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Ericaceous shrubs often interfere with the growth of black spruce seedlings on regenerating forest sites in Eastern Canada. Mechanical site preparation such as scarification may improve this situation, but it is uncertain whether this is solely due to a reduction in direct competition from the shrubs, or also from a sustained improvement in nutritional site quality. We sampled experimental plots in two boreal climate regions (i.e. warmer-drier Abitibi vs. cooler-wetter Côte-Nord) where scarification, performed 18 years earlier, had increased the growth of black spruce relative to non-scarified plots. Trees of scarified plots had closed the canopy more than trees of non-scarified plots in Côte-Nord, but not in Abitibi. Total ground cover of ericaceous shrubs was lower in scarified plots at both sites, the main species being Kalmia angustifolia (i.e. Kalmia) in Abitibi and Rhododendron groenlandicum (i.e. Labrador tea) in Côte-Nord. Scarified plots at both sites had significantly shorter current-year ericaceous rhizomes than non-scarified plots, but the difference between treatments was significantly greater in Côte-Nord than in Abitibi. In Côte-Nord, ericaceous shrubs on scarified plots had a lower specific rhizome mass, higher specific leaf area, lower tannin and higher N concentrations in leaves and litter, and lower N use efficiency than on non-scarified plots. By comparison, scarification in Abitibi affected only one foliar property, namely a reduction in the C:N ratio of Kalmia leaf litter. Forest floor N mineralization rates and black spruce needle N concentrations were higher in scarified than non-scarified plots across both sites. Taken collectively, results suggest that mechanical scarification on ericaceous shrub-dominated cutovers can reduce competitive traits of boreal ericaceous shrubs and improve nutritional site quality, especially in cooler-wetter climates. Highlights

Ecosystem-based management aims to preserve old-growth forest attributes using techniques mimicking natural disturbances. One such technique is irregular shelterwood logging, but its impacts on forest floor organisms are poorly known. Our objective was to quantify the effects of three different treatments of irregular shelterwood on population structure and the body condition of the eastern red-backed salamander (Plethodon cinereus) 5–6 years following harvesting. A total of 64 sites in western Québec were sampled using artificial refugia and quadrat searches. Large salamanders (>32 mm) were more abundant in the gap treatment than in strip, uniform, or control treatments. Small salamanders (≤32 mm) followed the same pattern, although the differences were marginal. For a given treatment, small salamanders were as abundant as large salamanders. Salamander body condition differed between the 2 years of sampling but did not differ among treatments, regardless of salamander size. We conclude that environmental conditions in irregular shelterwood treatments 5–6 years following harvesting support populations of small vertebrates on the forest floor.

Background: Short-term effects of silvicultural treatments on soil properties and understory vegetation in temperate hardwood forests are well documented, but few studies have examined longer term effects of treatment intensity. We hypothesized that short-term effects of silvicultural treatments on understory plant diversity do persist over the medium-term (20 years after treatment); the magnitude of these effects would be proportional to the intensity of canopy and soil disturbance.Methods: Soil properties (pH, total C and N, extractable P, exchangeable bases) and understory community diversity indices were measured in six experimental sites along a longitudinal gradient that covered different climatic and edaphic conditions in the yellow birch-sugar maple bioclimate domain. Reference condition, i.e. control forest with no anthropogenic disturbance for at least 80 years (CON) were compared to twenty years old regeneration treaments representing a gradient of canopy and soil disturbance intensity: single-tree selection cuts (SIN); group-selection cuts (GRP); and group-selection cuts with scarification (GRPS). Results: Geographic location of sites explained more variation in soil properties and community composition than did treatments. Species richness in both group-selection treatments was higher than that in CON forests. However, understory plant equitability and beta diversity among sites in GRP and GRPS were lower than in SIN and CON forests. More intense treatments (GRP and GRPS) increased the relative occurrence of vegetatively reproducing heliophilic plants, a trait syndrome associated with adaptations to disturbed environments. These treatments also contributed to the medium-term persistence of recalcitrant competitor species (e.g., Rubus idaeus, Prunus pensylvanica) whereas soil scarification appears to have negative sustained effects on species known to be sensitive to regeneration treatments (e.g. Monotropa uniflora, Dryopteris spinulosa).Conclusion: Of the treatments studied, single-tree selection cutting appears to be the most appropriate silvicultural treatment for maintaining soil functions and heterogeneous understory plant communities with compositions and structures similar to natural forests, while more intense treatments rather maintain and expand species that are better adapted to a wider range of environmental conditions, including open environments.

Species identification in Quebec, Canada, is usually performed with photo-interpretation at the stand level, and often results in a lack of precision which affects forest management. Very high spatial resolution imagery, such as WorldView-3 and Light Detection and Ranging have the potential to overcome this issue. The main objective of this study is to map 11 tree species at the tree level using an object-based approach. For modeling, 240 variables were derived from WorldView-3 with pixel-based and arithmetic feature calculation techniques. A global approach (11 species) was compared to a hierarchical approach at two levels: (1) tree type (broadleaf/conifer) and (2) individual broadleaf (five) and conifer (six) species. Five different model techniques were compared: support vector machine, classification and regression tree, random forest (RF), k-nearest neighbors, and linear discriminant analysis. Each model was assessed using 16-band or first 8-band derived variables, with the results indicating higher precision for the RF technique. Higher accuracies were found using 16-band instead of 8-band derived variables for the global approach (overall accuracy (OA): 75% vs. 71%, Kappa index of agreement (KIA): 0.72 vs. 0.67) and tree type level (OA: 99% vs. 97%, KIA: 0.97 vs. 0.95). For broadleaf individual species, higher accuracy was found using first 8-band derived variables (OA: 70% vs. 68%, KIA: 0.63 vs. 0.60). No distinction was found for individual conifer species (OA: 94%, KIA: 0.93). This paper demonstrates that a hierarchical classification approach gives better results for conifer species and that using an 8-band WorldView-3 instead of a 16-band is sufficient.

Boreal ericaceous shrubs, such as Kalmia angustifolia, have evolved various traits allowing them to interfere with the growth of conifer trees. These include the ability to spread through rhizomatous growth and to produce high amounts of tannins that interfere with soil N cycling. We examined how pre-commercial thinning (PCT) of young black spruce (Picea mariana) stands, a common silvicultural practice, increases the aboveground and belowground spread of various ericaceous shrubs, the chemical quality of leaves and litter, as well as soil nitrogen cycling. We compared these effects in relatively cool-moist and relatively warm-dry climates. Within the warm-dry climate, we also compared the effects of PCT on fertile clay and on nutrient-poor till deposits. The total cover of ericaceous shrubs was higher in PCT than in control plots in all three site types. On nutrient poor till deposits (in both climates), the current-year rhizome length and specific rhizome mass of K. angustifolia were higher in PCT than in control plots. Soil mineralizable NH4+-N was lower under patches of K. angustifolia than under patches of feather moss (Pleurozium schreberi). Across all 24 plots, canopy openness had a positive relationship with ericaceous shrub cover, current-year rhizome length, foliar tannins and phenolic concentrations. Although PCT might increase tree growth in the short-term, its positive effects on ericaceous shrubs increases the risk of conifer seedling growth check when the next clearcut harvest occurs, especially in cool moist climates and on nutrient poor soil deposits.

Kalmia angustifolia is a boreal ericaceous shrub that can rapidly spread on black spruce forest cutovers in eastern Canada, where CPRS (i.e. Cutting with Protection of Regeneration and Soils") is practiced. The proliferation of Kalmia often coincides with a reduction in the growth rate of regenerating black spruce seedlings. We report on a study where we compared the local effects of Kalmia and black spruce seedling patches (i.e. two types of "Vegetation") on chemical and biochemical soil properties in CPRS cutovers within mesic spruce-moss and xeric spruce-lichen ecosystems, as well as in four mature spruce-moss forests (i.e. three "Site Types"). Results from 13C-CPMAS-NMR revealed lower O-alkyl C (i.e. carbohydrates), higher aromatic C (i.e. lignin and other phenolics) and higher carbonyl-C (i.e. amide-C and carboxyl groups) in spruce-moss than in spruce-lichen forest floors (F-horizon). In spite of these distinctions, we observed only a small number of Site Type x Vegetation interactions controlling soil properties. Vegetation had a significant effect on ten forest floor properties. Most notably, Kalmia patches had higher concentrations of condensed tannins and lower mineral N cycling. On the other hand, Site Type had a relatively greater effect on the deeper podzolic-B horizons, where mineral N and microbial activity were higher in mature spruce-moss forests than in the cutovers. Green and senescent Kalmia leaves collected at these sites had higher N, tannin and phenolic concentrations than green and senescent spruce needles. A 25 month litter bag study found lower decomposition of Kalmia leaf litter in spruce patches on spruce-lichen cutovers compared to spruce patches on spruce-moss cutovers, or to Kalmia patches on spruce-lichen cutovers. Given that black spruce seedlings obtain most of their nutrients from the forest floor, our results suggest that CPRS may have long-term negative effects on black spruce forest productivity if the spread of Kalmia is left unchecked.

Irregular shelterwood cutting has been recently prescribed to improve the regeneration of semi-tolerant species such as yellow birch (Betula alleghaniensis B.), while also maintaining the complexity of natural mixed forests. However, its effects on forest dynamics are poorly known. In this study, we document the short-term effects of three irregular shelterwood cutting patterns on the establishment and composition of regeneration as well as on its use by snowshoe hare (Lepus americanus E.). Specifically, we compared uniform, gap, and strip cutting patterns with soil preparation, relative to uncut controls. We counted seedlings, browse, and hare pellets, and measured habitat characteristics after two growing seasons in micro-plots delimited in each of the shelterwood cutting patterns. The mixture of soil and humus resulting from scarification promoted yellow birch establishment. Yellow birch seedlings in gaps were more abundant than in controls, but their abundance was comparable to other irregular shelterwood patterns. All irregular shelterwood patterns promoted competition mainly by pin cherry (Prunus pensylvanica L.f.), beaked hazel (Corylus cornuta M.), and mountain maple (Acer spicatum Lam.). Snowshoe hare browse on yellow birch was low for all irregular shelterwood patterns. Moose browse pressure was higher than that from hare. We found no short-term impact of the snowshoe hare on yellow birch seedling establishment and survival. Snowshoe hare pellet counts suggested a preference for gaps. This result could be explained by increased food and protective cover from higher seedling and shrub densities in gaps than in other treatments. In the short-term, up to three years post-treatment, irregular shelterwood cutting helps to promote yellow birch regeneration, a semi-tolerant species, while maintaining habitat for snowshoe hare.

Sustainable management of boreal ecosystems involves the establishment of vigorous tree regeneration after harvest. However, two groups of understory plants influence regeneration success in eastern boreal Canada. Ericaceous shrubs are recognized to rapidly dominate susceptible boreal sites after harvest. Such dominance reduces recruitment and causes stagnant conifer growth, lasting decades on some sites. Additionally, peat accumulation due to Sphagnum growth after harvest forces the roots of regenerating conifers out of the relatively nutrient rich and warm mineral soil into the relatively nutrient poor and cool organic layer, with drastic effects on growth. Shifts from once productive black spruce forests to ericaceous heaths or paludified forests affect forest productivity and biodiversity. Under natural disturbance dynamics, fires severe enough to substantially reduce the organic layer thickness and affect ground cover species are required to establish a productive regeneration layer on such sites. We succinctly review how understory vegetation influences black spruce ecosystem dynamics in eastern boreal Canada, and present a multi-scale research model to understand, limit the loss and restore productive and diverse ecosystems in this region. Our model integrates knowledge of plant-level mechanisms in the development of silvicultural tools to sustain productivity. Fundamental knowledge is integrated at stand, landscape, regional and provincial levels to understand the distribution and dynamics of ericaceous shrubs and paludification processes and to support tactical and strategic forest management. The model can be adapted and applied to other natural resource management problems, in other biomes.

Summary • The role of litter tannins in controlling soil nitrogen (N) cycling may explain the competitive ability of Kalmia relative to black spruce (Picea mariana), although this has not been demonstrated experimentally. • Here, the protein-precipitation capacities of purified tannins and leaf extracts from Kalmia and black spruce were compared. The resistance to degradation of tannin–protein precipitates from both species were compared by monitoring carbon (C) and N dynamics in humus amended with protein, purified tannins or protein–tannin precipitates. The purity of the precipitates was verified using solid-state 13C nuclear magnetic resonance (NMR) spectra. The ability of mycorrhizal fungi associated with both species to grow on media amended with tannin–protein complexes as the principal N source was also compared. • The protein precipitation capacity of Kalmia tannins was superior to those of black spruce. Humus amended with protein increased both mineral and microbial N, whereas humus amended with tannin–protein precipitates increased dissolved organic N. Mycorrhizal fungi associated with Kalmia showed better growth than those associated with black spruce when N was provided as tannin–protein precipitates. • These data suggest that Kalmia litter increases the amount of soil N sequestered as tannin–protein complexes, which may improve the competitive ability of Kalmia relative to black spruce by favouring N uptake by mycorrhizas associated with the former.

Previous studies suggested that late-successional tannin-rich plant communities increase the amount of dissolved organic N (DON) relative to dissolved inorganic N (DIN) in decomposing litter. We devised an experiment to test this hypothesis by adding varying proportions of black spruce (Picea mariana) and tannin-rich Kalmia angustifolia litter to forest floor samples collected on six black spruce cutovers. An increasing proportion of Kalmia litter increased condensed tannin and total phenolic concentrations over the course of a 46-week incubation period. Mineral N concentrations did not vary among treatments in spite of much higher total N concentrations in Kalmia litter. This was more likely due to the formation of protein–tannin complexes rather than microbial immobilization of N, as indicated by the decline in available C with increasing Kalmia litter on two of the five sampling dates. There was a significant positive linear trend between the proportion of Kalmia litter and the DON/DIN ratio on one sampling date (week 13) only. Results suggest that the DON/DIN ratio is controlled by confounding factors (e.g., tannins bonding with non-extractable humus particles) and has limited value for describing ecological succession.

We compared mineral N concentrations, potential net mineralization rates and gross N mineralization rates in the forest floor of 4-year-old clearcut plots and adjacent mature forest stands, in three distinct coniferous ecosystems in British Columbia (coastal low elevation, coastal montane, interior montane). Our data showed that clearcutting has no effect on forest floor mineral N dynamics in some coniferous ecosystems, and significant effects in others. Among “responsive” sites, we noted contradictory effects of clearcutting on some of the measured N variables. Furthermore, the effects of clearcutting on potential net mineralization were not consistent with changes in gross production rates of mineral N. We discuss these observations in light of our knowledge of the ecology of each site, of the various sources and sinks of mineral N, and of the biotic and abiotic factors controlling mineral N dynamics. Our results suggest that generalizations cannot be made on the effects of clearcutting on mineral N supply to conifer seedlings, as these can lead to incorrect interpretations of ecosystem dynamics, with serious policy-relevant ramifications for the forest industry.

Kalmia angustifolia is an ericaceous shrub that can rapidly spread on recently harvested boreal forest sites, causing a slow-down in soil nutrient cycling and reduced growth of spruce seedlings. It has been hypothesized that tannins released from Kalmia litter suppress soil enzyme activity, and are thus important in controlling ecosystem structure and processes. Here the effects of different concentrations of tannins extracted from both Kalmia and black spruce (Picea mariana) foliage were tested on enzyme activities of soil extracts. Then the effects of various Kalmia-black spruce litter mixtures on soil enzyme activity were investigated. Lastly, the correlation between Kalmia cover in the field and soil enzyme activity was measured. Both tannin types suppressed beta-glucosidase and acid phosphatase activities, and the magnitude of these effects was concentration-dependent. beta-glucosidase and amidase activity decreased linearly with an increasing Kalmia : spruce litter ratio added to soil. A field survey of 24 sites revealed a negative relationship between percentage Kalmia cover and beta-glucosidase activity. Collectively, results of the three experiments converge to support the claim that enzyme inhibition by litter tannins has evolved as an important mechanism controlling ecosystem processes and structure following Kalmia invasion on recently disturbed forest sites.