• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 156
  • 60
  • 27
  • 17
  • 14
  • 9
  • 5
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 2
  • Tagged with
  • 343
  • 82
  • 61
  • 57
  • 49
  • 47
  • 35
  • 35
  • 35
  • 30
  • 28
  • 28
  • 28
  • 26
  • 24
  • 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.
81

Sensible heat flux estimation over a prairie grassland by neural networks

Abareshi, Behzad January 1996 (has links)
Sensible heat flux, a key component of the surface energy balance, is difficult to estimate in practice. This study was conducted to see if backpropagation neural networks could estimate sensible heat flux by using horizontal wind speed, air temperature, radiometric surface temperature, net radiation, and time as input. Ground measurements from the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE), collected in 1987 and 1989 over a prairie grassland in Kansas, were used for network training and validation. Networks trained on part of the data from a narrow range of space-time coordinates performed well over the other part, with error (root mean square error divided by mean of observations) values as low as 0.24. This indicates the potential in neural networks for linking sensible heat flux to routinely measured meteorological variables and variables amenable to remote sensing. When the networks were tested with data from other space-times, performance varied from good to poor, with average error values around 1.26. This was mainly due to lack of input variables parameterizing canopy morphology and soil moisture, indicating that such variables should be incorporated in the design of future networks intended for large scale applications.
82

Review of current vegetation monitoring on privately protected land under ongoing economic use (grazing)

Bloor, Marcus January 2009 (has links)
There has been a noticeable shift in focus in biodiversity research in New Zealand over recent decades. Research has traditionally focused on biodiversity protection on the public estate, which was comprised primarily of ecosystems with lower productive potential (generally over 500m asl). Private lands generally have higher production potential and are often used for intensive cultivation and agricultural practices. They still however have significant potential for protecting biodiversity values. One of the key tools for protecting biodiversity values on privately owned lands in the Canterbury region are through legally binding QEII open space covenants and there is significant potential through industry certifications. QEII covenants are placed on the land in perpetuity and provide legally binding protection for biodiversity or landscape values within the covenant. This protection is voluntary and allows the land owner to continue to use the land for economic benefit providing it does not prove detrimental to biodiversity through monitoring outcomes. Case studies of QEII covenants that contain grazing clauses in the Canterbury region were used to determine what values are present and what monitoring is occurring in the field within these ecosystems. Photopoints and informal visual monitoring were the primary methods used by the QEII representatives to monitor vegetation in all of the covenants. Monitoring forms a critical feedback for all biodiversity protection. It is especially important to have an accurate feedback on vegetation condition and change from monitoring on properties that are grazed. Monitoring needs to be capable of providing sufficient information on vegetation change on these sites so that the most suitable grazing levels can be obtained by land managers. This thesis focuses on monitoring methods to ensure that this feedback is suitable and that the methods are cost effective. Current vegetation monitoring techniques were reviewed to determine which methods would be most suited to monitoring in these ecosystems where resources are tightly restricted and observers may not have existing skills and experience in monitoring these ecosystems. Methods reviewed were quadrats, transects, height-frequencies, photopoints, needle point, biomass, tagged plants, visual rank and remote sensing. Each method is described and then assessed on its suitability for monitoring tussock shrublands, with cost effectiveness being an important criterion. Of these methods quadrats, transects and height-frequencies were the most robust but also the most intensive and least cost effective methods. Visual rank, needle point and photopoints were the most cost effective, but are generally suited to monitoring single objectives. In most cases a combination of methods would be ideal to suit the objectives of the monitoring. QEII photopoint monitoring should follow guidelines more closely and include more complimentary information with their photographs. Clear monitoring objectives should be developed for every covenant that is grazed and these need to be determined before it is possible to accurately select appropriate monitoring methods. These objectives will also provide the monitoring program with more structure and direction. If possible a detailed management plan for each grazed covenant would be beneficial for values present. QEII are in a unique position, where they have the potential to develop a data base of biodiversity information for private land and contribute to other projects like the National Vegetation Survey (NVS).
83

Effects of twice-over rotation grazing on the relative abundances of grassland birds in the mixed-grass prairie region of southwestern Manitoba

Ranellucci, Cristina lynn 16 September 2010 (has links)
The mixed-grass prairie region of southwestern Manitoba is a hotspot for many endangered grassland birds. This region has been degraded to less than a quarter of its historical amount of mixed-grass prairie. Remaining prairie is primarily used for livestock grazing. The objective of this study was to evaluate the contribution of sustainable land management practices, such as rotational grazing, in the conservation of this region. In 2008 and 2009, I compared the abundances of grassland birds on two grazing regimes, twice-over rotation and season-long, to ungrazed fields. Bird surveys were done during the breeding season and were conducted using 100-m fixed-radius point-count plots. I determined the effects of treatment, landscape and vegetation characteristics on songbird abundances using generalized linear mixed models. Grassland birds selected grazed pastures over ungrazed fields in both years, and species richness of obligate grassland birds was significantly greater (α = 0.10) on season-long than twice-over pastures (β = 0.419, p = 0.032, in 2008 and β = 0.502, p = 0.043 in 2009). Season-long grazing may actually benefit grassland bird communities by creating somewhat temporally stable areas of high use and low use within the pasture. However, nesting success studies and long-term monitoring are necessary to further understand how twice-over rotation grazing systems contribute to the conservation of grassland birds in southwestern Manitoba.
84

Review of current vegetation monitoring on privately protected land under ongoing economic use (grazing)

Bloor, Marcus January 2009 (has links)
There has been a noticeable shift in focus in biodiversity research in New Zealand over recent decades. Research has traditionally focused on biodiversity protection on the public estate, which was comprised primarily of ecosystems with lower productive potential (generally over 500m asl). Private lands generally have higher production potential and are often used for intensive cultivation and agricultural practices. They still however have significant potential for protecting biodiversity values. One of the key tools for protecting biodiversity values on privately owned lands in the Canterbury region are through legally binding QEII open space covenants and there is significant potential through industry certifications. QEII covenants are placed on the land in perpetuity and provide legally binding protection for biodiversity or landscape values within the covenant. This protection is voluntary and allows the land owner to continue to use the land for economic benefit providing it does not prove detrimental to biodiversity through monitoring outcomes. Case studies of QEII covenants that contain grazing clauses in the Canterbury region were used to determine what values are present and what monitoring is occurring in the field within these ecosystems. Photopoints and informal visual monitoring were the primary methods used by the QEII representatives to monitor vegetation in all of the covenants. Monitoring forms a critical feedback for all biodiversity protection. It is especially important to have an accurate feedback on vegetation condition and change from monitoring on properties that are grazed. Monitoring needs to be capable of providing sufficient information on vegetation change on these sites so that the most suitable grazing levels can be obtained by land managers. This thesis focuses on monitoring methods to ensure that this feedback is suitable and that the methods are cost effective. Current vegetation monitoring techniques were reviewed to determine which methods would be most suited to monitoring in these ecosystems where resources are tightly restricted and observers may not have existing skills and experience in monitoring these ecosystems. Methods reviewed were quadrats, transects, height-frequencies, photopoints, needle point, biomass, tagged plants, visual rank and remote sensing. Each method is described and then assessed on its suitability for monitoring tussock shrublands, with cost effectiveness being an important criterion. Of these methods quadrats, transects and height-frequencies were the most robust but also the most intensive and least cost effective methods. Visual rank, needle point and photopoints were the most cost effective, but are generally suited to monitoring single objectives. In most cases a combination of methods would be ideal to suit the objectives of the monitoring. QEII photopoint monitoring should follow guidelines more closely and include more complimentary information with their photographs. Clear monitoring objectives should be developed for every covenant that is grazed and these need to be determined before it is possible to accurately select appropriate monitoring methods. These objectives will also provide the monitoring program with more structure and direction. If possible a detailed management plan for each grazed covenant would be beneficial for values present. QEII are in a unique position, where they have the potential to develop a data base of biodiversity information for private land and contribute to other projects like the National Vegetation Survey (NVS).
85

Predicting semidesert range perennial grass production from recent precipitation and grazing levels

Rivers, William James, January 1977 (has links) (PDF)
Thesis (M.S. - Renewable Natural Resources)--University of Arizona. / Includes bibliographical references.
86

Factors determining location and species composition of wet grasslands in Southwest England /

Soest, Francien van. January 2005 (has links)
Univ., Diss.--Plymouth, 2002.
87

Image-based modelling of pattern dynamics in a semiarid grassland of the Pilbara, Australia /

Sadler, Rohan. January 2006 (has links)
Thesis (Ph.D.)--University of Western Australia, 2007.
88

Ökobilanzielle Abschätzung der Bereitstellung von Bioenergie : Strom und Wärme aus Gras-, Maissilage, Heu und Pappelhackschnitzeln /

Skarka, Johannes. January 2008 (has links)
Diplomarbeit - Universität, Karlsruhe. / University publication. Includes bibliographical references.
89

The influence of patch and landscape characteristics on grassland passerine density, nest success, and predators in southwestern Wisconsin pastures /

Renfrew, Rosalind B. January 2002 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 2002. / Includes bibliographical references. Also available on the Internet.
90

Variation in grassland vegetation on the central plateau of Shewa, Ethiopia in relation to edaphic factors and grazing conditions /

Woldu, Zerihun. January 1985 (has links)
Thesis (Ph. D.)--Uppsala University, 1985. / Includes bibliographical references (p. 103-110).

Page generated in 0.0531 seconds