by Claire Morin | 30 January 2019
Published in Forest Ecology and Management 263: 229-239
The introduction of logging associated with the industrial era (since ~ 1900) has modified the natural disturbance regime of the world’s boreal forests. The object of this study was to document, using forestry maps prepared in 1950 and 2005 from air photos, the dynamics of high-elevation boreal forest landscapes affected by 20th century logging and natural stand-replacing disturbances. In 1950, the majority of forests in the study area were unlogged (>88%) and dominated by old conifers (³81 years of age), predominantly balsam fir and black spruce. Logging activities affected 76.2% of the study area at least once between 1930 and 2005. Forests located at lower altitudes (710–880 m) were more intensively logged than those of higher altitudes (880–1050 m). The present-day forest landscape, in contrast to that of 1950, is fragmented and dominated by younger stands. The sectors that have been logged at least once have experienced more forest cover changes relative to undisturbed areas. The 2005 cover composition was relatively similar to that observed on 1950 maps. In the 20th century, natural stand-replacing disturbances were infrequent and had a less extensive effect on the forest landscape than did logging. The fire rotation in the 20th century was more than 3000 years, with the overall stand-replacing natural disturbance rotation approaching 800 years. Our study suggests, at least in the 20th century, that canopy gaps and small-scale windthrows seem to be the principal factors controlling high-altitude natural forest dynamics and that natural stand-replacing disturbances were of little consequence. Twentieth century forestry practices were the most important driving force explaining the present-day age structure of the forest landscape. Ecosystem-based management strategies for high-elevation boreal forests should take this into consideration, and implement silvicultural practices that mimic the natural disturbance regime more closely. We therefore suggest the adoption of strategies that favor partial cuts.
by André Boily | 30 January 2019
Published in Environmental Science and Pollution Research 19(2): 361-371. https://doi.org/10.1007/s11356-011-0565-6
Purpose
Increases in dissolved organic carbon (DOC) concentrations have been reported in surface waters worldwide in the last 10 to 20 years. The causes behind these increases have been attributed to many factors, including climate change and decreasing depositions of atmospheric sulphate (SO42-). Trends in DOC concentrations and their potential causal factors were examined in a network of 30 lakes lying in undisturbed temperate and boreal catchments in the province of Quebec, Canada.
Methods
Temporal trends in lake DOC concentrations were analysed with the seasonal Kendall test. For each lake, the variation in DOC concentration over time was assessed in light of the variation in SO42- concentration in precipitation, air temperature, precipitation and solar radiation using the forward stepwise multiple regression.
Results
Between 1989 and 2006, significant increases in DOC were observed in most of the lakes, the mean rate of change being 0.05 mg L−1 year−1. Lake DOC concentrations were significantly explained by different models that yielded a variance explanation ranging from 13% to 77%. The models included long-term temperature variables (i.e. averaged over intervals of 10 years), short-term precipitation variables (i.e. summed over intervals 6 months), radiation (i.e. ice-free period prior to the DOC observation) and precipitation SO42- concentration as explanatory variables.
Conclusion
Temporal changes in DOC concentrations seem more consistent with the evolution of climate parameters rather than SO42- concentrations despite the fact that most lakes were in the process of recovery, showing increases in pH.
by Svetlana Savin | 30 January 2019
Published in Communications in Soil Science and Plant Analysis 42: 2738-2750
Black spruce (Picea mariana) trees have needles that persist for a number of years, and it is not clear which age class should be evaluated for photosynthesis to best understand physiological responses. Moreover, the impact of sampling current versus older foliage is rarely acknowledged in published literature, even though it may influence the interpretation of results. We compared the photosynthesis rate of current and 1-year-old foliage of black spruce natural regeneration during three growing seasons. The photosynthesis rate was consistently greater for 1-year-old needles compared to current-year needles at the beginning of each growing season; however, after about 1 month, rates were similar between the two age classes. This same pattern was repeated every season and was independent of light availability induced by different harvesting treatments. We suggest that photosynthesis measurements of black spruce should be performed on 1-year-old needles instead of current-year foliage to ensure more uniform photosynthesis values throughout the season.
by Claire Morin | 30 January 2019
Published in Environmental Pollution 162: 354-360. https://doi.org/10.1016/j.envpol.2011.12.007
The interaction of atmospheric sulphur (S) was investigated within the canopies of two boreal forests in Québec, Canada. The net canopy exchange approach, i.e. the difference between S-SO4 in throughfall and precipitation, suggests high proportion of dry deposition in winter (up to 53%o) as compared to summer (1-9%). However, a 3.5%o decrease in d18O-SO4 throughfall in summer compared to incident precipitation points towards a much larger proportion of dry deposition during the warm season. We suggest that a significant fraction of dry deposition (about 1.2 kg ha-1 yr-1, representing 30-40% of annual wet S deposition) which contributed to the decreased d18O-SO4 in throughfall was taken up by the canopy. Overall, these results showed that, contrary to what is commonly considered, S interchanges in the canopy could be important in boreal forests with low absolute atmospheric S depositions.
by Claire Morin | 30 January 2019
Published in Forest Ecology and Management 270: 45-53
The commercial use of white spruce varieties produced by somatic embryogenesis (SE) permits increased forest productivity compared to other reproductive technologies. However, the use of SE in clonal forestry requires an accurate assessment of genetic parameters and the performance stability of clones in plantations. For these reasons, two clonal tests were established of 52 white spruce somatic clones. In each clonal tests, we measured survival, bud dormancy, stem form, growth and branching characteristics of clones 4 years after outplanting. There was a large variability among clones for characteristics related to growth and branching. At this juvenile stage, the clonal heritability estimates for all characteristics remained low. Of all the characteristics studied, height had the highest heritability. The selection of the top 20 clones (38% of the clones) provided a genotypic gain in height of about 4% for the two planting sites, which is reasonable for such a low selection intensity. High genotypic correlations were observed between growth and branching characteristics. Although a significant site effect was observed for most characteristics, the genotype x site (G x E) interaction was low and consequently the correlation between the two sites for the same characteristic was high. The performance stability of the somatic clones at both sites indicates that opportunities exist for selection of clones that adapt and perform well over different ecological regions, permitting a tangible increase in forest productivity.
