control sites, whereas fire sites generally had higher pH and concentrations of total nutrients than clearcut or control sites. Partitioning of the variance of the vegetation data between soil fertility and general site characteristic variables was carried out to evaluate the direct influence of post-disturbance soil fertility on the composition of regenerating vegetation. All explanatory variables accounted for 53.6% of the variance, of which 23.2% was exclusively attributed to soil fertility variables. Disturbance severity is suggested as an important factor, directly affecting the initial composition of the regenerating vegetation, and indirectly affecting soil fertility and stand productivity in the later stages of regeneration.

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