by Claire Morin | 30 January 2019
Published in Forest Ecology and Management 345: 39-49. https://doi.org/10.1016/j.foreco.2015.02.032
Two fertilization trials were carried out in young balsam fir (Abies balsamea (L.) Mill.) stands showing symptoms of tree decline or foliar chlorosis in boreal forests of eastern Laurentian Highlands in Quebec, Canada. In the first trial, trees showed strong decline symptoms; fertilization treatments consisted of combinations of two nutrients among N, K, and Mg, each at two rates. In the second trial, trees showed some needle chlorosis; various doses of N, K, K–Mg, and K-lime fertilizers were applied. In both trials, N fertilization (200 kg N ha-1) resulted only in a short-term (2–3 years) increase in foliar N concentrations and radial growth. Potassium fertilization (100–400 kg K2O ha-1), however, led to an increase of at least 33% in both foliar K concentrations and radial growth, which lasted for the duration of the experiments (7–11 years). Liming (1–4 t dolomitic lime ha-1) increased the pH, exchangeable calcium and exchangeable magnesium in the humus and top mineral soil horizons, but did not influence balsam fir foliar nutrient status or growth. Tree defoliation rate was mainly related to growth decrease and foliar K concentrations. The trials also show that K was the most limiting nutrient for balsam fir growth, and that the poor K nutrient status and vigor of balsam fir trees can be corrected by K fertilization. These results contrast with past fertilization studies that generally reported N as the most limiting nutrient in these boreal ecosystems. Climatic events may have also played a role in triggering the decline of balsam fir in one trial.
by Marie-Claude Boileau | 30 January 2019
Published in Applied Ergonomics 50: 68-78. http://dx.doi.org/10.1016/j.apergo.2015.03.001
This paper presents a new model based on adaptive neuro-fuzzy inference systems (ANFIS) to predict oxygen consumption (VO2) from easily measured variables. The ANFIS prediction model consists of three ANFIS modules for estimating the Flex-HR parameters. Each module was developed based on clustering a training set of data samples relevant to that module and then the ANFIS prediction model was tested against a validation data set. Fifty-eight participants performed the Meyer and Flenghi step-test, during which heart rate (HR) and VO2 were measured. Results indicated no significant difference between observed and estimated Flex-HR parameters and between measured and estimated VO2 in the overall HR range, and separately in different HR ranges. The ANFIS prediction model (MAE = 3 ml kg-1 min-1) demonstrated better performance than Rennie et al.’s (MAE = 7 ml kg-1 min-1) and Keytel et al.’s (MAE = 6 ml kg-1 min-1) models, and comparable performance with the standard Flex-HR method (MAE= 2.3 ml kg-1 min-1) throughout the HR range. The ANFIS model thus provides practitioners with a practical, cost- and time-efficient method for VO2 estimation without the need for individual calibration.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 329: 69-78. http://doi.org/10.1016/j.foreco.2014.06.020
Interactions between multiple disturbances can alter resilience mechanisms, thereby triggering alternative successional pathways. Regeneration processes are important mechanisms of forest resilience because they drive successional pathways. On Anticosti Island, chronic browsing by introduced whitetailed deer (Odocoileus virginianus) shifted composition of understory regeneration of overmature balsam fir (Abies balsamea) forests toward dominance by white spruce (Picea glauca). Historic clear-cutting of these altered forests generated mature second-growth white spruce stands. However, the cumulative effect of chronic deer browsing and recent clear-cutting on regeneration processes of mature secondgrowth white spruce stands has not yet been evaluated. Our objective is to evaluate if regeneration processes would enable white spruce stands to recover from the cumulative effects of these two disturbances. We studied regeneration in relation to seed availability, substrate suitability for seedling establishment, and substrate availability in mature second-growth white spruce stands and recent clear-cuts of mature second-growth white spruce stands. Our results indicate regeneration failure in both ecosystems, which can be explained by a lack of suitable rotten logs for sufficient establishment of white spruce seedlings. Hence, the cumulative effects of chronic deer browsing and clear-cutting of mature second-growth white spruce stands have altered regeneration processes and triggered an alternative successional pathway toward parklands, i.e., partial deforestation. We propose shelterwood cuttings that create nurse logs should be investigated to maintain white spruce stands without planting.
by Svetlana Savin | 30 January 2019
Published in Forest Ecology and Management 302: 390-403
Existing models that use the site-index concept (dominant canopy height of a tree species at a reference stand age) are fundamentally stand-level models that do not account for stand dynamics, limiting their use to only a part of successional trajectories. Given that stand dynamics is influenced by both large and fine scale processes, we took a multi-level look at aspen (Populus tremuloides Michaux) productivity by determining landscape- and plot-level factors related to productivity as rated with site index. The study area extends from latitude 45° to 50°N in western Québec, from which were sampled 62 landscapes made up of 4948 plots, 25% of which had aspen as dominant and/co-dominants in the canopy. There, aspen is most often found in mixed stands. A stepwise procedure with forward selection was used in building landscape- and plot-level models and models were then arranged hierarchically such that (a) predicted estimates of the landscape model were inputs to the plot-level model (top-down) and (b) significant landscape variables were added to selected plot level variables (bottom-up). For the plot-level model, none of the climate variables considered were selected but at the landscape level, annual sum of degree–days was only the third to enter. In both cases, aspen site index was more related to the proportion of spruce (Picea mariana (Mill.) B.S.P. and Picea glauca (Moench.) Voss). At the level of landscapes, this observation might be due to the existence of particular vegetation mosaics, of which spruce proportion could be a surrogate. At the level of plots, influence of spruce on aspen site index is probably indicative of niche sharing with aspen. A high random variability was associated with the plot-level model but not with the landscape-level model. The similarity in drivers of aspen site index at both levels and the fact that both top-down and bottom-up approaches provided the same information, suggest that the use of landscape variables when modelling site index in mixed stands may help distinguish peculiarities shared by plots located in a landscape and improve the signal between site index and explanatory variables by reducing the random noise observed at the level of plots.
by Claire Morin | 30 January 2019
Published in Tree Physiology https://doi.org/10.1093/treephys/tpt027
A 20–40% reduction in soil moisture is projected for the boreal forest of Eastern Canada for the period 2070–99 relative to 1971–2000. In order to better predict the effects of a reduced water supply on the growth of balsam fir (Abies balsamea (L.) Mill.), a dominant tree species of the boreal forest, we simulated 2 consecutive years of summer droughts (starting in July) by means of throughfall exclusion. Four 100-m2 plots were established in 2010 with polyethylene sheets maintained 1.3–2 m aboveground and redirecting the water outside the plots. Wood microcores were extracted weekly from mature trees from April to October 2011 to analyse the time dynamics of wood formation in that year. The number of tracheids formed during and before treatment and their anatomical characteristics were determined through microscopic analyses. The growth of lateral and terminal branches and the water potential of balsam fir seedlings were also monitored. Throughfall exclusion significantly reduced soil water content by 5.8% in 2010 and 10.5% in 2011. Xylogenesis was affected significantly by the treatment. Tracheids were 16.1% smaller in diameter and their cell wall was 14.1% thicker during both years. The treatment delayed by more than a week the start of the tracheid differentiation process in the second year with a concomitant decrease (26%) in the number of tracheids produced. The seedlings displayed a 32% reduction in growth and a 40% reduction in leaf water potential. Our results suggest that a future regime of increased frequency and intensity of droughts could have negative effects on the duration of xylogenesis and the production of xylem cells in balsam fir.
