by Audrey Verreault | 30 January 2019
Published in Frontiers in Plant Science 6: 877. https://doi.org/10.3389/fpls.2015.00877
The predicted climate warming and increased atmospheric inorganic nitrogen deposition are expected to have dramatic impacts on plant growth. However, the extent of these effects and their interactions remains unclear for boreal forest trees. The aim of this experiment was to investigate the effects of increased soil temperature and nitrogen (N) depositions on stem intra-annual growth of two mature stands of black spruce [Picea mariana (Mill.) BSP] in Québec, QC, Canada. During 2008–2013, the soil around mature trees was warmed up by 4°C with heating cables during the growing season and precipitations containing three times the current inorganic N concentration were added by frequent canopy applications. Xylem phenology and cell production were monitored weekly from April to October. The 6-year-long experiment performed in two sites at different altitude showed no substantial effect of warming and N-depositions on xylem phenological phases of cell enlargement, wall thickening and lignification. Cell production, in terms of number of tracheids along the radius, also did not differ significantly and followed the same patterns in control and treated trees. These findings allowed the hypothesis of a medium-term effect of soil warming and N depositions on the growth of mature black spruce to be rejected.
by Claire Morin | 30 January 2019
Published in Polymers & Polymer Composites 24(6): 387-394
The utilization of clays to enhance the water vapour barrier properties of polyethylene requires knowledge about factors associated with the constituents themselves. Hence, this paper presents combinations of two types of polyethylene and five different clays. Morphological, mechanical and thermal properties related to the water vapour permeability of clay/polyethylene composites were investigated. Although no evidence of clay exfoliation was observed according to morphological and spectral results, it was found that the enhanced water vapour barrier properties were linked to the clay aspect ratio, composites interface, polyethylene crystallinity and storage conditions. The best water vapour barrier properties were obtained by increasing polyethylene crystallinity with unmodified clay of high aspect ratio. Organoclays addition showed no improvement in barrier properties of polyethylene unless the interface was strongly compatibilized. Contrary to the results published elsewhere, clay addition brought about no mechanical improvements to polyethylene tested.
by Marie-Claude Boileau | 30 January 2019
Published in Forests 9(10): 588. https://doi.org/10.3390/f9100588
Many northern hardwood stands include several low-vigor trees as a result of past management. To restore these degraded stands, partial cuts are applied with partly validated tree classification systems that are based upon apparent stem defects. We sampled 214 sugar maple (Acer saccharum Marsh.) and 84 yellow birch (Betula alleghaniensis Britt.) trees from six sites covering the northern hardwood forest zone of the Province of Quebec, Canada. We evaluated their vigor with a four-class system, and quantified the growth efficiency index and several indices that were based solely upon radial growth. The growth efficiency index increased non-significantly with increasing tree vigor class. The five-year basal area increment (BAI-1-5) was significantly different between the lowest and highest tree vigor classes. Yet, temporal changes in BAI-1-5 helped classify correctly only 16% of high-vigor trees that became poorly vigorous 8–10 years later. Overall, these results suggest that the tree classification system is weakly related to actual tree vigor and its application likely generates few significant gains in future stand vigor. Modifying and simplifying the tree vigor system must be considered to facilitate the tree marking process that is required to improve the vigor of degraded stands.
by Marie-Claude Boileau | 30 January 2019
Published in Forestry 91(1): 62-72. https://doi.org/10.1093/forestry/cpy031
We used 11 silvicultural trials in forests dominated by sugar maple (Acer saccharum Marsh.) to compare the development of structural attributes between unmanaged stands and stands subjected to two selection cuttings. Results showed that managed stands had significantly lower amounts of large live and dead trees, lower downed coarse woody debris (CWD) volume and lower density of large trees with wildlife cavities compared to unmanaged stands. Despite these differences, both managed and unmanaged stands had sufficient amounts of large trees and large trees with wildlife cavities to maintain excavator bird habitat based on minimum target guidelines from the literature. In both managed and unmanaged stands, minimum target guidelines to emulate old-growth conditions were not met: at least 30 live trees ha−1 >49.0 cm in diameter at breast height, and at least 11 m3 ha−1 of downed CWD volume with large-end diameter >44.0 cm. We discuss management options to promote the development of structural attributes in managed, uneven-aged sugar maple stands.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 398(Suppl. C): 91-100. https://doi.org/10.1016/j.foreco.2017.04.042
Even-aged systems including clearcutting and its variants have been used for decades in North America for managing conifer-dominated stands with the goal to achieve sustainable wood production. Although clearcutting has been successfully applied in conifer-dominated stands of the boreal forest, it has proved maladapted in the temperate mixedwood forest where hardwood and shrub competition is more intense. Over time, regulated even-aged management has simplified the structure and composition of the temperate mixedwood forest which used to be dominated by late-successional stands with high conifer proportions. This study assesses alternative silvicultural systems inspired by natural dynamics for balsam fir (Abies balsamea [L.] Mill.) – yellow birch (Betula alleghaniensis Britton) stands growing in Québec, Eastern Canada. In absence of stand-replacing disturbances, spruce budworm outbreaks (Choristoneura fumiferana [Clem.]) and windthrow trigger regeneration phases through gap dynamics that result in multi-cohort, irregular stand structures. Here, we assess irregular shelterwood systems aiming at regenerating red spruce (Picea rubens Sarg.), balsam fir and yellow birch. In 2009, we established an experiment made of four randomized blocks comparing a gradient of treatments of increased cutting intensity: (i) uncut control (0% removal, 30m2/ha); (ii) continuous cover irregular shelterwood (19 m2/ha of residual basal area [RBA] at the first cut, 25–30 years intervals without final cut), (iii) extended irregular shelterwood (RBA 17 m2/ha, final cut at year 30), (iv) uniform regular shelterwood (RBA 15 m2/ha, final cut at year 10) and (v) clearcut (harvest of merchantable trees >9 cm DBH). We monitored light transmission, seedbed quality and lower vegetation (<3 m) during the first 5years postcut. Shelterwood treatments diversified both understory light and seedbed conditions, thereby increasing the array of available regeneration niches. Shade-tolerant red spruce and balsam fir established more successfully in the less intense irregular shelterwood treatment (continuous cover) and with a higher spruce: fir proportion. All cutting treatments increased seedling density >30 cm of mid-tolerant yellow birch. Interspecific competition dominated by pin cherry (Prunus pensylvanica L.f.) and red maple (Acer rubrum L.) was the main factor limiting conifer establishment and was more abundant in the clearcut. Maintaining a partial cover in shelterwood treatments successfully limited competition expansion while regenerating target species. Even if relatively short term, results show that irregular shelterwood systems could be a sound alternative to clearcutting for regenerating and maintaining the structure of late-successional balsam fir-yellow birch stands.
