by Marie-Claude Boileau | 30 January 2019
Published in Ergonomics. 58(12): 2040-2056. https://doi.org/10.1080/00140139.2015.1044920
Individual heart rate (HR) to workload relationships were determined using 93 submaximal step-tests administered to 26 healthy participants attending physical activities in a university training centre (laboratory study) and 41 experienced forest workers (field study). Predicted maximum aerobic capacity (MAC) was compared to measured MAC from a maximal treadmill test (laboratory study) to test the effect of two age-predicted maximum HR Equations (220-age and 207-0.7 x age) and two clothing insulation levels (0.4 and 0.91 clo) during the step-test. Work metabolism (WM) estimated from forest work HR was compared against concurrent work VO2 measurements while taking into account the HR thermal component. Results show that MAC and WM can be accurately predicted from work HR measurements and simple regression models developed in this study (1% group mean prediction bias and up to 25% expected prediction bias for a single individual). Clothing insulation had no impact on predicted MAC nor age-predicted maximum HR equations.
by Marie-Claude Boileau | 30 January 2019
Published in Applied Ergonomics 54: 148-157 https://doi.org/10.1016/j.apergo.2015.12.005
Heart rate (HR) was monitored continuously in 41 forest workers performing brushcutting or tree planting work. 10-min seated rest periods were imposed during the workday to estimate the HR thermal component (ΔHRT) per Vogt et al. (1970, 1973). VO2 was measured using a portable gas analyzer during a morning submaximal step-test conducted at the work site, during a work bout over the course of the day (range: 9–74 min), and during an ensuing 10-min rest pause taken at the worksite. The VO2 estimated, from measured HR and from corrected HR (thermal component removed), were compared to VO2 measured during work and rest. Varied levels of HR thermal component (ΔHRTavg range: 0–38 bpm) originating from a wide range of ambient thermal conditions, thermal clothing insulation worn, and physical load exerted during work were observed. Using raw HR significantly overestimated measured work VO2 by 30% on average (range: 1%–64%). 74% of VO2 prediction error variance was explained by the HR thermal component. VO2 estimated from corrected HR, was not statistically different from measured VO2. Work VO2 can be estimated accurately in the presence of thermal stress using Vogt et al.’s method, which can be implemented easily by the practitioner with inexpensive instruments.
by Audrey Verreault | 30 January 2019
Published in Geoderma 247-248: 12-23. http://dx.doi.org/10.1016/j.geoderma.2015-01-016
A number of methods exist for estimating mineral weathering rates. Yet, quantifying this crucial biogeochemical reaction in the field has always been a challenge because mineral weathering takes place in open systems whose initial state conditions are not well known and where material inputs and outputs vary in time and space. Here, using the soil profile mass balance method, we estimated long-term weathering rates of base cations (BCs) for a set of 21 watersheds, and we investigated the links between environmental variables and soil properties and the spatial variation in BC weathering rates in the study area. The watersheds are located in southern Quebec and vary with respect to hydro-climatic conditions, soil properties and forest cover. Average long-term estimates of annual BC weathering rates for the study area were 0.16, 0.10, 0.09 and 0.06 kmolc ha−1 year−1 for Ca, Mg, Na and K, respectively. Overall, redundancy analysis (RDA) indicated that soil surface area, percent deciduous canopy cover, elevation, as well as soil albite content were the most significant variables explaining together 56% of the total variation in BC weathering rates. Consistent with previous findings, our results showed that, beside soil properties, climate-related environmental variables played key roles in determining the variability of BC weathering rates in the study area. In the context of global climate change, more insights are needed for a better understanding of the effects of discrete climatic variables on BC weathering rates.
by Audrey Verreault | 30 January 2019
Published in Ecohydrology 9(2): 238-247. https://doi.org/10.1002/eco.1627
The Canadian Drought Code (CDC) is an empirical soil-drying model adapted to high-latitude forests and commonly used by Canadian fire managers and researchers to predict the water content of the organic soil layer. Better knowledge of the capacity of the CDC to predict the effect of droughts on the water content of the mineral soil could improve our capacity to predict the future response of Canadian boreal forests to future changes in drought frequency and intensity.
We tested the capacity of the CDC to predict mineral soil water content (SWC) and droughts against long-term (14–16 years) daily mineral SWC data from time domain reflectometry probes in multiple stations within three forest ecosystems of Eastern Canada respectively dominated by sugar maple, balsam fir and black spruce. Droughts were defined as SWC values lower than one standard deviation from their historical mean. The drought intensity and frequency of each growing season were computed as the sum of daily SWC departures from normal and the sum of days of drought, respectively.
Our results show that the CDC is a reliable predictor of mineral SWC (r=0.6–0.8), drought frequency (r=0.5–0.9) and intensity (r=0.7–0.9) for high-latitude forest ecosystems of Eastern Canada. Lower correlations were due to the poor accuracy of the model at predicting mild droughts at the sugar maple stand due to the SWC values close to the drought threshold. We detected a higher susceptibility to droughts at the black spruce stand due to a 1-month-earlier occurrence of severe droughts.
by Audrey Verreault | 30 January 2019
Published in Tree Physiology 35(8): 864–878. https://doi.org/10.1093/treephys/tpv054
Climate-related variations in functional traits of boreal tree species can result both from physiological acclimation and genetic adaptation of local populations to their biophysical environment. To improve our understanding and prediction of the physiological and growth responses of populations to climate change, we studied the role of climate of seed origin in determining variations in functional traits and its implications for tree improvement programs for a commonly reforested boreal conifer, white spruce (Picea glauca (Moench) Voss).
We evaluated growth, root-to-shoot ratio (R/S), specific leaf area (SLA), needle nitrogen (Nmass), total non-structural carbohydrates (NSC) and photosynthetic traits of 3-year-old seedlings in a greenhouse experiment using seed from six seed orchards (SO) representing the different regions where white spruce is reforested in Québec. Height and total dry mass (TDM) were positively correlated with photosynthetic capacity (Amax), stomatal conductance (gs) and mesophyll conductance (gm). Total dry mass, but not height growth, was strongly correlated with latitude of seed origin (SO) and associated climate variables. Amax, gs, gm and more marginally, photosynthetic nitrogen-use efficiency (PNUE) were positively associated with the mean July temperature of the SO, while water use efficiency (WUE) was negatively associated. Maximum rates of carboxylation (Vcmax), maximum rates of electron transport (Jmax), SLA, Nmass, NSC and R/S showed no pattern. Our results did not demonstrate a higher Amax for northern seed orchards, although this has been previously hypothesized as an adaptation mechanism for maintaining carbon uptake in northern regions. We suggest that gs, gm, WUE and PNUE are the functional traits most associated with fine-scale geographic clines and with the degree of local adaptation of white spruce populations to their biophysical environments. These geographic patterns may reflect in situ adaptive genetic differences in photosynthetic efficiency along the cline.
