The encroachment of woody species into grassland and savanna ecosystems has been well document since the early 1800s. Within the parkland ecoregion of western Canada, trembling aspen (Populus tremuloides Michx.) has been one of the key tree species increasing in dominance. Aspen encroachment is best explained not by single mechanism, but rather by a number of interacting ecological factors. In this study I examined the ecological consequences of the clonal biology in aspen as a means to explain persistence and observed tree-grass ratios within grassland savannas of western Canada. Results suggest that aspen stands cycle between a “stable” phase characterized by a dense mature canopy, and an “unstable” phase characterized by canopy breakup and increased regeneration from root suckers. It is during this unstable phase that clonal encroachment is likely to occur. Within these mature stands, different-aged ramets promote persistence by maximizing developmental variation. Such a mechanism overcomes the functional phenotypic uniformity of ramets within a single age-structured stand. Results from my study indicate that physiological integration is beneficial to the growth and survivorship of regenerating and encroaching aspen ramets. My results also suggest that the benefits of physiological integration are greatest in more stressful environments, and in recently established post-fire ramets. Finally, the consequences of variation in adaptive ecological relevant traits among individuals was examined by determining differences in vigor among aspen clones in relation to the production of secondary compounds (phenolic glycosides). My results demonstrate a high degree of variation in leaf phenolic glycosides production among clones. A significant amount of this variation was accounted for by differences in clone vigor (within population: individual susceptibility hypothesis), with a smaller amount related to environmental differences (among populations). In all instances, vigorous clones were significantly higher in levels of phenolic glycosides compared with dieback clones, suggesting that some individuals may be predisposed to undergo density-independent mortality. This has important ecological implications, because it implies that one of the key mechanisms regulating population dynamics, community interactions and biodiversity may be related to intrinsic adaptive differences in susceptibility among individuals.

This thesis explores the geomorphic implications of large woody debris (LWD) residing in the backshore of beach-dune systems along the northeastern coasts of Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada. Detailed topographic surveys were employed to quantify seasonal mass balance of the beach-dune systems along two distinctly different coastlines. Erosion and accretion potential models were applied to characterize sediment transport conditions. Holman’s (1986) R2% wave runup model was superimposed on total water levels, to model wave runup exceedence of the beach-dune junction elevation (6.5 m aCD). Modelled ‘erosion potential’ hours were demonstrated to correspond with observed erosion including removal of the LWD zone, resulting in decreased mass balance. Similarly, Fryberger and Dean’s (1979) Drift Potential model was used to model accretion potential hours. Modelled accretion potential hours were also able to effectively describe conditions when actual accretion occurred. The presence of LWD in the backshore offered two functions to the above processes: it acted effectively as an ‘accretion anchor’, promoting increased mass balance and rebuilding of the incipient foredune; and, it offered a mass of sediment fronting the foredune to protect the beach-dune system from storm wave attack and subsequent erosion.

Soil nitrogen (N) is a major factor limiting forest growth. While inorganic N forms such as ammonium (NH4) and nitrate (N03-) have been the focus of plant N nutrition studies, a growing body of research has shown direct uptake of organic N forms (including amino acids) is common across the plant kingdom. However, there are few examinations of the contribution amino acid N makes to plant nutrition in temperate forest regions. The main goals of this thesis were to determine i) potential contributions amino acid-N and inorganic-N could make to N-nutrition of some temperate forest plants, ii) N-form adaptations among species that could lead to N-niche partitioning among them, and iii) the influence of m ycorrhizae on plant growth and N-form uptake. I determined the relative availabilities of amino acid N and inorganic N in three sites near Jordan River, British Columbia, biomass production of four species of forest plants. some associated with m ycorrhizae, when given inorganic (NH4-, N03-) or organic (glycine, glutamic acid) N, and short-term uptake (24 hours) of labelled N H4+, N03-, glycine, and glutamic acid using Sitka spruce (Picea sitchensis ), Douglas-fir (Pseudotsuga menziesii ), blueberry (Vaccinium ovalifolium) and salmonberry (Rubus spectabilis). All species performed well when supplied with N prim arily as NH4+, and NH4+ tended to be the most available N -source in all soils tested. Soils dominated b y salmonberry tended to have greater N03- production and lower amino acid-N: inorganic-N ratios compared to soils dominated by blueberry. This corresponded to the good growth and short-term 15NO3-uptake of salmonberry when grown with N supplied primarily as N03-, compared to other N-form treatments. Blueberry grew significantly more when given NH4- and N03-compared to amino acids. Thus, while blueberry has the ability to take up and use N03-for growth, sites on which it was dominant had low N03- availability. Mycorrhization did not improve biomass production, and in some cases actually decreased biomass. However, 15N uptake tended to be improved in mycorrhizal plants compared to non¬mycorrhizal plants. The comparable rates of short-term 15N uptake from amino acids and inorganic-N by all plants. in addition to the coin parable amino acid-N and inorganic-N availability in soils, suggested that am ino acids may be significant contributors to the N - nutrition of these tern perate species. However, biomass production was often reduced in amino acid treatments, which this was not always reflected by short-term '5N uptake.

Harvest-related decreases of downed woody debris (DWD) in forests may have important ecological implications; however, patterns of nutrient release from decaying DWD are poorly understood. The importance of DWD was investigated relative to biomass and nutrient pools in six, second-growth boreal mixedwood forest stands, differing by harvest regime near Kapuskasing, Ontario. Nutrient concentrations and mineralization trends using ion exchange resins at three proximities during the decay of Abies balsamea and Populus tremuloides were also examined. Concentrations of N, P, Ca, and Mg increased with decay, whereas K decreased. DWD was a minor contributor to biomass and nutrient pools. Inorganic N, P, Ca, and Mn were significant between harvest types with decay class interaction for N, Ca, and Mn. Species and proximity effects were found for Al, Fe, and K. These results suggest DWD may be a minor contributor to biomass and nutrient pools, but highlights its dynamic nature.

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.

Harvest-related decreases of downed woody debris (DWD) in forests may have important ecological implications; however, patterns of nutrient release from decaying DWD are poorly understood. The importance of DWD was investigated relative to biomass and nutrient pools in six, second-growth boreal mixedwood forest stands, differing by harvest regime near Kapuskasing, Ontario. Nutrient concentrations and mineralization trends using ion exchange resins at three proximities during the decay of Abies balsamea and Populus tremuloides were also examined. Concentrations of N, P, Ca, and Mg increased with decay, whereas K decreased. DWD was a minor contributor to biomass and nutrient pools. Inorganic N, P, Ca, and Mn were significant between harvest types with decay class interaction for N, Ca, and Mn. Species and proximity effects were found for Al, Fe, and K. These results suggest DWD may be a minor contributor to biomass and nutrient pools, but highlights its dynamic nature.

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.

Classical approaches to evaluate the stability of large woody debris (LWD) introduced in streams for habitat restoration or flood management purposes are usually based on inappropriate assumptions and hydraulic equations. Results suggest that the physics of small cylindrical elements located in large channels cannot be transferred to the case of a large roughness elements placed in small channels. The introduction of LWD in a small channel can generate a significant modification of the upstream hydraulic conditions. This modification has direct implications on the stability of the LWD. Experiments were performed in a controlled environment: a small stream section was represented by a low roughness rectangular flume and LWD were modeled with smooth PVC cylinders. Direct force measurements were performed with a load cell and results were used to identify an equation that evaluates the drag force acting on a large cylindrical element place in a rectangular channel. This equation does not depend on a drag coefficient. Water depths were also measured during the experiments and results were used to develop an approach that evaluates the upstream hydraulic impacts of a large cylinder introduced in a rectangular channel. The effect of the variation of the unit discharge (discharge per unit of width), cylinder size, cylinder elevation from the channel bed, and downstream hydraulic conditions, could be related to the upstream hydraulic conditions with relative success. Dimensionless parameters were developed to increase the versatility of the approach. The application of this approach to field cases is expected to require adjustments, mainly because of the roughness of natural environments differs from the smoothness of the controlled environment described in this work.

Invasive plants cause ecosystem degradation throughout the world, including the reduction of native plant density and diversity, and changes in ecosystem structure and function. Woody weeds often grow faster than native species and in invaded habitats produce larger and/or more seed and outshade other mid- and under-storey species. Boneseed Chrysanthemoides monilifera ssp. monilifera (L.) T. Norl. has caused the degradation of many temperate woodlands in Australia and has not yet reached its full potential distribution in this country. The control of this weed is therefore a high priority in Australia. Biological control agents have not controlled boneseed populations to date and no detailed integrated control strategies exist for different densities of mature boneseed plants and soil seed banks in native vegetation of varying levels of degradation. Fire, herbicides and manual plant removal have previously been used to control boneseed; however, substantial landscape scale control has not yet been achieved. Boneseed population control experiments were undertaken in two temperate woodlands in Victoria, Australia. In highly degraded temperate grassy woodlands at the You Yangs Regional Park west of Melbourne in Victoria and in a highly diverse native closed woodland at Arthurs Seat State Park in south-eastern Victoria. Several combinations of the weed control techniques of fire, herbicide application, hand-pulling of seedlings and distribution of competitive native grasses were found to control both mature boneseed populations and the large reserves of viable boneseed seeds in the soil. The efficacy of controlled burning, and the combination and timing of control techniques were found to vary according to differing densities of boneseed plants, viable soil seed banks and post-fire emergent seedlings. Where sufficient fine fuel existed, a warm, even, autumn burn consumed above ground biomass, killed the majority of viable boneseed seed in the soil, and caused the remaining boneseed seed to germinate. Spraying with glyphosate herbicide was as effective as metsulfuron-methyl herbicide for killing boneseed seedlings along with the secondary climbing weed Billardiera heterophylla (Lindl.) L.W.Cayzer & Crisp after fire. However, the use of glyphosate also killed all native species, resulting in bare ground. After fire in species rich vegetation, boneseed was eliminated where seed of the native C3 grass Poa sieberiana Spreng. had been broadcast onto the post fire ash-bed, and seedlings had been sprayed five months after the burn or where seedlings had been sprayed 12 months after burning. Boneseed control occurred when seedlings were sprayed five months after the burn. In degraded vegetation few boneseed seedlings remained where seedlings were sprayed 17 months after fire. Where insufficient rainfall occurred, hand-pulling flowering boneseed seedlings prevented new seed fall for 6 to 12 months. Suggestions are made for the integration of these methods with the establishment and proliferation of biological control agents. A new protocol for utilising several integrated control strategies for boneseed and other woody weeds in a mosaic at both the site and landscape scale is described. A mosaic would allow for a variety of native species responses to fire and other control methods and thus lead to heterogeneous ages and structures within the native vegetation following weed control. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1457770 / Thesis (Ph.D.) - University of Adelaide, School of Agriculture, Food and Wine, 2009

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 88-102).