by Audrey Verreault | 30 January 2019
Published in Environmental Monitoring and Assessment 186(12): 8191-8202. https://doi.org/10.1007/s10661-014-3997-x
The projected increase in atmospheric N deposition and air/soil temperature will likely affect soil nutrient dynamics in boreal ecosystems. The potential effects of these changes on soil ion fluxes were studied in a mature balsam fir stand (Abies balsamea [L.] Mill) in Québec, Canada that was subjected to 3 years of experimentally increased soil temperature (+4 °C) and increased inorganic N concentration in artificial precipitation (three times the current N concentrations using NH4NO3). Soil element fluxes (NO3, NH4, PO4, K, Ca, Mg, SO4, Al, and Fe) in the organic and upper mineral horizons were monitored using buried ion-exchange membranes (PRS™ probes). While N additions did not affect soil element fluxes, 3 years of soil warming increased the cumulative fluxes of K, Mg, and SO4 in the forest floor by 43, 44, and 79 %, respectively, and Mg, SO4, and Al in the mineral horizon by 29, 66, and 23 %, respectively. We attribute these changes to increased rates of soil organic matter decomposition. Significant interactions of the heating treatment with time were observed for most elements although no clear seasonal patterns emerged. The increase in soil K and Mg in heated plots resulted in a significant but small K increase in balsam fir foliage while no change was observed for Mg. A 6–15 % decrease in foliar Ca content with soil warming could be related to the increase in soil-available Al in heated plots, as Al can interfere with the root uptake of Ca.
by Claire Morin | 30 January 2019
Published in Tree Genetics & Genomes 11: 58. https://doi.org/10.1007/s11295-015-0878-6
Genetic parameters of Picea abies resistance to the white pine weevil (Pissodes strobi Peck) were estimated from 193 full-sib and 166 half-sib families in six 10-year-old progeny trials. The estimated family and individual heritability values for the cumulative weevil attack rate between ages 6 and 10 (CWA6–10) were high and moderate for both full-sib families (0.61 and 0.28, respectively) and half-sib families (0.85 and 0.40, respectively), indicating strong genetic control for this trait in Norway spruce. The fact that specific combining ability (SCA) variance represents 35 % of the general combining ability (GCA) variance suggests that non-additive (dominant) effects are weak. The strong type B correlations found for CWA6–10 (r ˆ B =0.96 for full-sib families and r ˆ B =0.81 for half-sib families) indicate that family ranks were stable across sites. For three of the five sites with high attack levels, genetic correlations were not significant between CWA6–10 and tree height at age 5. Moderate positive genetic correlations were detected between CWA6–10 and tree diameter at age 10 (r ˆ A from 0.29 to 0.60), but specific families showing both high resistance and good diameter growth can be found. These results suggest that the genetic improvement of Norway spruce for resistance to white pine weevil can be achieved successfully without adversely affecting growth.
by Claire Morin | 30 January 2019
Published in Boreas 48(1): 131-146 https://doi.org/doi:10.1111/bor.12345
Forested peatlands are widespread in boreal regions of Canada, and these ecosystems, which are major terrestrial carbon sinks, are undergoing significant transformations linked to climate change, fires and human activities. This study targets millennial-scale vegetation dynamics and related hydrological variability in forested peatlands of the Clay Belt south of James Bay, eastern Canada, using palaeoecological data. Changes in peatland vegetation communities were reconstructed using plant macrofossil analyses, and variations in water-table depths were inferred using testate amoeba analyses. High-resolution analyses of macroscopic charcoal >0.5 mm were used to reconstruct local fire history. Our data showed two successional pathways towards the development of present-day forested peatlands influenced by autogenic processes such as vertical peat growth and related drying, and allogenic factors such as the occurrence of local fires. The oldest documented peatland initiated in a wet rich fen around 8000 cal. a BP shortly after land emergence and transformed into a drier forested bog rapidly after peat inception that persisted over millennia. In the second site, peat started to accumulate from ~5200 cal. a BP over a mesic coniferous forest that shifted into a wet forested peatland following a fire that partially consumed the organic layer ~4600 cal. a BP. The charcoal records show that fires rarely occurred in these peatlands, but they have favoured the process of forest paludification and influenced successional trajectories over millennia. The macrofossil data suggest that Picea mariana (black spruce) persisted on the peatlands throughout their development, although there were periods of more open canopy due to local fires in some cases. This study brings new understanding on the natural variability of boreal forested peatlands which may help predict their response to future changes in climate, fire regimes and anthropogenic disturbances.
by Claire Morin | 30 January 2019
Published in Nature Communications 9(1): 3213. https://doi.org/10.1038/s41467-018-05705-4
Predicted increases in temperature and aridity across the boreal forest region have the potential to alter timber supply and carbon sequestration. Given the widely-observed variation in species sensitivity to climate, there is an urgent need to develop species-specific predictive models that can account for local conditions. Here, we matched the growth of 270,000 trees across a 761,100 km2 region with detailed site-level data to quantify the growth responses of the seven most common boreal tree species in Eastern Canada to changes in climate. Accounting for spatially-explicit species-specific responses, we find that while 2 °C of warming may increase overall forest productivity by 13 ± 3% (mean ± SE) in the absence of disturbance, additional warming could reverse this trend and lead to substantial declines exacerbated by reductions in water availability. Our results confirm the transitory nature of warming-induced growth benefits in the boreal forest and highlight the vulnerability of the ecosystem to excess warming and drying.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Science 63(6): 559-568 https://doi.org/10.5849/FS-2017-062R2
In the boreal forest, ground-layer composition may modulate the effects of precommercial thinning (PCT) on stand productivity by affecting tree growth conditions. Based on data from 15 years of PCT monitoring in black spruce (Picea mariana) and jack pine (Pinus banksiana) stands, the objectives of this study were to investigate the effects of PCT on ground-layer composition and the way ground-layer composition is related to tree growth, stand productivity, and the PCT impact on stand productivity. PCT favored lichen expansion in xeric sites. The positive impact of PCT on stand productivity after 15 years was lower in sites with high year-one lichen cover, suggesting that the aboveground positive effect of PCT on growth may have been mitigated by a belowground negative feedback resulting from lichen expansion in xeric sites. Although Sphagnum spp. cover was not affected by PCT, 15-year increase in stand productivity was lower in sites with high year-one Sphagnum spp. cover. These results suggest that xeric stands with high lichen cover should not be targeted for PCT because of either null or negative effects on stand productivity. Subhydric stands with high Sphagnum spp. cover should also be avoided because of lower potential stand productivity.
