Forest Of Alberta Research Articles

Cut vs. fire: a comparative study of the temporal effects of timber harvest and wildfire on ecological indicators of the boreal forest

ContextLarge-scale natural disturbances are crucial drivers of ecosystem function and composition for many forested ecosystems. In the last century, the prevalence of anthropogenic disturbances has increased across Canada’s boreal forest. Habitat disturbance from timber harvest and wildfire is linked to declines of boreal species, including woodland caribou (Rangifer tarandus caribou).ObjectivesWe tested how disturbances influenced the recovery trajectory of ecological indicators of timber, biodiversity, and wildlife habitat through time following timber harvest and wildfire across the boreal forest of Alberta, Canada.MethodsDuring 2021 and 2022, we collected field data from 251 timber harvested and 264 burned stands (0–40 years since disturbance), as well as 256 older forest stands used by caribou (> 40 years since disturbance). Field data included metrics of stand attributes (e.g., basal area, stems per hectare), coarse woody debris (CWD), and abundance of forage for caribou, moose (Alces americanus), and bears (black bear: Ursus americanus, grizzly bear: Ursus arctos).ResultsBasal area of trees and stems per hectare recovered more quickly in timber harvest sites when compared to wildfire sites, but as time since disturbance increased there were no differences in these attributes among timber harvest, wildfire, and caribou use sites. CWD was greatest in recently burned sites, but declined over time to be similar in quantity as in harvested stands and older forest stands. Terrestrial lichens, important forage for caribou, were most abundant in the older caribou use sites, whereas forage for moose and bears, including shrubs, was most abundant in younger timber harvest and wildfire sites.ConclusionsOur results demonstrate that timber harvesting may result in a quicker development of timber volume when compared to wildfire. However, this anthropogenic disturbance is less advantageous for the development of caribou habitat.

The impact of reclamation and vegetation removal on compositional and functional attributes of soil microbial communities in the Athabasca Oil Sands Region

Large-scale mining for oil extraction in the boreal forests of Northern Alberta has led to a disturbance footprint of ~900 km2 of land; which must be reclaimed to equivalent land capabilities. Microorganisms are sensitive to anthropogenic disturbances and play an essential role in the cycling of soil nutrients and plant growth, making them potential indicators of ecosystem function. Thus, the objective of this work was to determine the impact of land reclamation on the composition and function of soil microbial communities in the Athabasca Oil Sands Region (AOSR). We evaluated bacterial community composition via high throughput sequencing of 16S rRNA genes and soil functional diversity by community-level physiological profiling (CLPP). The ranges of variability for these factors observed in soils reclaimed with either peat-mineral mix (PMM), forest floor-mineral mix (FFM), or FFM diluted with sand (Sand-FFM), were compared to that of undisturbed reference soils (NS) and a vegetation removed soil (VR). Differences between reclamation soils and natural soils were clearly discernible, with reclamation imposing a more drastic disturbance to the boreal forest than that of removal of vegetation alone. VR changed the structure of the soil microbial community and increased the overall diversity, within-community interactions, and heterogeneity; while reclamation shifted the microbial community structure to an even greater extent, placing it outside the range of natural variability. Among reclamation substrates, FFM showed the highest level of similarity to the range of natural variability and PMM showed the least. Altogether, our findings underscore the profound impact of anthropogenic activities associated with large-scale mining on soil biological activity, microbial communities, and edaphic profiles. These alterations are of such magnitude that they render the affected soils significant divergent from the reference undisturbed boreal forest soil.

Fire and retention island remnants have similar deadwood carbon stock a decade after disturbances in boreal forests of Alberta

In an attempt to reconcile wood extraction and forest biodiversity in managed boreal forests, ecosystem-based forest management (EBM) has become the de facto management approach. Retention forestry represents one prominent way that EBM is implemented in many parts of the world. Retention patches commonly left after harvesting serve as analogues of fire island remnants, which are patches of unburned forests in the burned forest matrix. Although the persistence of retention patches has been questioned, few studies have attempted to quantitatively compare forest attributes in both burned and harvested forests. As part of a larger program examining multiple aspects of ecosystem function in fire and harvest island remnants, we investigated the impact of disturbance type (fire/harvest) and forest edges on C stock in snags and coarse woody debris (CWD) found in island remnants in mixedwood boreal forests of Alberta, Canada. Total C stock (in snags and CWD) was similar between the two disturbance types and edge plots had similar total deadwood C stocks to interiors. The edges of island remnants had about two-fold more snag C stock than their interiors in both disturbance types, but C stock in CWD was unaffected by edge effects and disturbance type. Our results suggest that deadwood C dynamics in island remnants in fire and harvest disturbed boreal forests were similar, thus lending support for the continued implementation of retention forestry in Alberta.

Species identity and tree size drive residual tree mortality in island remnants in burned and harvested boreal forests

Ecosystem-based Forest Management (EBM) is a global paradigm with different forms of implementation. In North America, a key aspect of EBM is the emulation of natural disturbances such as wildfire, with retention forestry representing one dominant approach to implementation. Retention is intended to reduce the contrast between ecological legacies present in fire-disturbed and harvested stands by leaving unharvested patches or “island remnants”. These island remnants provide refugia for forest species, accelerate forest regeneration, and supply coarse woody material over time. However, the objectives of leaving retention patches could be compromised by excessive post-disturbance tree mortality, which may erode canopy cover in patches. Comparisons of residual tree mortality in dispersed retention or partial harvest to reference forests and clearcuts exist, but rarely have comparisons to island remnants created by wildfires been made, despite this being the model for these patches. Here, we sampled island remnants in burned and harvested areas in aspen-dominated mixedwood forests in Alberta, Canada, a decade after disturbance. We sought to: (i) test for differences in post-disturbance tree mortality in island remnants (fire versus harvest) (ii) determine if forest island edges experience higher tree mortality than plots located in the interior, and (iii) examine whether tree species, tree size, and stand density influence tree mortality patterns. Post-disturbance tree mortality was quantified using visual field surveys. Additionally, we dated a sub-sample of trees to quantify temporal patterns of tree mortality. We found that harvest-created island remnants did not exhibit higher residual tree mortality than similar-sized fire island remnants. Edge effects also had no impact on tree mortality, irrespective of disturbance type. Aspen (Populus tremuloides) had higher mortality than spruce (Picea glauca), and small-sized trees had a higher probability of mortality than large-sized trees. While previous studies have reported elevated rates of mortality for retention trees in relation to reference stands, we found similar mortality rates for trees in fire and harvest island remnants. These results support the continued implementation of retention forestry using island remnants within the scope of EBM in Alberta to promote forest recovery and resilience following disturbances.

Poor regeneration of pine after mountain pine beetle attack in colder boreal regions of Canada

The recent expansion of mountain pine beetle (MPB, Dendroctonus ponderosae) from its native range in western North America into northern boreal pine forests in Alberta, Canada has resulted in conditions for tree regeneration that are dramatically different from those after wildfire, the predominant natural disturbance in these forests. We assessed natural regeneration post-MPB for northern boreal lodgepole pine sites in Alberta, Canada via intensive surveys of small plots at 33 severely attacked pine stands and using data from 205 permanent sample plots representing various site types and levels of MPB mortality. We used model selection to identify factors explaining regeneration. Overall, pine regeneration was very poor 6–9 years post-MPB; only 42% of the 33 intensively surveyed plots and only 9% of the 205 permanent plots had pine seedlings. This poor regeneration is attributed to high levels of cone serotiny in these populations, unsuitable regeneration microsites due to undisturbed litter or feathermoss layers, and competition from the residual canopy and understory vegetation. Other species (aspen, birch, poplar, and black and white spruce) were found on most sites, either as post-attack regeneration or regeneration established in advance. Without intervention, many of these stands will likely transition away from pine, to broadleaf and other conifer species.

Multi‐level habitat selection of boreal breeding mallards

AbstractCanada's western boreal forest is a vital breeding habitat for North American duck populations. This region has experienced considerable demand for its valuable natural resources (e.g., oil and gas, forestry) resulting in extensive industrial development (e.g., infrastructure), which is predicted to continue. The potential effects of industrial development on breeding ducks in the western boreal forest, however, remains largely unexplored. We used backpack harness global positioning system (GPS) transmitters to document habitat selection by breeding female mallards (Anas platyrhynchos) across a gradient of industrial development in the western boreal forest of Alberta, Canada. We modeled breeding home range (second order) selection and habitat selection within the home range (third order) using resource selection functions, and spatially predicted our models across the landscape to highlight important breeding habitat. Contrary to our predictions, breeding female mallards did not avoid all industrial development at the second and third orders. Females established home ranges (second order) with greater proportions of marsh, graminoid fen, and well pads, and lower proportions of forest. Within their home range (third order), females selected shrub swamp, graminoid fen, marsh, well pads, and borrow pits, and avoided open water, swamp, treed peatland, forest, forest harvest areas, and industrials (e.g., buildings). Females also selected habitat that was close to pipelines and roads. Our results suggest that the magnitude and direction of breeding season habitat selection by female mallards varies depending on the scale and landscape features, but current levels of industrial development within our study area still allowed for the establishment of breeding season home ranges. Our spatially predicted maps contribute to the increasing body of work surrounding boreal waterfowl ecology by highlighting important breeding habitat for mallards in Canada's western boreal forest.

Effects of oil sands disturbances on shrub and tree structure along forest edges in Alberta's boreal forest

Deforestation causes forest fragmentation and associated edge effects. The boreal forest of Alberta, Canada has undergone substantial fragmentation via the creation of seismic lines, roads, and wellpads for resource exploration and extraction, but their associated edge effects have not been fully assessed, particularly for the latter two footprint types. We examined how these disturbances influence forest composition and structure along anthropogenic forest edges in the oil sands region of northeastern Alberta. We then used generalized linear models to test distance to edge responses in tree and shrub density given treatment (disturbance) type and forest canopy composition. Our results indicate the presence of edge effects, even along narrow seismic lines. Tree and shrub density and tree basal area were greater at the forest edge, being two times greater at 1 m from the forest edge relative to intermediate interior forest distances (∼30 m). Variations in tree basal area, tree density, and shrub and sapling density were best explained by interactions between disturbance type, distance from the forest edge, and % conifer composition. This study demonstrates that anthropogenic disturbances from energy exploration in the boreal forests cause changes in tree and shrub density (structure), and this effect is most pronounced in deciduous-dominated forests.

Intensive management increases flexibility in managing wood supply

We modelled the potential impact of intensification of plantation management and thinning, on timber supply of an ∼500 000 ha forest in Alberta, Canada over a 200-year planning horizon. Pre-commercial and commercial thinning were applied to a portion of the better sites, which allowed shortening of the time to merchantability and earlier harvest than unthinned stands; less than 25% of the forest was thinned over the course of the plan. The sustainable harvest rate, represented here as the annual allowable cut (AAC), increased by ∼14% above baseline, when thinning was applied. Similarly, there was a 20.7% increase in AAC projected with the relaxation of even flow rules if thinning was also applied. Finally, thinning offset the expected decline in AAC after a 20-year surge in cutting of mature pine, designed to slow an epidemic of mountain pine beetle. In terms of wood supply, the volume extracted at thinning was <2% of annual supply but volume from final harvest from thinned stands, at times, surpassed that of unthinned stands of the forest. Individual tree size from thinned stands was ∼twice that from unthinned areas in the second part of the planning period, offsetting the expected decline in piece size after the era of harvest of natural forests.

Maximum canopy height is associated with community phylogenetic structure in boreal forests

AbstractUnderstanding how maximum canopy height is related to forest community assembly is essential yet largely unexplored. Maximum canopy height is affected by competition and abiotic environmental factors through different ecological processes (e.g. niche differentiation and environmental filtering), as well as historical or stochastic factors. However, little has been done to empirically examine the ecological processes that influence maximum canopy height. We set out to examine the relationship between maximum canopy height and community phylogenic structure. We surveyed maximum canopy heights from a regional dataset of forest plots (466 sites of 50 m × 50 m) from the boreal forest of northeastern Alberta, Canada. We then explored the relationships between maximum canopy height as measured by airborne LiDAR (Light Detection and Ranging) and the phylogenetic structure of seed plants, represented by net relatedness index and nearest taxa index. We found stronger phylogenetic clustering among major evolutionary clades for communities with higher maximum canopy height, which implied that environmental filtering by abiotic factors is a driving factor for boreal forests. However, we also found stronger phylogenetic overdispersion within each clade for communities with higher maximum height, indicating more intense niche differentiation. Our results suggest that communities with higher maximum canopy height may have experienced more intense historical abiotic environmental filtering and recent niche differentiation in boreal forests. These findings will contribute to the monitoring and management of forest biodiversity.

Effect of variable retention forestry on wood frogs (Lithobates sylvaticus) in early successional boreal mixedwood forests

Variable retention forest harvesting aims to reduce negative effects of harvesting on forest biodiversity, but knowledge gaps remain regarding its effects on some taxa over longer post-harvest time frames. To better understand effects of variable retention and environmental features on amphibians, we used pitfall traps to capture wood frogs ( Lithobates sylvaticus (LeConte, 1825)) across four levels of retention (clearcut (0%), 20%, 50%, and unharvested control (100%)), and two forest types (deciduous and coniferous), in 17-year post-harvest forests in northwest Alberta. We mapped breeding sites and used a LiDAR-based terrain moisture index (depth-to-water) to examine relationships between relative abundance, breeding site proximity, and soil moisture. Retention level alone had no effect on relative abundance of adult wood frogs, but in late summer (July and August), there was a significant interaction between retention level and forest type: capture rates decreased with retention level for deciduous forests, but increased with retention level in conifer forests. During late summer, capture rates were higher in conifer forests than deciduous forests, with soil moisture (lower depth-to-water) positively related to capture rates. Though timber retention may be beneficial to wood frogs in the short term, any impacts of forest harvesting on wood frog abundance were undetectable in stands 17 years post-harvest.

Mid-Rotation Impacts of Stand Tending with Glyphosate on Plant Diversity in the Boreal Forest of West-Central Alberta

Stand tending using glyphosate to promote coniferous overstory trees has been a common practice in the boreal forests of Alberta. However, there are concerns about the impact of this practice on biodiversity of understory species. This study examined the impact of broadcast glyphosate application during the active reforestation phase, two to several years post-harvest, on forest plant diversity 25 to 40 years post-harvest. Herbicide treatments had the desired effect of shifting tree layer dominance from deciduous to coniferous species, driven by a 25-fold reduction in the density of trembling aspen (3927 vs. 154 stems·ha−1, untreated and treated, respectively). However, understory plant diversity was not significantly different between treated and untreated sites as examined by the Shannon–Wiener (H) and evenness (E) indices. Shared plant species (beta) across sites was high. Of the seven site-indicator species examined, three had significantly lower cover on treated sites: Wild sarsaparilla, low bush-cranberry and oak fern. Total understory plant cover was significantly greater in the treated portion (98.0%) versus untreated (71.4%); however, this difference was not significant when bryophytes were excluded in the analysis. The establishment, maintenance and monitoring of larger long-term trials is strongly recommended.

Multiscale nest-site selection of ducks in the western boreal forest of Alberta.

There is limited data regarding the nesting ecology of boreal ducks and their response to industrial development, despite this region being an important North American breeding area. We investigated how landcover and oil and gas development affect third‐order nest‐site selection of boreal ducks. We located duck nests in Alberta's western boreal forest between 2016 and 2018. We used multiscale analysis to identify how scale affects the selection of a resource using generalized linear mixed‐effects models and determined what scale‐optimized combination of landscape features were most important in describing where ducks nest. We located 136 nests of six species of upland nesting ducks between 2016 and 2018. The magnitude, direction, and best spatial scale varied by resource. For landcover, ducks selected nest‐sites associated with mineral wetlands (300 m) and open water (300 m). Ducks avoided greater densities of seismic lines (300 m) and pipelines (2500 m) but selected nest‐sites associated with borrow pits (300 m) and roads (1000 m). We used our models to predict important duck nesting habitat in the boreal forest, which can support conservation and management decisions. We recommend conservation actions target the conservation of mineral wetlands and associated habitats within this working landscape. Further research is necessary to understand the adaptive consequences of nest‐site selection and how industrial development influences important nest predators.

Emulating Succession of Boreal Mixedwood Forests in Alberta Using Understory Protection Harvesting

Understory protection harvesting is a form of partial cutting that can be used in aspen (Populus tremuloides Michx.)-dominated stands that have understories of white spruce (Picea glauca (Moench) Voss). This practice involves removing 75% to 85% of the merchantable aspen while minimizing damage to the advance spruce regeneration, in addition to leaving 15% to 25% of the aspen standing to reduce potential windthrow of the spruce understory. In this paper, we summarize results from 18 stands measured 10 to 12 years after understory protection harvest. Diameter growth of spruce increased during the first five years after harvest while height growth increased during the second five-year period (5 to 10 or 7 to 12 years after release). Consistent with other studies, mortality rates of aspen trees ≥7.1 cm DBH (diameter breast height, 1.3 m) averaged 45.0% over the 10–12 year period following harvesting. Spruce mortality averaged 27.5% over the same 10–12 year period. Substantial aspen regeneration was evident across most harvested blocks, with aspen sapling densities 10–12 years from harvest being higher in removal (14,637 stems⋅ha−1) than in buffer areas (6686 stems⋅ha−1) and in extraction trails (7654 stems⋅ha−1). Spruce sapling (>1.3 m height and <4 cm DBH) densities averaged 1140 stems⋅ha−1 in removal areas at ages 10–12, with these trees likely being present as seedlings at the time of harvest. Mixedwood Growth Model projections indicate merchantable volumes averaging 168 m3⋅ha−1 (conifer) and 106 m3⋅ha−1 (deciduous) 70 years from harvest, resulting in MAI (mean annual increment) for this period averaging 2.0 m3⋅ha−1⋅y−1 with MAI for a full 150-year rotation of approximately 2.5 m3⋅ha−1⋅y−1.

Mapping organic layer thickness and fuel load of the boreal forest in Alberta, Canada

Forest organic layers are important soil carbon pools that can, in the absence of disturbance, accumulate to great depths, especially in lowland areas. Across the Canadian boreal forest, fire is the primary disturbance agent, often limiting organic layer accumulation through the direct consumption of these fuels. Organic layer thickness (OLT) and fuel load (OLFL) are common physical attributes used to characterize these layers, especially for wildland fire science. Understanding the drivers and spatial distribution of these attributes is important to improve predictions of fire behaviour, emissions and effects models. We developed maps of OLT and OLFL using machine learning approaches (weighted K-nearest neighbour and random forests) for the forested region of the province of Alberta, Canada (538, 058 km2). The random forests approach was found to be the best approach to model the spatial distribution of these forest floor attributes. A databased of 3, 237 OLT and 594 OLFL plots were used to train the models. The error in our final model, particularly for OLT (5 cm), was relatively close to the variability we would expect to find naturally (3 cm). The dominant tree species was the most important covariate in the models. Age, solar radiation, spatial location, climate variables and surficial geology were also important drivers, although their level of importance varied between tree species and depended on the modelling method that was used.

Green islands in a sea of fire: the role of fire refugia in the forests of Alberta

Alberta wildfires vary greatly in severity, resulting in a mosaic of burnt, partially burnt, and unburnt forest. These unburnt patches (refugia) within the fire perimeter are critical for the survival of organisms during the fire and the regeneration process. We examined the literature to identify how the fire regimes and landscape features found in Alberta affect the creation and persistence of refugia, the role of refugia for the flora and fauna of Alberta, how climate change is likely to affect refugia, how humans may alter the creation and effectiveness of refugia, and management implications moving forward. Refugia can vary in scale from small areas of unburnt soil or boulders (centimetres to a few metres), to large stands of unburnt trees (many hectares) with different taxa using these refugia across all the spatial scales. Species reliant on habitat connectivity or old growth forest also benefit from refugia as they can use them as stepping-stones between intact habitats or as a lifeboat to recolonize from. The factors influencing what areas remain unburnt are complex and poorly understood but are likely tied to topography, aspect, proximity to waterbodies, weather changes (precipitation and wind direction), time of day during burning, and vegetation type. Areas with the right combination of topography, aspect, and proximity to water have cooler microclimates and higher moisture than the surrounding areas and may remain unburnt throughout multiple fire events, making them persistent refugia. Other areas may remain unburnt by a chance result of weather changes or having the fire pass through at night, making them random refugia. Many of the features that make persistent refugia unlikely to burn (cooler microclimate and higher moisture) will also buffer the effects of climate change. As a result, it is essential we manage the landscape in such a way as to protect areas that act as persistent refugia from industrial activities. In addition, we must restore fire in the landscape to maintain the mosaic of forest caused by mixed-severity fire, especially in the face of climate change, which is projected to increase the severity and frequency of wildfires in Alberta.

Effects of wildfire and soil compaction on recovery of narrow linear disturbances in upland mesic boreal forests

Energy exploration has led to fragmentation of habitats worldwide. In boreal forests of Alberta, Canada narrow clear-cut linear disturbances (3–14 m wide) called seismic lines are often the largest local source of forest fragmentation. Many lines have failed to recover decades after their creation leading to changes in forest dynamics and biodiversity. In some cases, these linear features function as habitat and/or corridors for species, while being detrimental in other species, most notably the threatened woodland caribou (Rangifer tarandus caribou). Recently, industry and government have focused on reforestation of these lines using silvicultural treatments and tree planting. However, these applications are expensive (> $12,500/km) and do not account for wildfires that can destroy restoration investments (planted trees), yet also initiate early seral conditions that favor natural recovery. Here, we examined soil compaction (bulk density) and tree regeneration density in burnt and unburnt seismic lines within mesic upland forest types and compared these to adjacent (paired) forest controls. Bulk density on seismic lines increased by 34% compared to undisturbed adjacent forests, but was not severe enough to impede regeneration. Despite increases in compaction, regeneration density was 19% higher on lines than in adjacent forests. Specifically, regeneration density averaged 19,622 stems/ha in burnt lines, 11,870 stems/ha in unburnt lines, 16,739 stems/ha in adjacent burnt forest, and 6,934 stems/ha in adjacent unburnt forest where regeneration rates are expected to be lower. We suggest that leave-for-natural recovery (passive restoration) of seismic lines can be expected post-fire in mesic upland forests with even the majority of unburnt seismic lines recovering to densities above the 5,000 stems/ha guidelines. Active restoration treatments using intensive silviculture treatments should therefore only be considered where recovery is not observed or wildfire likely.

Key factors determining scales of burned areas in state Victoria (Australia) and province Alberta (Canada) during 1980-2019

Regular wildfire supports balanced development of sclerophyll forests in Victoria (Australia), as well as, boreal forest in Alberta (Canada). Also, they are a major part of local Aboriginal culture in these regions and a means regulating ecological functions of flammable vegetation communities for improvement their productivity. Taking into consideration that burning is used as an effective tool for ecosystem management in Alberta and Victoria, it is relevant to assess impacts of fire practices on the environment and to find connections between fire spread and key factors determining scales and locations of burned areas. Basing on literary materials on fire practices, statistical data on wildfire cases occurring since 1980s, geospatial data on distribution of fire-prone plant communities’ locations, and on results of correlation analysis of fire cases with climatic, environmental, infrastructural, and social factors author reveals the following patterns: fires frequency depends on the landscape features; an increase in number of fire occurrences correlates with increase of dry periods duration (number of days); human settlements, where Aboriginal population reaches 50%, are subject to fires more frequent; the risk to the environment and settlements damage on small populated rural areas is higher, than on densely populated suburban and urban places. Reduction of out-of-control wildfire risk can be achieved through fire management practices directed to wildlife and biodiversity protection, considering these patterns.

Specialist or generalist? It depends. Context-dependent habitat relationships provide insight into forest disturbance effects for a boreal bird species

Understanding how disturbance affects species is a critical component of management in the boreal forest, particularly for disturbance specialist species that often help initiate the succession process through seed dispersal, nutrient cycling, and other means. Unfortunately, emulation of natural disturbance rarely incorporates the disturbance response of those specialist species, which may be potentially sensitive to disturbance characteristics because they are attracted to resources provided by the disturbance itself. Identifying disturbance specialist species and the reasons they occur in post-disturbance habitat is thus a priority for maintaining biodiversity in managed forests. We compared two types of habitat use to fill this information gap for a potential boreal forest disturbance specialist, the Common Nighthawk (Chordeiles minor). The Common Nighthawk is of particular interest to forest managers because this wide-ranging species is declining and listed as of conservation concern in multiple jurisdictions. We used passive acoustic monitoring to survey for nighthawks at 326 locations in the boreal forest of northeastern Alberta, Canada where land use pressure for resource extraction is high. We used an occupancy modelling framework to evaluate two hypotheses for why nighthawks use post-disturbance habitat: nesting or foraging resources. The nesting resource hypothesis was supported by all three lines of evidence that we examined. First, time since disturbance negatively affected territorial habitat use, but not extraterritorial habitat use, confirming that this species is only a disturbance specialist for the territorial component of its home range. Second, territorial habitat use differed between disturbance types, with a higher probability of habitat use for post-harvest and abandoned well sites, which are more likely to have lower amounts of residual vegetation. For our third line of evidence, open pine forest mitigated the effects of time since disturbance for territorial habitat use for all three disturbance types, but especially for postfire areas. We conclude that breeding Common Nighthawks require a combination of open habitat for nesting and wetland areas for foraging and provide industry-specific recommendations for incorporating the Common Nighthawk into boreal forest management plans. Our research emphasizes that understanding the context-dependence of species responses to disturbance provides insights that facilitate effective forest management. We advocate that understanding the behavioural context of habitat use can provide this insight and is often more likely to be aligned with the operational scale of forest management.

Linking functional diversity, trait composition, invasion, and environmental drivers in boreal wetland plant assemblages

AbstractQuestionsA range of landscape and local environmental factors, including invasion, interact with species functional diversity and trait composition to shape biodiversity patterns and ecosystem function of wetlands. A trait‐based, mechanistic understanding of community assembly holds promise for wetland conservation, but this has been rarely examined across scales. We examined: (a) the relative influence of climate, landscape matrix, and local physicochemistry on invasion intensity and functional diversity in boreal wetland plant assemblages; and (b) the ecological traits linked to these environmental factors.LocationOne hundred fifty‐three wetlands across the Boreal Forest of Alberta, Canada.MethodsWe used data on invasion intensity, using two terrestrial invaders (Sonchus arvensis and Cirsium arvense), and environmental factors at local and landscape levels. We used eight traits from 366 vascular plants to assess functional diversity and invasion responses to environmental gradients (generalized linear models) and individual species trait–environment relationships (community‐weighted mean redundancy analysis, fourth‐corner analysis).ResultsLandscape matrix and the degree of invasion were the primary drivers of functional diversity, while invasion intensity was driven by physicochemistry and functional diversity. Community trait–environment patterns clearly separated wetlands by invasion status. Uninvaded wetlands were surrounded by lowland conifers and composed of stress‐tolerant associated traits, while invaded wetlands contained high levels of disturbance and traits associated with high resource availability and reproduction rates. This division was further supported by individual trait–environment relationships.ConclusionsLandscape matrix was the dominant driver of functional diversity and composition pattern, while the local physicochemistry and surrounding land‐cover matrix helped explain invasion. Our analysis revealed some of the mechanistic relationships shaping plant community assembly across boreal wetlands, information that can help resource managers identify, predict, and alleviate possible threats from landscape anthropogenic disturbances to wetland ecological integrity.

Microbial Substrate Utilization and Vegetation Shifts in Boreal Forest Floors of Western Canada

Boreal forest soils are highly susceptible to global warming, and in the next few decades, are expected to face large increases in temperature and transformative vegetation shifts. The entire boreal biome will migrate northward, and within the main boreal forest of Western Canada, deciduous trees will replace conifers. The main objective of our research was to assess how these vegetation shifts will affect functioning of soil microbial communities and ultimately the overall persistence of boreal soil carbon. In this study, aspen and spruce forest floors from the boreal mixedwood forest of Alberta were incubated in the laboratory for 67 days without (control) and with the addition of three distinct 13C labeled substrates (glucose, aspen leaves, and aspen roots). Our first objective was to compare aspen and spruce substrate utilization efficiency (SUE) in the case of a labile C source (13C-glucose). For our second objective, addition of aspen litter to spruce forest floor mimicked future vegetation shifts, and we tested how this would alter substrate use efficiency in the spruce forest floor compared to the aspen. Tracking of carbon utilization by microbial communities was accomplished using 13C-PLFA analysis, and 13C-CO2 measurements allowed quantification of the relative contribution of each added substrate to microbial respiration. Following glucose addition, the aspen community showed a greater 13C-PLFA enrichment than the spruce throughout the 67-day incubation. The spruce community respired a greater amount of 13C glucose, and it also had a much lower glucose utilization efficiency compared to the aspen. Following addition of aspen litter, in particular aspen leaves, the aspen community originally showed greater total 13C-PLFA enrichment, although gram positive phospholipid fatty acids (PLFAs) were significantly more enriched in the spruce community. While the spruce community respired a greater amount of the added 13C-leaves, both forest floor types showed comparable substrate utilization efficiencies by Day 67. These results indicate that a shift from spruce to aspen may lead to a greater loss of the aspen litter through microbial respiration, but that incorporation into microbial biomass and eventually into the more persistent soil carbon pool may not be affected.