by Claire Morin | 30 January 2019
Published in PLOS ONE 11(3): e0152495. https://doi.org/10.1371/journal.pone.0152495
An impressive number of new climate change scenarios have recently become available to assess the ecological impacts of climate change. Among these impacts, shifts in species range analyzed with species distribution models are the most widely studied. Whereas it is widely recognized that the uncertainty in future climatic conditions must be taken into account in impact studies, many assessments of species range shifts still rely on just a few climate change scenarios, often selected arbitrarily. We describe a method to select objectively a subset of climate change scenarios among a large ensemble of available ones. Our k-means clustering approach reduces the number of climate change scenarios needed to project species distributions, while retaining the coverage of uncertainty in future climate conditions. We first show, for three biologically-relevant climatic variables, that a reduced number of six climate change scenarios generates average climatic conditions very close to those obtained from a set of 27 scenarios available before reduction. A case study on potential gains and losses of habitat by three northeastern American tree species shows that potential future species distributions projected from the selected six climate change scenarios are very similar to those obtained from the full set of 27, although with some spatial discrepancies at the edges of species distributions. In contrast, projections based on just a few climate models vary strongly according to the initial choice of climate models. We give clear guidance on how to reduce the number of climate change scenarios while retaining the central tendencies and coverage of uncertainty in future climatic conditions. This should be particularly useful during future climate change impact studies as more than twice as many climate models were reported in the fifth assessment report of IPCC compared to the previous one.
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 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.
