Guidelines for the use and interpretation of palaeofire reconstructions based on various archives and proxies
Published in Quat. Sci. Rev. 193: 312-322.
Bottom-up factors contribute to large-scale synchrony in spruce budworm populations
Published in Canadian Journal of Forest Research 48(3): 277-284. https://doi.org/10.1139/cjfr-2017-0051
Understanding the mechanisms that cause large-scale synchrony in insect population dynamics might yield key insights for predicting potential outbreak occurrence. Here, we evaluated which environmental factors best explain synchronous population fluctuations in the spruce budworm (Choristoneura fumiferana Clem.) (SBW), a major defoliator of coniferous forests in North America. SBW population levels were assessed with pheromone traps during the 1986–2014 period across a 625 000km2 territory located in the province of Québec (Canada). The populations were characterized by abundance fluctuations that were often synchronized across the whole study area. Interannual population fluctuations were correlated with host tree cone production (a source of food) and high May temperatures, suggesting that synchrony was influenced by food availability and phenological mismatch during shoot development. Cone production was itself correlated with low precipitation during the previous summer. This study indicates that bottom-up trophic factors can drive spatiotemporal synchrony in insect populations and contribute to explain important and sustained population increases during some years. We also suggest that several biological processes, all influenced by weather, are likely to interact to explain population synchrony during the different phases of the approximately 35 year SBW outbreak cycle, complicating the prediction of climate change effects on this insect.
Recovery of plant community functional traits following severe soil perturbation in plantations: a case-study
Published in International journal of biodiversity science, ecosystem services & management 12(1-2): 116-127 https://doi.org/10.1080/21513732.2016.1146334
We present a case study in which we assessed the effects of a severe soil perturbation on the plant community and soil variables in young hybrid poplar (Populus sp.) plantations of southern Québec (Canada). Our overall goal was to test if soil perturbation and planting fast-growing species could promote the reestablishment of a relatively diverse plant community. A chronosequence that included three plantations (4, 8, and 12-year old) established after soil scarification, paired with three natural stands representative of the local temperate mixedwood forest comprising both pioneer and late-successional tree species, was implemented. Vegetation surveys and soil collection were performed in 2012 and species traits were provided by the Traits Of Plants In Canada and TRY databases. Principal response curve analyses showed species and functional trait divergence between treated and natural stands at ages 4 and 8, but that those divergences were less at age 12. Species and trait convergences were slower in the scarification furrows than in the scarification berms (mounds between furrows). However, severe site preparation did not appear to affect soil variables on the study sites. Our results suggest that even following severe site preparation, gradual recovery of species and trait composition similar to that of natural stands appears possible in the long term, mainly through fast canopy development by hybrid poplar. However
An objective approach to select climate scenarios when projecting species distribution under climate change
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.
Joint inferences from cytoplasmic DNA and fossil data provide evidence for glacial vicariance and contrasted post-glacial dynamics in tamarack, a transcontinental conifer
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.
