Relationships between Stand Composition and Ectomycorrhizal Community Structure in Boreal Mixed-Wood Forests

We used multivariate analysis to model boreal forest stand structure and dynamics at Riding Mountain National Park, Manitoba based on data from 202 sampled stands. Eight forest stand-types were recognized based on canopy composition: black spruce on peat substrates, jack pine — black spruce, bur oak, eastern deciduous (green ash — American elm — Manitoba maple), balsam fir, trembling aspen — paper birch — mountain maple, trembling aspen — balsam poplar, and white spruce. The first four stand-types occur in edaphically distinct environments, while the four remaining boreal mixedwood stand-types occur in edaphically similar environments. We found that the composition and abundance of advance regeneration were best predicted by current canopy composition (redundancy = 54.4%); this reflects both the limited dispersal of conifer seeds and the strong vegetative reproductive capacity of hardwoods. Biotically-controlled site factors such as bareground, herb and shrub cover, ungulate browsing intensity, and stand age were also reasonably good predictors of advance regeneration (redundancy = 31.7%). Edaphic variables such as soil pH, conductivity, particle size, organic horizon depth and slope proved to be poor predictors of advance regeneration, however (redundancy = 18.1%). Size-class ordination indicated that many stand-types have relatively short successional trajectories, suggesting limited change in forest canopy composition over time. There are two exceptions: in the jack pine — black spruce stand-type, black spruce will increase over time, and in the trembling aspen — paper birch — mountain maple stand-type, eastern deciduous species (green ash, American elm, Manitoba maple, and bur oak) are forecast to become increasingly dominant. We also describe a synoptic model of mixedwood boreal forest stand dynamics for the Riding Mountain area. The model includes a number of factors that we consider to be critical determinants of forest dynamics, such as seed source availability, small and large-scale disturbances, species life-history characteristics, and environmental gradients. Our succession model is more similar those described for eastern than western Canada, which may reflect the lower frequency of catastrophic fires in the Riding Mountain area compared to boreal forests further west. Our model emphasizes that successional trajectories do not converge towards a single self-perpetuating “climax”. Instead, successional vectors may diverge, converge or remain cyclical, and multiple potential pathways are possible for each stand-type. Our results also illustrate that species assemblages, and the propensity for canopy change in the absence of fire, are governed by the cumulative and synergistic effects of climate, topography, disturbance frequency, size and intensity, edaphic conditions, and the proximity of parental seed sources. Fire suppression in the southern boreal forest has resulted in a paradigm shift in disturbance regime, from large, synchronous catastrophic fires to small-scale, asynchronous gap formation. A major challenge for boreal forest ecologists is to determine the long-term consequences of this paradigm shift on the composition, structure and health of boreal forest stands and landscapes.

Forest overstory composition influences both light and nutrient availability in the mixed boreal forest. The influence of stand composition on understory cover and biomass was investigated on two soil types (clay and till deposits). Four forest composition types were considered in this study: aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), jack pine (Pinus banksiana Lamb.) and a mixture of balsam-fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss). The cover of all understory species was recorded while the biomass of two important and ubiquitous species was measured: mountain maple (Acer spicatum Lam.) of the shrub layer and large-leaved aster (Aster macrophyllus L.) of the herb layer. Soil analyses were conducted to evaluate the influence of overstory composition on understory biomass through its influences on soil characteristics. Analyses of variance showed a significant effect of forest canopy type on mountain maple biomass, understory cover and shrub cover but not on herb cover and large-leaved aster biomass. Path analysis was performed to explore the relationships between canopy type, nutrient availability and understory biomass. Contrary to what was expected, the variation in plant biomass associated with forest composition was weakly related to soil nutrient availability and more strongly related to stand structural attributes.

Assessing the geochemical balance of managed boreal forests

This is the AmeriFlux version of the carbon flux data for the site CA-Gro Ontario - Groundhog River, Boreal Mixedwood Forest.. Site Description - Groundhog River (FCRN or CCP site ON-OMW) is situated in a typical boreal mixedwood forest in northeastern Ontario (48.217 degrees north and 82.156 degrees west) about 80 km southwest of Timmins in Reeves Twp. near the Groundhog River. Rowe (1972) places the site in the Missinaibi-Cabonga Section of the Boreal Forest Region. In terms of ecoregion and ecozone, the site is in the Lake Timiskaming Lowlands of the Boreal Shield. The forest developed after high-grade logging in the 1930's. The average age in 2013 is estimated at beteen 75 and 80 years. The forest is dominated by five species characteristic of Ontario boreal mixedwoods: trembling aspen (Populus tremuloides Michx.), black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench.) Voss.), white birch (Betula papyrifera Marsh.), and balsam fir (Abies balsamea (L.) Mill.). The surficial geology is a lacustrine deposit of varved or massive clays, silts and silty sands. The soil is an orthic gleysol with a soil moisture regime classified as fresh to very fresh. Plonski (1974) rates it as a site class 1. Themore » topography is simple and flat with an overall elevation of 340 m ASL.« less

We studied the relationships between assemblages of soil microfungi and plant communities in the southern boreal mixed-wood forests of Quebec. Sampling took place in 18,100 m2 plots from an existing research site. Plots were separated into three categories based on dominant overstory tree species: (i) trembling aspen, (ii) white birch and (iii) a mixture of white spruce and balsam fir. Within each plot a 1 m2 subplot was established in which the understory herbaceous layer was surveyed and soil cores were collected. Microfungi were isolated from soil cores with the soil-washing technique and isolates were identified morphologically. To support our morphological identifications DNA sequences were obtained for the most abundant microfungi. The most frequently occurring microfungal species were Penicillium thomii, P. spinulosum, P. janthinellum, Penicillium sp., P. melinii, Trichoderma polysporum, T. viride, T. hamatum, Mortierella ramanniana, Geomyces pannorum, Cylindrocarpon didymum, Mortierella sp. and Mucor hiemalis. Multivariate analyses (redundancy analysis followed by variance partitioning) revealed that most of the variation in microfungal communities was explained by understory plant species composition as opposed to soil chemistry or overstory tree species. In this floristically diverse system saprophytic microfungal assemblages were not correlated with the overstory tree species but were significantly correlated with the main understory herbs, thereby reflecting differences at a smaller spatial scale.

We studied the relationships between assemblages of soil microfungi and plant communities in the southern boreal mixed-wood forests of Québec. Sampling took place in 18 100 m2 plots from an existing research site. Plots were separated into three categories based on dominant overstory tree species: (i) trembling aspen, (ii) white birch and (iii) a mixture of white spruce and balsam fir. Within each plot a 1 m2 subplot was established in which the understory herbaceous layer was surveyed and soil cores were collected. Microfungi were isolated from soil cores with the soil-washing technique and isolates were identified morphologically. To support our morphological identifications DNA sequences were obtained for the most abundant microfungi. The most frequently occurring microfungal species were Penicillium thomii, P. spinulosum, P. janthinellum, Penicillium sp., P. melinii, Trichoderma polysporum, T. viride, T. hamatum, Mortierella ramanniana, Geomyces pannorum, Cylindrocarpon didymum, Mortierella sp. and Mucor hiemalis. Multivariate analyses (redundancy analysis followed by variance partitioning) revealed that most of the variation in microfungal communities was explained by understory plant species composition as opposed to soil chemistry or overstory tree species. In this floristically diverse system saprophytic microfungal assemblages were not correlated with the overstory tree species but were significantly correlated with the main understory herbs, thereby reflecting differences at a smaller spatial scale.

Bacterial communities mediate many of the processes in boreal forest floors that determine the functioning of these ecosystems, yet it remains uncertain whether the composition of these communities is distributed nonrandomly across the landscape. In a study performed in the southern boreal mixed wood forest of Québec, Canada, we tested the hypothesis that stand type (spruce/fir, aspen, paper birch), stand age (57, 78-85, and 131 years old), and geologic parent material (clay and till) were correlated with forest floor bacterial community composition. Forest floors in 54 independent forest stands were sampled to comprise a full factorial array of the three predictor variables. Bacterial community structure was examined by terminal restriction fragment (T-RF) length polymorphism analysis of genes encoding for 16S rRNA. Distance-based redundancy analysis of T-RF assemblages revealed that each predictor variable, as well as their interaction terms, had a significant effect on bacterial community composition, geologic parent material being the most discriminating factor. A survey of the 15 T-RFs with the highest percentage fit on the first two ordination axes describing the main effects indicated that each landscape feature correlated to a distinct group of bacteria. A survey of the most discriminant T-RFs describing the effect of stand type within each combination of stand age and geologic parent material indicated a strong dependency of several T-RFs on geologic parent material. Given the possible link between bacterial community composition and forest floor functioning, we also assessed the effects of the same three landscape features on community-level catabolic profiles (CLCP) of the extractable forest floor microbiota. Geologic parent material and stand type had significant effects on CLCPs. On clay plots, the effects of landscape features on T-RF patterns were highly consistent with their effects on CLCPs. In light of our results, we suggest that future research examine whether bacterial community composition or CLCPs can be used to detect latent environmental changes across landscape units.

A lack of local and regional markets for trembling aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.) can result in large numbers of merchantable-size hardwood stems with little commercial value, which complicates even-aged management of Ontario’s boreal mixedwood forests. To help identify potential management approaches to address this periodic economic situation, the relationship of stand structure with canopy transmittance was examined in recently harvested boreal mixedwood stands with differing hardwood tree retention levels. Canopy transmittance and residual stand structural features were measured in 483, 0.612 ha circular plots established in recently harvested stands in 12 locations across northern Ontario. For both trembling aspen- and white birch-dominated residual stands, canopy transmittance exhibited a negative exponential relationship with basal area, density, and stand density index. Nonlinear mixed effects models sometimes differed significantly between these two ...

In old-growth forests, natural disturbances form a complex mosaic of structures, providing a wide diversity of habitats and functions of great importance. Old-growth forests are still often seen as a homogeneous whole and few remote-sensing approaches have been tested to identify their structural diversity, especially in boreal forests. The aim of this study is to use a combination of airborne LiDAR and satellite imagery to identify and discriminate old-growth forest structures resulting from different disturbance histories. The study area, which was located in the mixed boreal forest of Quebec (Canada), is Monts Valin National Park and adjacent managed territories. Balsam fir (Abies balsamea (L.) Mill) is the dominant species in the study area, but hardwood species such as white birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) can also be abundant in the early succession stages. Four forest classes were studied: second-growth (logged between 1970 and 1980); transition old-growth (burned in 1920); undisturbed old-growth (unburned for at least 125 years); and disturbed old-growth forest (unburned for at least 125 years, but severely disturbed by an insect outbreak around 1980). A multivariate Random Forest model was used to discriminate the classes on 6466 1 ha tiles, based on 11 complementary LiDAR and satellite-derived indices describing stand vertical and horizontal structure, together with “greenness” and disturbance history over the last 30 years. This model had high predictive efficiency (AUC = 94.2), with 81.8% of the tiles accurately classified. Interestingly, undisturbed old-growth forests exhibited intermediate characteristics compared to transition and disturbed old-growth forests. This emphasizes that some structural attributes recognized as important for the classification of temperate and tropical old-growth forests, such as high vertical complexity, are of lesser relevance for boreal old-growth forests. In comparison to undisturbed old-growth forests, transition old-growth forests had a taller canopy of high “greenness” due to a greater hardwood abundance; disturbed old-growth forests had a higher gap fraction and heterogeneity in tree size; second-growth forests exhibited a lower and more even canopy. Misclassified tiles were explained by spatial variation in disturbance severity or different levels of forest resistance and resilience to disturbance. These misclassifications are also of ecological interest, as they highlight the nuances in structural diversity that are rarely identified by disturbance mapping. A reasonable combination of LiDAR and satellite indices was effective not only in discriminating old-growth forests from second-growth forests, but also identifying their different structures, which result from specific disturbance histories. This method could contribute to effective monitoring of changes in the areas and characteristics old-growth forest that are caused by anthropogenic and natural disturbances.

Forest successions following a forest fire that occurred in 1932 were studied on mesic sites of the boreal mixedwood forest of the Bas-Saint-Laurent region of Quebec, Canada. Physiographic, soil and vegetation data were collected in 28 ecosystems distributed on a topographic gradient. The vegetation composition of the main canopy, 64 years after the fire, varied according to topographic situation. The proportion of tolerant hardwood species (yellow birch (Betula alleghaniensis Britton), sugar maple (Acer saccharum Marsh.), red maple (Acer rubrum L.)) increased toward upper slopes whereas it was the opposite for coniferous species (white spruce (Picea glauca [Moench] Voss), balsam fir (Abies balsamea [L.] Mill.)), as their proportion increased toward lower slopes. Intolerant hardwood species (white birch (Betula papyrifera Marsh.), trembling aspen (Populus tremuloides Michx.)) were abundant in all ecosystems. The distribution pattern of regeneration density and stocking of tolerant hardwoods and conifers was similar to that of the main canopy. The majority of commercial species, including tolerant species, established rapidly after the fire. Only eastern white cedar (Thuya occidentalis L.), which is a species typical of late succession, did not grow back. Ten years after the fire, 78% of the sampled dominant trees were established. Competition caused by mountain maple (Acer spicatum Lam.) did not seem to be as important after fire compared with the situation after clearcutting. Results showed that after the elimination of intolerant species, the vegetation composition should evolve toward the potential vegetation (climax) of the toposequence, that is, the sugar maple - yellow birch type on upper slopes, the balsam fir - yellow birch type on midslopes and the balsam fir - yellow birch - cedar type on lower slopes. Key words: succession, fire, yellow birch, balsam fir, mountain maple.

Tree community structural development in young boreal forests: A comparison of fire and harvesting disturbance

Arbuscular mycorrhizal fungi (AMF) communities in Clintonia borealis roots from a boreal mixed forests in northwestern Québec were investigated. Roots were sampled from 100 m2 plots whose overstory was dominated by either trembling aspen (Populus tremuloides Michx.), white birch (Betula papyrifera Marsh.), or mixed white spruce (Picea glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.). Part of the 18S ribosomal gene of the AMF was amplified and the resulting PCR products were cloned. Restriction analysis of the 576 resulting clones yielded 92 different restriction patterns which were then sequenced. Fifty-two sequences closely matched other Glomus sequences from Genbank. Phylogenetic analysis revealed 10 different AMF sequence types, most of which clustered with other uncultured AM sequences from plant roots from various field sites. Compared with other AMF communities from comparable studies, richness and diversity were higher than observed in an arable field, but lower than seen in a tropical forest and a temperate wetland. The AMF communities from Clintonia roots under the different canopy types did not differ significantly and the dominant sequence type, which clustered with AM sequences from a variety of environments and hosts at distant geographical locations, represented 66.9% of all the clones analyzed.

Demographic data from a 15-year outbreak of the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), in a boreal mixedwood forest in Ontario, Canada, are used to interpret stand-level ecological disturbance in terms of susceptibility and vulnerability (mortality) of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP). All three host-tree species are highly susceptible for oviposition by the spruce budworm and all are suitable for completion of the budworm life cycle. Host-related differences in susceptibility arise from the degree of synchrony between spruce budworm phenology during the feeding stages and host-tree phenology. Spruce budworm density was highest on white spruce throughout the budworm's life cycle and over the course of the outbreak, but more rapid flushing and growth of current-year buds in white spruce reduced damage relative to that on balsam fir. Conversely, later flushing of current-year buds on black spruce led to a reduction in budworm density early in the season and a corresponding reduction in defoliation. The combination of high budworm densities and severe defoliation caused mortality first on balsam fir. By the end of the outbreak, 89% of the balsam fir component >10 cm DBH was eliminated compared with 49% of the white spruce in the same size class. The lower susceptibility of black spruce resulted in survival of all but the smallest size classes of that species. Nonhost species such as trembling aspen (Populus tremuloides Michx.) nearly doubled their basal area during the outbreak. The results link processes inherent in the insect–host relationship with the population ecology of the insect and the disturbance ecology of the forest.

Succession is generally well described above-ground in the boreal forest, and several studies have demonstrated the role of interspecific facilitation in tree species establishment. However, the role of mycorrhizal communities for tree establishment and interspecific facilitation, has been little explored. At the ecotone between the mixed boreal forest, dominated by balsam fir and hardwood species, and the boreal forest, dominated by black spruce, several stands of trembling aspen can be found, surrounded by black spruce forest. Regeneration of balsam fir seems to have increased in the recent decades within the boreal forest, and it seems better adapted to grow in trembling aspen stands than in black spruce stands, even when located in similar abiotic conditions. As black spruce stands are also covered by ericaceous shrubs, we investigated if differences in soil fungal communities and ericaceous shrubs abundance could explain the differences observed in balsam fir growth and nutrition. We conducted a study centered on individual saplings to link growth and foliar nutrient concentrations to local vegetation cover, mycorrhization rate, and mycorrhizal communities associated with balsam fir roots. We found that foliar nutrient concentrations and ramification indices (colonization by mycorrhiza per length of root) were greater in trembling aspen stands and were positively correlated to apical and lateral growth of balsam fir saplings. In black spruce stands, the presence of ericaceous shrubs near balsam fir saplings affected ectomycorrhizal communities associated with tree roots which in turn negatively correlated with N foliar concentrations. Our results reveal that fungal communities observed under aspen are drivers of balsam fir early growth and nutrition in boreal forest stands and may facilitate ecotone migration in a context of climate change.

Isle Royale National Park (IRNP) is an archipelago in west central Lake Superior. In 2010, the National Park Service Great Lakes Inventory and Monitoring Network initiated a long-term monitoring program at IRNP with the goals being to: (1) determine the current forest structure, (2) assess how succession and climate change will impact species assemblages, and (3) develop realistic management targets related to climate change impacts on IRNP forests. Five forest types were identified, with three of these (sugar maple (Acer saccharum Marsh.)/birch, eastern white cedar (Thuja occidentalis L), and balsam fir (Abies balsamea (L.) Mill.)) being climax types with little likelihood of succeeding into any other type over the next two to three decades. Two forest types (white spruce (Picea glauca (Moench) Voss),/trembling aspen (Populus tremuloides Michx.), and paper birch (Betula papyrifera Marsh.)) were in a state of transition. The long-term (> 50 year) successional pathways of all five forest types will be influenced by climate change, species' migration abilities, and disease. Many dominant species currently on the island, including balsam fir, black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.), and white spruce, are expected to become extirpated, while the abundance of other common species, including paper birch and trembling aspen, is expected to decline. The 21 km distance between the mainland and the islands will prohibit timely immigration of new species onto the island in the face of climate change. Immigration will likely be led by avian-dispersed species (Prunus spp., exotic Lonicera spp., and Rhamnus cathartica, another exotic species) with dispersal of other taxa relying on stochastic events or human transport. Managers should consider assisted migration to ensure that species assemblages remain congruent; otherwise, stable ecosystems dominated by a few non-native taxa may result. This is especially relevant on the eastern side of the island where balsam fir forests dominate in shallow, bedrock-derived soils.