by Marie-Claude Boileau | 30 January 2019
Published in Applied Ergonomics 54: 158-168 https://doi.org/10.1016/j.apergo.2015.12.006
In a new approach based on adaptive neuro-fuzzy inference systems (ANFIS), field heart rate (HR) measurements were used to classify work rate into four categories: very light, light, moderate, and heavy. Inter-participant variability (physiological and physical differences) was considered. Twenty-eight participants performed Meyer and Flenghi’s step-test and a maximal treadmill test, during which heart rate and oxygen consumption (VO2) were measured. Results indicated that heart rate monitoring (HR, HRmax, and HRrest) and body weight are significant variables for classifying work rate. The ANFIS classifier showed superior sensitivity, specificity, and accuracy compared to current practice using established work rate categories based on percent heart rate reserve (%HRR). The ANFIS classifier showed an overall 29.6% difference in classification accuracy and a good balance between sensitivity (90.7%) and specificity (95.2%) on average. With its ease of implementation and variable measurement, the ANFIS classifier shows potential for widespread use by practitioners for work rate assessment.
by Audrey Verreault | 30 January 2019
Pubished in Oecologia 177(1): 29-37. https://doi.org/10.1007/s00442-014-3118-0
A few studies have reported a recent and rapid decline in NO3− deposition in eastern North America. Whether this trend can be observed at remote boreal sites with low rates of N deposition and how it could impact canopy uptake (CU) of N remain unknown. Here we report trends between 1997/1999 and 2012 for precipitation, throughfall N deposition as well as inorganic N CU for two boreal forest sites of Québec, Canada, with contrasted N deposition rates and tree species composition. NO3− bulk deposition declined by approximately 50 % at both sites over the studied period while no change was observed for NH4+. As a result, the contribution of NH4+ to inorganic N deposition changed from ~33 % to more than 50 % during the study period. On average, 52–59 % of N deposition was intercepted by the canopy, the retention being higher for NH4+ (60–67 %) than for NO3– (45–54 %). The decrease in NO3– bulk deposition and the increase in the NH4+:NO3− ratio had important impacts on N–canopy interactions. The contribution of NH4+ CU to that of total inorganic N CU increased at both sites but the trend was significant only at Tirasse (lowest N deposition). At this site, absolute NO3− CU significantly decreased (as did total N CU) during the study period, a consequence of the strong relationship (r2 = 0.88) between NO3− bulk deposition and NO3− CU. Our data suggest that N interactions with forest canopies may change rapidly with changes in N deposition as well as with tree species composition.
by Marie-Claude Boileau | 30 January 2019
Published in Applied Ergonomics 45: 1475-1483. http://dx.doi.org/10.1016/j.apergo.2014.04.003
In new approaches based on adaptive neuro-fuzzy systems (ANFIS) and analytical method, heart rate (HR) measurements were used to estimate oxygen consumption (VO2). Thirty-five participants performed Meyer and Flenghi’s step-test (eight of which performed regeneration release work), during which heart rate and oxygen consumption were measured. Two individualized models and a General ANFIS model that does not require individual calibration were developed. Results indicated the superior precision achieved with individualized ANFIS modelling (RMSE = 1.0 and 2.8 ml/kg min in laboratory and field, respectively). The analytical model outperformed the traditional linear calibration and Flex-HR methods with field data. The General ANFIS model’s estimates of VO2 were not significantly different from actual field VO2 measurements (RMSE = 3.5 ml/kg min). With its ease of use and low implementation cost, the General ANFIS model shows potential to replace any of the traditional individualized methods for VO2 estimation from HR data collected in the field.
by Audrey Verreault | 30 January 2019
Published in Advances in Ecology https://dx.doi.org/10.1155/2014/917834
Many deer populations have recently increased worldwide leading to strong direct and indirect ecological and socioeconomical impacts on the composition, dynamic, and functions of forest ecosystems. Deer directly modify the composition and structure of vegetation communities, but they also indirectly affect other species of the ecosystem by modifying the structure of the vegetation. Here we review the results of a research program on overabundant white-tailed deer (Odocoileus virginianus) in the boreal forest of Anticosti Island (Québec, Canada) aimed at identifying deer densities compatible with forest regeneration. Various silvicultural systems and treatments failed to regenerate deer habitat at high deer densities, but planting size-adapted seedlings could be effective at moderate densities. Using a controlled deer density experiment, we found vegetation recovery at deer densities ≤ 15 deer/km2. The same experiment revealed that other groups of organisms such as insects and birds responded favorably to a reduction of deer density. We also found that alternative successional trajectories may occur after a certain period of heavy browsing during early succession.We conclude that one of the most important remaining research gaps is the need to identify habitat-specific threshold densities at which deer impacts occur and then to design effective wildlife and forest management strategies to limit deer impacts and sustain ecosystem integrity.
by Audrey Verreault | 30 January 2019
Published in Ecosphere 5(7): 1-33 http://dx.doi.org/10.1890/ES14-00111.1
Warming has been particularly strong at high latitudes in recent decades and bioclimatic models predict northern shifts in optimal conditions for most species. Climate is a strong predictor of site occupancy for trees at broad spatial scales and interacts with other drivers of forest dynamics. Recent changes in distribution and occupancy patterns should therefore provide the best evidence of a tree species’ potential to shift in the direction predicted by bioclimatic models. Studies examining recent distribution changes for plants, however, have mostly done so along altitudinal gradients or have used the latitudinal position of juvenile trees relative to adult ones to infer range dynamics. This study provides rare evidence of latitudinal shifts for 11 northern tree species by assessing recent changes in distribution using globally significant inventories from 1970 to 2002. It also compares observed trends with those inferred from the position of juveniles relative to trees in a single survey. Samplings cover 6456 forest plots in temperate and boreal forests up to treeline in eastern North America. The average overall latitudinal shift was 3.07 ± 4.37 km northward although responses were species-specific. Shifts were detected more for juvenile than for adult trees and significant northward ones were detected more at northern range limits than at the median. All species demonstrated increased frequency of plot occupancy for saplings while occupancy generally decreased for adult trees. Five out of the 11 species examined (Acer rubrum, Acer saccharum, Betula papyrifera, Fagus grandifolia, and Populus tremuloides) showed significant distributional shifts consistent with northward migration. Saplings of Abies balsamea, Picea glauca, and Picea mariana, on the other hand, showed southward shifting trends. Natural and human disturbances undoubtedly interact with climate to determine forest dynamics; this study shows whether their combined effect can shift distribution in the direction predicted by bioclimatic models. Only continued monitoring will reveal whether these observations are just transient dynamics or indicative of shifting range in this century. Our study provides a benchmark against which to assess future observations of latitudinal shifts for trees.
