The occurrence of pesticides in groundwater represents an important health issue, notably for population whose drinking water supply source is located in agricultural areas. However, few solutions have been considered with regard to this issue. We tested the efficacy of a vegetal filtering system made of shrub willows planted at a high density (16,000 plants ha(-1)) to filter or degrade pesticides found in the groundwater flowing out of an apple orchard. Ethylene urea (EU), ethylene thiourea (ETU), tetrahydrophthalimide (THPI), atrazine, and desethylatrazine were monitored in the soil solution in willow and control plots over one growing season. ETU and atrazine concentrations were lower in the willow plots relative to the control plots, whereas desethylatrazine concentration was higher in the willow plots. No significant difference was detected for EU and THPI. Furthermore, pesticide concentrations displayed complex temporal patterns. These results suggest that willow filter systems can filter or degrade pesticides, notably ETU and atrazine, and could be used for phytoremediation purposes. Yet, this potential remains to be quantified with further studies using experimental settings allowing more estimation in time and space.
The forest tent caterpillar (Malacosoma disstria) is a significant defoliator of hardwoods throughout Canada. Historically, infestations usually collapsed after one or two years of defoliation, but longer and more severe outbreaks have been observed in recent years, leading to mortality of both sugar maple and trembling aspen, and making the forest tent caterpillar another pest whose impacts are increasing under a changing climate.
This project examines how forest tent caterpillar outbreaks influence soil ecosystems, in both temperate deciduous and mixed boreal forests. We will assess inputs to soil ecosystems associated with forest tent caterpillar outbreaks and determine impacts on soil arthropod communities and tree regeneration. We also examine the different sources of mortality of the forest tent caterpillar colonies during and after the outbreak. It will thus provide empirical data to assess effects of forest tent caterpillar outbreaks on forest ecosystems and successional processes as well as population dynamics throughout the outbreaking cycle. Results suggest that defoliation favours the growth of non-host saplings. They also suggest that sources of mortality change during the different parts of the outbreak. Results will also contribute to the development of novel silvicultural approaches taking into account the effects of forest tent caterpillar outbreaks on forest regeneration and the need to keep process promoting regulation of forest tent caterpillar populations.
La livree des forets (Malacosoma disstria) est un defoliateur important des forets feuillues du Canada. Dans le passe, les epidemies s’effondraient generalement apres une ou deux annees de defoliation sans causer de dommages significatifs a la foret, mais l’observation recente d’epidemies plus longues et plus severes, suivies de mortalite des tiges de peuplier faux-tremble et d’erable a sucre, suggerent que les impacts de la livree des forets, comme de plusieurs autres insectes ravageurs, augmentent en raison des changements climatiques.
Ce projet examine les effets d’une epidemie de livree des forets sur l’ecosysteme du sol dans deux ecosystemes forestiers: la foret feuillue et la foret boreale mixte. Nous examinerons les apports en nutriments au sol associes aux epidemies de livree et evaluerons les effets sur la communaute d’arthropodes du sol et sur la regeneration des arbres. Nous avons aussi examine les sources de mortalite des colonies de livree des forets durant et apres l’epidemie. Les resultats fourniront des donnees empiriques pour evaluer les impacts des epidemies de livree sur les ecosystemes forestiers et les processus de succession ecologiques ainsi que les dynamiques de populations a travers les cycles epidemiques. Les resultats suggerent que la defoliation peut beneficier la croissance des jeunes arbres non-hotes. Ils suggerent aussi que les sources de mortalite different lors des differentes parties du cycles epidemiques. Les resultats contribueront aussi au developpement d’approches sylvicoles qui prennent en consideration le role de la livree dans la regeneration des forets.
Natural disturbances, such as fire and insect outbreaks, play important roles in natural forest dynamics, which are characterized over long time scales by changes in stand composition and structure. Individual-based forest simulators could help explain and predict the response of forest ecosystems to different disturbances, silvicultural treatments, or environmental stressors. This study evaluated the ability of the SORTIE-ND simulator to reproduce post-disturbance dynamics of the boreal mixedwoods of eastern Canada. In 1991 and 2009, we sampled all trees (including seedlings and saplings) in 431 (256 m2) plots located in the Lake Duparquet Research and Teaching Forest (western Quebec). These plots were distributed in stands originating from seven wildfires that occurred between 1760 and 1944, and which represented a chronosequence of post-disturbance stand development. We used the 1991 inventory data to parameterize the model, and simulated short- to long-term natural dynamics of post-fire stands in both the absence and presence of a spruce budworm outbreak. We compared short-term simulated stand composition and structure with those observed in 2009 using a chronosequence approach. The model successfully generated the composition and structure of empirical observations. In long-term simulations, species dominance of old-growth forests was not accurately estimated, due to possible differences in stand compositions following wildfires and to differences in stand disturbance histories. Mid- to long-term simulations showed that the secondary disturbance incurred by spruce budworm did not cause substantial changes in early successional stages while setting back the successional dynamics of middle-aged stands and accelerating the dominance of white cedar in late-successional post-fire stands. We conclude that constructing a model with appropriate information regarding stand composition and disturbance history considerably increases the strength and accuracy of the model to reproduce the natural dynamics of post-disturbance boreal mixedwoods.
It has been suggested that without sufficient soil disturbance, harvest in boreal forested peatlands may accelerate paludification and reduce forest productivity. The objectives of this study were to compare the effects of harvest methods (clearcutting vs. careful logging) and season (summer vs. winter harvest) on black spruce regeneration and growth in boreal forested peatlands of eastern Canada, and to identify the soil variables that favour tree growth following harvest. Moreover, we sought to determine how stand growth following harvest compared with that observed following fire. The average tree height of summer clearcuts was greater than that of summer carefully logged stands and that of all winter harvested sites. Summer clearcutting also resulted in a higher density of trees > 3 m and > 4 m tall and in a 50% reduction in Rhododendron groenlandicum cover, a species associated with reduced black spruce growth. Height growth of sample trees was related to foliar N and P concentrations, and to soil total N, pH and available Ca and Mg but not to harvest method or season. Our results also indicate that summer clearcutting could produce stand productivity levels comparable to those observed after high-severity soil burns. These results suggest that summer clearcutting could be used to restore forest productivity following harvest in forested peatlands, and offer further support to the idea that sufficient levels of soil disturbance may be required to restore productivity in ecosystems undergoing paludification.
Changes in the light availability in forests generated by diversified retention patterns (e.g., clear cut, partial harvest) have been shown to strongly filter the plant species present. Modified soil microsite conditions due to post-harvest site preparation (e.g., mechanical site preparation, prescribed fire) might also be an important determinant of plant diversity. The objective here was to detect how retention pattern and post-harvest site preparation act as filters that explain the understory functional diversity in boreal forests. We also assessed whether these effects were dependent on forest attributes (stand type, time since fire, and time since harvest). We retrieved data from seven different studies within 101 sites in boreal forests in Eastern Canada. Our data included forests harvested with two retention patterns: careful logging and clear cut, plus unharvested control forests. Three post-harvest site preparation techniques were applied: plow or disk trenching after careful logging, and prescribed fire after clear cut. We collected trait data (10 traits) representing plant morphology, regeneration strategy, or resource utilization for common species. Our results demonstrated significant variation in functional diversity after harvest. The combined effect of retention pattern and site preparation was the most important factor explaining understory diversity compared to retention pattern only and forest attributes. According to RLQ analysis, harvested forests with site preparation favored traits reflecting resistance or resilience ability after disturbance (clonal guerilla species, geophytes, and species with higher seed weight). Yet harvested forests without site preparation mainly affected understory plant species via their light requirements. Forest attributes did not play significant roles in affecting the relationship between site preparation and functional diversity or traits. Our results indicated the importance of the compounding effects of light variation and soil disturbance in filtering understory diversity and composition in boreal forests. Whether these results are also valid for other ecosystems still needs to be demonstrated.
"Montenach, Anne. Espaces et pratiques du commerce alimentaire à Lyon au XVIIe siècle. L’économie du quotidien." Urban History Review, 39(2), pp. 63–64
