by Audrey Verreault | 16 June 2020
Published in New Forests 9: 261-272
Paper bags equipped with a polyethylene window were placed on branchlets 6 and 9 weeks before the time of pollen dispersal of Japanese larch and Jack pine, respectively. This technique produced a localized greenhouse effect around the branchlets, accelerating male cone development. For Jack pine trees, buds in bags with the window oriented upward had the shortest maturation time. ln fact, it was possible to collect these pollen cones about 11 days before the unbagged control without decreasing the production of pollen. The mean germination rate of the pollen from the bags with the window pointed upward, however, was significantly lower than the control, by about 15%. Buds in bags with the window oriented downward had an accelerated development of about 9 days (compared to the control) but did not experience a decrease in pollen production or quality. This same technique caused the abortion of male cones of the Japanese larch trees. Thermal probes in the bags enabled us to follow the progression of temperature inside and outside the bags during the development of the male cone in each species. They revealed that the bags increased mean temperature, daily temperature range, and degree-day accumulation, and that this effect was most pronounced for Jack pine, when the polyethylene window was oriented upward.
by Audrey Verreault | 12 June 2020
Published in Grana 34: 367-370
ln Québec, 83 first-generation seed orchards destined to produce seeds from genetically improved trees have been established since 1973. Consequently, the Tree Genetic Improvement Program uses a very large quantity of pollen in order to carry out the controlled pollination projects in those seed orchards. Moreover, controlled pollination is carried out within a very short time-frame and very often the receptivity period occurs before the time of pollen dispersion. It is for these reasons that the pollen bank was created in Québec. This manuscript summarize the process of long term preservation of a large quantity of tree pollen. It is possible to preserve the pollen of coniferous trees on a large scale for up to five years. lt is more difficult to manipulate the pollen of deciduous trees.
by Marie-Claude Boileau | 12 June 2020
Published in Soil Science Society of America Journal 59(1): 38-43
With the recent development of improved time domain reflectometry (TDR) probe design, measurement systems, and calibration procedures, it is now possible to detect and quantify the effect of temperature on the soil apparent dielectric constant (Ka). We investigated measurement errors in Ka associated with soil temperature variations and compared measured changes in Ka with those predicted by a dielectric mixing model. After confirming the accuracy and resolution of our measurement system with a series of measurements on distilled water, we measured changes in Ka with temperature for a range of soil types, including sand, loam, and peat, at soil water contents (qv) ranging from 0.09 to 0.81 m3 m-3. The measured variation with temperature in the dielectric constant of distilled water (0.322°C-1) was very close to that reported in the literature (0.356°C-1). ln soils, changes in Ka with temperature were highest at high water contents. For soils near saturation, the overall changes observed in Ka with temperature were lower than those predicted by the dielectric mixing model by 17% for sand, 24% for loam, and 39% for peat. These results suggest that the temperature dependence of the dielectric constant of water in a soil matrix is lower than that of bulk water. Absolute water content errors increased linearly with the size of the water fraction, ranging from 8.75 x 10-5 m3 m-3°C-1 at 0.05 m3 m-3 soil water content to 1.40 x 10-3 m3 m-3°C-1 at 0.80 m3 m-3 soil water content. To obtain the highest measurement accuracy, particularly at higher qv, we suggest that a temperature correction of 0.00175qv°C-1 be employed.
by Marie-Claude Boileau | 12 June 2020
Published in Canadian Journal of Forestry Research 25: 536-544
The advance regeneration often present following clear-cutting in black spruce (Picea mariana (Mill.) B.S.P.) stands is generally composed of individuals of various heights. This initial height difference is hypothesized to affect the yield of the future stand. Height of the advance regeneration at time of release was determined on several black spruce trees within 33 stands distributed across the boreal forest of the province of Québec, Canada. From these data, a regeneration structure index was developed and used to explain a part of the variation in subsequent stand yield. Dominant trees of stands developing for 38 to 65 years since clear-cutting generally originated from the tallest advance regeneration at time of release. Stands with the tallest regeneration at time of release produced the largest yields for a given site quality and number of years since harvesting. A 3-m increase in advance-regeneration height resulted in a similar yield gain as a 3-m increase in site index. Site indices calculated from age-height relationships of dominant trees originating from tall advance regeneration were less than those calculated from trees that have undergone a relatively short period of suppression. These results suggest that traditional management tools developed for fire-origin black spruce stands, i.e., stands mainly composed of seed-origin trees established after perturbation, should be adjusted for clearcut-origin stands that largely develop from advance regeneration.
by Audrey Verreault | 12 June 2020
Published in Journal of Economic Entomology 88(3): 640-643
A method was developed for rearing Dioryctria abietivorella (Grote) under aseptic artificial conditions. Larvae fed with artificial diet completed their development from first instar to pupae with a survival level of 59.7 ± 2.5% (mean ± SEM). Development time, recorded in an incubator set at 25°C, 60% RH, and a photoperiod of 16:8 (L:D) h from first instar through pupation, was 22.54 ± 0.56 d for males and 22.80 ± 0.80 d for females. Larval development included five instars, and 25.6% of the time there was an additional sixth instar. Instars were identified by head-capsule width measurements. Sex identification was done by observation with a binocular microscope of the eighth and ninth abdominal segments of pupa. Fifty pairs of insects were placed per cage for mating. Adult cages for mating and oviposition were used successfully and a mean number of 24.68 ± 2.02 viable eggs were laid per female.
