by Claire Morin | 30 January 2019
Published in PLOS ONE 10(12): e0144844. https://doi.org/10.1371/journal.pone.0144844
Maple syrup production is an important economic activity in north-eastern North-America. The beginning and length of the production season is linked to daily variation in temperature. There are increasing concerns about the potential impact of climatic change on this industry. Here, we used weekly data of syrup yield for the 1999–2011 period from 121 maple stands in 11 regions of Québec (Canada) to predict how the period of production may be impacted by climate warming. The date at which the production begins is highly variable between years with an average range of 36 days among the regions. However, the average start date for a given region, which ranged from Julian day 65 to 83, was highly predictable (r2 = 0.88) using the average temperature from January to April (TJ-A). A logistic model predicting the weekly presence or absence of production was also developed. Using the inputs of 77 future climate scenarios issued from global models, projections of future production timing were made based on average TJ-A and on the logistic model. The projections of both approaches were in very good agreement and suggest that the sap season will be displaced to occur 15–19 days earlier on average in the 2080–2100 period. The data also show that the displacement in time will not be accompanied by a greater between years variability in the beginning of the season. However, in the southern part of Québec, very short periods of syrup production due to unfavourable conditions in the spring will occur more frequently in the future although their absolute frequencies will remain low.
by Audrey Verreault | 30 January 2019
Published in Forest Ecology and Management 350: 62-69. https://doi.org/10.1016/j.foreco.2015.04.019
Age-related decline of forest stand growth is a common phenomenon, but the associated physiological causes remain uncertain. This study investigated a possible mechanism that could explain stand growth decline observed after canopy closure. We hypothesised that the proportion of resource allocation to roots increases with stand age as a response to a decrease in nutrient availability, which is related to the long-term accumulation of organic matter in boreal forests. Proxies based on soil respiration measurements and stem biomass production were used to describe temporal changes in the proportion of carbon allocated to belowground and aboveground stand components along a 1067-year post-fire chronosequence. The proportion of resources that were allocated belowground increased in the first 200 years following fire and declined thereafter. The inverse pattern was observed for the organic matter decomposition rate. Stand-level decline in wood productivity that was observed during the first 60-year period after fire can be attributed to a greater proportion of carbohydrates being allocated to roots in response to a decrease in nutrient availability. However, the relatively low productivity of old-growth stands was not associated with high belowground allocation, suggesting that other mechanisms operating at the tree- or stand-level may be involved.
by Claire Morin | 30 January 2019
Published in Sensors 16(8): 1190. https://doi.org/10.3390/s16081190
The reduction of nitrate leaching to ensure greater protection of groundwater quality has become a global issue. The development of new technologies for more accurate dosing of nitrates helps optimize fertilization programs. This paper presents the practical application of a newly developed electrochemical sensor designed for in situ quantification of nitrate. To our knowledge, this paper is the first to report the use of electrochemical impedance to determine nitrate concentrations in growing media under forest nursery conditions. Using impedance measurements, the sensor has been tested in laboratory and compared to colorimetric measurements of the nitrate. The developed sensor has been used in water-saturated growing medium and showed good correlation to certified methods, even in samples obtained over a multi-ion fertilisation season. A linear and significant relationship was observed between the resistance and the concentration of nitrates (R2 = 0.972), for a range of concentrations of nitrates. We also observed stability of the sensor after exposure of one month to the real environmental conditions of the forest nursery.
by Claire Morin | 30 January 2019
Published in Ecology 99(9): 2047-2057. https://doi.org/10.1002/ecy.2417
Understanding the causal pathways through which forest insect outbreaks are triggered is important for resource managers. However, detailed population dynamics studies are hard to conduct in low-density, pre-outbreak populations because the insects are difficult to sample in sufficient numbers. Using laboratory-raised larvae installed in the field across a 1,000 km east–west gradient in Québec (Canada) over an 11-yr period, we examined if parasitism and predation were likely to explain fluctuations in low-density spruce budworm (Choristoneura fumiferana; SBW) populations. Parasitism rates by the two main larval parasitoid species, Elachertus cacoeciae and Tranosema rostrale, peaked during different years. This suggests that temporal fluctuations in overall parasitism were partly buffered by compensatory dynamics among parasitoid species. Still, spatial covariance analyses indicate that the residual interannual variation in parasitism rates was substantial and correlated over large distances (up to 700 km). On the other hand, interannual variation in predation rates was not spatially correlated. Piecewise structural equation models indicate that temporal variation in parasitism and predation does not influence temporal variation in wild SBW abundance. Spatially, however, SBWs installed in warmer locations tended to show higher parasitism rates, and these higher rates correlated with lower wild SBW population levels. Overall, the results indicate that large-scale drops in parasitism occur and could potentially contribute to SBW population increases. However, during the period covered by this study, other factors such as direct effects of weather on SBW larval development or indirect effects through host tree physiology or phenology were more likely to explain large-scale variation in wild SBW populations.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Science 62(2): 227-236 http://dx.doi.org/10.5849/forsci.15-023
Since two decades, patch cutting systems have been applied in Eastern Canada to regenerate uneven-aged yellow birch (Betula alleghaniensis Britton) – conifer stands. Yet, we still know very little about how the trees located in the between-patch matrix respond to treatments. This study compares growth, recruitment and tree mortality of yellow birch, red maple (Acer rubrum L.), balsam fir (Abies balsamea [L.] Mill.) and red spruce (Picea rubens Sarg.) in three 50% patch cutting treatments with 20-, 30-, 40-m diameter circular gaps combined with 33% single-tree cutting in the matrix between patches, and an uncut control. After 10 years, positive effects of cutting treatments on recruitment and growth were nullified by mortality, resulting in non-significant changes in stand net merchantable basal area. Mortality rate modeled at the tree-level was higher for trees with larger diameters, defects, and high crown ratios. Trees with small diameter and those located along the border of harvest gaps had the largest increments in basal area. This study questions the use of patch cutting in mixed uneven-aged stands comprising an important component of short-lived balsam fir. Silvicultural systems utilizing non-systematic placement of variably-sized gaps may prove more beneficial for managing wood production and complexity in yellow birch – conifer stands.
