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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Identification of Gypsy Moth Defoliation in Ohio Using Landsat Data

Hurley, Angela Lorraine 31 July 2003 (has links)
No description available.
12

Spatio-Temporal Vegetation Change as related to terrain factors at two Glacier Forefronts, Glacier National Park, Montana

Lambert, Callie Brooke 01 February 2019 (has links)
Glacier retreat is considered a clear sign of global climate change. Although a rich body of work has documented glacial response to climate warming trends, comparatively little research has assessed vegetation change in recently deglaciated areas. In this study, we assess vegetation change at two glacier forefronts in Glacier National Park, Montana, through remote sensing analysis, fieldwork validation, and statistical modelling. The research objectives were to: 1) quantify the spatial and temporal patterns of landcover change of five classes"ice, rock, tree, shrub, and herbaceous at the two glacier forefronts in Glacier National Park, and 2) determine the role of selected biophysical terrain factors (elevation, slope, aspect, solar radiation, flow accumulation, TWI, and geology) on vegetation change at the deglaciated areas. Landsat imagery of the study locations in 1991, 2003, and 2015 were classified and validated using ground truth points and visual interpretation for accuracy. Overall accuracies were above 75% for all classified images. To identify biophysical correlates of change, we used generalized linear mixed models with non-vegetated surfaces to vegetation (code=1) or stable non-vegetation class (code=0) as a binary response variable. Results revealed elevation, slope, TWI, geology, and aspect to be associated with increased vegetation over time at Jackson Glacier forefront, whereas elevation, slope, solar radiation, and geology were significant at Grinnell Glacier forefront. New case studies on vegetation change in recently deglaciated regions can deepen our knowledge about how glacier retreat at local scales results in recharged ecosystem dynamics. / Master of Science / Glacier retreat is considered a clear sign of global climate change. Although glaciers are retreating globally, comparatively little research has assessed how vegetation changes in recently deglaciated areas. The research objectives were to: 1) quantify patterns of landcover change of five classes—ice, rock, tree, shrub, and herbaceous at two glacier forefronts in Glacier National Park, and 2) determine the environmental and terrain factors that affect vegetation change at the deglaciated areas. Landsat imagery of the study locations in 1991, 2003, and 2015 were classified and validated using ground truth points and visual interpretation for accuracy. To identify terrain and environmental factors that influence change, we modeled change from nonvegetated surfaces to vegetation (code=1) and the stable non-vegetation class (code=0). Results revealed elevation, slope, topographic moisture, geology, and aspect to be associated with increased vegetation over time at Jackson Glacier forefront. Elevation, slope, solar radiation, and geology were significant at Grinnell Glacier forefront, indicating some geographic differences in important factors. New case studies on vegetation change in recently deglaciated regions can deepen our knowledge about how glacier retreat at local scales results in recharged ecosystem dynamics. This study provides further insight on the future of alpine ecosystems as they respond to global climate change and a compelling new perspective on the future of the Park. Additionally, we demonstrate the benefits of using remote sensing applications to study land cover change as a proxy for vegetation colonization, especially in remote mountainous environments.
13

Vegetation change analysis and ecological recovery of the copperbelt Miombo woodland of Zambia

Syampungani, Stephen 03 1900 (has links)
Thesis (PhD (Forest and Wood Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The study aimed at developing a new understanding of the Miombo woodland recovery dynamics when exposed to single tree selection, slash & burn agriculture and charcoal production. Five specific studies were conducted to examine different parts of this overall study: Miombo woodland utilization, management and conflict resolution among stakeholders; speciesstem curves as a tool in sampling the development of Miombo woodland species richness in charcoal and slash & burn regrowth stands over time; the impact of human disturbance on the floristic composition of Miombo woodland; regeneration and recruitment potentials of key Miombo woodland species after disturbance; and age and growth rate determination using selected Miombo woodland species. Different methods were developed for each specific study. The study of woodland utilization and management employed semi-structured and key informant interviews. STATISTICA statistical package version 6.0 was used for data collation and analysis. Chi-square tests were used to show levels of significance in differences that existed between different user groups. Species-stem curves were used to determine the sample size to assess Miombo woodland dynamics in regrowth stands after slash & burn and charcoal production, and a fixed-area method was used for the mature woodland stands. The study sites in each of three study areas were selected to represent ages ranging from 2 to 15+ years since each disturbance was terminated. The undisturbed woodland was chosen to act as a control. Various analyses using the STATISTICA statistical package and CANOCO version 4.0 were conducted to understand responses of Miombo woodland to these different disturbances. The research revealed that single tree selection, slash & burn agriculture and charcoal production are the main forms of Copperbelt Miombo woodland utilization which will always be there. Additionally, the the Miombo woodland stands were characterized based on the size class profile they exhibit on exposure to human disturbance factors through forest utilization. The characterization has revealed that the woodland is dominated by light demanding species. As such single tree selection harvesting does not support the regeneration and establishment of the timber species which are canopy species under shade conditions. This implies that selection harvesting of timber species, although it appears to be a non event in terms of disturbance at stand level may be a disaster at population level. The study also revealed that clearing of the woodland for either slash & burn agriculture or charcoal production results in enhanced regeneration and establishment of the dominant Miombo woodland species. The study concludes that charcoal production and slash & burn agriculture are important components to which the woodland ecosystem is adapted. As such these disturbance factors may be considered as incorporated disturbances. It is recommended from the study that woodland utilization and management should integrate charcoal production and slash & burn agriculture into forest management. Cutting cycles should be based on growth rate of the selected species. Timber species harvesting should go side by side with these disturbance factors so as to open up the canopy in order that maximum sunlight can reach the regeneration stock. The study also brings out the other management and utilization opportunities (such as managing for Uapaca kirkiana and Anisophyllea boehmii fruits) that arise from different development stages of the woodland. Lastly, it is recommended to ascertain the optimum gap sizes for both charcoal production or slash & burn agriculture which would still support the Miombo woodland recovery. / AFRIKAANSE OPSOMMING: Hierdie studie is gedoen om ‘n nuwe begrip te ontwikkel vir die hersteldinamika van Miombo boomveld na onderwerping aan enkelboomseleksie, kap & brand lanbou en houtskoolproduksie. Vyf spesifieke studies is gedoen om verskillende komponente van die total studie te ondersoek: benutting, bestuur en konflikresolusie tussen gebruikers van Miombo boomveld; species-stam kurwes as ‘n instrument in die bemonstering van die ontwikkeling van Miombo boomveld species-rykdom oor tyd na afloop van houtskoolproduksie en kap & brand landbou; die impak van menslike versteuring op die floristiese samestelling van Miombo boomveld; verjongingspotensiaal van sleutelsoorte in Miombo boomveld na versteuring; en bepaling van ouderdom en groeitempo in ge-selekteerde Miombo boomveldsoorte. Verskillende metodes is ontwikkel vir elke spesifieke studie. In die studie van boomveldgebruik en –bestuur is semigestruktureerde en sleutel-informant onderhoude gebruik. Die STATISTICA statistiese packet weergawe 6.0 is gebruik vir dataverwerking en -ontleding. Chi-kwadraat toetse is gebruik om vlakke van betekenisvolheid te toon wat bestaan tussen verskillende gebruikersgroepe. Speciesstamkruwes is gebruik om monstergrootte te bepaal vir die evaluering van Miombo boomvelddinamika in hergroeiopstande na kap & brand en houtskoolproduksie, terwyl vastegrootte persele gebruik is vir volwasse boomveldopstande. Die studieplekke in elk van drie studiegebiede is geselekteer om verskillende ouderdomme tussen 2 en 15+ jaar na be-eindiging van die versteuring te verteenwoordig. Onversteurde boomveld is gebruik as kontrole. Verskeie ontledings, met die STATISTICA statistiese pakket en CANOCO weergawe 4.0 is gedoen om die reaksie van Miombo boomveld op die verskillende versteurings te verstaan. Die navorsing het getoon dat enkelboomseleksie, kap & brand landbou en houtskoolproduksie is die hoof vorme van Copperbelt Miombo boomveld benutting wat altyd daar sal wees. Verder is die Miombo boomveldopstande gekarakteriseer gebaseer op die grootteklasprofiel wat hulle vertoon na menslike versteuringsfaktore in die vorm van boomveldbenutting. Die karakterisering het getoon dat die boomveld gedomineer word deur ligeisende soorte. Daarom ondersteun enkelboomseleksie nie die verjonging en vestiging van die dominante houtsoorte wat kroonsoorte is onder skadutoestande. Dit impliseer dat selektiewe inoesting van houtsoorte, alhoewel dit voorkom as ‘n onbelangrike gebeurtenis in terme van versteuring op opstandsvlak, ‘n ramp is op populasievlak. Die studie het ook getoon dat skoonmaak van die boomveld vir of kap & brand landbou of houtskoolproduksie, lei tot verbeterde verjonging en vestiging van die dominante Miombo boomveldsoorte. Die studie lei tot die gevolgtrekking dat houtskoolproduksie en kap & brand landbou belangrike komponente is waarby die boomveldsisteem aangepas is. Daarom kan hierdie versteuringsfaktore beskou word as ingeslote versteurings. Vanuit die studie word daarom aanbeveel dat boomveldbenutting en –bestuur houtskoolproduksie en kap & brand landbou binne die bosbestuur integreerd moet word. Kapsiklusse moet gebaseer word op die groeitempos van geselekteerde soorte. Inoesting van houtsoorte moet saamloop met hierdie versteuringsfaktore sodat die kroondak oopgemaak kan word sodat maksimum sonlig die verjonging bereik. Die studie bring ook na vore die bestuur en benuttingsgeleenthede (soos bestuur vir die vrugte van Uapaca kirkiana en Anisophyllea boehmii) wat voorkom in verskillende ontwikkelingstadiums van die boomveld. Laastens word aanbeveel dat die optimum openinggroottes vir beide kap & brand en houtskoolbereiding wat herstel van Miombo boomveld ondersteun, bepaal.
14

An Evaluation of the Effectiveness of Multiple Approaches to Long-Term Change Detection Applicable to Southwestern United States: A Case Study of the San Simon Watershed

Garcia, Denise Tanya January 2012 (has links)
Watersheds in the Southwest, particularly the San Simon Watershed in Arizona, have been experiencing degradation since the turn of the century through processes of erosion and vegetation change. Mitigation and management actions rely on long-term assessment of landcover change; however, traditional methods of ground assessment are time-consuming and specific to particular sites. Remote sensing techniques can be an alternative method to assess landcover change over extensive areas. Forage inventory surveys and historical monitoring data were assessed for utility in landcover change detection. The contemporary remotely-sensed classifications included 2001 SwReGAP data and a CART classification of 2010 Landsat TM data. The CART classification was aided by shrub cover analysis of NAIP aerial photography. It was found that 1930s Grazing inventories were compatible with contemporary satellite image classifications for large-scale landcover change detection.
15

Understanding structure and function in semiarid ecosystems : implications for terrestrial carbon dynamics in drylands

Cunliffe, Andrew Michael January 2016 (has links)
This study advances understanding of how the changes in ecosystem structure and function associated with woody shrub encroachment in semi-arid grasslands alter ecosystem carbon (C) dynamics. In terms of both magnitude and dynamism, dryland ecosystems represent a major component of the global C cycle. Woody shrub encroachment is a widespread phenomenon globally, which is known to substantially alter ecosystem structure and function, with resultant impacts on C dynamics. A series of focal sites were studied at the Sevilleta National Wildlife Refuge in central New Mexico, USA. A space-for-time analogue was used to identify how landscape structure and function change at four stages over a grassland to shrubland transition. The research had three key threads: 1. Soil-associated carbon: Stocks of organic and inorganic C in the near-surface soil, and the redistribution of these C stocks by erosion during high-intensity rainfall events were quantified using hillslope-scale monitoring plots. Coarse (>2 mm) clasts were found to account for a substantial proportion of the organic and inorganic C in these calcareous soils, and the erosional effluxes of both inorganic and organic C increased substantially across the vegetation ecotone. Eroded sediment was found to be significantly enriched in organic C relative to the contributing soil with systematic changes in OC enrichment across the vegetation transition. The OC enrichment dynamics observed were inconsistent with existing understanding (derived largely from reductionist, laboratory-based experiments) that OC enrichment is largely insignificant in the erosional redistribution of C. 2. Plant biomass: Cutting-edge proximal remote sensing approaches, using a remotely piloted lightweight multirotor drone combined with structure-from-motion (SfM) photogrammetry were developed and used to quantify biomass carbon stocks at the focal field sites. In such spatially heterogeneous and temporally dynamic ecosystems existing measurement techniques (e.g. on-the-ground observations or satellite- or aircraft-based remote sensing) struggle to capture the complexity of fine-grained vegetation structure, which is crucial for accurately estimating biomass. The data products available from the novel SfM approach developed for this research quantified plants just 15 mm high, achieving a fidelity nearly two orders of magnitude finer than previous implementations of the method. The approach developed here will revolutionise the study of biomass dynamics in short-sward ecogeomorphic systems. 3. Ecohydrological modelling: Understanding the effects of water-mediated degradation processes on ecosystem carbon dynamics over greater than observable spatio-temporal scales is complicated by significant scale-dependencies and thus requires detailed mechanistic understanding. A process-based, spatially-explicit ecohydrological modelling approach (MAHLERAN - Model for Assessing Hillslope to Landscape Erosion, Runoff and Nutrients) was therefore comprehensively evaluated against a large assemblage of rainfall runoff events. This evaluation highlighted both areas of strength in the current model structure, and also areas of weakness for further development. The research has improved understanding of ecosystem degradation processes in semi-arid rangelands, and demonstrates that woody shrub encroachment may lead to a long-term reduction in ecosystem C storage, which is contrary to the widely promulgated view that woody shrub encroachment increases C storage in terrestrial ecosystems.
16

The effects of fire on the characteristics of woody vegetation and encroachment in an African savanna

Devine, Aisling Patricia January 2015 (has links)
African savannas have experienced considerable woody encroachment over the last century, presenting an increasing problem from both ecological and socioeconomic viewpoints. Despite decades of work by savanna ecologists, the reasons for woody encroachment remain unclear. A major barrier to understanding the causes is the difficulty of disentangling the effects of broader-scale environmental changes, such as climate change and associated increases in atmospheric CO2, from localised effects such as fire. In this thesis I examine the effects of sixty years of experimental burning on the characteristics of woody vegetation in two climatically distinct African savannas, a wet and a dry savanna, to examine how long-term burning interacts with other potential drivers of woody encroachment. I examine tree abundance, woody cover, tree structure, diversity and community composition under four different fire regimes: annual, biennial, triennial and fire exclusion. Differences between sites and plots subject to different burning regimes are compared along with changes in these differences through time. Additionally, variation in the densities of Acacia, Combretum, Terminalia and Dichrostachys species were examined to establish how dominant species, particularly those responsible for encroachment, are affected by fire. Overall, I found that the effects of fire depend on savanna type. Fire lowered tree abundance and woody cover much more in the wet savanna than in the dry savanna. However, the maximal height of trees was much more constrained by increased fire frequency in the dry savanna than in the wet savanna. Woody encroachment occurred across both savanna types during the sixty year time period, but was much more rapid at the wet savanna. Additionally, encroaching species of Dichrostachys cinerea and Terminalia sericea in the wet savanna were shown to be more difficult to manage using fire. Overall as fire regimes were kept constant over the last sixty years, yet woody encroachment occurred across all fire treatments, it is most likely that an external driver is responsible. Rainfall change in both areas was minimal over the duration of the study, thus increased atmospheric CO2 would appear to be the most likely cause of woody encroachment. However, the magnitude and characteristics of woody encroachment are strongly mediated by fire and rainfall. Wet savannas would appear to be much more vulnerable to woody encroachment and existing management strategies are likely to become increasingly ineffective at keeping woody cover below potential maximum levels. Overall this thesis demonstrates that the effects of fire on woody vegetation in savannas vary depending on regional differences in rainfall and that processes of woody encroachment differ depending on savanna type.
17

Late Quaternary Glacier Fluctuations and Vegetation Change in the Northwestern Ahklun Mountains, Southwestern Alaska

Axford, Yarrow L. 01 May 2000 (has links)
This research examines moraine and lacustrine records of glacier fluctuations, in combination with palynological records of vegetation change, from the previously unstudied northwestern Ahklun Mountains in southwestern Alaska. Morain mapping reveals that ice-cap outlet glaciers in the study area extended ca. 60 km from the center of the Ahklun Mountians ice dome during the early Wisconsin (sensu lato), and ca. 40 km during the late Wisconsin. Correlations with well-studied moraines in the southern Ahklun Mountains indicate an asymmetry of glaciation over the range, with ice-cap outlet glaciers more extensive to the south. This asymmetry was more striking during the early Wisconsin (s.l.) than during the late Wisconsin. Alpine glaciers have repeatedly advanced from cirques within the study area. Because these alpine glaciers were confluent or sub-confluent with outlet glaciers during the late Wisconsin maximum, the alpine-glacier moraine record is relatively young. Lacustrine sedimentology from Little Swift Lake records significant retreat of alpine glaciers ca 12.8 ka (coeval with the onsent of the North Atlantic Younger Dryas). Moraines upvalley of the lake suggests a minor glacier (or rock glacier) advance occurred ca 5.5 ka. Lacustrine records of vegetation from Little Swift Lake extend back to ca. 13.4 ka. Most vegetation changes resulted from the post-glacial spread of trees and shrubs, including Betula, alnus, and Picea, to their modern ranges. However, pollen assemblages and other paleoclimate proxies suggest some major changes in late-glacial and Holocene climate. Major vegetation change, most notably the dramatic expansion of Poaceae, occurred ca. 100 yr after the 12.8-ka glacier retreat and persisted for more than 2 ka. The inferred reversal to dry (and possibly cool) climate was followed by a period of exceptionally productive mesic conditions during the early Holocene, ca. 11 to 9 ka. The pattern of latest-Quaternary climate changes documented in this study may be evidence that, as previous workers have concluded regarding the Pleistocene glaciations, the late-glacial and early Holocene climate of the Ahklun Mountains region was strongly modulated by changes in the proximity and temperature of the Bering Sea.
18

TEMPERATURE AND PRECIPITATION CONTROLS OVER SOIL, LEAF AND ECOSYSTEM LEVEL CO2 FLUX ALONG A WOODY PLANT ENCROACHMENT GRADIENT

Barron-Gafford, Greg Alan January 2010 (has links)
Woody plant encroachment (WPE) into historic grasslands not only alters ecosystem structure but also yields a mosaic of vegetative growth-forms that differ in their inherent physiological capacities and physical attributes. C₃ plants tend to have a relatively broad range of temperature function but at the expensive of a lower optimum rate of photosynthesis. In contrast, C₄ grasses have a greater capacity for maximum uptake but across a relatively narrow range of temperatures. In considering which of these functional groups will outcompete the other within these regions undergoing WPE, one must account not only for these leaf physiological traits, but also the growth form induced differences in rooting depth, and therefore, potential access to deeper subsurface water. Laid upon these competitive interactions is an ever-changing environment, which for the semiarid southwestern US is predicted to become progressively warmer and characterized by highly variable precipitation with longer interstorm periods. In addition to aboveground changes in CO₂ assimilation, WPE influences soil nutrient, water, and carbon cycling. The objectives of this dissertation were to quantify: (1) the influence that temperature and available soil moisture have on regulating soil respiratory efflux within the microhabitats that results from WPE to estimate the influence this vegetative change will have on ecosystem CO₂ efflux; (2) the sensitivity of CO₂ uptake within grassland and woodland ecosystems to temperature and precipitation input in an effort to characterize how WPE might influence regional carbon and water balance; and (3) the role access to stable groundwater has in regulating the temperature sensitivity of ecosystems and their component fluxes. Major findings and contributions of this research include illustrating seasonal patterns of soil respiration within the microhabitats that result from WPE, such that an analysis of the relative contributions of these different components could be made. We found that soil respiration was not only consistently greater under mesquites, but that the relative contributions of these microhabitats varied significantly throughout the year, the duration of soil respiration after each rain was habitat-specific, and that the relationship between soil respiration and temperature followed a hysteretic pattern rather than a linear function (Appendix A). We found that a woodland ecosystem demonstrated a lower temperature sensitivity than a grassland across all seasonal periods of varying soil moisture availability, and that by maintaining physiological function across a wider range of temperatures throughout periods of limited precipitation, C₃ mesquites were acquiring large amounts of carbon while C₄ grasses were limited to functioning within a narrower range of temperatures (Appendix B). Finally, we found that having a connectivity to stable groundwater decoupled leaf and ecosystem scale temperature sensitivities relative to comparable sites lacking such access. Access to groundwater not only resulted in the temperature sensitivity of a riparian shrubland being nearly half that of the upland site throughout all seasonal periods, but also actual rates of net ecosystem productivity and leaf level rates of photosynthesis being dramatically enhanced (Appendix C).
19

Habitat ecology and long-term development of the macrophyte vegetation of north-west German streams and rivers since the 1950s

Steffen, Kristina 28 May 2013 (has links)
Diese Arbeit behandelt die Charakterisierung der Habitate und die Langzeit-Entwicklung über sechs Jahrzehnte der Makrophytenvegetation nordwestdeutscher Bäche und Flüsse, um zum Wissen über die Ökologie aquatischer Makrophyten beizutragen und sie als Bioindikatoren zu nutzen. Siebzig Bäche und Flüsse der Regionen Ems-Hunte Geest, Lüneburger Heide, Allerflachland, nördliches Harzvorland, Fuß des Weser-Leine Berglandes und ostholsteinisches Hügelland sind Bestandteil der Studie, wobei der Schwerpunkt auf der überregionalen Betrachtungsebene liegt. Aus der Analyse der Zusammensetzung und Verbreitung der Makrophytengesellschaften im Zusammenhang mit Gewässergröße und physikalischen und chemischen Wasser- und Sedimenteigenschaften schlossen wir, dass Gewässertiefe und Fließgeschwindigkeit von den gemessenen Variablen den größten Einfluss auf die heutige Gesellschaftszusammensetzung haben, gefolgt vom Gehalt pflanzenverfügbaren Phosphors im Sediment. Es ist jedoch nicht auszuschließen, dass vor der im Untersuchungsgebiet seit den 1950ern stattfindenden, starken Intensivierung der landwirtschaftlichen Nutzung, als noch ausgeprägtere Gradienten bei den Nährstoffgehalten der Fließgewässer existiert haben, chemische Größen einen stärkeren Einfluss auf die Makrophytenvorkommen hatten als heute. Mittels semi-permanenter Dauerflächen haben wir den Vegetationswandel zwischen den 1950ern und 2010 untersucht und einen dramatischen Rückgang der Artenvielfalt festgestellt (der Gesamtartenpool sank um 27.5 % von 51 auf 37 Hydrophytenarten, die Artenzahl pro Aufnahmefläche um 19.4 % von 4.7 auf 3.8 Arten), begleitet von einem umfassenden Bestandsumbau vom Vorherrschen wurzelnder (v.a. potamider) Arten zur Dominanz freischwimmender (v.a. lemnider) Arten. Oligotraphente Arten wie Potamogeton gramineus und P. polygonifolius sind in den Probeflächen ausgestorben und die mesotraphenten Arten Myriophyllum alterniflorum und Ranunculus peltatus in ihrer Auftretenshäufigkeit um mehr als 50 % zurückgegangen, während die eutraphenten Arten Myriophyllum spicatum und Spirodela polyrhiza um mehr als 100 % zugenommen haben. In den Artmerkmalen Blattausdauer und spezifische Blattfläche (SLA) wurden Änderungen festgestellt: In den historischen Makrophytenbeständen der 1950er waren immergrüne Arten und Arten mit dünnen Blättern oder solchen mit viel arenchymatischem Gewebe häufig (große SLA), während die rezenten Bestände von 2010 durch sommergrüne Arten und solche mit robuster Struktur (geringe SLA) gekennzeichnet sind. Die Veränderungen in der Arten-zusammensetzung waren am tiefgreifendsten in der Region Ems-Hunte Geest, wo weitläufige Niedermoore durch Entwässerung insbesondere seit der Eindeichung des Dümmer Sees (1953) intensiv bewirtschaftetem Agrarland gewichen sind, und weniger ausgeprägt in der Lüneburger Heide, einer der wenigen Tieflandsregionen Deutschlands, in der noch Fließgewässer mit kaum durch den Menschen veränderter Struktur zu finden sind. Auf der syntaxonomischen Ebene zeigte die Anwendung zweier unterschiedlicher pflanzensoziologischer Klassifikationssysteme tiefe Veränderungen in der Struktur der Makrophytengesellschaften über sechs Jahrzehnte auf. Alle dokumentierten Vegetations-bestände konnten einer der Klassen Potamogetonetea, Lemnetea, Phragmitetea oder Fontinalietea zugeordnet werden. Während Batrachietalia/Batrachion und Potamogetonetalia /Potamogetonion-Bestände stark zurückgegangen sind, haben Nymphaeetalia/Nymphaeion-Gesellschaften zugenommen. Die beobachtete Zunahme pflanzensoziologisch schwach charakterisierter Bestände (Fragmentgesellschaften) deutet auf Verluste bei den hoch-spezialisierten Arten hin. Im Schnitt waren sich die rezenten Vegetationsbestände signifikant ähnlicher (SBC=0.25) als die historischen (0.22), was eine Homogenisierung der Fließgewässervegetation Nordwestdeutschlands offenbart. Beschleunigte Eutrophierungsprozesse in den Gewässern und wasserbauliche Maßnahmen in der intensiv genutzten Kulturlandschaft haben zu einer Uniformierung der Fließgewässerhabitate geführt, worin neben häufigen Störereignissen die Hauptursache für die Verluste in Artenreichtum und Vielfalt der Makrophytenvegetation gesehen werden kann. Weitere Anstrengungen zur Reduzierung der Nährstofffrachten, sowie eine Erhöhung der Habitatheterogenität durch strukturverbessernde Renaturierungsmaßnahmen und ökologisch verträgliche Unterhaltungstechniken und -zeitpunkte sind notwendig, um den Diversitäts-rückgang in der Makrophytenvegetation nordwestdeutscher Bäche und Flüsse aufzuhalten und umzukehren. Eine artenreiche Vegetation ist ein wichtiger Baustein in Fließgewässer-Ökosystemen, deren Funktionsfähigkeit nicht zuletzt auch für das menschliche Wohlergehen von Bedeutung ist.
20

A Multitemporal Analysis of Georgia's Coastal Vegetation, 1990-2005

Breeden, Charles, III F 17 April 2008 (has links)
Land and vegetation changes are part of the continuous and dynamic cycle of earth system variation. This research examines vegetation changes in the 21-county eco-region along coastal Georgia. The Advanced Very High Resolution Radiometer (AVHRR) with Normalized Difference Vegetation Index (NDVI) data is used in tandem with a Principal Component Analysis (PCA) and climatic variables to determine where, and to what extent vegetation and land cover change is occurring. This research is designed around a 16 year time-series from 1990-2005. Findings were that mean NDVI values were either steady or slightly improved, and that PC1 (Healthiness) and PC2 (Time-Change) explained nearly 99 percent of the total mean variance. Healthiness declines are primarily the result of expanding urban districts and decreased soil moisture while increases are the results of restoration, and increased soil moisture. This research aims to use this analysis for the assessment of land changes as the conduit for future environmental research.

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