by Marie-Claude Boileau | 28 May 2020
Published in Tree Physiology 20: 229-238
We investigated effects of nutrient addition on several physiological characteristics of 60-cm-tall black spruce (Picea mariana Mill. B.S.P.) layers (i.e., rooted branches of overstory trees) and 20-cm-tall planted seedlings on a clear-cut, N-limited boreal site. After two growing seasons, current-year and one-year-old needles of fertilized trees (layers and seedlings combined) had higher net photosynthetic rates (An) and maximum capacity of Rubisco for CO2 fixation (Vmax) than unfertilized trees. One-year-old needles of fertilized trees had higher stomatal conductance (gs), higher water-use efficiency, and lower intercellular to ambient CO2 ratio than unfertilized trees. Additionally, fertilized trees had higher predawn and midday shoot water potentials than unfertilized trees.
Stomatal conductance of 1-year-old needles was 23% higher in seedlings than in layers, but there were no significant differences in gs of current-year needles between the regeneration types. For both needle age-classes, An and Vmax of layers were 25 and 40% higher, respectively, than the corresponding values for seedlings. The higher values of An, Vmax and foliar N concentration of layers compared with seedlings after two growing seasons may be associated with the larger root systems of the layers compared with the transplanted seedlings.
by Audrey Verreault | 28 May 2020
Published in Proceedings of the National Academy of Science 97(21): 113311-11336
Black spruce (Picea mariana [B.S.P.] Mill.) and red spruce (Picea rubens Sarg.) are two conifer species known to hybridize naturally in northeastern North America. We hypothesized that there is a progenitor-derivative relationship between these two taxa and conducted a genetic investigation by using sequence-tagged-site markers of expressed genes. Based on the 26 sequence-tagged-site loci assayed in this study, the unbiased genetic identity between the two taxa was quite high with a value of 0.920. The mean number of polymorphic loci, the mean number of alleles per polymorphic locus, and the average observed heterozygosity were lower in red spruce (P = 35%, AP = 2.1, Ho = 0.069) than in black spruce (P = 54%, AP = 2.9, Ho = 0.103). No unique alleles were found in red spruce, and the observed patterns of allele distribution indicated that the genetic diversity of red spruce was essentially a subset of that found in black spruce. When considered in combination with ecological evidence and simulation results, these observations clearly support the existence of a progenitor-derivative relationship and suggest that the reduced level of genetic diversity in red spruce may result from allopatric speciation through glaciation-induced isolation of a preexisting black spruce population during the Pleistocene era. Our observations signal a need for a thorough reexamination of several conifer species complexes in which natural hybridization is known to occur.
by Marie-Claude Boileau | 28 May 2020
Published in Canadian Journal of Forest Research 30: 59-66
Regeneration of first-cut strips in a two-cut system of strip clear-cutting was compared to that of large clear-cutting in four different areas representative of the black spruce (Picea mariana (Mill.) BSP) stands of the boreal forest of Québec. Seedlings were more evenly distributed in clearcut strips than in large clearcuts. Differences of about 10 000 black spruce seedlings per hectare and 20% of stocking were observed in favour of clearcut strips compared to large clearcuts. Black spruce stocking was about 14% larger on lowland than on upland sites but height growth was better on upland sites. A regeneration problem similar to that of large clearcuts was observed when the second strips were cut. One year after cutting these second strips, winter harvesting resulted in a 23% gain in black spruce stocking as compared to summer harvesting. Even if black spruce stocking marginally increased during the years following winter harvesting, the height advantage of the preserved advance growth justifies the application of this harvesting method. The strip clear-cutting system effectively improved the stocking of former black spruce stands but if the stocking level of advance growth is adequate, careful harvesting to preserve advance regeneration should be the preferred method since it would be more cost-efficient.
by Audrey Verreault | 28 May 2020
Published in Canadian Journal of Forest Research 31: 1292-1295
by Audrey Verreault | 28 May 2020
Published in The Canadian Entomologist 133: 333-341
Studies were conducted to document the oviposition biology of female white pine weevil, Pissodes strobi Peck. Data were recorded on female fecundity and daily feeding and oviposition activities. In addition, we compared fecundity of 1- and 2-year-old females. Female white pine weevils laid a mean ± SE total number of 132.3 ± 7.5 eggs (range 40-344 eggs) during an average oviposition period of 5.8 ± 0.4 weeks. It is during the first 5 weeks that white pine weevils lay the most eggs, with an egg-laying peak in the second week of the oviposition period. For a few females, egg production did not cease until the 22nd week. There was no difference between the number of eggs laid in the photophase and in the scotophase, but higher numbers of feeding punctures were observed during the night than during the day. The oviposition and feeding results for 2-year-old female white pine weevils were similar to those for 1-year-old females. This information contributes to the management of white pine weevils by providing a better understanding of some of the mechanisms of its population dynamics.
