by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 357: 195-205. https://doi.org/10.1016/j.foreco.2015.08.003
We experimented three selection cutting patterns using different sizes of canopy opening, including single-tree (SIN, <100 m2 in area), hybrid single-tree and small groups of trees (HGR, 100–300 m2), hybrid single-tree and one larger gap (HGA, 700 m2), and an uncut control (CON) to regenerate tree species with a range of shade tolerance in a yellow birch (Betula alleghaniensis Britt.)–conifer stand, in Quebec, Canada. In this paper, we are presenting the 10-year effects on regeneration dynamics, seedbed coverage and light availability. During the six summers of monitoring, incoming solar radiation increased with canopy opening at a rate of 1.5, 3.9, 4.9 and 8.9 MJ/m2/day in microsites distinctive of the CON, SIN, HGR and HGA, respectively. Yellow birch established well in the three cutting patterns (including the matrix and openings), which contained 5–6 times more seedlings >5 cm in height than the control (2400/ha) after 10 years (all p < 0.001). Raspberry (Rubus idaeus L.) coverage was also higher in the three cuts (9–15% at year 10) than in the CON (<1%, p < 0.001). Pin cherry (Prunus pensylvanica L. f.) rapidly emerged independently from the cutting pattern (6000–7000 stems/ha, year 2), but had almost disappeared by year 10 (100–300 stems/ha). The 100–300 m2 groups and 700 m2 gap were favourable niches for yellow birch development. The gap, where light blade scarification was carried out in areas without conifer advance growth, was by far the worst niche for both red spruce and balsam fir (Abies balsamea [L.] Mill.). Therefore, the hybrid method that removed small groups of trees revealed the best option to maintain yellow birch and conifer species in the study site.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 401: 117-124. https://doi.org/10.1016/j.foreco.2017.07.012
In the absence of large-scale stand replacing disturbances, boreal forests can remain in the old-growth stage over time because of a dynamic equilibrium between small-scale mortality and regeneration processes. Although this gap paradigm has been a cornerstone of forest dynamics theory and practice for decades, evidence suggests that it could be disrupted, threatening the integrity and sustainability of continuous forest cover. The objective of this study was to evaluate the gap dynamics in old-growth boreal forests across a large landscape where deer populations currently exist at high abundance. We hypothesized that chronic deer browsing is limiting recruitment, particularly of palatable species, creating a demographic disequilibrium between canopy mortality and recruitment. We analysed understory regeneration density and distribution in relation to canopy gap size and condition on multiple sample areas within a 360 km2 area of old-growth balsam fir (Abies balsamea [L.] Miller) forest on Anticosti Island, Canada. The combined effect of accelerating canopy gap expansion and recruitment failure created a demographic disequilibrium important enough to cause a loss of forest cover. The forest is now at risk of shifting to alternative successional pathways that seem to be dependent upon gaps size. Rather than sustaining historic balsam fir composition, sucession in 57% of gap area was more susceptible to following a pathway leading toward white spruce parklands, while sucession in the other 43% was more susceptible to following a pathway toward white spruce forests. The occurrence of these novel ecosystems represents a threat to biodiversity and ecosystem services that are provided by preindustrial forests. Climate change could exacerbate these threats by allowing deer to go into as yet unoccupied boreal forests that are driven by gap dynamics. Novel management issues will arise in these boreal ecosystems and challenge forest managers. When the traditional approaches of identifying gaps will not work because the forest itself is losing cover, the method we have developed will help forest managers recognize demographic disequilibrium threatening maintenance of forests.
by Claire Morin | 30 January 2019
Published in Forests 9(3): 140. https://doi.org/10.3390/f9030140
This study aims to understand the phenotypic and genotypic correlations among wood anatomical, physical, and mechanical properties of hybrid poplar clones. Samples were taken from seven clones grown on three sites in Southern Quebec, Canada. Five trees per clone were randomly sampled from each site to measure anatomical (fiber length, fiber proportion, vessel proportion, fiber wall thickness, tension wood), physical (basic density, volumetric, longitudinal, tangential, and radial shrinkage), and mechanical wood properties (flexural modulus of elasticity (MOE), modulus of rupture (MOR), ultimate crushing strength parallel to the grain). The observed phenotypic and genotypic correlations between these wood properties were moderate to strong, except for fiber length and vessel proportion. Genotypic correlations for all wood properties were higher than for corresponding phenotypic correlations. Furthermore, fiber length showed weak correlations, whereas, vessel proportion showed strongly negative correlations with all other properties. Strong correlations were also found among fiber proportion, fiber wall thickness, basic density, and mechanical properties. Furthermore, results from this study show close genotypic and phenotypic correlations between fiber proportion, fiber wall thickness, and wood density, which consequently affect the mechanical performance of wood products. These findings indicate that there is a substantial opportunity to improve wood quality by selecting several wood properties for different end uses.
by Marie-Claude Boileau | 30 January 2019
Published in Forestry 1-13. https://doi.org/10.1093/forestry/cpx043
Northern hardwoods are an ecologically and economically important forest type in eastern North America. Historically, the hardwood supply came from old-growth forests dominated by large-diameter trees. Unfortunately, the repeated removal of high-quality trees has substantially degraded hardwood forests and reduced the profitability of the primary manufacturing sector. In this context, forest managers need tools to guide silvicultural investment decisions and to estimate pre-harvest stand value based on forest inventories. The objective of this study was to evaluate the performance of classification systems and measured variables used at the tree level to predict sawn product volumes of sugar maple (Acer saccharum Marsh.), yellow birch (Betula alleghaniensis Britton) and American beech (Fagus grandifolia Ehrh.). We developed statistical models to estimate the volume of lumber products, pulpwood, sawdust and residues based on tree DBH, species, tree grades in different combinations and tree height. Results show that the tree grade variable increased the explained variation in product volumes. As expected, the accuracy of product volumes estimation, based on root mean square error (RMSE), was poor for an individual tree, but improved as the number of trees increased.
by Marie-Claude Boileau | 30 January 2019
Published in Soil Biology and Biochemistry 116: 203-212. https://doi.org/10.1016/j.soilbio.2017.10.018
Under a warming climate, the boreal forest could become one of the largest terrestrial net CO2 sources, as increasing disturbances and soil organic matter decomposition rates (heterotrophic respiration, Rh) could offset net primary production. Since soil represents the boreal forest’s largest C pool, it is critical of correctly predicting future changes in Rh, as well as its sensitivity to temperature (Q10 of Rh). We simulated a soil warming by transplanting soil cores from boreal balsam fir (Abies balsamea, BF) and black spruce (Picea mariana, BS) stands to a more southern Eastern hemlock stand (Tsuga canadensis, EH). We measured Rh and soil properties over 3 years, from June to October. Over three snow-free seasons, soil temperature (first 10 cm, including the FH organic layers) and Rh increased for BF (+3.2 °C, +60% of Rh) and BS cores (+2.3 °C, +27% of Rh). Microbial C concentration decreased by 54–73% in the FH layers of warmed and control cores relative to initial values, despite unchanged chemically labile C, probably due to excised roots and mycorrhizal hyphae. This suggests a possible underestimation of Rh during the experiment. In BF soils only, the increase in Rh was accompanied by an increase in its sensitivity to temperature. Under a +5 °C soil warming, mean predicted Rh of BF soils would increase by 83% rather than by 56%. Relative to BS soils, such increase in sensitivity could be partly due to a higher fraction of chemically labile C (+52%) in the FH layers and a higher mean warming effect. It suggests that for BF forest soils, predicting decomposition rates for a warmer climate based on current temperature sensitivities could be inadequate. However, longer-term studies are needed to see if this increase in Q10 of Rh for BF soils would be maintained for longer periods.
