• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1379
  • 641
  • 150
  • 115
  • 95
  • 78
  • 23
  • 23
  • 20
  • 14
  • 13
  • 10
  • 9
  • 9
  • 8
  • Tagged with
  • 3203
  • 666
  • 500
  • 424
  • 308
  • 302
  • 251
  • 244
  • 227
  • 219
  • 216
  • 195
  • 175
  • 163
  • 153
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
171

EFFECTS OF TIME, SEED SOURCE, AND PLANT COMPOSITION ON MACROINVERTEBRATES IN RESTORED PRAIRIE

Wodika, Ben 01 August 2015 (has links)
Invertebrates influence primary productivity and nutrient cycling in ecosystems. They are also important links between producer and higher trophic levels. Despite their important role in terrestrial ecosystem function, invertebrates are frequently overlooked in ecological restorations. Thus, the objective of this research was to quantify how belowground macroinvertebrate ecosystem engineers and communities change over time following ecological restoration and examine whether the source of dominant plant species and the composition of non-dominant plant species influence aboveground macroinvertebrates community structure in restored prairie. A chronosequence design (space for time substitution) was used to determine the role of restoration age, plant community, and soil structure on the recovery of two belowground macroinvertebrate ecosystem engineers (Chapter 2). Ants and earthworms were sampled from cultivated fields, grasslands restored for 1-21 years, and native prairie. Earthworm abundance increased with time since cessation of cultivation, concomitant with prairie establishment. The abundance and biomass of ants were more related to the structure of restored plant communities than time since restoration. The dominance of exotic earthworms, and a generalist ant species in these restorations, coupled with their known capacity to alter soil properties and processes, may represent novel conditions for grassland development. The same chronosequence of agricultural fields, restored prairies, and prairies that were never cultivated was used to address the second objective of this research, which was to quantify how the belowground macroinvertebrate community composition changed in response to ecological restoration and whether the communities became representative of undisturbed (“target”) communities. Macroinvertebrate communities in the two remnant prairie sampled were distinct from restorations and continuouslycultivated fields. The macroinvertebrate communities in prairie that had never been cultivated were also distince from each other, indicating a “target” community is hard to define. Belowground macroinvertebrates changed in a trajectory that was not representative of either remnant prairie, but was representative of the an average of both remnant prairies. Thus, if you reconstruct prairie from cultivated soil conditions (“build it”), macroinvertebrates will colonize (“come”), but attaining a community representative of a specific target may require introduction from that target. Colonization of macroinvertebrates in restorations aboveground are most likely to be influenced by aspects of the plant community. A third objective of this research was to quantify whether variation in dominant species (cultivars vs. local ecotypes) and composition of subordinate species (local species pools) influence the composition of aboveground macroinvertebrates. Macronvertebrate abundance, richness, diversity, trophic groups and community composition in late summer did not vary between prairie restored with cultivar and local ecotypes of the dominant grasses. This was observed in two field experiments. The species pool treatment did influence the macroinvertebrate community, as one species pool had slightly higher morphospecies diversity and hymenopterans that the other two species pools. This was likely due to the presence of an ant-tended legume, Chamaecrista facsciculata Michx., in one species pool. Overall, this research demonstrates that time since the cessation of disturbance (cultivatation) and plant communities influence macroinvertebrate communities in restored prairie. Restored prairies in the Midwest are likely to be colonized by exotic earthworms and cosmopolitan ants. More research is needed to reveal how they influence ecosystem functioning.Belowground, macroinvertebrate communities may not represent restoration “targets” and these “targets” may be hard to define if remnants are rare or there is a high degree of spatial variation on the landscape. Variation in plant communities above ground appears to influence the structure of aboveground macroinvertebrate communities more than variation within dominant species. Whether this aboveground variation is reflected is reflected belowground deserves further investigation.
172

Integrative Management of Lespedeza cuneata in Prairie Restorations

Shupert, Lindsay Anne 01 May 2016 (has links)
Background: Lespedeza cuneata is a perennial invasive legume native to Asia that is common across grasslands in the eastern half of the United States and parts of Canada. The competitive nature and limited palatability of L. cuneata for grazers in the tallgrass prairie has made it an undesirable and invasive weed. Objectives: This study was conducted to investigate an invasive species management plan for restored grasslands and prairie areas. Methods: Study plots (n=144) for experiment 1 (summer treatment) were established at Crab Orchard Wildlife Refuge in Jackson County Illinois in August of 2012 and were situated to contain infestations of the target species. Two herbicides, in five concentrations were applied in August of 2012. A native seed mix was added to a portion of the summer plots later, in February of 2013. These treatments were assessed in June and August of 2013 to determine herbicide effects on stem count and percent cover of L. cuneata, along with the composition and percent cover of other species present. Spring herbicide applications (n=18) for experiment 2 were established, assessed for L. cuneata cover and density, and treated with two herbicide treatments in May of 2013. Spring treatments were identical to existing plots and were re-assessed in August 2013 to determine species composition and the abundance of L. cuneata. Seed was not added to these plots. Analysis: Mixed Model analysis by site was performed to test the effect of herbicide and seeding treatments on L. cuneata for both experiments 1 &2. The summer plots were also tested for effects on other plant groups. A repeated measures PERMANOVA along with ANOSIM and PERMADISP was performed to assess community composition response to seeding and herbicide treatments in the summer plots. Results: Abundance of L. cuneata was reduced 67 to <90% following herbicide treatment in Experiments 1 and 2. There were no differences in the effectiveness of herbicide treatments in in experiment 1, sites 1 &3, and in experiment 2. Supplemental seeding in the summer plots did not reduce the abundance of L. cuneata consistently across sites. Conclusion: Considerable short-term control of the target species was achieved in both the summer and spring plots, providing a window of opportunity for the imposition of additional methods of control. However, data from the summer plots suggest recovery of L. cuneata some sites, indicating further control would be necessary, with potentially the addition of other control methods or site alterations.
173

HABITAT SELECTION OF REINTRODUCED BISON IN NORTHERN ILLINOIS

Brockman, Julia C. 01 August 2017 (has links)
In one of the first reintroductions of a semi-wild population of bison (Bison bison) east of the Mississippi River, The Nature Conservancy reintroduced bison to the Nachusa Grasslands in northern Illinois in October 2014. Given the novelty of such efforts, questions remain regarding how human activity and prairie management affect bison habitat selection. My objective was to quantify bison habitat selection during 2014-16 to address literature gaps while investigating seasonal and annual changes. In October 2014, The Nature Conservancy collared 7 female bison with Lotek Iridium TrackM 3D and 4D collars programmed to take hourly locations. I randomly selected 1 bison location each hour to represent herd location and divided the resulting locations by season. Using resource selection functions, I compared the influence of land cover type, fire management, and concentrated human activity on habitat selection across seasons and at 2 scales: patch and enclosure. Land cover was consistently the best-fit model across seasons and scales with the exception of Winter 2016 at the enclosure scale. Bison strongly selected for partial restorations but showed no strong seasonal land cover selection trends. Bison selected for recently-burned prairie with the exception of Summer 2015 at the enclosure scale. At the patch scale, bison selected for areas closer to disturbed areas but did not show a strong trend at the enclosure scale. With a better understanding of how bison grazing is influenced by restoration management, wildlife managers can make better-informed decisions regarding bison restoration and public use.
174

Restored Prairie Response to Reduction in Ectophagous Insects

Black, Sarah 01 May 2018 (has links)
Tallgrass prairie restorations generally aim to reconstruct native plant assemblages altered by disturbance to a composition of species characteristic of undegraded communities the region. Most prairie restorations, however, lack large herbivores such as Bison bison and Cervus canadensis, therefore leaving herbivory to Odocoileus virginanus, other small mammals, and insects. Although insects are more abundant by comparison, it is hypothesized that their influence as ecological drivers is often obscured by fire, grazing, and climate. Previous study in remnant prairie has shown that insects eat very little of above net primary productivity (ANPP), however they can alter the forb:grass ratio in prairies. Nonetheless, studies have shown that younger plants (particularly forbs) are more susceptible to insect herbivory due to higher nitrogen (N) content and physical and chemical defenses not yet fully developed. This research used an experimental approach (insecticide application) to reducing insect abundance and ectophagy to determine whether insects preferentially feed on forbs, alter forb:grass ratios, and affect diversity and aboveground net primary productivity (ANPP) in young (1-2 y) and more established (7-8 y) restored prairies. Ectophagy measurements showed that forbs were preferred over C4 grasses. Reduced herbivory decreased diversity of forbs and sown grasses, decreased percent cover of forbs, and species richness of sown grasses, and increased evenness in the youngest prairie. Contrary to expectations, ANPP and forb:grass ratios were not affected by treatment. Nevertheless, interactions between year and restoration age were often significant, suggesting that climate variability between seasons and maturity of community may influence how insect herbivores affect restored prairie. There was a positive correlation between herbivore morphospecies richness and sown forb richness. Insect communities were also characterized in restored prairies to evaluate treatment success. Insects were collected by sweep-netting. I collected 10 orders, 83 families, and 150 morphospecies. The largest number of species present was from Hemiptera (suborder Auchenorrhyncha). Species richness decreased through time. Pesticide application reduced diversity of families. Ectophagous insect abundance and richness were impacted by treatment, but piercing-sucking herbivores (Hemiptera) did not respond to insect reduction treatment. Predator/parasitoid insects were also reduced by treatment, indicating a larger sensitivity at higher trophic levels. Like plant diversity, interactions between restoration age and year affected almost all insect variables, suggesting that insect populations are dynamic and sensitive to nearby land-use.
175

Návrh ekologického monitoringu revitalizované nivy Hučiny (NP Šumava) / (Proposal for ecological monitoring of the restored Hučina floodplain (Šumava National Park)

SLÁMA, Miroslav January 2012 (has links)
The aim of this work was to design long-term monitoring of vegetation and environmental factors which would document the effect of the planned revitalization of Hučina brook floodplain. In order to monitor the dynamics of plant communities the system of permanent plots have been designed and established. Visual estimation of cover or graphical methods were proposed for the monitoring of the development of the moss and herb layers. The method of basal cover is considered best for the monitoring of the development of the tree layer. Mapping of plant communites should be made in the form of direct mapping. The monitored water characteristics should include the groundwater level, water conductivity and pH. Beneficial additional measurement comprise estimation of total NH4+, PO43-, NO32-, SO42-, Mg2+, Ca2+, total Fe, K+, Na+, humic acids and total organic carbon (TOC). The important soil characteristics include actual soil moisture content (Wmom), the maximum capillary capacity (MKK), water-holding capacity (RVK24), bulk density, porosity and soil organic matter. In addition to the monitoring design, this work brings data on vegetation composition gathered by direct mapping and measurement of the breast height diameter of trees.
176

Planting Pole Cuttings in Riparian Ecosystems

Schalau, Jeff 08 1900 (has links)
2 p. / Originally published 2000. / Riparian ecosystems are found in the transition between aquatic and adjacent terrestrial ecosystems where unique vegetative communities can occur due to free water at or near the soil surface. A healthy, functional riparian plant community provides a rich environment for insects, mollusks, amphibians, reptiles, fishes, birds, and animals. In Arizona, many naturally occurring riparian ecosystems have been impacted, altered or removed by natural processes and land management activities. This publication provides information to assist residents, landowners, and agency personnel in successfully establishing pole plantings in riparian ecosystems of Arizona. Reviewed 10/2016, Originally published 2000.
177

The effects of diferent reinforcements on the fracture toughness of provisional restorative materials

Overturf, Jan Hendrik January 2006 (has links)
Magister Chirurgiae Dentium - MChD / One of the most critical aspects of successful crown and bridgework is temporary restorations. Failure of temporary restoratins often affects the patient's confidence and mau result in unscheduled appointments for repair. This study compared the the fracture toughness of two materials commonly used to fabricate provisional restorations, namely Coldpac, a polymethyl methacrylate and Protemp 3 Garant, a bis-acryl composite. It also compard the fracture toughness of the two materials when reinforced with stainless steel wire, glass fibers and polythylene fibers. / South Africa
178

An evaluation of bird presence and breeding activity in regenerating coastal dune forests, Maputaland, South Africa

Taylor, Martin Russell 17 April 2008 (has links)
Researchers use changes in bird community composition to illustrate ecological succession in restoration studies. These studies utilise a variety of methods, some of which may bias their outcomes. Here I used the point and line transect methods to obtain community compositions as well as to estimate total density, species richness and species diversity for bird communities living in a successional sere of coastal dune habitats. The two methods yielded similar estimates of community variables in the younger regenerating sites with the point transect method giving higher estimates in the older regenerating sites. The line transect method provided higher density estimates than the point transect method across all sites but there was no significant difference between variance estimates for the two methods. The point transect method reached the maximum number of detectable species in half the time that it took the line transect method. In contrast to my expectations, the point transect method proved to be superior in terms of efficiency. Past research suggests that bird presence itself does not reflect on colonisation success. I compared the community composition, variables and age related trends of point transect and breeding assemblages within the study area. The breeding assemblages represented a subset of the point transect assemblage. Age related trends were significantly similar with both assemblages approaching the variables noted on an undisturbed reference site with an increase in regeneration site age. I concluded that presence based surveys of bird communities adequately captured age related trends to make valid conclusions about patterns of succession. / Dissertation (MSc (Zoology))--University of Pretoria, 2008. / Zoology and Entomology / MSc / Unrestricted
179

Reformation Landscape

Nel, Stephanie January 2018 (has links)
The Berlin Mission Station, Botshabelo, situated nearby the town of Middelburg in Mpumalanga presents a multi-cultural landscape that is emblematic of the complex questions facing heritage sites in South Africa today. Botshabelo mission station is a historically, physically and culturally layered landscape with a shared heritage and an assemblage of narratives. The following dissertation examines the two cultures that influenced the establishment of the mission station, namely the local African cultures and the German missionaries of the 19th Century, and their relationship with the landscape. The embedded layers of meaning and heritage within Botshabelo’s landscape relating to these cultures were translated into a contemporary landscape design with the aim of reviving the neglected historic site. / Mini Dissertation ML(Prof)--University of Pretoria, 2018. / Architecture / ML(Prof) / Unrestricted
180

Lime and Cement Technology: Transition from Traditional to Standardized treatment Methods

Krumnacher, Paul J. 22 February 2001 (has links)
During the late eighteenth and throughout the nineteenth century masonry technology underwent a major transition, whereby, the production process increasingly absorbed techniques traditionally carried out by craftsmen. This transition also involved an increasing shift from lime technology to cement technology1. This influenced traditional work methods involving lime mortars as well as creating new methods for preparation of cement. Development of cement assisted the expansion of vital infrastructure such as roads, bridges, dams, sewers, and high-rise structures. In order to facilitate high-rise construction with cement, masonry units such as commercially produced brick were developed with similar strength and compression characteristics as cement. Historically, lime mortar preparation involved multiple and variant treatment methods. These practices arose from generations of experimental practice, in order to determine which methods were most beneficial. Development of these skills was transferred from master to apprentice and from father to son. These treatment methods involved a calcium carbonate raw material and its conversion into a lime suitable for blending with aggregates, which resulted in a workable mortar for uniting building materials. Such lime building compounds included, stuccos, frescos, plasters, and mortars. The scope of this project involves primarily lime mortar, although treatment methods and materials are very similar for all of these five lime compounds. Restoration of historic structures built with lime mortar creates challenges for architects, conservators, masons and all persons tasked with masonry restoration. Original masonry Materials and methods involving lime technology have been superseded by cement technology with its own materials and techniques. Cement has failed to provide a successful role as a binder for the restoration of historic structures built with lime mortar. In order to maintain the integrity of historic structures, rediscovery and application of traditional lime technology can further bridge the gap between past and present masonry mortar. / Master of Science

Page generated in 0.1116 seconds