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.
by Marie-Claude Boileau | 16 July 2020
Published in Tree Physiology 14: 759-768
A computer-controlled whole-plant cuvette system is described that allows precise and independent control of temperature (± 0.05 °C), vapor pressure (± 0.02 kPa), CO2 concentration (± 2 mmol mol-1) and photosynthetic photon flux density (± 5 mmol m-2 s-1), and allows the continuous measurement of net photosynthesis and transpiration rates. Vapor pressure is controlled by circulating chamber air through a CaSO4 desiccant column supported on a digital balance. Transpiration rate is calculated from the change in desiccant mass with time. Photosynthesis rate is measured by integrating the output of a mass flow controller used to inject CO2 into the chamber to compensate for that assimilated by the plant.
The control system can be driven by set points that can be varied, for example, as a function of time, or held constant. We were able to simulate weather data obtained from climate stations and accurately follow, in real time, the output of sensors measuring outside conditions.
Experiments on well-watered one- and two-year-old nursery-raised western red cedar (Thuja plicata Donn.) and white spruce (Picea glauca (Moench) Voss) seedlings showed that if the mean daily temperature was increased from 20 to 22 °C with vapor pressure remaining constant at 1 kPa, CO2 concentrations must almost double to compensate for the decrease in net photosynthesis rate.
by Audrey Verreault | 15 July 2020
Published in Journal of Economic Entomology 87(1): 96-100
Variations in concentrations of ground white pine bark incorporated into artificial diet were studied to determine their effect on egg laying and feeding behavior of white pine weevils, Pissodes strobi (Peck). Significant differences in feeding and egg laying responses were detected between adults fed diets containing 5 and 10% ground bark. White pine weevil larvae reared on the diet containing 1% ground bark had a higher mortality level than those reared on the diet containing 5% ground bark. Weevil females fed the diet containing 5% ground bark were significantly heavier than those reared on the diet with 1% ground bark. Insect development times did not differ significantly between the two concentrations of ground bark. Adults exposed to a natural substrate were stimulated to oviposit, and viable eggs were laid.
by Marie-Claude Boileau | 16 June 2020
Published in Canadian Journal of Soil Science 75: 343-348
A Podzolic soil from an old-growth maple hardwood forest in eastern Canada was systematically sampled from a 16.5-m-long trench in 1975. ln 1986, the upper 10 cm of the B horizon was resampled from two sampling lines located on each side and parallel to the 1975 trench, one at a distance of 1 m downhill and the other at a distance of 4 m uphill. Total N, organic C, pH, and exchangeable Ca, Mg and K were measured. The objectives were to evaluate the change in the chemical status of the B horizon from 1975 to 1986 and to characterize the spatial variability of the horizon. No significant change was found in the soil chemical properties tested during this 11-yr period. No significant autocorrelation was observed between soil samples 60 cm apart, except for the downhill sampling line, which was located 1 m from the trench. For most properties, the magnitude of the difference between two soil sampling units was not proportional to the distance separating them over the range of 0.6-4.2 m. Except for pH, a difference in soil properties of more than 30% was observed in 37-56% of sampIe pairs 60 cm apart. Resampling near (1 m) an old soil pit may not be valid because of possible local modifications of soil properties created by the pit, even when it is filled in.
