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 Claire Morin | 30 January 2019
Published in The Forestry Chronicle 92(2): 221-231. https://doi.org/10.5558/tfc2016-041
Scarification contributes to creating planting microsites for reforestation by mixing organic matter (OM) with the upper layers of mineral soil. However, on some boreal sites characterized by a thick humus layer and dominated by ericaceous shrubs, competition seems to limit the benefits of scarification. A potential solution would be to remove OM completely through scalping. The objective of our study was to compare the short-term effects of scarification and scalping on the growth of Picea mariana and Pinus banksiana on such sites. After three growing seasons, we explored the relationships between seedling growth, groups of competing vegetation species, planting depth and distance to the nearest OM accumulation. The two treatments had similar effects on these variables. Growth on plots subjected to scalping was independent from the distance to OM. Planting depth had a nil or positive effect on seedling growth. Pinus seedlings largely outgrew Picea seedlings. However, the lack of short-term difference between scarification and scalping must be interpreted with caution, given the potential mid- and long-term effects of OM exportation on soil fertility, erosion and seedling nutrition.
by Claire Morin | 30 January 2019
Published in Ecology 96(6): 1480-1491 http://dx.doi.org/10.1890/13-2366.1
Climate change is altering insect disturbance regimes via temperature-mediated phenological changes and trophic interactions among host trees, herbivorous insects and their natural enemies in boreal forests. Range expansion and increase in outbreak severity of forest insects are occurring in Europe and North America. The degree to which northern forest ecosystems are resilient to novel disturbance regimes will have direct consequences for the provisioning of goods and services from these forests and on long-term forest management planning. Among major ecological disturbance agents in the boreal forests of North America is a tortricid moth, the eastern spruce budworm, which defoliates fir (Abies spp.) and spruce (Picea spp.). Northern expansion of this defoliator in eastern North America and climate-induced narrowing of the phenological mismatch between the insect and its secondary host, black spruce (Picea mariana), may permit greater defoliation and mortality in extensive northern black spruce forests. Although spruce budworm outbreak centers have appeared in the boreal black spruce zone historically, defoliation and mortality were minor. Potential increases in outbreak severity and tree mortality raise concerns about the future state of this northern ecosystem. Severe spruce budworm outbreaks could decrease stand productivity compared with their occurrence in more diverse, southern balsam fir forest landscapes that have coevolved with outbreaks. Furthermore, depending on the proportion of balsam fir and deciduous species present and fire recurrence, changes in regeneration patterns and in nutrient cycling could alter ecosystem dynamics and replace black spruce by more productive mixed-wood forest, or by less productive ericaceous shrublands. Long-term monitoring, manipulative experiments and process modeling of climate-induced phenological changes on herbivorous insect pests, their host tree species and natural enemies in northern forests are therefore crucial to predicting species range shifts and assessing ecological and economic impacts.
by Marie-Claude Boileau | 30 January 2019
Published in PLOS ONE 10(8): e0136674. https://doi.org/10.1371/journal.pone.0136674
Silvicultural restoration measures have been implemented in the northern hardwoods forests of southern Quebec, Canada, but their financial applicability is often hampered by the depleted state of the resource. To help identify sites most suited for the production of high quality timber, where the potential return on silvicultural investments should be the highest, this study assessed the impact of stand and site characteristics on timber quality in sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britt.). For this purpose, lumber value recovery (LVR), an estimate of the summed value of boards contained in a unit volume of round wood, was used as an indicator of timber quality. Predictions of LVR were made for yellow birch and sugar maple trees contained in a network of more than 22000 temporary sample plots across the Province. Next, stand-level variables were selected and models to predict LVR were built using the boosted regression trees method. Finally, the occurrence of spatial clusters was verified by a hotspot analysis. Results showed that in both species LVR was positively correlated with the stand age and structural diversity index, and negatively correlated with the number of merchantable stems. Yellow birch had higher LVR in areas with shallower soils, whereas sugar maple had higher LVR in regions with deeper soils. The hotspot analysis indicated that clusters of high and low LVR exist across the province for both species. Although it remains uncertain to what extent the variability of LVR may result from variations in past management practices or in inherent site quality, we argue that efforts to produce high quality timber should be prioritized in sites where LVR is predicted to be the highest.
