Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 108-111). Also available via the Internet.

Statistical evidence indicates that the positions of the moon, Mercury, and Venus affect magnetic activity frequency observed at the earth, and the position of the earth affects the frequency of blue clearings on Mars. This study shows that these effects may be explained as a result of the action of shock and bow waves formed by these bodies in the supersonically streaming interplanetary plasma. The attenuation of large kinetic energy variations in the streaming plasma behind such bodies is shown to be equal to the square of the ratio of the Mach number upstream to the Mach number downstream. For typical solar induced activity, this implies an attenuation coefficient of approximately 1/2 - 1/3. It is also shown that an activity increase is expected in the bow wave. The observational data fits a model with bow waves of Mach numbers 2.5 and 15 corresponding to the two bow waves predicted by the theory. The moon's effect varies from that of the planets in a manner that can be explained by its closeness to the magnetosphere. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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Created wetlands are often limited in soil organic matter, usually a long-term product of ecosystem succession. Although many studies have tested the effect of adding organic material to these systems, few if any, have quantified the effect of various loadings of organic matter in created wetlands. The goal of this study was to determine how vegetation composition, standing crop biomass, woody vegetation development, and ecosystem gas exchange varied in a created freshwater wetland along a gradient of soil organic carbon (0 to 336 Mg ha-1 loading rates). Plot surface elevation varied positively with OM loadings, suggesting that inundation/aeration may modify OM effects. Soil nutrients (C, N, C:N, and P) also positively correlated with loading rate. Vegetation measurements suggested an overall similarity of plant assemblage composition and biomass regardless of loading rate, and a slight increase in tree size with loading rate. Gross primary production and net ecosystem exchange were weakly positively and negatively correlated with loading rate, respectively. Respiration was strongly positively correlated with loading rate, and was likely the controlling factor of CO2 gas flux among treatments. Soil nutrient values and vegetation composition, as well as ecosystem gas flux balance appear to be the best parameters upon which to base an organic matter loading rate decision. In this study, adding an organic matter amendment between LR 2 (56 Mg ha-1) and 3 (112 Mg ha-1) seems most appropriate, and may provide a “jumpstart” for the created non-tidal wetlands while also minimizing changes in surface elevation due to the added bulk material.

<p>According to the exploitation ecosystem hypothesis (EEH), terrestrial ecosystems are characterized by well defined trophic levels and strong trophic interactions with community level tropic cascades. In unproductive terrestrial habitats as tundra heaths, the energy shunt from litter and apparent competition between herbivores and detritivores are expected to be important for the structure and dynamics of the invertebrate community. The aim of this study was to test this hypothesis by investigating if plant litter accumulation was affecting the invertebrate community on a nutrient-poor tundra heath. The study was performed during one summer on the highland part of Joatka research area, in the north of Norway.</p><p>The experimental area included 16 plots (100 m² each), of which 12 had been littermanipulated. On four plots the amount of litter was increased by 100 %, on four by 200 % and on four by 400 %. Four plots were untreated and used as control plots. Invertebrates were collected by emergence traps (which cover an area of 1 m²), one trap on each plot and one pitfall trap inside each emergence trap. During the study period, traps were emptied and moved twice, resulting in three sampling periods. The invertebrates collected were counted and their length was measured, than all invertebrates were sorted into taxa and trophic guilds. During the study period, herbivore grazing damage was investigated on all 16 experimental plots, signs of herbivores on leaves of vascular plants in an area covering 3 m2 per plot were noted, for every leaf with signs of herbivory the percentage of leaf area removed was estimated.</p><p>Plant biomass and plant species composition were estimated in all experimental plots by harvesting above-ground plant parts. In each plot, two squares were randomly chosen and all biomass in this square was collected. Plant biomass was sorted in to following groups: dwarf birch, billberry, Salix herbacea, Salix spp, graminoids, herbs, lichens, mosses and dwarf shrub. Before weighing the plant material, it was stored in paper bags at room temperature and then dried for 48 h at 40°C. In order to detect fertilisation effects, all bilberry shoots that had been produced during the actual summer were separately weighted when analyzing the plant biomass.</p><p>The result showed that the invertebrate community in this area is dominated by carnivores while detritivores, parasitoids and herbivores are quite rare, this was in accordance with previous studies made in the area. Litter manipulation did not create any significant variation in the community structure, but there was a slight tendency that carnivore biomass increased and biomass of herbivores decreased when litter was added to the system. In contrary to this,</p><p>gracing activity especially on dwarf willow (Salix herbacea) increased in plots were 100 % and 200 % more litter was added. There is a positive correlation between biomass of herbivores and detritivores but the reason for this seems unclear. No fertilisation effect was detected in litter manipulated plots. The structure and dynamics of the actual community could not be described by the food web theory EEH and energy shunt from litter and apparent competition between herbivores and detritivores. It seems to be several complicating factors to take into consideration when describing this community.</p>

According to the exploitation ecosystem hypothesis (EEH), terrestrial ecosystems are characterized by well defined trophic levels and strong trophic interactions with community level tropic cascades. In unproductive terrestrial habitats as tundra heaths, the energy shunt from litter and apparent competition between herbivores and detritivores are expected to be important for the structure and dynamics of the invertebrate community. The aim of this study was to test this hypothesis by investigating if plant litter accumulation was affecting the invertebrate community on a nutrient-poor tundra heath. The study was performed during one summer on the highland part of Joatka research area, in the north of Norway. The experimental area included 16 plots (100 m2 each), of which 12 had been littermanipulated. On four plots the amount of litter was increased by 100 %, on four by 200 % and on four by 400 %. Four plots were untreated and used as control plots. Invertebrates were collected by emergence traps (which cover an area of 1 m2), one trap on each plot and one pitfall trap inside each emergence trap. During the study period, traps were emptied and moved twice, resulting in three sampling periods. The invertebrates collected were counted and their length was measured, than all invertebrates were sorted into taxa and trophic guilds. During the study period, herbivore grazing damage was investigated on all 16 experimental plots, signs of herbivores on leaves of vascular plants in an area covering 3 m2 per plot were noted, for every leaf with signs of herbivory the percentage of leaf area removed was estimated. Plant biomass and plant species composition were estimated in all experimental plots by harvesting above-ground plant parts. In each plot, two squares were randomly chosen and all biomass in this square was collected. Plant biomass was sorted in to following groups: dwarf birch, billberry, Salix herbacea, Salix spp, graminoids, herbs, lichens, mosses and dwarf shrub. Before weighing the plant material, it was stored in paper bags at room temperature and then dried for 48 h at 40°C. In order to detect fertilisation effects, all bilberry shoots that had been produced during the actual summer were separately weighted when analyzing the plant biomass. The result showed that the invertebrate community in this area is dominated by carnivores while detritivores, parasitoids and herbivores are quite rare, this was in accordance with previous studies made in the area. Litter manipulation did not create any significant variation in the community structure, but there was a slight tendency that carnivore biomass increased and biomass of herbivores decreased when litter was added to the system. In contrary to this, gracing activity especially on dwarf willow (Salix herbacea) increased in plots were 100 % and 200 % more litter was added. There is a positive correlation between biomass of herbivores and detritivores but the reason for this seems unclear. No fertilisation effect was detected in litter manipulated plots. The structure and dynamics of the actual community could not be described by the food web theory EEH and energy shunt from litter and apparent competition between herbivores and detritivores. It seems to be several complicating factors to take into consideration when describing this community.

Community assembly is the process deciding inclusion/exclusion of species in a developing community. Spatial ecology integrates spatial habitat factors with local biotic interactions within a given patch. I used standardized tree bolts (0.35-1 m long) to sample saproxylic (wood living) beetles in natural and managed forest types. Density-dependent effects were more intense in old-growth coniferous forest than in burnt forest. The final-state assemblages in these two forest types diverged regarding species composition but converged regarding community structure. The communities also followed forest-type specific assembly trajectories. Order of arrival can influence the species assemblage, I found priority effects when comparing the reproductive success of two cerambycid species. A two-week head start had a positive effect on fitness in both species. Different fitness components were affected in the two species: offspring number in Acanthocinus aedilis and offspring quality in Rhagium inquisitor. In birch-living Coleoptera a large part of variance in species composition could be explained by habitat variables (22.9 %), such as forest type, or spatial variables (15.8 %), such as distance apart. The assemblages in deciduous sites responded to distance apart and showed positive spatial autocorrelation up to a distance of 80 km. For assemblages in deciduous sites a metacommunity perspective is warranted – on a surprisingly large scale. I compared two regions, one more fragmented and one less fragmented, (with 2.2 % more deciduous forest in the landscape). The effects of habitat fragmentation was primarily found in mature coniferous forest. Host-tree patches in this matrix forest were perceived as matrix by the Coleoptera in the more fragmented region but as habitat in the less fragmented region. Some of my study sites consisted of protected old-growth forest. These were embedded in a landscape dominated by forestry. These protected areas were invaded by generalist species, thriving in managed forests.

As climate-driven changes in phenology are becoming more apparent, the need to quantify these changes is increasing. An important challenge in detecting phenological changes is that between-year variation in phenology is large. Between-year variation determines the statistical power of comparisons between contemporary and historical observations. For 44 plant species with different distributions across Sweden, geographicand inter-specific differences in between-year variation in different phenophases (budburst, flowering, ripe fruits, and leaf fall) was studied. I also modeled and evaluated theresponse of bud burst, and flowering, to temperature using three different temperature sum models over a latitudinal gradient. The data used was a sub-sample from a dataset collected by a Swedish nation-wide phenology network between 1873-1917. In agreement with previous studies, I show that early spring phases have a higher variability than phases occurring later in the season. However, the relation between onset and variation was not monotonically decreasing. In the geographical analyses, a unimodal relation between between-year variation and latitude was found, that is, the between-year variation decreased along the latitudinal gradient for early- and late season events, while it increased over latitude for summer events. These patterns are, to a great extent, reflections of patterns in air temperatures which is discussed using meteorological data from adjacent climate stations. Models were evaluated using Akaike's Information Criterion, and in 60% of all fits, the Spring warming CF2 model (SWCF2; the model with the least number of parameters) was selected as the best model to describe the data. For Sorbus aucuparia bud burst, in the two parameter model SWCF2, both parameters (threshold temperature andtemperature sum) correlated with latitude. However, future analysis using more locations and a wider span of species will be needed to understand the generality in these findings. In conclusion, future efforts to detect and quantify phenological changes need to consider differences in between-year phenological variability along geographical gradients and among species with different phenology.