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.
by Marie-Claude Boileau | 26 May 2020
Published in Oecologia 133: 1-9
The long-term responses of forests to atmospheric CO2 enrichment have been difficult to determine experimentally given the large scale and complex structure of their canopy. We have developed a CO2 exposure system that uses the free-air CO2 enrichment (FACE) approach but was designed for tall canopy trees. The system consists of a CO2 -release system installed within the crown of adult trees using a 45-m tower crane, a CO2 monitoring system and an automated regulation system. Pure CO2 gas is released from a network of small tubes woven into the forest canopy (web-FACE), and CO2 is emitted from small laser-punched holes. The set point CO2 concentration ([CO2 ]) of 500 mmol mol-1 is controlled by a pulse-width modulation routine that adjusts the rate of CO2 injection as a function of measured [CO2 ] in the canopy. CO2 consumption for the enrichment of 14 tall canopy trees was about 2 tons per day over the whole growing season. The seasonal daytime mean CO2 concentration was 520 mmol mol-1. One-minute averages of CO2 measurements conducted at canopy height in the center of the CO2-enriched zone were within ±20% and ±10% of the target concentration for 76% and 47% of the exposure time, respectively. Despite the size of the canopy and the windy site conditions, performance values correspond to about 75% of that reported for conventional forest FACE with the added advantage of a much simpler and less intrusive infrastructure. Stable carbon isotope signals captured by 80 Bermuda grass (Cynodon dactylon) seedlings distributed within the canopy of treated and control tree districts showed a clearly delineated area, with some nearby individuals having been exposed to a gradiant of [CO2], which is seen as added value. Time-integrated values of [CO2] derived from the C isotope composition of C. dactylon leaves indicated a mean (±SD) concentration of 513±63 mmol mol-1 in the web-FACE canopy area. In view of the size of the forest and the rough natural canopy, web-FACE is a most promising avenue towards natural forest experiments, which are greatly needed.
