Benoit Lafleur

Response of northeastern North American forests to climate change: Will soil conditions constrain tree species migration?

Plant species distribution and plant community composition vary along environmental gradients. At the continental scale, climate plays a major role in determining plant distribution, while at the local and regional scales vegetation patterns are more strongly related to edaphic and topographic factors. The projected global warming and alteration of the precipitation regime will influence tree physiology and phenology, and is likely to promote northward migration of tree species. However the influence of soil characteristics on tree species migration is not as well understood. Considering the broad tolerance of most tree species to variations in soil factors, soils should not represent a major constraint for the northward shift of tree species. However, locally or regionally, soil properties may constrain species migration. Thus, while climate change has the potential to induce a northward migration of tree species, local or regional soil properties may hinder their migratory response. These antagonistic f...

Soil modifications created by ants along a post-fire chronosequence in lichen-spruce woodland

Abstract Ants appeared to be an important component of the soil fauna in azonal lichen-spruce woodland in southern Québec, but their role in nutrient distribution and vegetation dynamics remained unknown. A study was undertaken to compare physical, chemical, and microbial properties of nest mound soils to those of surrounding soils to test the hypothesis that ants create patches of fertile soil and that these modifications are greater than changes in soil fertility due to forest succession. We also quantified ground cover, sexually regenerated black spruce seedlings, and ant nests along the chronosequence and verified whether nest mounds constituted safe sites for black spruce seedling establishment. Surface nest mounds had a significant effect on most measured soil variables. Compared to surrounding soils, nest soils had lower moisture content and bulk density, higher organic matter content and pH, higher available C for microbial growth, higher plant-available N, and were enriched in several major nutrients (K, Ca, Mg). Extractable-P was, however, lower in nest mounds than in surrounding soils. On the other hand, age-class significantly affected fewer soil variables (moisture, microbial biomass, extractable Na, and total Ca), and these changes could be explained by fire disturbance and the subsequent development of the tree stratum. Exposed mineral soil was the dominant ground cover in the 1-year-old and 9-year-old plots, while lichen cover was dominant in the three older age-classes. Sexually regenerated black spruce seedlings occurred mainly in the sparse moss layer in the 1-year-old and 9-year-old age-classes and almost exclusively in the lichen layer in the two older age-classes. Seedling density was 15 ha-1 the year following fire disturbance, but varied between 52 and 121 ha-1 in the four older age-classes. The average densities of occupied ant nests varied between 137-188 nests ha-1 across age-classes and occurred directly in lichen or moss, under bare mineral soil, in coarse woody debris, or under conspicuous sand mounds. We found no seedlings growing on occupied or abandoned nest mounds, which numbered only 15 ha-1 in the 1-year-old age-class and between 44 and 74 ha-1 in subsequent age-classes. We conclude that ants in this lichen-spruce woodland create nutrient-rich patches that can have a positive effect on tree growth and accelerate canopy closure, but we reject the hypothesis that nest mounds are safe sites for black spruce seedling establishment.

Ground-Nesting Ant Assemblages and Their Relationships to Habitat Factors Along a Chronosequence of Postfire-Regenerated Lichen–Spruce Woodland

Abstract Ground-nest densities and nesting habits of 13 ant species were quantified in five postfire age classes (1, 9, 23, 47, and 79 yr old) in the lichen–spruce woodland of Quebec, Canada. There were no significant differences in ant nest densities between age-classes (average of 163 nests/ha), but there were significant differences in ant community structure. Ant communities were dominated by Formica podzolica, F. aserva, F. hewetti, and Myrmica detritinodis, which accounted for 77% of occupied nests. Some species (e.g., F. podzolica) were specialists in their nesting habits, whereas others (e.g., F. aserva) were generalists and built their nest in a variety of substrates. Nest densities of F. aserva correlated with several habitat factors, but these correlations could have been spurious because they were not related to this species’ nesting habits. However, significant positive correlations found between Camponotus herculeanus and Leptothorax canadensis and coarse woody debris (CWD) may be biologically significant, because these two species nested exclusively within CWD. Nest densities of M. detritinodis and M. fracticornis were relatively high in the youngest and the oldest age classes, resulting in a negative correlation with CWD. We suggest that the distribution of these two species is caused by their preference for older forests to a high rate of fire survival and possibly to competitive release in the year after disturbance. According to canonical correspondence analysis, at least 75% of the variation in ant species cannot be explained by the habitat factors measured. Future research should include, therefore, experimental manipulations to determine the extent to which other factors, such as interspecific interactions, may structure ant communities in lichen–spruce woodland.

Growth of planted black spruce seedlings following mechanical site preparation in boreal forested peatlands with variable organic layer thickness: 5-year results

ContextFollowing forest harvest, mechanical site preparation (MSP) is commonly used to regenerate harvested sites. In boreal forested peatlands, however, the effectiveness of MSP to regenerate harvested sites is likely to be hampered by thick organic layers.AimWe sought to determine the capability of different MSP techniques to improve growth conditions of planted black spruce seedlings in boreal forested peatlands where closed-crown productive forests could revert to unproductive forested peatlands in the absence of severe soil disturbance.MethodsThe effects of disc scarification, mounding and patch scarification on soil chemistry and seedling growth were contrasted.ResultsSeedlings of site-prepared plots were 15% taller than those of untreated ones, irrespective of the MSP technique used, likely owing to the greater abundance of exposed mineral soil and mesic substrates created. Mounding and patch scarification were able to expose mineral soil over a greater proportion (>25% vs. <10%) of the treated area compared with disc scarification and control, whereas the combined surface area of exposed mineral soil and mesic substrates was higher in every MSP treatments relative to the control (>57% vs. 41%, respectively). Individual seedling growth was influenced by substrate type and drainage. Seedlings planted in moderately and well-drained mesic substrates and mineral soil were 25% taller than those planted in poorly drained fibric substrates.ConclusionAll three MSP techniques were effective because they succeeded in creating high-quality microsites despite thick organic layers.

Large Planting Stock Type and Mechanical Release Effects on the Establishment Success of Picea glauca Plantations in Quebec, Canada

We established four experimental plantations to evaluate the main and interaction effects of timing (year of application) of mechanical release and stock type (containerized or bareroot) on the establishment success of large Picea glauca seedlings eight years after outplanting on high-competition sites in Quebec (Canada). We also monitored percent cover and height of target vegetation groups as well as the amount of photosynthetically active radiation available to crop trees. Our results indicate that the use of large containerized or bareroot stock had limited effects on seedling growth, although bareroot seedlings presented higher mortality than containerized seedlings. Mechanical release enhanced seedling growth, compared to the control. Delaying treatment by two years impacted crop tree dimensions, although differences were minimal. Survival was not affected. We conclude that large containerized seedlings should be favoured over bareroot stock for reforestation on high-competition sites and that the release guidelines developed for standard size seedlings are applicable to the large dimension P. glauca stock tested in this study.

Phytoremediation of groundwater contaminated with pesticides using short-rotation willow crops: a case study of an apple orchard

ABSTRACT 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.

Ecosystem management in paludified boreal forests: enhancing wood production, biodiversity, and carbon sequestration at the landscape level

Canada’s boreal forest represents an important contributor of the world’s wood supply industry. However, maintaining or increasing productivity of the boreal forest may be challenging in areas dominated by forested peatlands. Moreover, sustainable management of these forests must also consider other important aspects of the forest ecosystem such as biodiversity and carbon sequestration. To address these concerns, ecosystem-based management has been implemented in some Canadian jurisdictions, such as in regions where a large portion of the boreal forest is dominated by forested peatlands. The objectives of this paper are (1) to summarize our current understanding of how natural disturbances influence stand dynamics and biodiversity in forested peatlands, and (2) to review the main differences between natural and managed forest stands with respect to soil properties, stand productivity, understory plant communities. We also discuss how even-age management regime succeeds or fails to preserve old forests and how this loss affects both forest structure and habitat diversity at the landscape level. We conclude by showing how, in boreal forested peatlands, forest management could contribute to carbon sequestration and mitigate projected climate change.