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.
by Claire Morin | 30 January 2019
Published in Forest Ecology and Management 430: 157-165. https://doi.org/10.1016/j.foreco.2018.08.007
Ecosystem based management in Québec is framed by reference conditions defining percentage of old-growth forest (>100-years-old) and forest composition characterizing pre-industrial forest landscapes. In the western spruce-moss bioclimatic subdomain (154 184 km2) a fire cycle estimated at 150 years was used to target that 49% of the landscape has to be composed of old-growth forest. Yet, this target was developed using past (19th–20th C.) climate and vegetation data and assume that environment and ecosystem processes are homogeneous for the entire western spruce-moss bioclimatic subdomain. The wide spatial and narrow temporal windows limit the application of reference conditions under ongoing climate change. Our aim was to classify current vegetation heterogeneity of the western spruce-moss subdomain into homogeneous zones and to study the long-term history of fire and vegetation within these zones. This approach will help to refine forest management targets that are based upon short-term records by providing a long-term perspective that is needed for the forests to be managed within their natural range of variability. Modern forest inventories data were used along with climate, physical variables, and natural and human disturbances to study the current vegetation-environment interactions among the western spruce-moss subdomain. We also used 18 published sedimentary pollen and charcoal series to reconstruct Holocene vegetation and Fire Return Intervals (FRI). Contemporary data revealed 4 zones with homogeneous interactions between vegetation and environment. Pollen analysis revealed three long-term vegetation paths: early successional species dominance, late to early species transition and late successional species dominance. These suggest that modern forest composition results from Holocene trajectories occurring within each zone. Holocene mean FRI (mFRI) ranged from 222 to 258 years across the subdomain, resulting in old-growth forests ranging between 64% and 68%, depending upon the zone. Paleoecological and contemporary results support that to make forest management more sustainable, current landscape heterogeneity that arises from millennial forest composition trajectories and fire cycle dynamics should be taken into account by down-scaling the previously established reference conditions.
by Claire Morin | 30 January 2019
Published in Journal of Biogeography 43(6): 1227-1241. https://doi.org/10.1111/jbi.12675
Aim : Tamarack (Larix laricina) is an early-successional transcontinental boreal conifer occurring within the spruce-fir dominated forest. The aim was to infer the species biogeographical history and to assess the putative genetic imprint left by interspecific competition during post-glacial migration, using cytoplasmic DNA and fossil data.
Location: Forty-five locations were sampled across the transcontinental range spanning the North American boreal forest.
Methods: A total of 621 trees were scanned for mitochondrial and chloroplast DNA polymorphisms to reveal geographical patterns of genetic diversity, differentiation, and population structure throughout the species range. Published pollen records were analysed to assess the chronology of post-glacial colonization of Larix sp. relative to more competitive tree taxa, Picea sp. and Abies sp..
Results: Genotyping resulted in two mitotypes (one locus) and 24 chlorotypes (three cpSSR loci). Bayesian assignment test based on cpDNA data detected three groups: eastern North America, western North America and Alaska. CpDNA population differentiation was higher in the western part of the range relative to the eastern part. Post-glacial colonization chronology derived from fossil data indicated that Larix colonized western North America at least 4000 years after Picea and Abies, but shortly preceded them in eastern North America.
Main conclusions: Cytoplasmic and fossil data provided support for four distinct glacial lineages. Two lineages would have persisted south of the Laurentide ice sheet, while the two remaining ones likely originate from northern refugia located in Beringia and Labrador. Larix establishment was possibly hindered by earlier establishment of more competitive taxa in western North America, which resulted in high genetic differentiation among western populations. These results provide support for a putative role of interspecific competition in structuring the standing genetic variation at the time of post-glacial colonization.
by André Boily | 30 January 2019
Published in PeerJ 4: e2218. https://doi.org/10.7717/peerj.2218
Projecting suitable conditions for a species as a function of future climate provides a reasonable, although admittedly imperfect, spatially explicit estimate of species vulnerability associated with climate change. Projections emphasizing range shifts at continental scale, however, can mask contrasting patterns at local or regional scale where management and policy decisions are made. Moreover, models usually show potential for areas to become climatically unsuitable, remain suitable, or become suitable for a particular species with climate change, but each of these outcomes raises markedly different ecological and management issues. Managing forest decline at sites where climatic stress is projected to increase is likely to be the most immediate challenge resulting from climate change. Here we assess habitat suitability with climate change for five dominant tree species of eastern North American forests, focusing on areas of greatest vulnerability (loss of suitability in the baseline range) in Quebec (Canada) rather than opportunities (increase in suitability). Results show that these species are at risk of maladaptation over a remarkably large proportion of their baseline range. Depending on species, 5-21% of currently climatically suitable habitats are projected to be at risk of becoming unsuitable. This suggests that species that have traditionally defined whole regional vegetation assemblages could become less adapted to these regions, with significant impact on ecosystems and forest economy. In spite of their well-recognised limitations and the uncertainty that remains, regionally-explicit risk assessment approaches remain one of the best options to convey that message and the need for climate policies and forest management adaptation strategies.
