The maintenance of downed woody debris supplies is increasingly being recognized as an integral part of forest management. In order to better manage this resource, it is important to assess its role in supporting biodiversity. In this thesis, I investigate the responses of carabid communities to variation in woody debris availability in an experimental manipulation of woody debris volume in closed canopy forests and following a biomass harvest in a clearcut. Within closed-canopy forests, total carabid abundance and the abundances of eight species increased significantly with increasing volumes of various types of woody debris, particularly large diameter, late-decay conifer wood. Similarly, a strong affinity with woody debris was observed in the clearcut. These findings suggest that reductions in woody debris will have negative consequences for carabids and indicate the need to ensure a diverse and abundant supply of woody debris during stand development.

Anthropogenic disruptions in the form of hydrological alterations, such as dam construction and the associated water diversions are a cause of much upheaval to local and regional ecosystems. Lake 626 within the Experimental Lakes Area of north-west Ontario, along with its downstream wetlands, 626A and 626B are one such system. Construction of a dam at the L626 inflow has completely restricted water flow, reducing and reshaping the watershed, increasing water retention time, and decreasing outflow into the wetlands. This study investigates the state of each wetland through physical and geochemical characterization during the first year following the diversion. Previous studies have found that hydrological diversions in wetlands can lower water table levels, altering soil chemistry and producing a shift in floral and faunal communities. Ultimate consequences involve significant loss of wetland area through conversion to upland habitat. This provides a model for climatic warming scenarios, wherein sustained drought conditions can produce the same result. Boreal wetlands are surprising fragile ecosystems that store massive quantities of carbon and are at risk of releasing it in such situations. One study showed that an extended summer drought in an otherwise average year with above average precipitation produced losses of 90 g C/m2 over the course of the year. Maintenance of reduced-flow in wetlands 626A and 626B is expected to convert the system into a carbon source and reduce overall wetland area. Radiocarbon dating has revealed that following deglaciation, both 626A and 626B basins were open water wetlands, depositing limnic peat for about 3200 and 1300 years respectively. Each site then transitioned into open sedge dominated fen – 626B to the present and 626A until about 2.5 ka BP when Sphagnum began to develop. Wetland 626B is decidedly an open shrub/sedge fen, supporting Myrica gale, Chamaedaphne calyculata and Carex rostrata / lasiocarpa communities. Wetland 626A is a bog/fen complex, sharing similar communities in the fen areas, but housing a large, centrally located bog of shrub species overlying Sphagnum hummocks. Tritium values in 626A were similar to cosmic background levels, indicating that recharge of basal pore water has not occurred in at least 60 years. Tritium in 626B was much higher, suggesting a substantial difference in hydrology or peat hydraulic conductivity between the basins. Measurement of DOC profiles showed high concentrations in near-surface water, reaching over 80 mg/L, and dropping to about 20 mg/L at maximum depths. An opposite trend was seen for DIC and CH4 profiles which increased concentration with depth (25 – 70 mg/L DIC; 75 – 700 μmol/L CH4). Isotopically however, 13C signatures from basal DIC were more positive while signatures from CH4 were typically more negative (-6 ‰ to +4 ‰ DIC; -57 ‰ to -73 ‰ CH4). Breakdown of DOC by LC-OCD showed high concentrations of humic substances and low molecular weight neutrals. The origin of humic substances in surface water became more pedogenic with increasing distance from the L626 outflow, indicating the influence of decaying wetland vegetation on the DOC of adjacent water. A comparison between contemporary and future characterization of boreal peatlands under drought-like conditions will provide a better understanding of the impacts suffered by wetlands during hydrological alterations. The high sensitivity of wetlands to changing hydrology should also provide a measure for gauging the effects of long term climate warming. This will assist in the development of environmental policies to better govern both the establishment of water diversions and the multitude of other practices leading to climate change.

In this thesis I examined the impacts of variable retention harvesting on residual tree mortality and natural regeneration of white spruce [Picea glauca (Moench (Voss)] in northern Alberta. The VR was done in four overstory canopy compositions (ranging from deciduous dominated to conifer dominated) and at six rates of canopy retention (2%, 10%, 20%, 50%, 75% and 100%). After 10 years there was 32.9 % mortality of aspen (Populus tremuloides Michx.) and 16.9 % mortality of spruce in the VR cuts. Mortality of individual trees was greater with low density of trees, in the conifer stands and for trees with short live crowns, which are large and trees near machine corridors. Natural regeneration of spruce was greatest with higher availability of seed trees (>30 ha-1) and on machine corridors, where stocking reached 74%. By contrast, stocking was 14% on retention strips, when seed tree density was 11 seed trees ha-1. / Forest Biology and Management

Boreal mixedwood forest stands are comprised of a mixture of small canopy patches of varying dominance by conifer (mostly white spruce (Picea glauca (Moench) Voss)) and broadleaf (mostly trembling aspen (Populus tremuloides Michx.) trees. The purpose of this work was to extend our understanding of the patterns and causes of variation in understory vascular plant communities in unmanaged, mature boreal mixedwood forests. First, I assessed variation in understory community composition in relation to canopy patch type (conifer, mixed conifer-broadleaf, broadleaf, gaps) within mixedwood stands. The mosaic of canopy patches leads to different micro-habitat conditions for understory species, allowing for communities that include both early and late successional species and contributing to greater understory diversity. This study suggests that the mosaic of small canopy patches within mixed forest stands resembles a microcosm of the boreal mixedwood landscape, across which understory community composition varies with canopy composition at the stand scale. Second, I investigated the hierarchical organization of understory diversity in relation to the heterogeneous mosaic of canopy patch types through additive partitioning of diversity. The largest proportion of species richness was due to turnover among patches within patch type while individual patches had higher evenness. The mosaic of canopy patch types within mixedwood forests likely plays a crucial role in maintaining the hierarchical levels at which understory diversity is maximized. Third, I examined interactions among understory plant species by investigating the effect of shrub removal on biomass, composition and diversity of herbs using a 3-yr removal study in a natural understory community. There is asymmetric competition for light between erect shrub and herb species but herb response to erect shrub removal was species-specific. Plant interactions play an important role in structuring boreal understory communities. Finally, I explored the relative influence of space, environmental variables, and their joint effects, on understory composition and richness. The environmental variation caused by small canopy patches and biotic processes, such as species interactions, converge at the fine scale to create a spatially patchy structure in understory communities in boreal mixedwood forests. Modifications in the natural mixture of small canopy patches could disrupt the spatial and environmental structures that shape understory composition and diversity patterns. / Forest Biology & Management

Boreal mixedwood forest stands are comprised of a mixture of small canopy patches of varying dominance by conifer (mostly white spruce (Picea glauca (Moench) Voss)) and broadleaf (mostly trembling aspen (Populus tremuloides Michx.) trees. The purpose of this work was to extend our understanding of the patterns and causes of variation in understory vascular plant communities in unmanaged, mature boreal mixedwood forests. First, I assessed variation in understory community composition in relation to canopy patch type (conifer, mixed conifer-broadleaf, broadleaf, gaps) within mixedwood stands. The mosaic of canopy patches leads to different micro-habitat conditions for understory species, allowing for communities that include both early and late successional species and contributing to greater understory diversity. This study suggests that the mosaic of small canopy patches within mixed forest stands resembles a microcosm of the boreal mixedwood landscape, across which understory community composition varies with canopy composition at the stand scale. Second, I investigated the hierarchical organization of understory diversity in relation to the heterogeneous mosaic of canopy patch types through additive partitioning of diversity. The largest proportion of species richness was due to turnover among patches within patch type while individual patches had higher evenness. The mosaic of canopy patch types within mixedwood forests likely plays a crucial role in maintaining the hierarchical levels at which understory diversity is maximized. Third, I examined interactions among understory plant species by investigating the effect of shrub removal on biomass, composition and diversity of herbs using a 3-yr removal study in a natural understory community. There is asymmetric competition for light between erect shrub and herb species but herb response to erect shrub removal was species-specific. Plant interactions play an important role in structuring boreal understory communities. Finally, I explored the relative influence of space, environmental variables, and their joint effects, on understory composition and richness. The environmental variation caused by small canopy patches and biotic processes, such as species interactions, converge at the fine scale to create a spatially patchy structure in understory communities in boreal mixedwood forests. Modifications in the natural mixture of small canopy patches could disrupt the spatial and environmental structures that shape understory composition and diversity patterns. / Forest Biology & Management

主催：JST/CREST，Vrije University, ALTERRA, IBPC

During oil-sands mining all vegetation cover, soil, overburden and oil-sand is removed, leaving pits several kilometres wide and hundreds of metres deep. These pits are reclaimed by a variety of treatments using mineral soil or a mixed peat and mineral soil as the capping layer and planted with trees with natural colonisation from adjacent sites. A number of reclamation treatments covering different age classes were compared with a range of natural forest ecotypes to identify the age at which the treatments become similar to a natural site with respect to vegetation composition and key soil attributes relevant to nutrient cycling. Ecosystem function was estimated from plant community composition, litter decomposition, development of an organic layer and bio-available nutrients. Key response variables including moisture, pH, C:N ratios, bio-available nutrients and ground-cover were analysed by non-metric multidimensional scaling and cluster analysis to discover which reclamation treatments were moving towards or merging with natural forest ecotypes and at what age this occurs. On reclaimed sites, bio-available nutrients including nitrate generally were above the natural range of variability but ammonium, phosphorus, potassium, sodium and manganese were generally very low and limiting to ecosystem development. Plant diversity was similar to natural sites from 5 years to 30 years after reclamation, but declined as reclaimed sites approached canopy closure. Grass and forb leaf litters decomposed faster than aspen or pine in the first year, but decomposition on one reclamation treatment fell below the natural range of variability. Development of an organic layer appeared to be facilitated by the presence of shrubs, while forbs correlated negatively with first-year decomposition of aspen litter. The better restoration amendments for tailings sands involved repeated fertilisation of peat: mineral mixtures in the early years of plant establishment, these became similar to a target ecotype at about 25 years. Good results were also shown by subsoil laid over non-saline overburden and fertilised once, these became similar to a target ecotype at about 15 years. Other treatments receiving a single application of fertiliser remain entrenched in the early reclamation phase for up to 25 years.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2002. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 5 uppsatser.