The purpose of this investigation was to examine the effects of species composition and crown section on withincrown foliage distribution and the relationship of basal area growth rate to amount of foliage on young white spruce (Picea glauca) growing in pure composition and in mixture with trembling aspen (Populus tremuloides). Branch and needle biomass, projected leaf area, specific leaf area, and ratio of needle biomass to branch biomass, along with several whole-tree metrics, including height and diameter at breast height (1.3 m), were measured on thirteen 20-y-old white spruce trees, 7 from pure composition and 6 from mixed composition. While there was no effect of composition on whole-tree differences among subject trees, within-crown distribution of branch and foliage amount and morphology and concentration of foliage were significantly affected by both composition (mixed and pure) and crown section (lower, mid, upper). There was a positive relationship between periodic annual basal area increment and foliage amount (biomass and projected area) on subject white spruce trees that did not differ between trees in pure and mixed compositions. Despite the significant effect of species composition on the vertical within-crown distribution of foliage and branch amount and foliage morphology, similar changes in total foliage biomass and area had similar effects on periodic annual increment of basal area regardless of composition.

In the Canadian boreal forest, jack pine stands generally have a thin forest floor and occupy sites with coarsetextured soils and good drainage. Black spruce occurs more often on poorly drained sites and develops a thick mossdominated forest floor, but the common attribution of this development to poor quality of black spruce foliar litter has not been tested. We determined needle, twig, cone, and bark litter inputs during 10 y for black spruce and jack pine along the Boreal Forest Transect Case Study in northern Saskatchewan and Manitoba. Analysis of C, N, total phenolics, condensed tannins, and solid-state ¹³C NMR spectra from years 1–3 showed only small differences between species, notably higher tannins in black spruce cones. There was similarly little difference between area-based inputs, including classes of C structures determined by NMR. Condensed tannin input for black spruce was approximately twice that for jack pine, but both were in the very low range of reported values. Similar analyses showed that black spruce forest floor was less decomposed than that of jack pine, and for both species, aromatic litter C inputs appear to be poorly conserved, with a large influence of mosses and lichen. It is unlikely, however, that these large differences are mainly due to the small differences in aboveground litter inputs.

Tree planting is a useful means of integrating reclaimed mine sites into natural forested landscapes. The main objective of this study was to evaluate the effect of soil thickness and nature on the establishment and metal accumulation of trees planted in low sulfur mine wastes under boreal conditions. Two field experiments were conducted to evaluate survival, growth, and nutrient and trace metal concentrations of several trees, including 2 fast-growing species (Pinus banksiana, Larix laricina, Populus maximowiczii × P. balsamifera, P. × canadensis × P. maximowiczii, and Salix viminalis), planted in soils (topsoil or subsoil, 50 or 20 cm thick) above waste rock and thickened tailings, respectively. As expected, tree growth increased (×2) in the topsoil compared to the subsoil above waste rock, despite mineral fertilization. Tree growth also decreased in thin topsoils, concomitantly with a decrease in foliar N concentrations, but soil thickness had no effect on tree survival. The basket willow appeared well adapted and multi-purpose for mine-waste revegetation over the short term since its survival remained maximal whatever the nature (topsoil or subsoil) or thickness (50 versus 20 cm) of the soil layer or waste type (waste rock versus tailings). The tamarack showed good survival and growth on both waste types (except in subsoil alone). By contrast, the survival (waste rock) and growth (thin soils above tailings) of hybrid poplars was poor under the tested conditions. On these non-acid-generating wastes with low total trace metal concentrations, none of the tree species accumulated trace metals from soil in their foliage, but basket willow survival should be followed over the longer term to check for deleterious effects of Zn accumulation.

Permanent forest plots (PSP) were used to investigate long-term basal-area tree growth rates across the boreal forests in Canada. The objectives were to discern whether or not these rates i) are similar across the boreal zone and ii) correlate to change in climate from 1970 to 2010. The results show that rates vary by region, with decreasing growth rates for about 60% of individual trees in western Canada (Alberta, Saskatchewan, Manitoba) but increasing rates for about 70% of individual trees in eastern Canada (Ontario and Quebec). These changes are interpreted from an overall carbon sequestration perspective and within the context of available precipitation and air temperature data and an annual climate moisture index. This study provides long-term plot-based evidence for the ecological variability and regional differences in tree growth detected by satellite-based remote-sensing and tree-ring studies in Canada's boreal forests.

The variation in nitrogen, insoluble and soluble proteins, and chlorophyll concentrations (mg·g^-1) and contents per unit leaf area (mg·cm^-2) as a function of specific leaf area (SLA) was examined in leaves sampled at the bottom, middle, and upper sections of the crowns of balsam fir (Abies balsamea) and black spruce (Picea mariana) trees located along a temperature gradient in Quebec, Canada. Differences in needle dimensions, mass, surface, and SLA among crown sections and needle age were more pronounced for balsam fir than for black spruce. Relationships of foliage nitrogen, insoluble and soluble proteins, and chlorophyll content per unit leaf area as a function of SLA were generally more significant than those based on concentration. However, the different variables varied little along a temperature gradient. The higher significance of area-based relationships in comparison with mass-based relationships was attributed to the change in leaf morphology in response to light availability within the crown. Yet, nitrogen availability most likely restricted light acclimation to changes in morphology, since there was very limited modulation of nitrogen partitioning among the different protein fractions as a function of light environment.

The individual-based EFIMOD simulation model was used for regional-scale assessments of the dynamics of basic characteristics of the carbon and nitrogen balance in the forest ecosystems of north central Russia. Two forest strict nature reserves were chosen as case studies. Data from the National Forest Inventory were used for model initialization. Initial soil data were taken from a soil survey database containing data on soil organic matter and nitrogen content in the organic layer and mineral soil for different forest types and regions of European Russia. Standard meteorological data were used as climatic inputs. Two simulation scenarios (without disturbances and with forest fires) were coupled with 2 climatic ones (actual climate and the scenario of climate change). The main sources of uncertainty were analyzed and the model parameters were evaluated. A Monte Carlo procedure was applied for evaluation of the robustness of coefficients. Simulation results showed that the greatest carbon accumulation occurred in the scenario without disturbances. Fires resulted in significant losses in soil organic matter and tree biomass through direct and indirect carbon dioxide emissions. Simulated climate change led to an increased decomposition rate of soil organic matter and a related increase in the productivity of vegetation; however, for this region, the carbon balance was positive. This was primarily because young and middle-aged stands are prevalent in the region modeled. A full analysis would require analytical data on the possible dynamics of mature and over-mature forests in the same scenarios of climate change and forest fires.

Carbon (C) content in several forest ecosystem pools, including trees, understory species, downed logs, litter, soil organic and mineral layers, and fine roots, and tree growth were compared in balsam fir (Abies balsamea) and black spruce (Picea mariana) ecosystems located along a climatic gradient in eastern Canada spanning regions that differed by 4 °C in mean annual temperature. A total of 19 experimental sites were established, 12 in balsam fir ecosystems and 7 in black spruce ecosystems. Diameter at breast height (dbh), height growth rate, and C contents in trees, understory species, downed logs, litter, and soil organic and mineral layers did not differ significantly between northern and southern experimental sites (P < 0.05). The only C pool that differed significantly among the regions was fine roots. Tree ring data collected on trees greater than 5 cm in dbh at all the sites were related to monthly climatic data between April and October, the active physiological season at the latitudes of the study. The relationships derived indicated that the differential effects of significant climatic variables along the climatic gradient were more important for black spruce than balsam fir. These results suggest that the changes in climatic conditions in the next 100 y may have a relatively small effect on the productivity and C allocation of both forest types when located within a range of climatic conditions similar to those of this study.

This study compared growth of hybrid poplar in relation to soil mounding and mechanical weed control on a former agricultural site under boreal climate in order to assess optimal management scenarios. Height and basal diameter growth of 2 clones (Populus maximowiczii × P. balsamifera [915319] and P. × euramericana × P. maximowiczii [916401]) were evaluated after 3 growing seasons in 2 mounding (mounded, unmounded) and 4 weed control treatments (0: no weed control; 1, 2, and 3: 1, 2, or 3 passes of mechanical weed control). Net photosynthesis, stomatal conductance, soil temperature, and percent cover and height of competing vegetation were measured to explain the effects of soil mounding and weed control on tree growth. Two passes of weed control increased growth of trees by 23% in basal diameter and 12% in height, while mounding had no effect on growth. Both mounding and weed control reduced the cover of weedy vegetation, which was negatively correlated with growth of clone 915 319. Mounding did not increase mean soil temperatures in spring and even reduced them in the fall, while weed control had no effect on soil temperature. Finally, mounding significantly reduced the frequency and severity of damage (girdling) caused by voles during 2005–2006, especially for the plots that were not weeded.

This study examines the influence of the increased atmospheric nitrogen (N) deposition observed in central Russia between 1960 and 2010 (with a peak in 1990) on biodiversity and the availability of N in soil in pine forests. Shifts in N availability in soils of 3 pine plots were analyzed using presence/absence chronosequence records of the dynamics of ground vegetation plants and a set of specialist plant species with a narrow range of tolerance as bioindicators of soil richness. We assumed that changes in plant communities might be caused by increased atmospheric N input. To examine this assumption, (i) the species composition of forest ground vegetation was analyzed using the Ellenberg N scale and the Tsyganov N scale, which was developed for forest vegetation in European Russia, and (ii) the dynamics of the main N pools were examined using simulation models of forest growth and elements cycling in the forest—soil system. Our results confirm that changes in the ground vegetation communities experiencing eutrophication occurred in all plots. The number of indicators of N-rich conditions for these plots reached a maximum in 1990, the year N deposition reached its maximum in this area. The decline in the number of oligotrophic species indicated that N-poor soils decreased over the monitoring period. Model simulations showed an increase in labile N compounds in the soil and in the total N pool in forest ecosystems. Our results demonstrate an acceleration of natural succession due to atmospheric nitrogen deposition in this region.

Boreal Forest Transect Case Study with a natural climate gradient resulting from latitudinal variation provides a spatial proxy for expected climate change, and can help to understand its impact on different ecosystem processes and how the forest species are adapting to these changes. We investigated year to year variation in aboveground litter production for 2001–2010 in 13 different mature jack pine (JP) and black spruce (BS) stands in relationship to climatic variables. Simple linear and step-wise regression analysis showed that tree species interacted differently with climate and stand variables affecting litterfall. Annual total and woody litterfall varied from 57 to 164 g·m^-2·y^-1 in JP and 18 to 63 g·m^-2·y^-1 in BS. Needle litterfall accounted for about 70% of the total litter production in JP and BS and about 80% in mixed wood stands, and explained significant variation in total litter production. On regional scale, needle litter production was strongly influenced by growing degree days (R² = 0.96). Woody litterfall decreased with winter precipitation (R² = 0.95) in JP, and increased with productivity (R² = 0.88) in BS. Regression models developed here are useful tools in carbon budget models.

The changes in temperature and precipitation regimes predicted for boreal regions are expected to profoundly affect the productivity of trees situated on waterlogged soils, which underlie large areas of boreal forest in Canada. The consequences for productivity of climatic variation likely depend on site ecology and differ between species. To investigate potential site-dependent responses to climate, we compared the growth of jack pine (Pinus banksiana) trees growing within the same climate conditions but along a transect extending from a fen margin to a sandy ridge. On the fen-margin site, black spruce trees (Picea mariana) were also sampled, allowing for a comparison of the sensitivity of both species. Growth variations at interannual and decadal frequency were analyzed from tree-rings. Our study revealed that the response to climate varied substantially between sites, but, surprisingly, trees growing on the fen margin proved to be very sensitive to fluctuations of precipitation at both interannual and decadal time scales. Black spruce trees responded more sensitively to climate variation than jack pine sampled at the same site. Our study also showed a modest response to temperature even in the driest site. For both species, decadal signals show precipitation as a common, strong productivity driver regardless of water table constraints. These results suggest that the predicted climate warming is therefore less of a threat to the productivity of peatland forested zones than fluctuations in the precipitation regime. Changes in precipitation are expected to have much stronger consequences at both interannual and decadal time scales than projected temperature fluctuations.

Throughout much of the northern temperate and boreal forests of Canada, intensifying silviculture to enhance fibre production is of increasing interest. However, some oppose the application of intensive silviculture, citing possible negative effects on biodiversity. Using fifth-year post-harvest data from the NEBIE Plot Network in Ontario, Canada, we studied the relationship between plant diversity, silviculture intensity, and contemporary climate. Neutral, linear (positive and negative), exponential (positive and negative), quadratic (concave up and concave down), cubic, and higher-order models were fit to the data. Here we discuss the potential influence of climate and silviculture on observed biodiversity patterns. As well, we address their effects on regional species pools, succession, hierarchical structure, invasibility by exotic species, and species resilience.

This study aims to demonstrate that contemporary landscape vegetation heterogeneity is controlled by a combination of natural disturbances with other sets of explanatory variables. Integration of these drivers should be considered the key to explaining vegetation changes along ecological gradients characterizing the boreal forest. Forest inventory plots and maps produced from about 1970 to 2000 were used to characterize a large area (175 000 km2) according to 3 vegetation themes constituting distinct aspects of forest community composition (tree species, forest types, and potential vegetation–successional stages) and 4 sets of explanatory variables (climate, natural disturbances, physical environment, and human disturbances). Canonical ordinations were performed to define ecological gradients as well as the overlap between vegetation themes and sets of explanatory variables along each gradient. For each vegetation theme, we quantified the relative proportion of vegetation variation explained by unique as well as combined sets of explanatory variables. The landscape vegetation heterogeneity described by species and potential vegetation–successional stage was mostly explained by natural disturbances and climate in association with other sets of explanatory variables. The influence of physical environment was higher for landscape vegetation heterogeneity related to forest types than for the other themes, but this theme also was dominated by natural disturbances and climate. Compared to natural sets of explanatory variables, human disturbances played a secondary but significant role in the 3 vegetation themes. This research contributes to a better understanding of the relationship between vegetation and the factors underlying its development in the boreal forest and represents an important step toward ecosystem-based management.

Persistence for woodland caribou (Rangifer tarandus) in Pukaskwa National Park (PNP, Ontario, Canada; 1878 km²) was tied to females finding safe calving areas on offshore islands with a water barrier created by Lake Superior. During 1975–1988, PNP caribou fluctuated around a carrying capacity of 24, but after 1988 the population declined, falling to 5 individuals by 2009. Caribou are now likely extirpated from PNP, even in the absence of any local or increased anthropogenic disturbance since the protected area was created in 1978. As moose (Alces alces) in the region declined concurrently, their relative density remained higher along the Lake Superior coastal strip than further inland, the reverse of the situation during 1975–1988; moose especially held to the coast during heavy snow years. Wolves (Canis lupus) accordingly shifted more of their hunting effort to the coast, likely encountering both moose and caribou with increasing search efficiency. These behaviours are described as a predator—prey “space race” that wolves eventually won.

To improve our understanding of climate-driven long-term dynamics of eastern Asian mountain forests, we used field surveys and dendrochronological techniques to examine regeneration density, growth rate of mature trees, and growth sensitivity to climate of 3 common coniferous tree species at their respective altitudinal distribution limits on Changbai Mountain, northeastern China. The studied species were Manchurian fir (Abies nephrolepis, distributed between 780 and 1750 m asl), Korean pine (Pinus koraiensis, 780 and 1300 m asl), and Jezo spruce (Picea jezoensis var. komarovii, 1000 and 1750 m asl). Regeneration densities did not differ significantly among the elevations except for Jezo spruce, which showed a significantly lower regeneration density at 1000 m asl as compared to 1300 and 1750 m asl. All 3 species showed a significantly higher basal area increment (BAI) at the middle part of their distribution ranges than at their limits. The growth of Manchurian fir and Jezo spruce exhibited higher sensitivity to precipitation than to temperature at their lower distribution limits, and the inverse pattern was observed at the upper limit. In all cases the correlations between growth and the respective climate variable were positive, except for the correlation between Jezo spruce growth and precipitation. Growth of Korean pine was positively correlated with spring temperature and summer moisture at its lower distribution limit and with summer temperature at its upper limit. Our study suggests that elevational limits of forest vegetation were likely constrained by climate factors affecting growth of dominant species rather than those controlling regeneration density.

We studied geographic patterns in the soil microarthropods associated with moss carpets on exposed rocky outcrops in southwestern British Columbia, Canada. We related microarthropod composition, abundance, and species richness to 15 ecological variables relevant to either spatial or environmental filtering. Our survey identified 352 morphospecies in 32 sites spanning a 130- × 60-km area. We tested whether the relative importance of spatial and environmental factors was concordant between community composition, abundance, species richness, and 3 major taxonomic groups (Oribatida, Mesostigmata, Collembola). The results depended on the variance partitioning methods used and whether composition was defined by species abundance or presence. Distance-based Mantel tests showed that dissimilarity in species composition between sites was better predicted by spatial distance than by environmental dissimilarity. In contrast, variance partitioning of ordinated abundance data concluded that environmental rather than spatial variables explained most variance in the composition of total microarthropod, especially Collembola, assemblages. Total abundance and species richness were only weakly correlated across space, even though both were explained by environmental factors such as temperature and soil moisture. Given the surprising contradictions between methods, we suggest that different analyses should always be compared to fully uncover the spatial and environmental factors structuring communities.

Arctic ecosystems at the forest-tundra ecotone are particularly sensitive to climate-driven vegetation changes. Many recent studies have observed shifts in vegetation cover, particularly an increase in shrub growth. Here, vegetation changes were assessed at the local scale near Umiujaq, northern Quebec (Canada, 56.55°N, 76.55°W) using colour aerial photographs (1994 and 2010). By applying semi-automated image classification methods and change-detection analysis, we were able to detect and map the dominant vegetation cover changes. Comparison of classification results shows a 12% increase in shrub cover, loss of nearly 8% of lichen cover, stability of the spruce zones, and disappearance of nearly a quarter of thermokarst ponds. The 2 resulting maps were superimposed to spatialize the change. Change-detection analysis revealed that a shift toward shrub-dominated landscape was the most important change in the 1994 vegetation classes. This shift affected 18% of the studied area in the valley. The resulting “from-to” land-cover change map illustrates the general ongoing shrubification in the region.