The objective of this study was to examine the distribution of exotic plants and determine the potential threats in the mixedwood section of the boreal forest. The invasion of exotic plants into natural areas is a growing concern among ecologists. Exotic species have no previous exposure to the invaded area and have been introduced, either intentionally or accidentally, by humans. These plants have the potential to suppress surrounding vegetation and acquire the majority of available resources. This dominance alters important ecosystem functions and negatively affects ecosystem structure and composition. This study examined three types of land use (roadside right-of-way maintenance, timber harvesting and wildfire) to identify the density, frequency and cover of exotic plants within the mixedwood forest. There were also separate categories of the time since disturbance (re-current, recent and mature) for each disturbance type. Data were collected in the summer field seasons of 2000 and 2001 in and nearby the Prince Albert Model Forest (approximately 70 km north of Prince Albert, Saskatchewan). Surveying was completed in mature forest, harvested and wildfire areas using 10 x 10 m quadrats. These quadrats were adjacent to or remote from roadside right-of-ways that were deliberately seeded with exotic species. Seeding the right-of-ways with exotic species occurred along principal and secondary highways. Surveying was also conducted within roadside right-of-ways using 1 x 1 m quadrats. These quadrats were adjacent to the recently disturbed and mature quadrats surveyed in the previous year. Each plant species observed in the quadrats had a cover value assigned, while stem counts were also conducted for exotic species. A total of 23 exotic species were observed within the quadrats. The exotic herb species belong to the Gramineae (9 species), Leguminosae (7), Compositae (5) families with one species each in Plantaginaceae and Boraginaceae. No exotic trees or shrubs were observed within the study sites. Areas that were recently disturbed either by timber harvesting or wildfire had 6 different exotic species with an average density of 0.2 ± 0.1 stems/m2 and a frequency of 72 %. Similar exotic frequencies and species in both recently harvested and burned survey sites suggests that these disturbances have a comparable affect on exotic distributions. Exotic species capable of wind dispersal had the highest frequencies in the recently disturbed survey sites. Common dandelion (Taraxacum officinale) had a frequency of 57 %, perennial sow thistle (Sonchus arvensis) was observed in 38 % of the sites and annual hawksbeard (Crepis tectorum) was at 25 %. Mature forest had a lower population of exotic plants, with only 2 exotic species observed. Taraxacum officinale and Canada bluegrass (Poa compressa) were observed in 13 % of the mature quadrats with an average density of 0.002 ± 0.002 stems/m2. The right-of-way quadrats contained the highest amount of exotics with 22 observed species. The average density of exotic species in roadside right-of-ways was 117 ± 22 stems/m2 with 94 % of the quadrats containing at least one exotic plant. The deliberate introduction, frequency of disturbance and the physical environment of roadside right-of-ways appear to influence the distribution of exotic plant species. The most frequently observed exotic species in the right-of-way areas were Taraxacum officinale (observed in 73 % of the quadrats at 8 stems/m2) followed by alsike clover (Trifolium hybridum at 45 % and 17 stems/m2), Sonchus arvensis (43 % and 4 stems/m2), creeping red fescue (Festuca rubra at 36 % and 31 stems/m2) and smooth brome grass (Bromus inermis at 31 % and 17 stems/m2). These species are either common in urban areas, agricultural weeds or have been deliberately seeded into right-of-way areas. The distribution of exotic species suggests that land use contributes to increased densities and frequencies of exotic plants. Each exotic species observed was ranked according to a system developed by Hiebert and Stubbendieck (1993). The ranking system was used to determine the current and potential threat of exotic plant species to become detrimental to ecosystem structure, composition and function. The ranking identified 14 species that were a lesser threat and easy to control, 8 species that were a lesser threat and hard to control, and one species, Bromus inermis, that was ranked as a serious threat and hard to control. Additional monitoring is required as the species observed in this study may be exhibiting a lag phase of population expansion, which typically precedes an exponential increase. Other species (scentless chamomile (Matricaria perforata) and caragana (Caragana arborescens)) that were not observed in the study area, but are known to occur within the region, are also a concern with respect to future exotic species invasions. Anticipated climatic changes are also expected to increase the distribution of exotic species as changes to environmental attributes will produce a longer growing season and increased plant growth and productivity.

The objective of this study was to examine the distribution of exotic plants and determine the potential threats in the mixedwood section of the boreal forest. The invasion of exotic plants into natural areas is a growing concern among ecologists. Exotic species have no previous exposure to the invaded area and have been introduced, either intentionally or accidentally, by humans. These plants have the potential to suppress surrounding vegetation and acquire the majority of available resources. This dominance alters important ecosystem functions and negatively affects ecosystem structure and composition. This study examined three types of land use (roadside right-of-way maintenance, timber harvesting and wildfire) to identify the density, frequency and cover of exotic plants within the mixedwood forest. There were also separate categories of the time since disturbance (re-current, recent and mature) for each disturbance type. Data were collected in the summer field seasons of 2000 and 2001 in and nearby the Prince Albert Model Forest (approximately 70 km north of Prince Albert, Saskatchewan). Surveying was completed in mature forest, harvested and wildfire areas using 10 x 10 m quadrats. These quadrats were adjacent to or remote from roadside right-of-ways that were deliberately seeded with exotic species. Seeding the right-of-ways with exotic species occurred along principal and secondary highways. Surveying was also conducted within roadside right-of-ways using 1 x 1 m quadrats. These quadrats were adjacent to the recently disturbed and mature quadrats surveyed in the previous year. Each plant species observed in the quadrats had a cover value assigned, while stem counts were also conducted for exotic species. A total of 23 exotic species were observed within the quadrats. The exotic herb species belong to the Gramineae (9 species), Leguminosae (7), Compositae (5) families with one species each in Plantaginaceae and Boraginaceae. No exotic trees or shrubs were observed within the study sites. Areas that were recently disturbed either by timber harvesting or wildfire had 6 different exotic species with an average density of 0.2 ± 0.1 stems/m2 and a frequency of 72 %. Similar exotic frequencies and species in both recently harvested and burned survey sites suggests that these disturbances have a comparable affect on exotic distributions. Exotic species capable of wind dispersal had the highest frequencies in the recently disturbed survey sites. Common dandelion (Taraxacum officinale) had a frequency of 57 %, perennial sow thistle (Sonchus arvensis) was observed in 38 % of the sites and annual hawksbeard (Crepis tectorum) was at 25 %. Mature forest had a lower population of exotic plants, with only 2 exotic species observed. Taraxacum officinale and Canada bluegrass (Poa compressa) were observed in 13 % of the mature quadrats with an average density of 0.002 ± 0.002 stems/m2. The right-of-way quadrats contained the highest amount of exotics with 22 observed species. The average density of exotic species in roadside right-of-ways was 117 ± 22 stems/m2 with 94 % of the quadrats containing at least one exotic plant. The deliberate introduction, frequency of disturbance and the physical environment of roadside right-of-ways appear to influence the distribution of exotic plant species. The most frequently observed exotic species in the right-of-way areas were Taraxacum officinale (observed in 73 % of the quadrats at 8 stems/m2) followed by alsike clover (Trifolium hybridum at 45 % and 17 stems/m2), Sonchus arvensis (43 % and 4 stems/m2), creeping red fescue (Festuca rubra at 36 % and 31 stems/m2) and smooth brome grass (Bromus inermis at 31 % and 17 stems/m2). These species are either common in urban areas, agricultural weeds or have been deliberately seeded into right-of-way areas. The distribution of exotic species suggests that land use contributes to increased densities and frequencies of exotic plants. Each exotic species observed was ranked according to a system developed by Hiebert and Stubbendieck (1993). The ranking system was used to determine the current and potential threat of exotic plant species to become detrimental to ecosystem structure, composition and function. The ranking identified 14 species that were a lesser threat and easy to control, 8 species that were a lesser threat and hard to control, and one species, Bromus inermis, that was ranked as a serious threat and hard to control. Additional monitoring is required as the species observed in this study may be exhibiting a lag phase of population expansion, which typically precedes an exponential increase. Other species (scentless chamomile (Matricaria perforata) and caragana (Caragana arborescens)) that were not observed in the study area, but are known to occur within the region, are also a concern with respect to future exotic species invasions. Anticipated climatic changes are also expected to increase the distribution of exotic species as changes to environmental attributes will produce a longer growing season and increased plant growth and productivity.

During the summer of 1982, trapping and vegetation surveys were carried out on permanent study plots within 6 of 7 different types of plant communities within the South-eastern Manitoba Taiga, which had been subjected to fire in May of 1980. A unique feature of this study area was the existence of an 8 year pre-fire data base. A total of 129 mammals, 123 of which are typified as "small mammals" were captured in 2100 trap nights. The number captured in each plant community were as follows: Jack Pine Ridge 19, Alder Jack Pine Ecotone 30, Alder Tamarack Bog 20, Jack Pine Sand Plain 5, Black Spruce Bog 5, Aspen Upland 21, Black Spruce Tamarack Bog 29. Pre-fire small mammal data for the permanent study plots were available, and up to ten years of data were used for comparative evaluation of fire effects. The effects of the fire vary according to the severity of the burn, but small mammal population numbers and biomass estimates for most plots increased the fall immediately after the burn, and then dropped in 1981. Specifically, Clethrionomys gapperi and Peromyscus maniculatus increased with the fire, and Sorex cinereus continued to fluctuate. Three growing seasons after the fire, population numbers and biomass estimates have declined, but are equal to or above minimum pre-fire levels. The effects of fire on other local wildlife, such as ungulates, fur bearers, and birds are discussed briefly. Current vegetation data were compared with pre-fire data and some basic post-fire reproductive strategies were observed. Pioneer or fugitive species with numerous light-weight wind-disseminated seeds, or those with Long-lived seeds stored in soil seed banks, which grow and mature rapidly were present. Frugivores are also suspected to have been an agent of post-fire seed dispersal. Vegetative reproduction through root sprouting or suckering was a dominant strategy observed on some plots. Relatively slow growing, late maturing species with larger, heavier seeds were also observed, and these are expected eventually to regain their upper canopy status. In an attempt to place a dollar value on the study area, the user's willingness to pay for benefits from use of the resources of the area, was combined with the potential attainable revenue from exploitation of local resources. The combined value is calculated to be in excess of $597,208.93. Interest in timber resources 80 years hence could present a conflict for land use management. It is recommended that the Taiga Biological Station study area be protected in its natural state, with controlled educational, research, traditional, and recreational activities permitted.

This thesis examines the politics of managing the boreal forest in the Abitibi region of Québec in Canada. It pays particular attention to how the plurality of forest users produces multiple forest imaginaries that are involved in the constitution of the micropolitics of quotidian practices of the forest. The aim is to show how different forest imaginaries and their politics could inform current forest management and open up other possibilities for the governance of, and relationships with, the boreal forest. By investigating the power relationships involved in the production of boreal forest politics, this work shows how forestry science and ecology have established and exercised their authority over how the forest is imagined and experienced. This territoriality has been articulated through discourses and practices that promote dominant industrial relationships with the forest which undermine other ways of imagining the relationships between forest users and non-humans. Engaging with post-structuralism theory, phenomenology and political ecology, I demonstrate how the multiplicity of forest users comes to know and experience the boreal forest in various and unstructured ways which destabilise efforts to imagine and construct the forest as a static entity. By paying attention to everyday life practices of various forest users, I show how contestations and negotiations about different imaginaries and places of the boreal forest are interrelated and mutually constituted. These practices and the imaginaries that they construct work together to produce the forest as an open space which is capable of embodying a wide range of meanings. By investigating how the boreal forest is constituted by various unstable imaginary places and politics, I argue that the current territoriality and politics produced by the imbrication of forestry science and industrial forestry should be challenged by another form of governance. This new form of governance needs to acknowledge the relational quality of imaginaries and to democratize the politics of the forest. By showing how abstract concepts such as relational politics can become implemented in current forest policies, the significance of institutions that are already in place and that can serve to embody other politics of the forest is highlighted. Apart from contributing to political ecology and environmental politics, the findings of this research show that political projects which can seem utopian at first glance have the potential to become tangible agents of social and environmental change.

During the summer of 1982, trapping and vegetation surveys were carried out on permanent study plots within 6 of 7 different types of plant communities within the South-eastern Manitoba Taiga, which had been subjected to fire in May of 1980. A unique feature of this study area was the existence of an 8 year pre-fire data base. A total of 129 mammals, 123 of which are typified as "small mammals" were captured in 2100 trap nights. The number captured in each plant community were as follows: Jack Pine Ridge 19, Alder Jack Pine Ecotone 30, Alder Tamarack Bog 20, Jack Pine Sand Plain 5, Black Spruce Bog 5, Aspen Upland 21, Black Spruce Tamarack Bog 29. Pre-fire small mammal data for the permanent study plots were available, and up to ten years of data were used for comparative evaluation of fire effects. The effects of the fire vary according to the severity of the burn, but small mammal population numbers and biomass estimates for most plots increased the fall immediately after the burn, and then dropped in 1981. Specifically, Clethrionomys gapperi and Peromyscus maniculatus increased with the fire, and Sorex cinereus continued to fluctuate. Three growing seasons after the fire, population numbers and biomass estimates have declined, but are equal to or above minimum pre-fire levels. The effects of fire on other local wildlife, such as ungulates, fur bearers, and birds are discussed briefly. Current vegetation data were compared with pre-fire data and some basic post-fire reproductive strategies were observed. Pioneer or fugitive species with numerous light-weight wind-disseminated seeds, or those with Long-lived seeds stored in soil seed banks, which grow and mature rapidly were present. Frugivores are also suspected to have been an agent of post-fire seed dispersal. Vegetative reproduction through root sprouting or suckering was a dominant strategy observed on some plots. Relatively slow growing, late maturing species with larger, heavier seeds were also observed, and these are expected eventually to regain their upper canopy status. In an attempt to place a dollar value on the study area, the user's willingness to pay for benefits from use of the resources of the area, was combined with the potential attainable revenue from exploitation of local resources. The combined value is calculated to be in excess of $597,208.93. Interest in timber resources 80 years hence could present a conflict for land use management. It is recommended that the Taiga Biological Station study area be protected in its natural state, with controlled educational, research, traditional, and recreational activities permitted.

No description available.

In this thesis, I describe three experimental studies that investigate the hotly debated role of competition in structuring communities in unproductive habitats. The studies were done in a boreal forest understory plant community in the southwestern Yukon. The first study was a traditional neighbour removal experiment. Ten of the most common species were transplanted as seedlings into transects with and without neighbours in a factorial design with two levels of water addition and two levels of fertilizer addition. The presence of neighbours increased survival and biomass of 6 species indicating a facilitative effect of neighbouring plants. The second study used the Community Density Series (CDS) methodology. The first of these was a 10-speciesexperimental community established from seed and grown in sandboxes at 6 densities with 2 watering levels and 2 fertilizer levels in a factorial design. At the community level, density dependence was observed at all life stages, but was not consistently competitive or facilitative - both emergence and final per plant shoot mass were density dependent, while survival to the end of the season was inversely density dependent. The effect of water was positive at seed emergence whereas fertilizer negatively affected survival. Species specific responses were also dependent on life stage. The final study was a 4-year CDS in the field using 9 common understory species at 6 densities and 3 fertilizer levels. Density negatively affected the community every year except for the first with competition being important at all densities above x1/8th the average community density. Constant final yield was reached in plots above the naturalx1 density for the last two years of the study. Responses to density were species-specific and 7 species declined with increasing density. No facilitative effects were observed. These studies demonstrate that density dependence is important in structuring this unproductive boreal understory habitat. The CDS approach allows us to quantify both the intensity and importance of plant competition at the community and species levels and to determine whether the importance of these biotic interactions depend on abiotic factors. The results clearly show that species-specific responses to biotic interactions are not necessarily the same as community level responses and if we are to understand community structure, it is necessary to use appropriate methodologies.

In this thesis, I describe three experimental studies that investigate the hotly debated role of competition in structuring communities in unproductive habitats. The studies were done in a boreal forest understory plant community in the southwestern Yukon. The first study was a traditional neighbour removal experiment. Ten of the most common species were transplanted as seedlings into transects with and without neighbours in a factorial design with two levels of water addition and two levels of fertilizer addition. The presence of neighbours increased survival and biomass of 6 species indicating a facilitative effect of neighbouring plants. The second study used the Community Density Series (CDS) methodology. The first of these was a 10-speciesexperimental community established from seed and grown in sandboxes at 6 densities with 2 watering levels and 2 fertilizer levels in a factorial design. At the community level, density dependence was observed at all life stages, but was not consistently competitive or facilitative - both emergence and final per plant shoot mass were density dependent, while survival to the end of the season was inversely density dependent. The effect of water was positive at seed emergence whereas fertilizer negatively affected survival. Species specific responses were also dependent on life stage. The final study was a 4-year CDS in the field using 9 common understory species at 6 densities and 3 fertilizer levels. Density negatively affected the community every year except for the first with competition being important at all densities above x1/8th the average community density. Constant final yield was reached in plots above the naturalx1 density for the last two years of the study. Responses to density were species-specific and 7 species declined with increasing density. No facilitative effects were observed. These studies demonstrate that density dependence is important in structuring this unproductive boreal understory habitat. The CDS approach allows us to quantify both the intensity and importance of plant competition at the community and species levels and to determine whether the importance of these biotic interactions depend on abiotic factors. The results clearly show that species-specific responses to biotic interactions are not necessarily the same as community level responses and if we are to understand community structure, it is necessary to use appropriate methodologies.

In this thesis, I describe three experimental studies that investigate the hotly debated role of competition in structuring communities in unproductive habitats. The studies were done in a boreal forest understory plant community in the southwestern Yukon. The first study was a traditional neighbour removal experiment. Ten of the most common species were transplanted as seedlings into transects with and without neighbours in a factorial design with two levels of water addition and two levels of fertilizer addition. The presence of neighbours increased survival and biomass of 6 species indicating a facilitative effect of neighbouring plants. The second study used the Community Density Series (CDS) methodology. The first of these was a 10-speciesexperimental community established from seed and grown in sandboxes at 6 densities with 2 watering levels and 2 fertilizer levels in a factorial design. At the community level, density dependence was observed at all life stages, but was not consistently competitive or facilitative - both emergence and final per plant shoot mass were density dependent, while survival to the end of the season was inversely density dependent. The effect of water was positive at seed emergence whereas fertilizer negatively affected survival. Species specific responses were also dependent on life stage. The final study was a 4-year CDS in the field using 9 common understory species at 6 densities and 3 fertilizer levels. Density negatively affected the community every year except for the first with competition being important at all densities above x1/8th the average community density. Constant final yield was reached in plots above the naturalx1 density for the last two years of the study. Responses to density were species-specific and 7 species declined with increasing density. No facilitative effects were observed. These studies demonstrate that density dependence is important in structuring this unproductive boreal understory habitat. The CDS approach allows us to quantify both the intensity and importance of plant competition at the community and species levels and to determine whether the importance of these biotic interactions depend on abiotic factors. The results clearly show that species-specific responses to biotic interactions are not necessarily the same as community level responses and if we are to understand community structure, it is necessary to use appropriate methodologies. / Science, Faculty of / Botany, Department of / Graduate

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.