Rozprawy doktorskie: „Ecological disturbances”

1

Christianou, Maria. "Interaction strength and responses of ecological communities to disturbances /". Linköping : Linköpings universitet, 2006. http://www.bibl.liu.se/liupubl/disp/disp2006/tek1002s.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

2

Dogwiler, Toby J. "Fluvial disturbances in karst streams /". free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3060093.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

3

Yang, Jian. "Spatially explicit and stochastic forest landscape model of fire disturbance and succession". Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/4174.

Pełny tekst źródła

Streszczenie:

Thesis (Ph. D.)--University of Missouri-Columbia, 2005.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (November 14, 2006) Vita. Includes bibliographical references.

Style APA, Harvard, Vancouver, ISO itp.

4

Morgan, Michael Boyce. "Assessing coral stress responses at the level of gene expression". Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/27985.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

5

Pearson, Audrey F. "Natural disturbance patterns in a coastal temperate rain forest watershed, Clayoquot Sound, British Columbia /". Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/5513.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

6

Pankey, Joel Robert. "Centaurea in the Columbia basin ecoregion : disturbance, invasion, and competition". Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Dissertations/Spring2009/j_pankey_042109.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

7

Owusu-Afriyie, Kennedy. "Forest fire incidence, damage and control measures in Ghana". Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=26030.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

8

Sun, Wei. "Velvet mesquite (Prosopis velutina) encroachment and ecosystem CO₂ exchange in semiarid grassland insights from stable isotope measurements /". Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1960208391&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

9

Thomas, Jonathan Armstrong White Joseph Daniel. "Modeling canopy foliar traits and disturbance interactions in central Texas woodlands". Waco, Tex. : Baylor University, 2009. http://hdl.handle.net/2104/5337.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

10

Kariuki, Maina. "Modelling dynamics including recruitment, growth, and mortality for sustainable management in uneven-aged mixed-species rainforests". Connect to this title online, 2004. http://epubs.scu.edu.au/theses/27/.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

11

Sanford, Monte Paul. "Using insect responses to anthropogenic disturbance to improve land management and conservation planning decisions". abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3289458.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

12

Tronstad, Lusha M. "Ecosystem consequences of declining Yellowstone cutthroat trout in Yellowstone Lake and spawning streams". Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1597617351&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

13

Allen, Bruce Peter. "Vegetation dynamics and response to disturbance, in floodplain forest ecosystems with a focus on lianas". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1179427491.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

14

Abdelnour, Alex Gabriel. "Assessing ecosystem response to natural and anthropogenic disturbances using an eco-hydrological model". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42899.

Pełny tekst źródła

Streszczenie:

The impact of natural and anthropogenic disturbances on catchment hydrological and biogeochemical dynamics are difficult or impossible to capture through experimentation or observation alone. Process-based simulation models can address this need by providing a framework for synthesizing data describing catchment responses to climate, harvest, fire, and other disturbances. However, existing models are either too simple to capture important process-level hydrological and biogeochemical controls on ecosystem responses to disturbance, or are too computationally expensive to simulate the local dynamics over large watershed areas, or require a high level of expertise to implement. To this end, a spatially distributed, physically based, eco-hydrological model (VELMA: Visualizing Ecosystems for Land Management Assessments) that is both computationally efficient and relatively easy to implement is developed. VELMA is a state-of-the-art model with real-time visualization tools that shows temporal and spatial patterns of state and flux variables, and is used to address the effects of changes in climate, land-use, and other interacting stressors on multiple ecosystem services such as timber production, carbon sequestration, regulation of water quality and quantity and reduction of greenhouse gases at scales relevant to formulating management decisions. In this study, VELMA was applied to the H.J. Andrews Experimental forest, an intensively studied watershed with observed daily temperature, precipitation, streamflow, and nutrient losses data. VELMA was first used to explore the factors that controls catchment response to forest harvest. Specifically, elucidate how forest harvest factors such as harvest location and amount control watershed hydrological and biogeochemical fluxes. Thereafter, VELMA was used to reconstruct and analyze the impact of two significant disturbance events − a stand replacing fire and a 100% clearcut − on vegetation and soil carbon and nitrogen dynamics. Finally, VELMA was used to explore the potential impact of climate change on catchment hydrological regime, site productivity and carbon and nitrogen dynamics at high spatial resolution relevant to formulating management decision. The main insights from this study include: (1) streamflow, nutrient losses to the stream, and gaseous carbon and nitrogen losses to the atmosphere are strongly sensitive to the location of harvest as a result of the spatial variation in soil water content, plant nitrogen uptake, soil organic carbon decomposition, nitrification, and denitrification within the watershed, (2) forested riparian buffers reduce water and nutrient losses to the stream through plant transpiration, plant nitrogen uptake, soil storage, and soil microbial decomposition, (3) following fire and harvest, losses of N from the terrestrial system to the stream are tightly constrained by the hydrological cycle and driven mainly by wet-season rain events large enough to generate hydrologic connectivity and flushing of nutrients along hillslopes, (4) climate change strongly impacts the hydrological regime in the Pacific Northwest as a result of less snowpack, earlier snowmelt, higher winter streamflow, lower summer streamflow, and soil moisture deficit, and (5) climate change increases plant and soil biomass accumulation as a result of longer growing season and higher soil organic decomposition, reduce water quality by increasing the amount of nutrients that reach the stream, and transforms the ecosystem into a net source of carbon to the atmosphere.

Style APA, Harvard, Vancouver, ISO itp.

15

Larouche, Julia Rose. "Thermokarst And Wildfire: Effects Of Disturbances Related To Climate Change On The Ecological Characteristics And Functions Of Arctic Headwater Streams". ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/520.

Pełny tekst źródła

Streszczenie:

The Arctic is warming rapidly as a result of global climate change. Permafrost - permanently frozen ground - plays a critical role in shaping arctic ecosystems and stores nearly one half of the global soil organic matter. Therefore, disturbance of permafrost will likely impact the carbon and related biogeochemical processes on local and global scales. In the Alaskan Arctic, fire and thermokarst (permafrost thaw) have become more common and have been hypothesized to accelerate the hydrological export of inorganic nutrients and sediment, as well as biodegradable dissolved organic carbon (BDOC), which may alter ecosystem processes of impacted streams. The biogeochemical characteristics of two tundra streams were quantified several years after the development of gully thermokarst features. The observed responses in sediment and nutrient loading four years after gully formation were more subtle than expected, likely due to the stabilization of the features and the dynamics controlling the hydrologic connectivity between the gully and the stream. The response of impacted streams may depend on the presence of water tracks, particularly their location in reference to the thermokarst and downslope aquatic ecosystem. We found evidence of altered ecosystem structure (benthic standing stocks, algal biomass, and macroinvertebrate composition) and function (stream metabolism and nutrient uptake), which may be attributable to the previous years' allochthonous gully inputs. The patterns between the reference and impacted reaches were different for both stream sites. Rates of ecosystem production and respiration and benthic chlorophyll-a in the impacted reaches of the alluvial and peat-lined streams were significantly lower and greater, respectively, compared to the reference reaches, even though minimal differences in sediment and nutrient loading were detected. Rates of ammonium and soluble reactive phosphorus uptake were consistently lower in the impacted reach at the alluvial site. The observed differences in metabolism, nutrient uptake and macroinvertebrate community composition suggest that even though the geochemical signal diminished, gully features may have long-lasting impacts on the biological aspects of downstream ecosystem function. In a separate study, a suite of streams impacted by thermokarst and fire were sampled seasonally and spatially. Regional differences in water chemistry and BDOC were more significant than the influences of fire or thermokarst, likely due to differences in glacial age and elevation of the landscape. The streams of the older (>700 ka), lower elevation landscape contained higher concentrations of dissolved nitrogen and phosphorus and DOC and lower BDOC compared to the streams of the younger (50-200 ka) landscapes that had lower dissolved nutrient and DOC quantity of higher biodegradability. The findings in this dissertation indicate that arctic stream ecosystems are more resilient than we expected to small-scale, rapidly stabilizing gully thermokarst features and disturbance caused by fire. Scaling the results of these types of studies should consider the size of thermokarst features in relation to the size of impacted rivers and streams. It remains to be determined how general permafrost thaw will affect the structure and function of arctic streams in the future.

Style APA, Harvard, Vancouver, ISO itp.

16

Gray, Curtis A. "Impact of Climate Variability on the Frequency and Severity of Ecological Disturbances in Great Basin Bristlecone Pine Sky Island Ecosystems". DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6529.

Pełny tekst źródła

Streszczenie:

Great Basin bristlecone pine (GBBP) (Pinus longaevaBailey) is one of the longest-lived organisms on Earth, and is one of the most highly fragmented high elevation conifer species. Throughout the Great Basin of the Intermountain West, GBBP are being impacted by changing disturbance regimes, invasive species, and climate change. To better understand the effects of climate variability and ecological disturbances in GBBP systems, three studies were designed and implemented. The first characterized the distribution of forest fuel in stands of GBBP and predicted how fuels may change under future climate scenarios. Using the Forest Inventory Analysis (FIA) plot variables of tree species, height, diameter at breast height (DBH), canopy base height (CBH), coarse (CWD) and fine (FWD) woody debris across elevational gradients, this study examined the effects of changes to fuel loading on predicted changes in fire behavior and severity. All classes of FWD decreased with elevation, and only 1000-hr fuels remained constant across elevational transects. This, combined with lower CBH and foliar moisture and increasing temperatures due to climate change, suggested increased fire potential at the GBBP treeline. The second study examined the role of volatile organic compounds (VOCs) and tree chemistry and their response to the environment. VOCs and within needle chemistry were collected and analyzed along elevational gradients near the northern and southern limits of GBBP. Random Forest analysis distinguished elevation using VOCs, with 83% accuracy, and identified the compounds most important for classification. Ordination revealed that temperature, heat load index, and relative humidity were each significantly correlated with VOCs. Within-needle chemistry provided less predictive value in classifying elevation (68% accuracy) and was correlated only with heat load index. These findings suggest that GBBP VOCs are highly sensitive to the environment. The final study explored the role of VOCs in host selection of mountain pine beetle (MPB). Mountain pine beetles oriented toward VOCs from host limber pine (Pinus flexilis James) and away from VOCs of non-host GBBP using a Y-tube olfactometer. When presented with VOCs of both trees, females overwhelmingly chose limber pine over GBBP. While there were only a few notable differences in VOCs collected from co-occurring GBBP and limber pine, 3-carene and D-limonene were produced in greater amounts by limber pine. There was no evidence that 3-carene is important for beetles when selecting trees, however, addition of D-limonene to GBBP VOCs disrupted the ability of beetles to distinguish between tree species. Climate change will impact how forests are managed and this research could provide insight into the mechanisms underlying the incredible longevity of this iconic tree species.

Style APA, Harvard, Vancouver, ISO itp.

17

Ljunggren, Johannes. "Störningsregimer vid Skövde övnings- och skjutfält : Stridsfordons påverkan på olika naturtyper i militära övningsområden". Thesis, Linnéuniversitetet, Institutionen för naturvetenskap, NV, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-21619.

Pełny tekst źródła

Streszczenie:

A lot of habitats have declined or disappeared as the old cultural landscape changed to the modern agricultural landscape of today. Places such as power line corridors, racing tracks, gravel pits and military training sites have become refuges for many species associated with the old cultural landscape. These sites have been exposed to ecological disturbances that create the same type of habitats that were found in the old cultural landscape. The military training sites in Sweden has an impressive diversity of species. Disturbances from the military exercises have created habitats that are important for a wide range of species. The purpose of this thesis is to study some of the ecological disturbances occurring in the military training sites of the Swedish Armed Forces and examine how they affect different types of habitats. The thesis explains through litterateur and field studies the reason to the rich biodiversity often found at military training sites. The training sites and firing ranges of Skövde garrison were used as an example to show how the disturbances affect the environment. The study shows that military exercises (e.g. with combat vehicles) creates habitats that previously existed in the old cultural landscape. Soil damage from combat vehicles benefits insects and creates pools for amphibians. Damages on trees create snags and woody debris which favors a large amount of species. The military exercises also keep an open landscape.

Style APA, Harvard, Vancouver, ISO itp.

18

Bottoms, Richard M. "Grass-knapweed interference involves allelopathic factors associated with ecosystem mineral cycling /". free to MU campus, to others for purchase, 2001. http://wwwlib.umi.com/cr/mo/fullcit?p3036807.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

19

Scherrer, Pascal, i n/a. "Monitoring Vegetation Change in the Kosciuszko Alpine Zone, Australia". Griffith University. Australian School of Environmental Studies, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040715.125310.

Pełny tekst źródła

Streszczenie:

This thesis examined vegetation change over the last 43 years in Australia's largest contiguous alpine area, the Kosciuszko alpine zone in south-eastern Australia. Using historical and current data about the state of the most common vegetation community, tall alpine herbfield, this thesis addressed the questions: (1) what were the patterns of change at the species/genera and life form levels during this time period; (2) what were the patterns of recovery, if recovery occurred, from anthropogenic disturbances such as livestock grazing or trampling by tourists; (3) what impacts did natural disturbances such as drought have on the vegetation and how does it compare to anthropogenic disturbances; and (4) What are the benefits, limitations and management considerations when using long-term data for assessing vegetation changes at the species/genera, life form and community levels? The Kosciuszko alpine zone has important economic, cultural and ecological values. It is of great scientific and biological importance, maintaining an assemblage of vegetation communities found nowhere else in the world. It is one of the few alpine regions in the world with deep loamy soils, and contains endemic flora and fauna and some of the few periglacial and glacial features in Australia. The area also forms the core of the Australian mainland's most important water catchment and is a popular tourist destination, offering a range of recreational opportunities. The vegetation of the Kosciuszko alpine zone is recovering from impacts of livestock grazing and is increasingly exposed to pressures from tourism and anthropogenic climate change. At the same time, natural disturbances such as drought and fire can influence the distribution, composition and diversity of plants. Thus, there is a need for detailed environmental data on this area in order to: (1) better understand ecological relationships; (2) understand existing and potential effects of recreational and management pressures on the region; (3) provide data against which future changes can be assessed; and (4) provide better information on many features of this area, including vegetation, for interpretation, education and management. The research in this thesis utilised three types of ecological information: (1) scientific long-term datasets; (2) photographic records; and (3) a comparison of disturbed and undisturbed vegetation. This research analysed data from one of the longest ongoing monitoring programs in the Australian Alps established by Alec Costin and Dane Wimbush in 1959. Permanent plots (6 transects and 30 photoquadrats) were established at two locations that differed in the time since grazing and have been repeatedly surveyed. Plots near Mt Kosciuszko had not been grazed for 15 years and had nearly complete vegetation cover in 1959, while plots near Mt Gungartan showed extensive impacts of grazing and associated activities which only ceased in 1958. Some transect data from 1959 to 1978 have been analysed by the original researchers. The research presented in this thesis extends this monitoring program with data from additional surveys in 1990, 1999 and 2002 and applies current methods of statistical evaluation, such as ordination techniques, to the whole data set for the first time. Results indicated that the recovery from livestock grazing and the effects of drought have been the main factors affecting vegetation. Recovery from livestock grazing at the three transects at Gungartan was slow and involved: (1) increasing genera diversity; (2) increasing vegetation cover; (3) decreasing amounts of bare ground; and (4) a directional change over time in species composition. Patterns of colonisation and species succession were also documented. In 2002, 44 years after the cessation of grazing, transects near Mt Gungartan had similar vegetation cover and genera diversity to the transects near Mt Kosciuszko, but cover by exposed rock remained higher. A drought in the 1960s resulted in a temporary increase of litter and a shift in the proportional cover of life forms, as grasses died and herb cover increased at both locations. Proportions of cover for life forms reverted to pre-drought levels within a few years. The results also highlighted the spatial variability of tall alpine herbfield. The photoquadrats were surveyed in the years 1959, 1964, 1968, 1978 and 2001 and are analysed for the first time in this thesis. After comparing a range of methods, visual assessment using a 130 point grid was found to be the most suitable technique to measure vegetation cover and genera diversity. At the 18 quadrats near Mt Gungartan, there was a pattern of increasing vegetation cover as bare areas were colonised by native cudweeds and the naturalized herb Acetosella vulgaris. Revegetation from within bare areas largely occurred by herb species, while graminoids and shrub species predominately colonised bare ground by lateral expansion from the edges, eventually replacing the colonising herbs. At the 12 quadrats near Mt Kosciuszko, vegetation cover was almost complete in all years surveyed except 1968, which was at the end of a six year drought. Similar to the results from the transect study, the drought caused an increase in litter at both locations as graminoid cover declined. Initially herb cover increased, potentially as a result of decreased competition from the graminoids and a nutrient spike from decaying litter, but as the drought became more severe, herb cover also declined. Graminoid cover rapidly recovered after the drought, reaching pre-drought levels by 1978, and was at similar levels in 2001. Herb cover continued to decline after peaking in 1964. The photoquadrat study also documented the longevity and growth rates of several species indicating that many taxa may persist for several decades. It further provided insights into replacement patterns amongst life forms. In addition to assessing vegetation change following livestock grazing and drought at the long-term plots, recovery from tourism impacts was examined by comparing vegetation and soils on a closed walking track, with that of adjacent undisturbed tall alpine herbfield at a series of 22 paired quadrats. Fifteen years after the track was closed there was limited success in restoration. Over a quarter of the closed track was still bare ground with non-native species the dominant vegetation. Plant species composition differed and vegetation height, soil nutrients and soil moisture were lower on the track which had a higher compaction level than adjacent natural vegetation. The results presented in this thesis highlight that tall alpine herbfield is characterised by nearly entire vegetation cover which is dominated by graminoids, followed by herbs and shrubs in the absence of disturbance by livestock grazing, trampling or drought. The studies also showed that under quot;average" conditions, the relative cover of herbs and graminoids remained fairly stable even though there can be considerable cycling between them. Spatial variability in terms of taxa composition was high. The only common introduced species in unrehabilitated sites was Acetosella vulgaris, which was effective at colonising bare ground but was eventually replaced by other native species. However, in areas actively rehabilitated, such as on the closed track, non-native species introduced during revegetation efforts still persist with high cover 15 years after their introduction. Monitoring of vegetation change is also important at the landscape scale. This thesis provides a review of the potential use, the limitations and the benefits of aerial photography to examine vegetation change in the Kosciuszko alpine zone. Numerous aerial photography runs have been flown over the area since the 1930s for government agencies, industry and the military. Some of these records have been used to map vegetation communities and eroding areas at a point in time. Other studies compared different types and scales of photographs, highlighting in particular the benefits and potential of large scale colour aerial photography to map alpine vegetation. However, despite their potential to assess vegetation change over time, a temporal comparison of vegetation in the Kosciuszko alpine zone from aerial photographs has not been completed to this date. Historical photographs may not be easy to locate or access and difficulties with vegetation classification may restrict the practicality of using historical aerial photographs to assess vegetation change. Despite these issues, aerial photography may provide a very useful and efficient tool to assess changes over time when applied appropriately, even in alpine environments. The development of digital classification techniques, the application of statistical measures of error to both methodology and data, and the application of geographic information systems are likely to further improve the practicality of historical aerial photographs for the detection of vegetation change and assist in overcoming some of the limitations. The results presented in this thesis highlight the need for limiting disturbance, for ongoing rehabilitation of disturbed areas and for long-term monitoring in the Kosciuszko alpine zone. The results contribute to our understanding of how vegetation may change in the future and may be affected by new land use activities and climate change. This type of information, which otherwise would require the establishment of long-term studies and years of monitoring, can assist land managers of this and other important protected areas. The study highlights how the use and expansion of already existing datasets to gather ecological information can save considerable money and time, providing valuable data for current and emerging issues.

Style APA, Harvard, Vancouver, ISO itp.

20

Scherrer, Pascal. "Monitoring Vegetation Change in the Kosciuszko Alpine Zone, Australia". Thesis, Griffith University, 2004. http://hdl.handle.net/10072/366283.

Pełny tekst źródła

Streszczenie:

This thesis examined vegetation change over the last 43 years in Australia's largest contiguous alpine area, the Kosciuszko alpine zone in south-eastern Australia. Using historical and current data about the state of the most common vegetation community, tall alpine herbfield, this thesis addressed the questions: (1) what were the patterns of change at the species/genera and life form levels during this time period; (2) what were the patterns of recovery, if recovery occurred, from anthropogenic disturbances such as livestock grazing or trampling by tourists; (3) what impacts did natural disturbances such as drought have on the vegetation and how does it compare to anthropogenic disturbances; and (4) What are the benefits, limitations and management considerations when using long-term data for assessing vegetation changes at the species/genera, life form and community levels? The Kosciuszko alpine zone has important economic, cultural and ecological values. It is of great scientific and biological importance, maintaining an assemblage of vegetation communities found nowhere else in the world. It is one of the few alpine regions in the world with deep loamy soils, and contains endemic flora and fauna and some of the few periglacial and glacial features in Australia. The area also forms the core of the Australian mainland's most important water catchment and is a popular tourist destination, offering a range of recreational opportunities. The vegetation of the Kosciuszko alpine zone is recovering from impacts of livestock grazing and is increasingly exposed to pressures from tourism and anthropogenic climate change. At the same time, natural disturbances such as drought and fire can influence the distribution, composition and diversity of plants. Thus, there is a need for detailed environmental data on this area in order to: (1) better understand ecological relationships; (2) understand existing and potential effects of recreational and management pressures on the region; (3) provide data against which future changes can be assessed; and (4) provide better information on many features of this area, including vegetation, for interpretation, education and management. The research in this thesis utilised three types of ecological information: (1) scientific long-term datasets; (2) photographic records; and (3) a comparison of disturbed and undisturbed vegetation. This research analysed data from one of the longest ongoing monitoring programs in the Australian Alps established by Alec Costin and Dane Wimbush in 1959. Permanent plots (6 transects and 30 photoquadrats) were established at two locations that differed in the time since grazing and have been repeatedly surveyed. Plots near Mt Kosciuszko had not been grazed for 15 years and had nearly complete vegetation cover in 1959, while plots near Mt Gungartan showed extensive impacts of grazing and associated activities which only ceased in 1958. Some transect data from 1959 to 1978 have been analysed by the original researchers. The research presented in this thesis extends this monitoring program with data from additional surveys in 1990, 1999 and 2002 and applies current methods of statistical evaluation, such as ordination techniques, to the whole data set for the first time. Results indicated that the recovery from livestock grazing and the effects of drought have been the main factors affecting vegetation. Recovery from livestock grazing at the three transects at Gungartan was slow and involved: (1) increasing genera diversity; (2) increasing vegetation cover; (3) decreasing amounts of bare ground; and (4) a directional change over time in species composition. Patterns of colonisation and species succession were also documented. In 2002, 44 years after the cessation of grazing, transects near Mt Gungartan had similar vegetation cover and genera diversity to the transects near Mt Kosciuszko, but cover by exposed rock remained higher. A drought in the 1960s resulted in a temporary increase of litter and a shift in the proportional cover of life forms, as grasses died and herb cover increased at both locations. Proportions of cover for life forms reverted to pre-drought levels within a few years. The results also highlighted the spatial variability of tall alpine herbfield. The photoquadrats were surveyed in the years 1959, 1964, 1968, 1978 and 2001 and are analysed for the first time in this thesis. After comparing a range of methods, visual assessment using a 130 point grid was found to be the most suitable technique to measure vegetation cover and genera diversity. At the 18 quadrats near Mt Gungartan, there was a pattern of increasing vegetation cover as bare areas were colonised by native cudweeds and the naturalized herb Acetosella vulgaris. Revegetation from within bare areas largely occurred by herb species, while graminoids and shrub species predominately colonised bare ground by lateral expansion from the edges, eventually replacing the colonising herbs. At the 12 quadrats near Mt Kosciuszko, vegetation cover was almost complete in all years surveyed except 1968, which was at the end of a six year drought. Similar to the results from the transect study, the drought caused an increase in litter at both locations as graminoid cover declined. Initially herb cover increased, potentially as a result of decreased competition from the graminoids and a nutrient spike from decaying litter, but as the drought became more severe, herb cover also declined. Graminoid cover rapidly recovered after the drought, reaching pre-drought levels by 1978, and was at similar levels in 2001. Herb cover continued to decline after peaking in 1964. The photoquadrat study also documented the longevity and growth rates of several species indicating that many taxa may persist for several decades. It further provided insights into replacement patterns amongst life forms. In addition to assessing vegetation change following livestock grazing and drought at the long-term plots, recovery from tourism impacts was examined by comparing vegetation and soils on a closed walking track, with that of adjacent undisturbed tall alpine herbfield at a series of 22 paired quadrats. Fifteen years after the track was closed there was limited success in restoration. Over a quarter of the closed track was still bare ground with non-native species the dominant vegetation. Plant species composition differed and vegetation height, soil nutrients and soil moisture were lower on the track which had a higher compaction level than adjacent natural vegetation. The results presented in this thesis highlight that tall alpine herbfield is characterised by nearly entire vegetation cover which is dominated by graminoids, followed by herbs and shrubs in the absence of disturbance by livestock grazing, trampling or drought. The studies also showed that under quot;average" conditions, the relative cover of herbs and graminoids remained fairly stable even though there can be considerable cycling between them. Spatial variability in terms of taxa composition was high. The only common introduced species in unrehabilitated sites was Acetosella vulgaris, which was effective at colonising bare ground but was eventually replaced by other native species. However, in areas actively rehabilitated, such as on the closed track, non-native species introduced during revegetation efforts still persist with high cover 15 years after their introduction. Monitoring of vegetation change is also important at the landscape scale. This thesis provides a review of the potential use, the limitations and the benefits of aerial photography to examine vegetation change in the Kosciuszko alpine zone. Numerous aerial photography runs have been flown over the area since the 1930s for government agencies, industry and the military. Some of these records have been used to map vegetation communities and eroding areas at a point in time. Other studies compared different types and scales of photographs, highlighting in particular the benefits and potential of large scale colour aerial photography to map alpine vegetation. However, despite their potential to assess vegetation change over time, a temporal comparison of vegetation in the Kosciuszko alpine zone from aerial photographs has not been completed to this date. Historical photographs may not be easy to locate or access and difficulties with vegetation classification may restrict the practicality of using historical aerial photographs to assess vegetation change. Despite these issues, aerial photography may provide a very useful and efficient tool to assess changes over time when applied appropriately, even in alpine environments. The development of digital classification techniques, the application of statistical measures of error to both methodology and data, and the application of geographic information systems are likely to further improve the practicality of historical aerial photographs for the detection of vegetation change and assist in overcoming some of the limitations. The results presented in this thesis highlight the need for limiting disturbance, for ongoing rehabilitation of disturbed areas and for long-term monitoring in the Kosciuszko alpine zone. The results contribute to our understanding of how vegetation may change in the future and may be affected by new land use activities and climate change. This type of information, which otherwise would require the establishment of long-term studies and years of monitoring, can assist land managers of this and other important protected areas. The study highlights how the use and expansion of already existing datasets to gather ecological information can save considerable money and time, providing valuable data for current and emerging issues.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Australian School of Environmental Studies
Full Text

Style APA, Harvard, Vancouver, ISO itp.

21

Cheng, Yiwei. "Impacts of self-organizing mechanism and topography on wetland ecosystem dynamics". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47705.

Pełny tekst źródła

Streszczenie:

Understanding the first order controls over resource cycling and limitation in ecosystems is critical for predicting ecosystem response to disturbances. Topography and vegetation self-organizing mechanisms are first order controls over resource fluxes across the landscape. Topography controls downslope flow of resources (i.e water and nutrients). Through spatial feedbacks, vegetation is able to actively modify its environment and maximize resource flows towards it. To date, the impacts of these controls on ecosystem dynamics have mostly been investigated separately. As such, there is a knowledge gap in the understanding of how these first order controls together dictate the dynamics of the ecosystem. This dissertation aims to gain a better understanding of how self-organizing mechanisms and topography operate together to affect wetland ecosystem dynamics. A spatially explicit, wetland vegetation patterning model that includes for both vegetation self-organizing control and topographic control is developed (Nutrient Depletion Model, NDM). The model describes a scale dependent feedback between vegetation, transpiration and nutrient accumulation that drives the formation of vegetation patterns. The model is applied to investigate the effects of topography and self-organizing mechanisms on form and orientation of vegetation patterns and vegetation growth dynamics of wetland ecosystems. Results show that the two first order controls synergistically impact the formation of the various patterns as observed in wetland ecosystems. Results also show the following: (1) Self-organizing mechanisms result in a more efficient retention of resources, which result in higher biomass in the model that include for both self-organizing mechanism and topographic control (SO+TC) than in the model that that includes only for topographic control (TC). (2) However, when resources or topographic gradients increase or annual rainfall decrease, the vegetation growth dynamics of the TC+SO and TC models converge. The NDM is applied to arctic Alaska to investigate how do the two first order controls impact present and future C-N dynamics of an arctic ecosystem. Simulation results show no significant difference in the dynamics between the SO+TC model and the TC model. The climate change simulation results suggest that changes in daily variability of temperature and precipitation can impact ecosystem dynamics as much as the changes in mean temperature and precipitation. Results from this dissertation provide a more complete picture on the relative roles of the two first order controls over ecosystem nutrient cycling and vegetative growth dynamics. Finally, in this thesis, in order to simulate small-scale feedbacks over large spatial domains, the NDM is implemented in a GPU computing language, which accelerates computational simulation by at least two orders of magnitude. These tools for grid-based simulations can provide a platform for using GPUs in other areas of scientific investigation.

Style APA, Harvard, Vancouver, ISO itp.

22

Bockino, Nancy Karin. "Interactions of white pine blister rust, host species, and mountain pine beetle in whitebark pine ecosystems in the Greater Yellowstone". Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1594498141&sid=3&Fmt=2&clientId=18949&RQT=309&VName=PQD.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

23

Adams, Jennifer Karen. "Multiproxy reconstructions of recent environmental change : understanding the ecological response of shallow lakes within the Selenga River basin, southeast Siberia, to anthropogenic and natural disturbances". Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/10040922/.

Pełny tekst źródła

Streszczenie:

Floodplain delta wetlands are highly productive and critical ecosystems between terrestrial uplands and large, aquatic systems. The largest inland freshwater floodplain delta in the world is the Selenga Delta. The Selenga Delta serves a crucial function between UNESCO World Heritage Site Lake Baikal, and the lake’s primary inflow, the Selenga River, and its tributaries. The Selenga River flows approximately 950 km through northern Mongolia and southern Siberia prior to reaching the Selenga Delta, and within the Selenga River basin, numerous anthropogenic activities, including industry, urban settlements, agriculture, and mining, have the potential to cause ecological damage to the Selenga River and its tributaries. The aims of this thesis were to assess the extent of current and historical contamination in Selenga River basin shallow lakes, investigate the primary environmental drivers of variability in ecological structure and function of shallow lakes within the basin, and understand the ecological responses and sensitivity to disturbance. Multiproxy palaeolimnological investigstions of three shallow lakes with the Selenga River basin (two from within the Selenga Delta and one from a more heavily industrialized region), were chosen to undertake a multiproxy palaeolimnological approach to addressing these aims. Investigations on shallow lakes across the Selenga Delta revealed that variability and composition of contemporary ecological communities are determined by degree of connectivity, trophic interactions, and physical landscape parameters such as lake surface area and depth. The greatest period of contamination of shallow lakes (by trace metals and persistent organic pollutants) occurred in the mid-20th century, closely linked with periods of economic development in Russia. However the main drivers of ecological variability since the 19th century have been natural and anthropogenically-induced changes in hydrological regimes, and nutrient pollution, which resulted in significant ecological shifts across multiple trophic levels in shallow lakes.

Style APA, Harvard, Vancouver, ISO itp.

24

Matthee, Willem. "Factors affecting the success of reseeding rehabilitation in the semi-arid Karoo, South Africa". Thesis, Nelson Mandela Metropolitan University, 2015. http://hdl.handle.net/10948/2889.

Pełny tekst źródła

Streszczenie:

Due to overgrazing, mining and other anthropogenic disturbances, large sections of the Karoo region have been degraded, resulting in areas with low vegetation cover, where erosion rates are high and vegetation is dominated by unpalatable species. These areas have low and unpredictable rainfall, with slow to non-existent autogenic recovery, and this often forces landowners to implement reseeding rehabilitation in an attempt to increase both overall vegetation cover and the relative abundance of palatable plants. Landowners use soil preparation treatments, which include creating micro-catchments, ripping, mulching and brush packing, to supplement land rehabilitation. This study investigated the significance of initial rainfall, mean monthly rainfall, soil preparation techniques, slope, existing vegetation cover, litter, mulch and stone cover in determining the success of reseeding rehabilitation. Rainfall had the most significant influence, where long-lived shrubs established best under low initial rainfall and high mean monthly rainfall, and grasses established best after receiving high initial rainfall. Micro-catchments proved the most successful soil preparation technique for the establishment of long-lived shrubs, while ripping and mulching impacted negatively on grass establishment. A combination of mulch and micro-catchments aided Osteospermum sinuatum establishment in soils where soil shrinkage cracks occurred. Temperature influenced seed germination and drought tolerance of Lessertia annularis, Fingerhuthia africana and O. sinuatum, with higher germination success of O. sinuatum under temperatures simulating summer, and of F. africana under temperatures simulating winter. L. annularis germination had a faster growth rate and higher survival when germinated under autumn/spring temperatures. Landowners are advised to sow seeds of more than one species during rehabilitation, to include micro-catchments as soil preparation treatment, and to sow seeds during a time when rainfall is predicted to be high.

Style APA, Harvard, Vancouver, ISO itp.

25

Courret, Dominique. "Problématique des impacts de la gestion par éclusées des aménagements hydroélectriques sur les populations de poissons : caractérisation des régimes d’éclusées et du niveau de perturbation hydrologique". Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0127/document.

Pełny tekst źródła

Streszczenie:

La gestion par éclusées des aménagements hydroélectriques (plus de 150 en France) pour la production d'énergie de pointe engendre de brusques variations de débit sur les cours d'eau et est susceptible d’altérer la composition, l’abondance et la structure des populations de poissons et d’invertébrés, sur de longues distances. Les objectifs de cette thèse ont été (1) de développer une méthode de caractérisation des éclusées au sein des hydrogrammes, ainsi qu'un indicateur synthétique du niveau de perturbation hydrologique, et (2) de progresser dans la définition des mesures de mitigation des impacts des éclusées sur les poissons. A partir de l'analyse de 97 stations et 1575 années de données de débit, les gradients des variations naturelles de débit ont tout d’abord été caractérisés sur 8 gammes entre 5% et 4 fois le débit moyen interannuel (module). Des formules représentant les variations de débit « les plus rapides possibles naturellement » ont été construites en tenant compte du type de variation (hausse ou baisse), de la taille du cours d'eau (via le module) et de la gamme de débit sur laquelle se déroule la variation, pour ensuite discriminer les éclusées des événements naturels. A partir de l'analyse de 80 stations et 491 années de données de débit influencées par les éclusées, une méthode a été mise au point pour repérer au sein des hydrogrammes les éclusées dont les caractéristiques sont au-delà de ce qui peut se rencontrer en hydrologie naturelle, à partir de 3 critères : une amplitude minimale (≥ à 10% du module et ≥ à 20% du débit de base de l’éclusées), un gradient minimal (> au gradient naturel maximal) et une limite haute sur le débit maximum (pour éliminer les événements de crues). Une grande variabilité des régimes d'éclusées du fait de la diversité des aménagements hydroélectriques et des fluctuations des apports hydrologiques et de la demande énergétique, a été constatée et illustrée […]
Hydropeaking management of hydroelectric facilities (more than 150 in France) generates sudden changes in flow on the river and can affect the composition, the abundance and the structure of fish and invertebrates populations over long distances. The objectives of this thesis were (1) to develop a method for characterizing hydropeaks within hydrograph and a synthetic indicator of hydrological disturbance, and (2) to progress in defining mitigation measures of hydropeaking impacts on fish. From the analysis of 97 stations and 1575 years of flow data, rate of change of natural flow variations have been characterized within 8 ranges between 5% and 4 times the mean inter-annual discharge. Formulas representing the "fastest variations possible naturally" and taking into account the type of change (increase or decrease), the size of the stream (via the mean inter-annual discharge) and the flow range over which the variation takes place have been constructed and then used to discriminate hydropeaks and natural events. From the analysis of 80 stations and 491 years of flow data affected by hydropeaks, a method was developed to identify, within the hydrograph, hydropeaks whose characteristics are beyond what can occur in natural hydrology, using 3 criteria: a minimum range (≥ 10% of the mean inter-annual discharge and ≥ 20% of the hydropeak base flow), a minimal rate of change (> to the maximum natural rate of change) and an upper limit on the maximum flow rate (to remove flood events). A large variation in hydropeaking regimes, due to the diversity of hydroelectric schemes and fluctuations in incoming flow and energy demand, was observed and illustrated […]

Style APA, Harvard, Vancouver, ISO itp.

26

Clough, Elizabeth Anne, i n/a. "Factors Influencing Ant Assemblages and Ant Community Composition in a Sub-Tropical Suburban Environment". Griffith University. School of Environmental and Applied Science, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040719.141317.

Pełny tekst źródła

Streszczenie:

The main objective of this study was to examine the abundance and diversity of ants in suburban sites following vegetation removal or modification for development. This research examines the capacity of suburban sites to support ant diversity, which is dependent on the site characteristics and their surrounding environment. The study focused on 29 suburban garden and 3 suburban reserve sites on the Gold Coast, Queensland, Australia. This region, through continuing land development, undergoes ongoing habitat disturbance and modification. Ground-dwelling ants were collected by pitfall trapping in study sites over three summers between 1997 and 1999. In total, 28,512 ants from 60 species in 31 genera were collected. Garden sites that maintain vegetation structural diversity were found to be most similar to reserve sites in terms of ant community composition. These sites were highest in ant richness and diversity and contained particularly high proportions of specialized ant species. Sites in close proximity to remnants of native vegetation contained higher species diversity and a greater proportion of specialized ant species. The introduced tramp ant, Pheidole megacephala was found in 28 of the 32 sites and was found to significantly reduce ant species richness and diversity and displace the dominant ant Iridomyrmex sp. 1 in suburban environments. This ant poses a serious threat to the recovery of a diverse ant fauna to suburban environments. Ant community composition was shown to vary significantly among suburban sites. The ant functional groups commonly found in disturbed sites were abundant in open sites with little canopy cover in this study. Sites that provided vegetation structural diversity and areas of closed canopy supported similar functional groups to natural vegetation remnants. These results indicate that ant communities in suburban environments respond to disturbance in a similar manner to ant communities in tropical forests and rainforests. The dominance by functional groups and presence of specialized species may therefore be used as an indicator of disturbance and the restoration of suitable habitat in suburban sites. The presence of specialized species of ants in suburban garden sites and their clear preference for particular site characteristics indicate that these species utilize resources available in the suburban matrix. These results indicate that residential suburban sites are of value in the enhancement of ant diversity in fragmented landscapes and that they may provide supportive habitat to, and act as corridors between, vegetation fragments. In order to preserve biodiversity within suburban environments, landowners should be advised to retain as much existing vegetation within a site as possible. Clearing should be limited to that necessary to allow construction of dwellings and for safety. In addition, landowners should be encouraged to establish or maintain structurally diverse vegetation layers within sites in order to provide diverse microenvironments for fauna habitat.

Style APA, Harvard, Vancouver, ISO itp.

27

Clough, Elizabeth Anne. "Factors Influencing Ant Assemblages and Ant Community Composition in a Sub-Tropical Suburban Environment". Thesis, Griffith University, 2004. http://hdl.handle.net/10072/366528.

Pełny tekst źródła

Streszczenie:

The main objective of this study was to examine the abundance and diversity of ants in suburban sites following vegetation removal or modification for development. This research examines the capacity of suburban sites to support ant diversity, which is dependent on the site characteristics and their surrounding environment. The study focused on 29 suburban garden and 3 suburban reserve sites on the Gold Coast, Queensland, Australia. This region, through continuing land development, undergoes ongoing habitat disturbance and modification. Ground-dwelling ants were collected by pitfall trapping in study sites over three summers between 1997 and 1999. In total, 28,512 ants from 60 species in 31 genera were collected. Garden sites that maintain vegetation structural diversity were found to be most similar to reserve sites in terms of ant community composition. These sites were highest in ant richness and diversity and contained particularly high proportions of specialized ant species. Sites in close proximity to remnants of native vegetation contained higher species diversity and a greater proportion of specialized ant species. The introduced tramp ant, Pheidole megacephala was found in 28 of the 32 sites and was found to significantly reduce ant species richness and diversity and displace the dominant ant Iridomyrmex sp. 1 in suburban environments. This ant poses a serious threat to the recovery of a diverse ant fauna to suburban environments. Ant community composition was shown to vary significantly among suburban sites. The ant functional groups commonly found in disturbed sites were abundant in open sites with little canopy cover in this study. Sites that provided vegetation structural diversity and areas of closed canopy supported similar functional groups to natural vegetation remnants. These results indicate that ant communities in suburban environments respond to disturbance in a similar manner to ant communities in tropical forests and rainforests. The dominance by functional groups and presence of specialized species may therefore be used as an indicator of disturbance and the restoration of suitable habitat in suburban sites. The presence of specialized species of ants in suburban garden sites and their clear preference for particular site characteristics indicate that these species utilize resources available in the suburban matrix. These results indicate that residential suburban sites are of value in the enhancement of ant diversity in fragmented landscapes and that they may provide supportive habitat to, and act as corridors between, vegetation fragments. In order to preserve biodiversity within suburban environments, landowners should be advised to retain as much existing vegetation within a site as possible. Clearing should be limited to that necessary to allow construction of dwellings and for safety. In addition, landowners should be encouraged to establish or maintain structurally diverse vegetation layers within sites in order to provide diverse microenvironments for fauna habitat.
Thesis (Masters)
Master of Philosophy (MPhil)
School of Environmental and Applied Science
Full Text

Style APA, Harvard, Vancouver, ISO itp.

28

Michelsen-Correa, Stephani. "Geomorphic response to restoration and disturbance: Grazing, fire, and flooding on the Middle Fork John Day River, OR". Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11290.

Pełny tekst źródła

Streszczenie:

xii, 64 p. : ill. (some col.), maps
Salmon habitat restoration is ongoing at a Nature Conservancy preserve on the Middle Fork John Day River in the Columbia River Basin in north-central Oregon. The site has a long history of disturbance including dredge mining upstream, channelization, grazing, logging, fire, and floods. Using historic aerial photos, habitat unit surveys, and cross sectional profiles, this thesis shows how the channel morphology, particularly habitat unit diversity, has changed since 1939, just before placer mining began. Results show that the dominant influence on present day channel morphology is channelization from the 1930's. Other changes including dredge mining in the late 1930's to early 1940's, cessation of cattle grazing in 1991, and a fire followed by a flood in the winter of 1996-1997, had less impact because of the straightened, stabilized channel morphology.
Committee in charge: Patricia McDowell, Chairperson; W. Andrew Marcus, Member
10000-01-01

Style APA, Harvard, Vancouver, ISO itp.

29

Coulston, John Wesley Riitters Kurt Smith Gretchen Cole. "Large-scale analysis of sustainable forest management indicators assessments of air pollution, forest disturbance, and biodiviersity [sic] /". Connect to this title online, 2004. http://www.lib.ncsu.edu/theses/available/etd-03282004-103433/.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

30

Imbeau, Louis. "Comparaison et suivi des communautés d'oiseaux nicheurs dans des pessières noires boréales issues de coupes et de feux /". Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1996. http://theses.uqac.ca.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

31

Thorn, Simon Otto Verfasser], Jörg [Akademischer Betreuer] [Gutachter] Müller, Roland [Gutachter] Brandl i Hanno [Gutachter] [Schäfer. "Effects of salvage logging on biodiversity - Ecological evidence for conservation-oriented management of natural disturbances / Simon Otto Thorn. Betreuer: Jörg Müller. Gutachter: Roland Brandl ; Jörg Müller ; Hanno Schäfer". München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1100689141/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

32

Kisaka, Lily. "Modelling payment systems for environmental services in the Mt Elgon ecosystem of Kenya". Thesis, University of Fort Hare, 2014. http://hdl.handle.net/10353/d1013123.

Pełny tekst źródła

Streszczenie:

Unsustainable patterns of consumption by humankind have increased the rate of change in the natural ecosystems and consequently the levels of stress experienced within the environment. Access to sufficient good quality water is essential and a requirement to meet a number of the Millennium Development Goals (MDGs). However, poor land management and untenable agricultural practices have become the main drivers of the declining watershed services. Upstream farmers often have little or no incentives to take these impacts into account in their decision-making process. Therefore, without investment in ensuring proper land management, the trend in watersheds degradation will continue. Payment for Environmental Services (PES) has emerged as an incentive–based tool that is expected to motivate farmers to improve their agricultural practices. PES is set up to facilitate the process whereby the beneficiaries of environmental services pay compensation to providers of environmental services for conserving the ecosystem. This tool has received increasing attention as a means of creating incentive measures for managing the ecosystem, addressing livelihood issues for the rural poor, and providing sustainable financing for protected areas. The Government of Kenya, as part of its efforts to improve water resource management, is considering use of economic incentive. However, there is insufficient information to guide policy making in that direction. Little is known about the farmers’ preferences for management schemes that will affect land use patterns, their willingness to accept compensation and the willingness of potential buyers to pay for the services. This study evaluates the willingness to accept and the willingness to pay for environmental services with a view to assessing the viability of a PES scheme for the Kuywa Watershed in particular, as well as the Mt. Elgon Ecosystem and other areas with similar conditions. The objectives of the study are threefold (i) to examine respondents preferences for management options for the provision of environmental services in the watershed of River Kuywa of Mt. Elgon Ecosystem; (ii) to evaluate households’ willingness to pay (WTP) and willingness to accept (WTA) payment for improved environmental services from the River Kuywa watershed; and (iii) to propose viable PES approaches for the management of the natural resource of the Kuywa watershed and the Mt. Elgon ecosystem in general. Using six land management attributes relevant to the local situation, the study applied the conjoint method to evaluate farmers’ preferences for management options for the provision of environmental service and assess farmers’ willingness to pay and willingness to accept payment for environmental services. To enable assessment of viability, an analysis was done of the institutional and legal framework within which the PES scheme would operate. Data were collected using literature review and document analysis, questionnaires, focus group discussions and key informant interviews. Results indicate that poor water quality was the most acute problem, followed by deforestation. Results from the conjoint models show that the length of commitment period and land size that is 40% or more of the total land holding influence the farmers’ rating of the management scenarios. The study found that a management contract that requires use of 20% of land holding for a period of 5 years, combined with a cash incentive, harvesting partially permitted, administered by a local NGO and requiring contribution of free labour for two days had the highest likelihood of being selected. The conjoint valuation exercise also came up with a WTA by farmers upstream of KSh. 7,080/= per year. The corresponding value downstream was KSh. 43/= per month over and above their regular water bill. In terms of the institutional and regulatory framework, Kenya has a wide range of policies, laws and regulation on water and other natural resources which provide an enabling environment for PES. With the decentralized institutional setup implemented in both the water sector and the agricultural sector, the institutional setting also provides an enabling environment for PES. With a positive WTA and WTP coupled with an enabling legal and institutional environment, the study concludes that PES is a viable environmental management tool for the Kuywa water shed and similar watersheds.

Style APA, Harvard, Vancouver, ISO itp.

33

Wijk, Madelene. "Biologisk mångfald på Torhamns övnings- och skjutfält". Thesis, Linnéuniversitetet, Institutionen för biologi och miljö (BOM), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-66925.

Pełny tekst źródła

Streszczenie:

En ökad exploatering och markanvändning har under det senaste århundradet kraftigt reducerat odlingslandskapets variationsrikedom och biodiversitet, vilket medfört drastiskt förändrade livsvillkor för många arter på jorden. Forskning visar att militära övnings- och skjutfält har kommit att bli en tillflyktsort för många hotade arter, dels på grund av att de blivit förskonade från annan markexploatering och dels för att de militära störningarna visat sig gynna många arter. Denna studie har som syfte att utreda vilka störningsregimer som historiskt gynnat biodiversiteten på Torhamns övnings- och skjutfält i sydöstra Blekinge. I denna undersökning analyseras biodiversitet på landskaps- och artnivå. Tidigare resultat från pollenanalyser ca en mil norr om undersökningsområdet visar att regionen har präglats av markanvändningsformerna bete och slåtter under flera tusen år och att den floristiska diversiteten varit hög sedan tidig järnålder. Den militära verksamhet som bedrivits på Torhamns udde under de senaste 100 åren har med stor sannolikhet bidragit till att bevara de unika naturvärden som finns där idag. En viktig slutsats som kunnat dras av denna studie är att biologisk mångfald förändras över tiden och att det finns en tydlig koppling till markanvändningsförändringar. Det är med kunskap om den historiska markanvändningen som det går att förklara varför flora och fauna ser ut som den gör idag och för att kunna främja biologisk mångfald på militära övnings- och skjutfält, är det därför av största vikt, att ha ett paleoekologiskt perspektiv vid upprättandet av bevarandemål och hållbara handlingsplaner.
The increasing exploitation of land and the changes in land use over the last few hundred years has led to a marked reduction in the biodiversity of the landscape. Species populations have diminished in number or even gone locally extinct due to habitat loss. Research has shown that military training areas have become a refuge for many endangered species, partly due to the fact that these areas have been spared from exploitation of the land and partly due to the fact that these species have thrived as a result of the disturbance of habitat caused by military activity. This study aims to clarify which types of disturbance have had a positive effect on the biodiversity of Torhamns udde in South East Blekinge through history. In this investigation biodiversity is analyzed at the landscape and species levels. Earlier results from a pollen analysis north of the study area show that the region has been affected by land use over a period of several thousand years. The military activity that has taken place in the area over the last hundred years, has contributed to the preservation of the unique natural environment that exists there today. An important conclusion from this study is that changes in biodiversity are strongly connected with changes in land use. The present composition in the flora and fauna may thus largely be explained by the historical land use. In order to positively influence the biodiversity of a military training area, it is important to have a palaeoecological approach, when conservation and management plans are being set up.

Style APA, Harvard, Vancouver, ISO itp.

34

Doherty, Kevin Eric. "Sage-grouse and energy development integrating science with conservation planning to reduce impacts /". [Missoula, Mont.] : The University of Montana, 2008. http://etd.lib.umt.edu/theses/available/etd-03262009-132629/unrestricted/doherty.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

35

Akama, Pierre. "Evaluation des perturbations de l'oléoduc Tchad-Cameroun sur les assemblages de termites". Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209574.

Pełny tekst źródła

Streszczenie:

Les perturbations sont des événements séparés dans le temps qui modifient une population, un écosystème ou un paysage, en changent la structure, le milieu physique et le fonctionnement. Ces événements font partie intégrante de la dynamique des écosystèmes, mais les hommes en ont changé le régime par l’agriculture, les travaux de génie civil, etc. Elles sont devenues une menace pour la biodiversité. C’est ainsi qu’une étude a été menée pour évaluer l’influence du projet de pipeline Tchad-Cameroun sur les assemblages de termites, cinq ans après son achèvement.

Les recherches ont été menées dans les écosystèmes de savane et de forêts camerounaises via deux méthodes d’échantillonnage. La méthode des transects belts d’Eggleton et Jones (2000) a permis de collecter 99 espèces de termites (36 transects dans 4 écosystèmes) ;en complément à celle-ci, la méthode quantitative des carottages de Wood et Sands (1978) a permis de récolter 70 espèces de termites (480 carottes). La différence de richesse spécifique résulte du sous échantillonnage par la méthode des carottages parce que certains habitats susceptibles d’abriter des termites ne sont pas explorés.

Les résultats obtenus montrent que l’infrastructure a perturbé sensiblement les paramètres texturaux, la densité apparente, les propriétés hydriques et la matière organique du sol. Il a diminué la richesse spécifique globale des termites, et essentiellement celle des humivores. Il a augmenté la densité des termites du groupe II et diminué celle des termites du groupe IV mais la densité globale des termites n’a pas été modifiée. En fait, les milieux témoins que nous avons échantillonnés étaient déjà moyennement dégradés avant la pose de l’oléoduc.

L’étude de l’évolution de la litière de Milicia excelsa en litter bags a permis de montrer que ni le l’infrastructure ni la variabilité des écosystèmes n’exercent un effet sur la vitesse de décomposition de cette litière ;en revanche, la dimension de la maille, autorisant ou non le passage des termites, a montré que ceux-ci interviennent pour environ 20 % dans la perte de masse de la litière.

L’apport expérimental d’infusions à base de Chromolaena odorata et d’Alchornea cordifolia a sensiblement abaissé le rapport C/N du sol mais n’a eu qu’un effet très limité sur les assemblages de termites.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Style APA, Harvard, Vancouver, ISO itp.

36

Winberg, Pia Carmen. "Confronting the challenges of tidal flat conservation spatial patterns and human impacts in a Marine Protected Area in southern NSW, Australia /". Access electronically, 2008. http://ro.uow.edu.au/theses/123.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

37

Hellberg, Erik. "Historical variability of deciduous trees and deciduous forests in northern Sweden : effects of forest fires, land-use and climate /". Umeå : Dept. of Forest Vegetation Ecology, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/s308.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

38

Peterson, Garry D. "Contagious disturbance and ecological resilience". [Florida] : State University System of Florida, 1999. http://etd.fcla.edu/etd/uf/1999/amg2055/peterson%5Fg.pdf.

Pełny tekst źródła

Streszczenie:

Thesis (Ph. D.)--University of Florida, 1999.
Title from first page of PDF file. Document formatted into pages; contains ix, 261 p.; also includes graphics. Vita. Includes bibliographical references (p. 248-260).

Style APA, Harvard, Vancouver, ISO itp.

39

Guttmann, E. B. "Continuity and change in arable land management in the Northern Isles : evidence from anthropogenic soils". Thesis, University of Stirling, 2001. http://hdl.handle.net/1893/3551.

Pełny tekst źródła

Streszczenie:

Human activity can affect the soil in ways which are traceable long after the land has been given over to other uses, and past land management practices can be reconstructed by investigation of these relict characteristics. In some regions the addition of fertilising materials to the arable soils has created artificially deepened anthropogenic topsoils which can be over 1m thick. Such relict soils are found all over the world, and are widespread in north-western Europe. This work focuses on the anthropogenic soils in the Northern Isles, which were formed from the Neolithic period up until the 20th century. Three multi-period sites were investigated using thin section micromorphology, organic/inorganic phosphate analysis, soil magnetism, particle size distribution, loss on ignition and soil pH. Current views of anthropogenic soil formation, based on pedological investigation and historical documentary sources, are that they are formed as a result of the addition of domestic animal manures and turf used as animal bedding to arable areas. This project sets out to test the hypothesis that in fact anthropogenic soils are the result of a wide range of formation processes which took place over extended periods of time. The hypothesis has been tested by analysing soils and associated middens of different dates, which have been sealed and protected by blown sand deposits. The results have shown that in the Neolithic period arable soils were created by cultivating the settlement's midden heaps as well as by adding midden material to the surrounding soils. In the Bronze Age human manure, ash and domestic waste were spread onto the fields around the settlements to create arable topsoils up to 35cm thick. In the Iron Age arable agriculture was intensified by selective use of organic manures on one of the sites investigated, but organic waste material was not used as efficiently as it was in later periods, and on both sites it was allowed to accumulate within the settlements. In the Norse period, when the intensive system used in historical times appears to have originated, organic waste may have been used more efficiently. These changes appear to reflect a greater organisation of land resources and manuring strategies and increased demand for arable production over time.

Style APA, Harvard, Vancouver, ISO itp.

40

Raicevich, Sasa <1973&gt. "Assessment of ecological disturbance in marine environments". Doctoral thesis, Università Ca' Foscari Venezia, 2004. http://hdl.handle.net/10579/540.

Pełny tekst źródła

Streszczenie:

Questa ricerca ha avuto come oggetto di studio le modificazioni ecologiche indotte da un disturbo su vasta scala, analizzate a diversi livelli gerarchici di organizzazione biologica (individuo, popolazione, comunità, ecosistema). Lo scopo è stato quello di compararne l'importanza e considerare le risposte omeostatiche che conferiscono stabilità ai sistemi ecologici. Come fonte di disturbo ecologico è stata considerata l'attività di pesca demersale. A livello individuale, il processo di cattura dovuto all'azione di pesca è stato analizzato nei suoi componenti principali (danneggiamento fisico, esposizione all'aria, shock termico) considerando gli effetti singoli e sinergici rispetto ad una specie di crostaceo brachiuro Liocarcinus depurator, in termini di alterazioni metaboliche, stress a livello fisiologico, sopravvivenza ed eventuali modificazioni di alcuni moduli comportamentali (Capp. 2, 3, 4). I risultati hanno mostrato che l'esposizione all'aria ad elevate temperature determina i maggiori effetti su questo decapode, in quanto esso è adattato e diffuso in ambienti sublirtorali caratterizzati da fluttuazioni ambientali ridotte. A livello di popolazione la valutazione del danneggiamento fisico conseguente alle fasi di cattura e sorting a bordo dei pescherecci, è stata realizzata quantificando numero e tipologia delle appendici perdute, e confrontando i danneggi amenti cronici e quelli recenti in aree soggette a diverso sforzo di pesca (Ch. 5). Le analisi condotte hanno permesso di evidenziare una maggiore incidenza di danneggiamenti cronici nelle aree intensamente sfruttate. Nonostante l'elevata mortalità legata al disturbo della pesca, L. depurator è tuttora piuttosto diffuso anche in aree intensamente sfruttate. Tutto ciò è da porsi in relazione alla presenza di una sorta di "trade-off ' tra i costi energetici associati al disturbo della pesca (stress, mortalità, perdita di appendici, menomazione di alcune funzioni) ed i ridotti costi energetici di foraggiamento, associati alla capacità di questo brachiuro di nutrirsi degli organismi scartati dall'attività di pesca. Tutto ciò potrebbe rendere meno deleteri gli effetti del disturbo indotto dalla pesca conferendo una maggiore stabilità alle popolazioni disturbante. A livello intra-specifico, le caratteristiche strutturali e di stabilità dell'emocianina di L. depurator sono state considerate confrontando 7 differenti popolazioni provenienti dal mare Adriatico e dall'Oceano Atlantico Nord occidentale, mentre per un confronto inter-specifico sono state analizzate emocianine provenienti da 6 specie congeneri o appartenenti, comunque, alla famiglia dei Portunidi (Cap. 6) provenienti dalle medesime aree. I risultati hanno permesso di evidenziare una marcata eterogeneità sia a livello intra che interspecifico, che è stata messa in relazione all'ecologia delle specie (in termini di habitat occupati) ed alla variabilità ambientale delle diverse aree campionate. A livello di comunità bentonica, sono stati considerati gli aspetti funzionali in merito al processo di ricolonizzazione a seguito di un singolo evento di disturbo fisico. Le analisi sono state condotte comparativamente in due comunità del Nord Adriatico adottando uno schema sperimentale del tipo BACI ed esaminando i pattern relativi ad i principali gruppi trofici (Cap. 7). Il fenomeno di ricolonizzazione è guidato, nelle fasi iniziali, dagli "scavengers" potenziali in entrambi gli habitat, sebbene, come evidenziato mediante l'applicazione di indici termodinamici quali l'exergia, i processi coinvolti abbiano caratteristiche e tempistica sito-specifiche. Il confronto tra i siti sperimentali ed aree intensamente sfruttate contigue, ha permesso di verificare come l'intensa attività di pesca induca una riduzione della produzione e della biomassa della comunità bentonica. Gli effetti cronici dell'attività di pesca a livello di Nord Adriatico sono stati valutati comparando quantità e composizione dello scarto delle diverse attività di pesca a strascico durante il 2002 con dati storici relativi a campagne di monitoraggio della pesca e precedenti descrizioni delle comunità bentoniche (Cap. 8). Queste analisi hanno evidenziato fenomeni rilevanti quali la forte riduzione del rapporto scarto:commerciale, l'omogenizzazione della comunità bentonica e la scomparsa delle specie più vulnerabili (elevate dimensioni, crescita lenta). I risultati ottenuti hanno permesso infine di stimare in 25-35%, la frazione di produzione primaria del bacino Nord Adriatico necessaria per sostenere l'attività di pesca in tale bacino (Cap. 9). In conclusione, la ricerca realizzata ha permesso di descrivere come l'applicazione di un disturbo ecologico su vasta scala induca negli organismi delle risposte a livello individuale legate alle caratteristiche ecologiche delle specie ed alle peculiarità degli agenti di disturbo. I risultati conseguiti, hanno evidenziato come l'insieme delle relazioni dirette ed indirette influenzino le risposte dei livelli gerarchici superiori, mediante la comparsa di proprietà emergenti, quali la stabilità dinamica e le traiettorie dello sviluppo, determinando così la configurazione strutturale e funzionale delle comunità e dell'ecosistema nel suo complesso. This research focused on the effect of large-scale disturbance at several hierarchical levels of biological organisation (individual, population, community, ecosystem) and aimed to provide a comparison between the magnitude of the agents of disturbance and the homeostatic responses which confer stability on the ecological systems. Demersal fishing activity was considered as the source of ecological disturbance. At an individual level, the process of capture associated with fishing was analysed in its components (i.e. physical damage, exposure to air, thermal shock) taking into account both their individual and synergistic effects. Alterations in the metabolism and homeostatic capabilities, physiological stress, survival rates and the agonistic behaviour in the crustacean Brachyura Liocarcinus depurator were assessed (Ch. 2, 3, 4). Results highlighted that exposure to air at high temperatures during the sorting operations has the most detrimental effects on this decapod, due to the fact that L. depurator is a sublittoral species, adapted to rather stable environments. At a population level the sub-lethal injury frequencies, in terms of limbs lost resulting from the capture process, were assessed by comparing the level of chronic and recent damage (induced by the fishing activity itself) among different populations in the Northern Adriatic Sea (Ch. 5). Chronic damage was shown to be more frequent in the high fishing effort areas confirming a link with the trawl fishing activity. Notwithstanding the high damage and fishing mortality suffered in these areas, L. depurator revealed to be one of the dominant species, and this could be associated with a sort of trade-off between the high energetic costs payed by the populations due to the fishing activities (mortality, sub-lethal damages and subsequent function impairment) and the low costs associated to feeding on species discarded by the fishing activity. At an intra-specific level, the patterns of haemocyanin expression were compared among 7 populations of L. depurator from the Northern Adriatic Sea and the North West Atlantic Ocean. At an inter-specific level the haemocyanin stability of 6 species belonging to the same genus or family and collected in the same areas were carried out (Ch. 6). Results revealed an intra- and inter-specific structural variability in the sub-unit composition and stability of haemocyanins, which were to species ecology (habitat) and sampling sites environmental variability. At a community level, the shift from equilibrium and the recovery dynamics after a pulse disturbance were compared between two different benthic communities (mud and sand grounds) in the Northern Adriatic Sea, by adopting a BACI experimental scheme and paying special attention to the functional role of the trophic guilds (Ch. 7). In both habitats, the early successional stages of the recovery were driven by the potential scavengers even if, as highlighted by the application of the Exergy, some differences occurred in the patterns and timing of this process. The analyses of the benthic communities in heavily fished grounds allowed us to show that in these sites the intensive fishing activies induced a reduction in the benthic community biomass and production. At an ecosystem level, the chronic effects of fishing disturbance on the Northern Adriatic Sea were assessed by comparing the quantity and composition of the species discarded by different demersal fishing activities in 2002 to historical data from trawl surveys and the pre-existing benthic communities (Ch. 8). These analyses highlighted a steep reduction in the discard ratio (discarded catch:commercial catch) and the occurrence of a homogenisation of the benthic community and the depletion of highly vulnerable populations (large sized individuals, slow growth). The primary production required to sustain demersal fishery was estimated to be 25-35% of the total primary production of this area (Ch. 9). In conclusion, this research allowed us to show that large-scale ecological disturbance induces on organisms individual responses which depend both on the ecological features of the disturbed species and on the characteristics of the agents of disturbance. Results showed that the direct and the indirect relationshps determine the response of the higher hierarchical levels of organisation through emerging properties like their dynamic stability and development trajectories, thus determining the structure and functioning of the community and the ecosystem.

Style APA, Harvard, Vancouver, ISO itp.

41

McCallum, Barry R. "The impact of mobile fishing gear on benthic habitat and the implications for fisheries management". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ62398.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

42

Roderick, Mary J. "Ecological Restoration and Urban Planning: Integrating to end distURBANce". University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1242941905.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

43

Roderick, Mary. "Ecological restoration and urban planning integrating to end distURBANce /". Cincinnati, Ohio : University of Cincinnati, 2009. http://rave.ohiolink.edu/etdc/view.cgi?acc_num=ucin1242941905.

Pełny tekst źródła

Streszczenie:

Thesis (Master of Community Planning)--University of Cincinnati, 2009.
Advisor: Menelaos Triantafillou. Title from electronic thesis title page (viewed Aug. 18, 2009). Includes abstract. Keywords: Ecological Restoration; Urban Planning; Integration; Landscape Ecology. Includes bibliographical references.

Style APA, Harvard, Vancouver, ISO itp.

44

Michalski, Fernanda. "Ecological consequences of habitat fragmentation and disturbance in Amazonian forests". Thesis, University of East Anglia, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432441.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

45

Tomblin, David Christian. "Ecological niche responses of small mammals to gypsy moth disturbance". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06302009-040517/.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

46

Navarra, Jennifer J. "Species composition and spatiotemporal pattern of the seed bank and vegetation in native and degraded Florida rosemary scrub". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4645.

Pełny tekst źródła

Streszczenie:

Due to large pulses of recruitment immediately after fire and population decline with time-since-fire, I predicted seed density with time-since-fire would follow a unimodal function with low density in early and late years post-fire, and highest density at intermediate time-since-fire. I compared seed density data among sites with different time-since-fire: two sites each of three, six, ten and 24 years time-since-fire and three long-unburned sites (greather than]24 years). Variability in seed bank composition and density increased with time-since-fire and only recently burned stands were distinctly different from the other time-since-fire age classes. Some species and functional groups did exhibit a quadratic or cubic association to time-since-fire (ruderal herbs, subshrubs, Ceratiola ericoides, Lechea cernua, Paronychia chartacea, Phyllanthus tenellus); however, timing of the peak in seed density varied depending on life span and age of reproductive maturity. Scrub herbs were the most abundant functional group in the seed bank and showed highest density in the first ten years post-fire. This pattern corresponds to the pattern of aboveground species abundance and suggests abundances above- and belowground are closely linked. Understanding the dynamics of the seed bank in both naturally and anthropogenically disturbed communities in Florida rosemary scrub is important for the restoration of scrub habitat and management of existing populations of endangered and threatened scrub species endemic to the Lake Wales Ridge in central Florida.; The soil seed bank plays a dynamic role in the regeneration of plant communities after natural and anthropogenic disturbance. In this thesis, I addressed how disturbances influence the vegetation and seed bank of Florida rosemary scrub. In Chapter One I evaluated changes in species composition and spatiotemporal pattern of the vegetation and seed bank along a gradient of disturbance. During the summers and winters of 2007-2009 percent ground cover and seed bank species composition were assessed among replicates of three vegetation types subjected to minimal, moderate, and extreme anthropogenic disturbance (native rosemary scrub, degraded scrub, and agriculturally improved pasture, respectively). These vegetation types shared the same soil and topographic characteristics but differed in disturbance history. I found that species composition and spatial pattern varied with disturbance. In pastures the compositional and structural characteristics of rosemary scrub were lost and only native scrub species able to evade herbivory persisted in this community. Native and degraded scrub differed most from each other in species abundances and spatial pattern. Degraded scrub showed highest abundance of subshrubs and a spike moss species, while rosemary scrub was dominated by shrubs. The seed banks of scrub herbs in degraded scrub had a tendency towards a random spatial distribution that lacked association with aboveground cover. Conversely, rosemary scrub seed banks tended to have an aggregated distribution and were associated with occurrence of conspecific species aboveground, litter, and shrub cover. These results indicated a change in the spatial heterogeneity of the seed banks of scrub herbs in degraded scrub. In Chapter Two I evaluated changes in seed bank density with time-since-fire in native rosemary scrub.
ID: 028917091; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.)--University of Central Florida, 2010.; Includes bibliographical references (p. 108-123).
M.S.
Masters
Department of Biology
Sciences

Style APA, Harvard, Vancouver, ISO itp.

47

Underwood, Emma Clare. "Consequences of ecological disturbance on ground dwelling invertebrates : implications for conservation /". For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

48

O'Connor, Christopher Daniel. "Spatial and temporal dynamics of disturbance interactions along an ecological gradient". Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311565.

Pełny tekst źródła

Streszczenie:

Interactions among site conditions, disturbance events, and climate determine the patterns of forest species recruitment and mortality across landscapes. Forests of the American Southwest have undergone significant changes over a century of altered disturbance regimes, human land uses, and changing environmental conditions. This study reconstructs the interactions between fire, spruce beetle outbreaks, climate, and anthropogenic factors and their influence on the species composition, spatial extent, and structure of four upper elevation forest types. We found that fire-climate associations changed following fire exclusion and recent high-severity fires occurred during less severe conditions than in several larger, lower severity fires in the historical record. Contemporary fires are burning with higher severity than similarly-sized historical fires, suggesting a shift toward higher-severity fire as a result of changes to forest structure and fuels over much of the upper elevation forest. In high elevation forests, the area occupied by Engelmann spruce and corkbark fir doubled in size over the four decades following fire exclusion. The increase in spruce beetle outbreak size and severity in the 20th century appears to be linked to significant expansion of host extent, accelerated growth of spruce in mixed-conifer forest, and incidence of anomalously warm summer temperatures followed by up to a decade of low precipitation. Trends toward warming, drying conditions are expected to increase the risk of future high-severity outbreaks, especially in locations of recent spruce population expansion. Forest conversion from disturbance-adapted to competition-adapted species following fire exclusion was a function of site productivity. Species assemblages in the lowest and highest productivity sites were the most stable over the century following fire exclusion. Frequent low severity fires maintained the stocking of forests in moderate productivity sites below their biological potential, conferring a degree of resistance to drought, insect outbreaks, and high-severity fire prior to fire exclusion. Current forests located on moderate productivity sites are now the most vulnerable to drought and future disturbance. Aggressive action to restore historical species composition, stocking and fire component of these forests may return resilience to this system in the face of projected changes to fire and climate dynamics.

Style APA, Harvard, Vancouver, ISO itp.

49

Schmitt, Susanne F. "Disturbance and succession on the Krakatau Islands, Indonesia". Thesis, University of Oxford, 1997. http://ora.ox.ac.uk/objects/uuid:a2b3257d-0a00-4286-a38a-01e3016da708.

Pełny tekst źródła

Streszczenie:

This thesis set out to investigate the influence of disturbance on the succession of the Krakatau islands (Rakata, Sertung, Panjang). The hierarchical model of succession by S. Pickett and colleagues (1987) was adopted as a research framework, and provided the basis for an alternative model of succession on Krakatau that focuses on processes rather than successional pathways. Investigations were conducted on (i) the meso-scale, and (ii) the patch-scale, (i) quantified the recent disturbance regime, and inter- and intra-island differences in diversity, (ii) compared sapling performance (growth, mortality and recruitment), and species compositional patterning in space and time for saplings and the seed bank with respect to island, gap size and severity of disturbance. Multivariate techniques were used, and amongst other attempts at characterising the light environment, hemispherical photography was employed. For the first time the effect of a continuous period of volcanic activity (1992-1995) of Anak Krakatau could be directly quantified and compared between Panjang and Sertung (ash-affected) and Rakata (receiving no ash). Increased rates of gap formation in the volcanically active period in comparison to the previous decade were found for all islands. This supports the disturbance-driven model of Whittaker and colleagues. However, an extension is required, because, contrary to expectation, Rakata also experienced more disturbance. This increase is argued to be a result of more severe weather conditions, and an increased number of earth tremors, during times of volcanic activity. The disturbance factors of extreme climatic events (e.g. ENSO events) and human impact are also proposed for inclusion in the alternative model. Drought associated with the 1994 El Niño is of relevance to short-term and potential long-term impact on regeneration dynamics and succession. Attention was drawn to the local human influence of pumice mining on the coastal forests. Supporting previous findings on the plot- and whole island scales, data from species presence/absence transects established that species richness and beta-diversity on the ash- affected islands was also lower on the meso-scale. Panjang's canopy composition is less uniform, and locally more species-rich than Sertung's. More evidence of the suggested decline of the mono-dominant species Neonauclea calycina and Timonius compressicaulis was gathered. The third dominant, Dysoxylum gaudichaudianum, is expanding in the lowlands of all islands. This is aided by its ability to regenerate in moderate shade, to grow rapidly in gap environments, and its tolerance of ash-fall, drought and herbivory. However, on Rakata, it is not expected to become generally mono-dominant because a considerable number of other potential canopy species are present. Sapling performance and species composition and its changes were in general strongly affected by ash-fall and drought. These factors tended to override effects of gap size and severity of disturbance. Advance regeneration, and the composition of the local forest type were identified as important factors influencing the composition of the early stages of gap-fill. The local forest type also seemed to contribute most to seed bank composition. As rarer species tended to have clumped distributions, and 'safe sites' for regeneration seemed not to be limiting, dispersal constraints were argued to be the most likely factors slowing diversification, unless further severe volcanic disturbance leads to successional set-back. The latter also strongly limits the predictability of succession on Krakatau.

Style APA, Harvard, Vancouver, ISO itp.

50

Pearson, Neil. "Ecological genetics of Arabidopsis thaliana from reservoir populations in low-disturbance habitats". Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/61699/.

Pełny tekst źródła

Streszczenie:

The Arabidopsis HapMap project, and follow-on work carried out by the Bergelson and Nordborg groups, established in broad outline the demographic history and population structure of wild Arabidopsis thaliana. Genome‐wide association studies are likewise making considerable advances in identifying genes associated with ecologically significant traits, and thus in identifying candidate genes likely to be under the action of natural selection. The aim of this project has been to further expand and combine these lines of investigation, by using genomic data to test ecological hypotheses and to grant more complete insight into the rangeof selection pressures acting upon wildpopulations. A method to measure and elucidate the genetic similarity of genomic regions between sampled accessions was therefore developed to facilitate this. 250K SNP data from RegMap accessions was then examined for evidence of patterns of migration and gene flow across Europe. Those observations formed the basis of a simple model of the history of the UK population relative to that of Europe. Comparisons of observed genotypes against expectations derived from the modelallowed the identification of genomic regions under the influence of selection. Loci corresponding to signatures of selection indicated positive selection acting upon phenotypes of disease resistance, flowering time, and seed size.

Style APA, Harvard, Vancouver, ISO itp.

Rozprawy doktorskie na temat „Ecological disturbances”

Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych