• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1657
  • 379
  • 195
  • 113
  • 89
  • 80
  • 52
  • 50
  • 42
  • 36
  • 28
  • 18
  • 12
  • 12
  • 12
  • Tagged with
  • 3279
  • 2561
  • 810
  • 728
  • 613
  • 509
  • 396
  • 339
  • 338
  • 337
  • 306
  • 306
  • 285
  • 264
  • 247
  • 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.
101

The Feasibility of Using GPS Technology for Continuous Time Studies of Rubber-Tired Grapple Skidders

Dupre, Robert Henry 06 April 2006 (has links)
Skidders are one of the most common timber harvesting machines used on mechanized logging operations in the southern United States and can represent the greatest single capital investment for a logging contractor. Time studies of skidders have been conducted on nearly every type of mechanized logging operation and are a key part of the productivity studies conducted on logging operation. GPS technologies have enabled researchers to move away from the typical manual time data collection for productivity studies and start conducting unattended time studies on skidding equipment. For this study a Trimble GeoXT with external antenna was installed in a skidder conducting a second thin of plantation loblolly pine. The GPS was set to record line data on a 5 second and 1 second time interval to determine which type of line file was easiest to analyze. Time data from the skidder was compared to time data collected manually on the ground to test for accuracy of the data recorded by the GPS unit. Statistical analysis was used to compare travel empty, grapple time, travel loaded, un-grapple time and total cycle time between the two methods of time data collection. It was found that GPS times were not significantly different for travel empty and grapple time, but travel loaded and un-grapple time showed significant differences between the two techniques. GPS was shown to be a useful tool for collecting data on trail work, idle time and searching for logs unsuccessfully. Also, the 5 second time interval proved to be easier and quicker to analyze that the 1 second time interval. Ideally GPS in combination with some manual time data collection on the logging deck would give the most reliable and accurate time data for productivity studies on rubber-tired grapple skidders.
102

Breeding Waterbird Use of Rice Fields in Southwestern Louisiana

Pierluissi, Sergio 04 April 2006 (has links)
Rice fields are agricultural wetlands concentrated in several areas in the U.S., including southwestern Louisiana. Rice fields are flooded for much of the year and support thick emergent vegetation, potentially providing high-quality habitat for several species of breeding waterbirds. The objectives of this study were to (1) determine relative nest density, nest success, and habitat associations of breeding waterbirds in southwestern Louisiana rice fields and (2) determine the effectiveness of callback surveys as a monitoring tool. In the summers of 2004 and 2005, marsh bird surveys and nest searches were conducted in Cameron, Jefferson Davis, Vermilion, and Acadia Parishes in southwestern Louisiana. In 2004, 42 fields were searched and 30 of those were surveyed. In 2005, 40 fields were searched and 60 were surveyed. Purple gallinules nested in the highest densities in both years, followed by fulvous whistling-ducks, king rails, common moorhens, and least bitterns. A total of 283 purple gallinule nests, 176 fulvous whistling-duck nests, 77 king rail nests, 59 common moorhen nests, and 12 least bittern nests were found. The highest nest densities for purple gallinules and king rails were in fields with a high proportion of irrigation canals around the perimeters and a low proportion of trees. High relative nest density for purple gallinules was also associated with a high proportion of rice fields within 1 km of each field. Fulvous whistling-ducks responded the least to the local and landscape characteristics, but were associated with a high proportion of soybean fields near rice fields. Birds began nesting at the beginning of June and most nests were terminated by the time of harvest. Nest survival, or the percentage of nests to hatch at least one egg, was between 52% and 79% for purple gallinules, ~50% for king rails, and ~40% for fulvous whistling-ducks. Most survey responses were detected in June, and survey detections were concentrated in similar areas as the highest nest densities. Callback surveys were an effective technique for monitoring secretive marsh birds in this region.
103

Winter Diet, Seed Preferences and Foraging Behavior of Henslow's Sparrows (Ammodramus henslowii) in Southeastern Louisiana

DiMiceli, Jennifer K. 04 April 2006 (has links)
Henslow's Sparrow (Ammodramus henslowii) is a grassland bird whose population is declining throughout its range, mainly due to habitat loss. The Longleaf Pine forest ecosystems in which Henslow's Sparrows spend their winters are reduced to 5% of their former range. The winter ecology of Henslow's Sparrow remains understudied, especially regarding important aspects of diet and foraging behavior. To determine winter diet, I collected fecal samples from Henslow's Sparrows during banding operations in southeastern Louisiana pine savannas from October 2003-March 2004 and October 2004-April 2005. I then analyzed the samples for presence of seeds and arthropod parts, identified them to the lowest classification possible, and then used both multivariate and univariate techniques to look for variations in diet due to a savannas burn history, month of year and their interaction. I also conducted multiple-offer and simple-offer seed preference experiments on captive Henslow's Sparrows in December 2004 and February 2005 to test a variety of seed types found at differing abundances within the study sites. Commonly consumed seeds included Scleria spp., Rhynchospora spp., the category including Dichanthelium spp. and Panicum spp., and the combined category of Aristida spp., Schizachyrium spp. and Andropogon spp. Frequently consumed arthropods included Arachnids and insects from the orders Coleoptera, Hymenoptera, Hemiptera and Orthoptera. Diets varied significantly among months, most likely due to resource availability and timing of seed senescence. Results of seed preference experiments suggest that Henslow's Sparrows preferred Dichanthelium angustifolium, Muhlenbergia expansa and Eupatorium leucolepis while they avoided Schizachyrium scoparium. Ctenium aromaticum and Panicum anceps appeared to be secondarily preferred food items.
104

Reliability of Determining Adults from Juvenile Ducks by Presence or Absence of Notched Tail Feathers in Various Species of North American Ducks

Siwarski, Thomas Michael 07 April 2006 (has links)
I estimated when juvenile tail molt occurs for several commonly harvested duck species, mallards (Anas platyrhynchos), northern pintails (A. acuta) (hereafter referred to as pintails), gadwalls (A. strepera), lesser scaup (Aythya affinis), and redheads (A. americana). Tests showed that aging mallards by notched tail feathers became unreliable the earliest (early September), followed closely by pintails (mid-late September), with gadwalls being the latest of the dabbling ducks to lose reliability in aging by notched tail feathers (late November). Lesser scaup and redheads retained their notched tail feathers throughout January and the completion of hunting season. Based on initial banding and band recovery data I was able to separate birds into three age classes, juvenile (59), 1.5 years old adults (11), and adults 2.5 years old or older (23), creating a total sample size of 93 birds. From this sample of known-age banded birds I recorded five morhpometric variables including weight, wing length, bill length, tarsus length, and total length to determine if body size is related to ages over 1 year. Tests revealed that the only significant difference between the age classes was in wing length. However further tests showed that differences were not apparent between the 1.5 year old and 2.5 year old or older adults.
105

Effects of Fire on Habitat Associations, Abundance, and Survival of Wintering Henslow's Sparrows (Ammodramus henslowii) in Southeastern Louisiana Longleaf Pine Savannas

Johnson, Erik Ivan 10 April 2006 (has links)
The Henslows Sparrow (Ammodramus henslowii) is the fastest declining short-distance migrant and fastest declining grassland bird in North America. Declines in longleaf pine (Pinus palustris) savannas, its primary wintering habitat, have exceeded 97%. Other than basic habitat requirements, very little is known about its wintering ecology. I examined habitat associations of wintering Henslows Sparrows resulting from fire in longleaf pine savannas in southeastern Louisiana during two winters. Because it is important to understand the relative importance of habitat parameters, which include structure, species composition, and food availability, I measured these to determine their relative importance to Henslows Sparrow densities. I aged birds to understand the effects of fire on age-specific distributions and body condition, employed a mark-recapture analysis to determine over-winter survival, and determined over-wintering home ranges starting when Henslows Sparrows first arrived in October until they departed in April. Bird density was higher in savannas burned during the previous growing season (burn-year) than in savannas burned two growing seasons before (non-burn-year) in a two-year fire rotation scenario. Burning caused plant species compositions to shift from a Rhychospora spp. dominated habitat to an Andropogon/Schizachyrium spp. dominated habitat, however, total seed availability was not significantly different between burn-year and non-burn-year savannas. Because habitat-mediated age distributions, body condition, and home range size were also not significantly different between fire treatments, these findings are consistent with the idea that wintering Henslows Sparrows are generalist foragers. Bird density was best predicted by habitat structure, specifically reduced ground-level herbaceous vegetation and fewer shrubs. A higher survival probability was detected in burn-year savannas and may be responsible for habitat selection in this species. It is not clear how Henslows Sparrows locate apparently high quality habitat due to unpredictable changes from one year to the next. I therefore determined the extent of post-migration movements and between-year site fidelity. There was evidence of post-migration movements, while nine of 154 birds exhibited between-year site fidelity, suggesting that a variety of spatial use strategies occur in this population. Land managers can manipulate savanna structure through frequent growing-season prescribed fires, which are critical to Henslows Sparrow conservation.
106

Effects of Terraces on Submerged Aquatic Vegetation in Shallow Marsh Ponds in Coastal Southwest Louisiana

Cannaday, Christopher Dean 14 June 2006 (has links)
The wetlands of coastal Louisiana are disappearing at a rate of 65 to 80 km<sup>2</sup>yr<sup>-1</sup>. Most of the loss is the conversion of emergent marsh to shallow marsh ponds. Terracing is one restoration technique that has been used frequently in recent years. Terraces are small intertidal ridges built in shallow marsh ponds to reduce wave action. It is assumed that this will slow erosion of adjacent emergent marsh and increase Submerged Aquatic Vegetation (SAV) production, a key habitat component for many marsh fauna. Yet both relevant previous studies failed to show that terraces increased SAV abundance. In April of 2004 this study was initiated to test this assumption. Three study sites with paired terraced and unterraced ponds were selected in southwest Louisiana; two at Rockefeller State Wildlife Refuge and one at Sabine National Wildlife Refuge. SAV abundance was estimated every other month for one year. SAV biomass and frequency were significantly higher in terraced ponds. SAV frequency in unterraced ponds averaged 20% (SE 13 to 33%) but frequency for unterraced ponds was 9% (SE 5 to 14%). Terraced ponds had approximately three and half times the biomass of unterraced ponds. This indicates that terraces improve SAV production as had been suspected. Turbidity and organic matter content were lower in terraced ponds indicating a possible causal mechanism. My results confirm some assumptions of wetland restoration planners who have used terraces.
107

Dendrochronological Analysis of Productivity and Hydrology in Two Louisiana Swamps

Amos, John Blake 28 June 2006 (has links)
Modified river flows and land subsidence have subjected many coastal swamp forests in the delta of the Mississippi River to greatly altered flooding, sediment, and nutrient regimes. These areas have become inundated to greater depth, duration, and frequency and either are connected to the river and receive drastically increased sediment and nutrients (riverine swamps) or have become disconnected from riverine flooding (stagnant swamps) and receive little or no sediment and nutrient input. To better understand how these changes are affecting ecosystems, dendrochronological techniques for baldcypress (Taxodium distichum L. Rich.) were used at three sites in each of two contrasting swamps to compare how productivity has been historically related to climate and hydrology. The historical responses of baldcypress radial growth to 111 years of climatic variables and 51 years of hydrological data were analyzed by separate and simultaneous multiple linear regression analysis of effects. The effect of flooding on growth of baldcypress depended on the temporal scale and type of floodwater. Seasonal flooding increased growth in flood years for both stagnant and riverine swamps but decreased growth in the ensuing year. Long-term, riverine flooding was positively correlated to growth, but long-term, stagnant flooding was negatively correlated to growth. Growth in both swamps increased at onset of greater flooding, then decreased after several decades of continued frequent flooding. Climatic controls on growth depended upon interactions with hydrology but correlations between growth and flooding variables were consistent and much stronger than climate. When climate was analyzed separately, warm winters and cool, rainy growing seasons were important for higher growth. When hydrology was included in simultaneous analysis with climate, cool, dry fall weather of the previous year was also important. A model of baldcypress growth that only includes hydrologic regime is insufficient to understand growth. Climate, stand history, hydrological regime and the interaction of these effects must be considered to accurately understand changes in growth.
108

Swamp Tours in Louisiana Post Hurricane Katrina and Hurricane Rita

Schaffer, Dawn 11 July 2006 (has links)
Hurricanes Katrina and Rita made landfall in southern Louisiana during August and September 2005, respectively. Prior to these storms swamp tours were a popular nature-based tourism experience that entertained visitors while teaching them about local flora, fauna, and culture. The number of swamp tour businesses in the state was slowly increasing. The purpose of this study was to determine how many swamp tours were operating after the hurricanes, what type of damage they sustained, and how they repaired their businesses. Differences between those tours that remained open after the hurricanes and those that closed were also examined. A 3-phase mail survey was used to collect data throughout the winter and spring 2006 with a response rate of 74%. Respondents included 22 open businesses and nine closed businesses, seven of which planned to re-open eventually. The most common damages reported were loss of telephone service and damage to the swamp. Fewer tourists were also a problem for swamp tours, as 72% reported business was much lower than before the storms. Significantly more swamp tour businesses that had been operating for more than 15 years remained open after the storms than those businesses operating for less than 15 years. Swamp tour businesses in Louisiana were primarily family owned and employed fewer than five people. The majority of swamp tour owners believed their businesses were important to both the state tourism industry and the local economy of their area. This study also found that a new type of tour, the New Orleans disaster tour, was offered by four businesses that conduct swamp tours. A follow up survey after a period of one or more years is suggested to determine if the number of fully operational swamp tour businesses in the state has increased and detect any changes in the number of tourists in the area.
109

Factors Influencing the Participation in Environmental Stewardship Programs: A Case Study of the Agricultural and Forestry Sectors in Louisiana

Mendoza, Carrie Castille 08 November 2006 (has links)
Considerable research has been conducted to evaluate the adoption of agricultural best management practices and their overall impact on improving environmental quality. However, limited studies have been conducted to evaluate the behavioral factors that influence the adoption of these practices in the context of educational programs The goal of this study is to determine the factors that influence farmer conservation behavior that might lead to an increased probability of improving agriculture and forestry watersheds. A conceptual model was developed to identify the: 1) identify landowner participation in watershed conservation projects, and 2) determine the factors influencing agriculture and forestry landowners to participate in watershed conservation projects. The model includes four major sets of explanatory variables including: 1) social-psychological, 2) farm structural, 3) ecological, and 4) institutional. This study indicates that both farmers and loggers that are younger, more educated and of Caucasian ethnicity tend to participate in environmental stewardship programs which lead to the implementation of conservation practices. Farmers with strong local organization relationships have a greater tendency to participate in environmental stewardship programs which leads to the adoption of conservation practices. Agricultural producers with higher income resulting from farming, higher total acres, and farms legal structure indicated as incorporated tended to participate in environmental stewardship programs. Loggers that produced larger loads per week, which is an indicator of size, tended to participate in environmental stewardship programs. The study also found that agricultural producers who spend more time in a job off-farm and have a family owned operation have a lower tendency to participate in environmental stewardship programs. The study indicates that farmers that have modified their operation due to the Clean Water Act as well as awareness of efforts to control non-point source pollution through the Clean Water Act have a lower tendency to participate in environmental stewardship programs, thus viewed upon as institutional barriers. Also found was loggers with negative relationships toward regulatory agencies and lending institutions have a lower tendency to participate in environmental stewardship programs. Farmers have mixed attitudes toward government involvement in agriculture. These conclusions are supported by earlier studies.
110

Evaluation of Harvesting Disturbance and Establishment Practices on Early Height Growth of Loblolly Pine (Pinus Taeda L.)

McCarty, Shanna Marie 17 January 2007 (has links)
Land for forest plantations is declining while demand for forest products is increasing, creating concern over sustainable forest management. Maintenance of site productivity is fundamental to forest sustainability, and an assessment of cumulative height growth is a useful index of productivity. Loblolly pine height data were used from four research plantations installed by the project Cooperative Research in Sustainable Silviculture and Soil Productivity from Texas to Georgia. The sites vary in soil characteristics, management history, nutrient status at time of planting, and age (from 4 to 9 years). Each site is a randomized complete block design with a factorial treatment arrangement of harvesting practices (minimum and maximum disturbance) and different establishment practices (e.g., bedding, fertilization, herbaceous weed control, herbaceous weed control plus fertilizer, and burning). An integrated statistical analysis using the change in height with age was used for the evaluation of longer-term treatment effects. Harvesting practices had a significant treatment effect on the change in height with age (p < 0.03) at one site, but did not significantly affect early height growth at the other three sites (p > 0.37). On the other hand, establishment practices had a significant effect on the change in height with age (p < 0.01), independent of accompanying harvesting practice.

Page generated in 0.3094 seconds