by Marie-Claude Boileau | 27 July 2020
Published in Annales des Sciences Forestières 48: 123-132
A precommercial thinning was conducted on young balsam fir (Abies balsamea (L) Mill) and white birch (Betula papyrifera Marsh) trees. Changes in light environment and growth response of the trees were followed during the next 2 growing seasons. The relative growth rate (RGR) of thinned balsam firs increased during both the first and the second growing season. This increase in growth was attributed to a greater net assimilation rate (NAR) which was associated with a higher level of light availability. Thinning tended to positively affect the RGR of white birch during the first summer following treatment but not during the second growing season. Similar fluctuations were noted for NAR even though light levels remained high for thinned white birch trees during both the first and the second growing season. Balsam fir produced more sapwood per unit of additional leaf area than controls during the first summer following treatment but no differences were observed during the second. The sapwood area growth to leaf area growth ratios of thinned and control white birches were similar during both the first and the second summer following thinning. Thus the sapwood area-leaf area relationship appears to be more stable following abrupt changes in environmental conditions for the indeterminate growth species, white birch, than for the determinate growth species, balsam fir.
by Marie-Claude Boileau | 24 July 2020
Published in Canadian Journal of Forest Research 22: 534-540
The calibration of time domain reflectometry, previously established for an organic soil of 0.422 Mg.m-3 bulk density, was established for peat blocks with bulk densities ranging from 0.06 to 0.25 Mg.m-3. An empirical relationship between the volumetric water content and the measured apparent dielectric constant was established in the laboratory. This relationship can be used to estimate volumetric water content between 0.21 and 0.95 cm3.cm-3 with a standard deviation of 0.03 cm3.cm-3. The large variations observed during the calibration were mainly attributed to the size and heterogeneousness of peat samples. When water tables in the field were high, standard deviation decreased to 0.02 cm3.cm-3, which agrees very well with other time domain reflectometry experiments.
by Audrey Verreault | 24 July 2020
Published in Journal of Ecology 81: 719-727
1 The postglacial history of jack pine (Pinus banksiana Lamb.) at its northernmost distribution limit in the upper boreal forest, along the Grande Rivière de la Baleine (northern Québec), was reconstructed by using radiocarbon-dated conifer macrofossils found in dune palaeosols.
2 Black spruce (Picea mariana (Mill.) B.S.P.) was the first conifer species to colonize the area at 6000 BP, immediately after deglaciation. Jack pine first invaded the sandy terraces at 3050 BP, apparently at a low density. The species most likely survived for several centuries at this low density before experiencing a regional expansion between 2400 and 1750 BP.
3 From the period of regional expansion of jack pine to the present, mixed and monospecific stands of jack pine and black spruce developed concurrently, indicating that both species responded positively to fire and climate conditions.
4 The regional expansion of jack pine was not followed by a northward spread of the species into the forest tundra. The formation and expansion of the forest tundra during the last 3000 years restricted jack pine to the boreal forest. A lower fire frequency with colder conditions in the forest tundra may have been responsible for the inability of jack pine to expand northwards.
by Audrey Verreault | 24 July 2020
Published in Forest Ecology and Management 59: 115-125
In an attempt to identify whether the phenological development of an associated plant species would be well synchronized with spruce seed maturation, we examined the floral development of fireweed (Epilobium angustifolium L.) by dividing the inflorescence into six distinct parts. Weekly harvest on five different sites across the distribution of white spruce in Québec, showed a good correlation between the timing of white spruce seed maturation and the beginning of capsule bursting at the base of fireweed inflorescence (rs = 0.92). These two stages of development correspond to 1276 ± 112 degree-days or 1943 ± 155 thermal units, the latter yielding the greatest precision. Development of each section of the inflorescence progressed successively from the base to the top with a delay ranging between 3 and 7 days. Therefore, it appears possible to forecast the optimal moment for collection of white spruce cones 2 weeks in advance by monitoring the acropetal progression of the floral axis of fireweed. The influence of other factors, such as drainage class, light environment, and intra-population variations are also discussed.
by Audrey Verreault | 16 July 2020
Published in Canadian Journal of Forest Research 23: 871-872
This note complements an article published by the authors in 1988 in this journal. Another method is given for constructing confidence intervals in regression using the logarithmic transformation. The procedure is easy to use and is appropriate for most situations.
