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-In Québec (Canada), the use of large planting stock is being applied in combination with scarification, since herbicide use is forbidden in public forest. Large containerized and bare-root stock of black spruce were planted on two sites located within the sub-boreal mixedwood region of eastern Québec. We analyzed data to detect main effects and interactions among scarification, competing vegetation and stock type on seedling growth and physiology during the first three growing seasons. Scarification did not improve seedling water relations, third-year height and ground-level diameter, and foliar nutrient concentration. After three years, the two stock types showed similar water relations and nutritional status but the large containerized seedlings performed slightly better than the large bare-root stock in terms of diameter and height growth. Competing vegetation greatly reduced seedling diameter, foliar-N concentration, compared to competition-free seedlings. We discuss results in relation with treatment effects on above-and belowground resource availability to newly planted conifers.

Conifer-regeneration failure is often observed on sites invaded by ericaceous shrubs. In northeastern Quebec, Canada, these sites are frequently characterized by dense Kalmia angustifolia L. – Rhododendron groenlandicum (Oeder) K.A. Kron & Judd cover. Such failures are potential consequences of nutrient limitation, allelopathy, or low soil temperatures. Conversion of productive forests into heaths poses a threat to the maintenance of forest productivity and biodiversity. We evaluated scarification, spot fertilization, and increased seedling foliar N concentration as treatments to promote planted black spruce (Picea mariana (Mill.) BSP) seedling survival and growth. We measured seedling, vegetation, and soil responses to the treatments for 5 years following planting. Scarification had positive impacts on seedling growth: the differences between scarified and unscarified plots increased over time, and double-pass scarification proved slightly more effective than a single-pass treatment. Responses to scarification were enhanced when seedlings were fertilized. A slow-release fertilizer with micronutrients proved slightly more effective than the 26N–12P–6K formulation; the latter also induced higher mortality than the former or no fertilizer. Gains due to increased N concentrations based on nursery practices were significant but short-lived. Our results demonstrate how silviculture and nursery practices can be used for resetting the secondary succession where ecosystem retrogression is observed following K. angustifolia – R. groenlandicum invasion.

-A study was established in 1993 to determine the response of four black spruce (Picea mariana) and white spruce (P. glauca) stock sizes on two sites located in Québec (Canada), each representing a different type of competing vegetation. At each site, a split-split-plot design with 15 to 17 replicates was used, in which the presence of competition (weedy and bare plots), seedling initial size, and spruce species were assigned respectively to the whole plot, the subplot, and the sub-subplot. Larger initial seedling size provided a greater competitive ability for light and had higher growth rates than the standard stock size for both species. Growth gains from combining plantation of large stock with vegetation control were multiplicative. Non-crop vegetation significantly lowered the seasonal profile of 10-cm depth soil temperature on both sites. This study shows that early release treatment is required on sites dominated by raspberry-hardwood competition complex and planting large spruce stock on such harsh competition sites will help reduce the need for repeated vegetation control. large seedling / competition / vegetation control / soil temperature / release treatment Résumé -Effet net de la végétation de compétition sur certaines conditions environnementales et sur la performance de quatre dimensions de plants d'épinette après huit ans. Une étude a été établie en 1993 afin de déterminer la performance de quatre dimensions de semis d'épinette noire (Picea mariana) et d'épinette blanche (P. glauca) mis en terre sur deux sites situés au Québec (Canada), chacun représentant un type de compétition. À chaque site d'étude, un dispositif en tiroirs subdivisés avec 15 et 17 répétitions a été utilisé, avec la présence de compétition, la dimension initiale des semis et l'espèce, assignées à la parcelle principale, la sous-parcelle et la sous sous-parcelle, respectivement. Les plants de fortes dimensions (PFD) ont reçu plus de lumière et ils affichaient une meilleure croissance que le plant de dimension standard. Les gains de croissance découlant de la combinaison d'une plantation de PFD avec contrôle de la compétition ont été multiplicatifs. La végétation de compétition a significativement abaissé le profil saisonnier de la température du sol mesurée à 10 cm de profondeur. Cette étude démontre qu'un dégagement hâtif est nécessaire sur les stations caractérisées par une forte compétition de framboisiers et de feuillus intolérants. De plus, sur ces mêmes stations, un reboisement avec des PFD devrait limiter le besoin de répéter les dégagements mécaniques. plant de fortes dimensions / compétition / gestion de la végétation / température du sol / dégagement mécanique

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Light threshold is suggested as a method for quantifying brush competition in black spruce (Piceamariana (Mill.) B.S.P) plantations and predicting losses in tree growth as measured by the relative growth rate (RGR). The severity of the competing vegetation (expressed in terms of density and height) around 300 planted tree seedlings, and the growth status of the seedlings (expressed in terms of total height and current height growth increment), were analyzed simultaneously with multivariate analysis of variance (MANOVA), with one level of light quantity (photosynthetically active radiation) reaching the upper one-half of the tree seedlings as the predictor variable. This study showed that it is possible to establish a competitive status based on light interception, thus allowing a grouping of seedlings with similar growth characteristics and severity of competition. Canonical analysis showed that 60% of full sunlight reaching the upper one half of spruce seedlings can be defined as a threshold to significantly discriminate between stressed and unstressed tree seedlings, based on the above-mentioned variables and also based on spruce basal stem diameter. For spruce total height, current height increment, and basal stem diameter, significant differences were found between plots above and below this threshold, averaging 18.5, 44.7, and 23.2%, respectively. Measuring the intensity of light reaching the upper one half of the spruce seedlings also significantly explains spruce relative growth rates, expressed in terms of height growth increment and basal stem diameter growth increment over the following two growing seasons. The light threshold used in the MANOVA and the ANOVA showed significant differences between plots above and below the threshold, averaging 70 and 58% for spruce height and basal stem diameter RGRs, respectively. Instead of measuring competing vegetation variables and relative height of a crop species to infer light interception, this study demonstrated that a direct measure of light attenuation at the tree seedling level can be used to assess the competitive status and predict losses in tree growth for the period of time required by the seedlings to emerge from the vegetation cover. Moreover, this study demonstrated that canonical relations, rather than linear relations, explain the pattern of competition for light between young spruce seedlings and brushlike vegetation. The light threshold suggested in this study has potential for assessing interspecific competition problems in young black spruce plantations and is proposed as a tool to support a containment strategy of vegetation management.