Natural fire return intervals are relatively long in eastern Canadian boreal forests and often allow for the development of stands with multiple, successive cohorts of trees. Multi-cohort forest management (MCM) provides a strategy to maintain such multi-cohort stands that focuses on three broad phases of increasingly complex, post-fire stand development, termed “cohorts”, and recommends different silvicultural approaches be applied to emulate different cohort types. Previous research on structural cohort typing has relied upon primarily subjective classification methods; in this thesis, I develop more comprehensive and objective methods for three common boreal mixedwood and black spruce forest types in northeastern Ontario. Additionally, I examine relationships between cohort types and stand age, productivity, and disturbance history and the utility of airborne LiDAR to retrieve ground based classifications and to extend structural cohort typing from plot to stand-levels. In both mixedwood and black spruce forest types, stand age and age related deadwood features varied systematically with cohort classes in support of an age-based interpretation of increasing cohort complexity. However, correlations of stand age with cohort classes were surprisingly weak. Differences in site productivity had a significant effect on the accrual of increasingly complex multi-cohort stand structure in both forest types, especially in black spruce stands. The effects of past harvesting in predictive models of class membership were only significant when considered in isolation of age. As an age emulation strategy, the three cohort model appeared to be poorly suited to black spruce forests where the accrual of structural complexity appeared to be more a function of site productivity than age. Airborne LiDAR data appear to be particularly useful in recovering plot-based cohort types and extending them to the stand-level. The main gradients of structural variability detected using LiDAR were similar between boreal mixedwood and black spruce forest types; the best LiDAR-based models of cohort type relied upon combinations of tree size, size heterogeneity, and tree density related variables. The methods described here to measure, classify, and predict cohort-related structural complexity assist in translating the conceptual three cohort model to a more precise, measurement based management system. In addition, the approaches presented here to measure and classify stand structural complexity promise to significantly enhance the detail of structural information in operational forest inventories in support of a wide array of forest management and conservation applications.

Although boreal forest management typically results in an increased frequency of even-aged forest stands in managed landscapes, fire history research suggests that much of the natural forest mosaic is composed of stands characterised by multiple cohorts of trees. To aid in the development of multicohort management, I investigated stand structural characteristics and small mammal communities as a function of their tree cohort structures. I also tested key alternatives: stand age, productivity, and tree species composition, as correlates of structural variation and small mammal communities. Results reveal that in mixedwood and black spruce forests, three-dimensional structure of boreal forests is strongly correlated with small mammal community structure, and indicate that tree diameter distribution is a succinct descriptor of such structural variation, performing better than alternative stand characteristics. This represents a new approach to characterising habitat supply as a function of within-stand heterogeneity, contrasting with existing approaches that focus on among-stand characteristics.

Methylmercury (MeHg) is a potent vertebrate neurotoxin and a contaminant of global concern. Increased anthropogenic emissions of mercury (Hg) to the atmosphere have led to increased bioaccumulation of MeHg in top predatory organisms such as fish, the consumption of which is the main exposure pathway of this toxin to humans and other animals. Forest canopies significantly increase the deposition of Hg in general to watersheds, but sources and fates of MeHg deposition in particular remain poorly understood. In this study, wet and dry loadings of MeHg to a watershed were quantified, and the retention and (photo)reduction of MeHg on foliage were measured using unique stable isotope experiments. We found that traditional methods of quantifying net deposition underestimate incoming sources of MeHg, and that retention of MeHg on forest canopies results in delayed transport of a significant portion of newly deposited MeHg from terrestrial catchments into adjacent lakes. / Ecology

This thesis examined the efficacy of residual forest structure for the preservation and recovery of bryophytes five to six years after partial canopy harvest in boreal mixed-wood forests of northwestern Alberta, Canada. Bryophytes were sampled in two forest types that differed in pre-harvest abundance of broadleaf (primarily Populus tremuloides Michx. and P. balsamifera L.) and coniferous (primarily Picea glauca (Moench) Voss) canopy trees. In Chapter 2, epiphytic bryophytes growing on aspen (P. tremuloides) were characterized by species viability and nearest-neighbour relationships. Epiphyte assemblage structure showed increasing impact with declining retention owing to degradation of growing conditions for species on trees. Chapter 3 provided an analysis of species richness and abundance patterns in relation to residual canopy structure. Bryophytes generally benefitted from higher canopy retention; however, epixylic and epiphytic species were more sensitive to partial harvesting than species on other substrates, and liverworts were more sensitive than mosses. Liverworts exhibited higher among-site differences in richness as retention declined, which partly resulted from increasing numbers of local species extinctions. In an analysis of species-environment relations in partially-harvested forests in Chapter 4, forest moisture was reduced with any degree of harvesting in both forest types. Lower canopy retention and forest moisture levels were associated with reduced abundances of species with particular biological traits, such as limited reproduction and dispersal capacities. Their re-establishment after harvesting may be impeded because of biological and environmental limitations. Coniferous-dominated forests supported higher abundances of liverworts and species with greater moisture requirements than did mixed-wood broadleaf-coniferous forests, and are potentially important refuges of bryophyte source populations. Chapter 5 examined the capacity for bryophyte species to germinate from diaspore banks in forest soils. Species germinated readily from mineral soil samples obtained from harvested sites, including several perennials characteristic of intact forests. Diaspore banks may serve as a persistent source for species colonization at post-disturbance sites, but only under appropriate growing conditions and not for species that were most sensitive to harvesting. Overall, both amount and composition of forest structure retained after partial harvesting are important management considerations for ensuring conservation of the wide variety of bryophyte species in mixed-wood landscapes. / Conservation Biology

Identifying amphibian habitats within a landscape provides a tool for managing their populations. I identified if and how amphibians used small ephemeral wetlands (≤ 0.1ha) and streams within the mixedwood forest area managed by Daishowa Marubeni International Ltd. near Peace River, north-western Alberta. Twenty-seven wetlands and their riparian zones were sampled for all life stages of amphibians in 2008 using timed visual encounter surveys. The riparian zones of 11 small streams were sampled with pitfall traps within 120 m of their beds from 2006 to 2008. Habitat features were also measured. Lithobates sylvaticus, Anaxyrus boreas and Pseudacris maculata used small ephemeral wetlands and the riparian zones of ephemeral, intermittent and permanent streams at different life stages. Water temperature and canopy cover influenced amphibian presence and abundance in wetlands. Coniferous and deciduous tree density were associated with L. sylvaticus abundance at the stream sites. I conclude that small waterbodies are amphibian habitats in the mixedwood forest of boreal Alberta. / Ecology

The impacts of aspen clear-cutting on upland groundwater recharge are presented based on two years (2007-2008) of the five year (2005-2009) HEAD2 NSERC-CRD paired-catchment experiment. Research was conducted at the Utikuma Region Study Area (URSA), 370 km north of Edmonton, Alberta, Canada, in the Boreal Plain ecozone. Results show greater soil water content in the root zone and potential for recharge into the deeper unsaturated zone during the first year of regeneration. Sites with shallow water table levels (<600 cm) increased more than sites under uncut conditions. Sites with deeper water table levels (>600 cm) responded minimally, if at all, to spring-melt and summer storms suggesting that water exchanges with the atmosphere occurred to and from the unsaturated zone only during the first-year regeneration. Upland groundwater gradients to adjacent pond-peatland complexes persisted at least ten times longer under clear-cut than under uncut conditions. Water table trends recovered to uncut conditions by the second year of regeneration. / Ecology

Forest tent caterpillar (Malacosoma disstria Hübner; FTC), a major defoliator of aspen trees, occupies both aspen and mixedwood forest stands in Alberta’s boreal forest. Forest stand composition could influence the spatial pattern of FTC outbreaks if mortality from natural enemies differs between stand types. I conducted field experiments to determine whether predator- or parasitoid-caused mortality of FTC differed between aspen and mixedwood forest stands and developed a spatial population model to determine the effects of variation in generalist predation on the spread of an FTC outbreak, including the effects of potential predator-caused Allee effects. Generalist predation on FTC was higher in aspen stands than in mixedwood stands, and the spatial model suggests that these observed differences may be sufficiently large to impact FTC outbreak spread rates. Forest stand composition may contribute to the spatial pattern of FTC outbreaks through variation in the impacts of predators on FTC populations. / Ecology

To understand the communicative functions of any vocalization it is important to first classify, describe, and measure the elements of that vocalization. Mexican (Poecile sclateri) and boreal (P. hudsonica) chickadees both produce a name-sake chick-a-dee call. Here, the note types present in samples of Mexican and boreal chick-a-dee calls are identified and described. Frequency and temporal measures of each note type are analyzed and show that frequency measures may be useful for note-type and individual discrimination. Call syntax is also analyzed and shows that both Mexican and boreal chickadees produce the notes within their chick-a-dee calls in a fixed order with the potential for any note type to be repeated or omitted within the sequence. This work provides a foundation for future studies aimed at understanding the communicative significance of this call within these species, as well as for comparative work on the chick-a-dee call among all chickadee species.

This research investigated the natural recovery of upland boreal forest vegetation on a peat-mineral mix substrate in the Athabasca Oil Sands Region, Alberta. Three sites, aged 26 to 34 years, were assessed to determine effects of substrate (pH, electrical conductivity, texture), topography, slope, aspect, hummock size, litter depth, tall shrub and tree stem densities, canopy cover, and tree ages on community composition and cover of upland boreal vegetation. Environmental variables that had the most influence on the plant communities were substrate texture (clay), tree canopy cover, and tall shrub stem density. The plant communities, which likely developed from early successional lowland communities, most closely approximate an upland boreal mixedwood forest in transition from an early to mid successional stage. Community development was concluded to be a product of measured environmental variables, with unmeasured factors such as propagule dispersal, germination conditions, and initial species composition also playing important roles. / Land Reclamation and Remediation

Understanding the controls on water movement on forested uplands is critical in predicting the potential effects of disturbance on the sustainability of water resources. I examined the controls on vertical and lateral water movement on forested uplands on a range of landforms (coarse textured outwash, fine textured moraine) and time periods (individual events, during snowmelt, through the growing season, annually, and long-term) at the Utikuma Region Study Area (URSA) on the sub-humid Boreal Plains of Alberta, Canada. To quantify vertical and lateral water movement, hydrometric and tracer measurements were made under natural and experimental conditions at plot and hillslope scales. Vertical flow and unsaturated zone storage dominated hydrologic response to snowmelt and rainfall at the plot and hillslope scales. Plot-scale snowmelt infiltration was greater than near-surface runoff, and when runoff occurred it was limited to south-facing outwash hillslopes underlain by concrete frost. Rainfall simulation studies showed that even under the extreme conditions tested, vertical flow and storage dominated the hydrologic response. Soils at field capacity and precipitation inputs of 15-20 mm or greater at high intensities were required to generate lateral flow via the transmissivity feedback mechanism. The threshold soil moisture and precipitation conditions are such that lateral flow will occur infrequently under natural conditions. Seasonal vertical water movement under natural conditions was greater on outwash than moraine uplands. The maximum downward vertical movement occurred in response to snowmelt, with little subsequent movement over the growing season. Recharge following snowmelt was similar for outwash and moraine sites and was followed by declining water tables through the growing season. Tracer estimates of long-term root zone drainage were low, while estimates of recharge for the moraine were high, raising questions about the appropriateness of this method for these sites. These results emphasize the dominance of vertical relative to lateral water flow on Boreal Plain uplands. Detailed understanding of the controls on water movement can be used to predict the potential effects of disturbance on hydrology and water resources. / Ecology