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 Claire Morin | 30 January 2019
Published in Forest Ecology and Management 323:148-157. http://dx.doi.org/10.1016/j.foreco.2014.03.015
Stratified mixtures of pioneer hardwoods sheltering shade-tolerant conifers are commonly encountered in the southern boreal forest. We used two-step shelterwood cutting to release conifer advance growth and limit trembling aspen (Populus tremuloides Michx.) development in a stratified mixed aspen–conifer stand in Quebec, Canada. This paper presents 10-year regeneration dynamics after the establishment cut applied with different cutting intensities (0%, 35%, 50%, 65%, and 100% basal area removal). Aspen suckering was proportional to cutting intensity (p < 0.001) and its survival was limited under all four densities of residual cover. After 10 years, aspen density was <600 stems/ha in the 0%, 35%, and 50% cuts, 1600 stems/ha in the 65% cut and 4700 stems/ha in the clearcut. Adequate protection of balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea glauca (Moench) Voss and Picea mariana (Mill.) BSP) advance regeneration strongly contributed to limiting aspen development. The release treatment affected conifer sapling height growth, stem diameter, crown length growth and live crown ratio. Generally, the growth reaction to canopy removal was better in the clearcut than in partial cuts. Balsam fir response was good in the two initial height classes studied (130–300 and 301–500 cm), but a significant spruce response occurred only in the smallest class. The final cut will be necessary to assess the overall effect of two-step shelterwood cutting on species composition and growth of the new cohort.
by Claire Morin | 30 January 2019
Published in New Forests 44: 827-847. https://doi.org/10.1007/s11056-013-9368-6
In arid zones, the use of compost for plant production in forest nurseries is hindered by a lack of water. The main objectives of this study were
(1) to evaluate the physical stability of composts produced from shredded branches of Acacia cyanophylla and A. cyclops subjected to a repeated drying and wetting cycles, similar to those used at the operational scale in nurseries in arid regions and to compare these composts with a standard peat-vermiculite (PV) substrate;
(2) to identify the relevant substrate physical variables that correlate with seedling growth.
Carob (Ceratonia siliqua L.) was cultivated during a production cycle of 27 weeks in a completely randomized block experiment. Substrate physical variables were measured at the beginning, middle and end of the experiment. Seedling growth variables were evaluated over the course of the production cycle, while gas exchange and water-relation variables were measured during a wetting and drying cycle at the end of the experiment. All three substrates produced vigorous seedlings with well-developed root systems that colonized the entire root plug. The growth of seedlings produced in the PV substrate was better than those grown in the compost-based substrates. No significant differences in gas exchange capacities and water relation variables were observed among the three substrates at the end of experiment with the exception of net photosynthesis, which was higher for the PV substrate at high substrate matric potential. Excessive drainage was negatively correlated with growth variables while water availability in the early growth phase and air porosity towards the end of experiment were positively correlated. Performance of the two composts could be increased by improving their initial structure and stability and by adjusting the irrigation regime.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 307: 333-340. https://doi.org/10.1016/j.foreco.2013.07.031
Using planted trees to restore the attributes of natural forest is especially challenging when disturbances are still effective. Chronic browsing by large herbivores can act as such a chronic disturbance curtailing natural regeneration and potentially altering successional trajectory of forest. In the context of herbivore overabundance encountered in many regions of the world, plantation strategies must thus address both the top-down pressure exerted by consumers on planted trees and the bottom-up control related to competition for resources. In this paper, we explore whether selection of competition-adapted balsam fir (Abies balsamea L.) seedling stock types (small, 110 cm3 container; medium; 200 cm3; or large, 350 cm3) could be used together with the management of white-tailed deer (Odocoileus virginianus) populations in order to lower the effect of local competition as well as minimizing browsing on seedlings. When the top-down pressure from herbivores is low or absent, we hypothesize that height and diameter growth as well as survival will be proportional to the initial size and biomass of seedlings. Inversely, in plantations exposed to deer, the apparency hypothesis predicts that herbivores are most likely to feed on taller, more obvious seedlings. Overall, we predict that medium stock size seedlings will outperform small and larger ones as they offer the best size compromise to withstand competition while maintaining a minimum level of apparency in the establishment phase. After 3 growing seasons, the height and diameter of medium stock size seedlings (48.6 ± 0.7 cm and 1.06 ± 0.05 cm, respectively) were similar to large ones (51.7 ± 1.1 cm, p = 0.12 and, 1.22 ± 0.05 cm, p = 0.07) that had been almost twice their biomass at the onset of plantation. The overall browsing occurrence was under 10% for all stock types exposed to browsing, yet the relative risk of being browsed increased by almost 20% for seedlings 30 cm vs. 60 cm at the end of the previous growing season. Mortality rate was unrelated to the browsing regime (p = 0.14) but overall, medium stock seedlings performed slightly better (2.9 ± 0.3%) than both small (7.0 ± 0.2%, p = 0.10) and large ones (10.5 ± 0.4%, p = 0.03). Based on the prominent effect of bottom-up control over top-down control in our experimental plantation, we conclude that choosing a size-adapted stock can optimize the cost of the restoration scheme following herbivore population reduction.
by Marie-Claude Boileau | 30 January 2019
Published in Forests 4: 613-631. https://doi.org/10.3390/f4030613
Sustainable management of boreal ecosystems involves the establishment of vigorous tree regeneration after harvest. However, two groups of understory plants influence regeneration success in eastern boreal Canada. Ericaceous shrubs are recognized to rapidly dominate susceptible boreal sites after harvest. Such dominance reduces recruitment and causes stagnant conifer growth, lasting decades on some sites. Additionally, peat accumulation due to Sphagnum growth after harvest forces the roots of regenerating conifers out of the relatively nutrient rich and warm mineral soil into the relatively nutrient poor and cool organic layer, with drastic effects on growth. Shifts from once productive black spruce forests to ericaceous heaths or paludified forests affect forest productivity and biodiversity. Under natural disturbance dynamics, fires severe enough to substantially reduce the organic layer thickness and affect ground cover species are required to establish a productive regeneration layer on such sites. We succinctly review how understory vegetation influences black spruce ecosystem dynamics in eastern boreal Canada, and present a multi-scale research model to understand, limit the loss and restore productive and diverse ecosystems in this region. Our model integrates knowledge of plant-level mechanisms in the development of silvicultural tools to sustain productivity. Fundamental knowledge is integrated at stand, landscape, regional and provincial levels to understand the distribution and dynamics of ericaceous shrubs and paludification processes and to support tactical and strategic forest management. The model can be adapted and applied to other natural resource management problems, in other biomes.
