by Claire Morin | 30 January 2019
Published in Canadian Journal of Forest Research 42: 1277-1288 https://doi.org/10.1139/x2012-055
Since plant growth in the boreal forest is often considered to be limited by low temperatures and low N availability and these variables are projected to increase due to climate warming and increased anthropogenic activities, it is important to understand whether and to what extent these disturbances may affect the growth of boreal trees. In this study, the hypotheses that wood phenology and anatomy were affected by increased soil temperatures and N depositions have been tested in two mature black spruce (Picea mariana (Mill.) BSP) stands at different altitudes in Quebec, Canada. For 3 years, soil temperature was increased by 4 °C during the first part of the growing season and precipitations containing three times the current N concentration were added in the field by frequent canopy applications. Soil warming resulted in earlier onsets of xylogenesis and interacted with N addition producing longer durations of xylogenesis for the treated trees. The effect of warming was especially marked in the phenology of roots, while wood production, in terms of number of tracheids, was not affected by the treatment. Xylem anatomy and soil and needle chemistry showed no effect of the treatments, except for an increase of cell wall thickness in earlywood of treated trees. This short-term experiment with black spruce suggested that previous fertilization studies that used large and unrealistic rates of N addition may have overestimated the impact of N depositions on boreal forest productivity.
by Claire Morin | 30 January 2019
Published in Tree Planters’ Notes 56(1): 35-46
A short-day (SD) treatment was applied to containerized 1+0 black spruce (Picea mariana [Mill.] B.S.P.) with the objective of increasing root mass and root-plug cohesion. The SD treatment resulted in the induction of bud formation, cessation of height growth, and significant increases in carbohydrate content (sucrose, pinitol, and starch), root nutrient contents, and root dry mass. Allometric models showed that given the same shoot mass, the average seedling grown under the SD treatment had 25 percent more root mass than those in the control treatment, which led to a significant improvement in root-plug cohesion. Seedling quality evaluation before delivery to the planting site showed that 91 percent of 1+0 black spruce seedlings subjected to SD treatments conformed to quality standards compared with 71 percent for those subjected to the control treatment. These results indicate that the use of an SD treatment may improve the profitability of forest nurseries by increasing the quality and quantity of shippable seedlings.
by Claire Morin | 30 January 2019
Published in International Journal of Plant & Soil Science 2(2): 155-189. https://doi.org/10.9734/IJPSS/2013/4233
Nitrogen is considered the most important element in plant nutrition and growth. However its role and availability for boreal forest conifers is still debated. Boreal conifers have adapted strategies to cope with the reduced availability of N. ECM fungi, associated with boreal conifer roots, increase soil exploration and N nutrition, especially where organic N predominates. Conifers usually take up ammonium at levels comparable to simple organic N, which probably grows in importance as organic matter accumulates with stand age, while estimates of nitrate uptake are generally lower. Conifers, especially slow growing species, may rely on internal N cycling to sustain the development of new tissues in spring. N increases photosynthesis and leaf area and thus increases growth and wood formation, leading to wider radial rings mostly because of increased earlywood production. N-depositions and disturbances (e.g. fire and harvest) may alter the soil Ncycle and affect boreal forest growth. N depositions are considered responsible for the increase in boreal forest growth during the last century. Intensive harvest and high Ndepositions may shift limitation from N to another element (e.g. P, K, and B). Climate change should affect the N cycle through complex mechanisms, including changes in the fire return interval, direct effects of warmer soils on N mineralization and stimulating plant growth modifying the balance between N stored in soils and in the living and dead (e.g. wood) biomass. Future research should try to improve our understanding of the possible outcomes of changes in disturbance regimes, N-depositions and climate, including the role of N fixation by mosses, canopy N uptake and the responses of conifers in relation to changes in microbial (symbiotic and not) communities.
by Marie-Claude Boileau | 30 January 2019
Published in New Forests 45: 875–891. https://doi.org/10.1007/s11056-014-9443-7
Planting stock selection is an integral part of plantation management, as forest nursery practices influence the physiological status of the seedlings and their capacity to cope with resource availability on different planting sites. We thus compared the 11th-year dimensions and survival of large white spruce (Picea glauca) and black spruce (P. mariana) seedlings produced as 2 + 2 bareroot or 2 + 0 container stock (cell volume of 350 cm3), used to reduce the need for competition control. Using complete split-block designs, we evaluated the seedling competitive potential and response to mechanical release on two sites of contrasting ecological fertility and vegetation dominance in Quebec, Canada. We found that large spruce seedlings can be successfully established on highcompetition sites in a context where chemical herbicides cannot be used. These stock types had a limited impact on survival and growth, and both stock responded similarly to mechanical vegetation control. In this context, the choice of stock type should prioritize the highest quality large seedling based on operational considerations such as availability and ease of transportation. Mechanical site preparation was not necessary to promote seedling growth and survival on these sub-boreal sites.
by Svetlana Savin | 30 January 2019
Published in Journal of Forestry 112(3): 276-286. http://dx.doi.org/10.5849/jof.13-035
We evaluated silvicultural scenarios for the rehabilitation of impoverished northern hardwood stands in Québec (Canada). The experiment comprises five treatments: a control, a hybrid single-tree and group selection (SC), two continuous cover irregular shelterwoods (CCIS) with respective residual basal areas (BAs) of 16 m2.ha-1 and 14 m2.ha-1, and an extended irregular shelterwood (EIS) with a residual BA of 14 m2.ha-1. American beech (Fagus grandifolia Ehrh) advance regeneration was removed with brush saws and the soil was mechanically scarified in all cutting treatments. Postcut values showed significant improvements of acceptable growing stock and a significant reduction of American beech; both effects were proportional to the intensity of removal. Simulated outcomes of the four scenarios were compared over a 120-year period. Results show that the EIS scenario should require a longer period to restore the desired uneven-aged stand structure; also, its harvests removed less BA of large-diameter trees than the SC scenario.
