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1
Eliasson, Jacob. "Vegetation på dammar". Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-66827.
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2
Green, Janet Alexis. "An application of predictive vegetation mapping to mountain vegetation in Sweden". Texas A&M University, 2005. http://hdl.handle.net/1969.1/3089.
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Predictive vegetation mapping was employed to predict the distribution of vegetation
communities and physiognomies in the portion of the Scandinavian mountains in
Sweden. This was done to address three main research questions: (1) what
environmental variables are important in structuring vegetation patterns in the study
area? (2) how well does a classification tree predict the composition of mountain
vegetation in the study area using the chosen environmental variables for the study? and
(3) are vegetation patterns better predicted at higher levels of physiognomic
aggregation? Using GIS, a spatial dataset was first developed consisting of sampled
points across the full geographic range of the study area. The sample contained existing
vegetation community data as the dependent variable and various environmental data as
the independent variables thought to control or correlate with vegetation distributions.
The environmental data were either obtained from existing digital datasets or derived
from Digital Elevation Models (DEMs). Utilizing classification tree methodology, three
model frameworks were developed in which vegetation was increasingly aggregated into
higher levels of physiognomic organization. The models were then pruned, and
accuracy statistics were obtained. Results indicated that accuracy improved with increasing aggregation of the dependent variable. The three model frameworks were
then applied to the Abisko portion of the study area in northwestern Sweden to produce
predictive maps which were compared to the current vegetation distribution.
Compositional patterns were critically analyzed in order to: (1) assess the ability of the
models to correctly classify general vegetation patterns at the three levels of
physiognomic classification, (2) address the extent to which three specific ecological
relationships thought to control vegetation distribution in this area were manifested by
the model, and (3) speculate as to possible sources of error and factors affecting
accuracy of the models.
3
Lloyd, D. "An evaluation of small scale shortwave vegetation index imagery for vegetation mapping". Thesis, University of Bristol, 1988. http://hdl.handle.net/1983/d1ea0ff2-2c0d-4b41-849c-bd8ce3c3649f.
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4
Roderick, Michael L. "Satellite derived vegetation indices for monitoring seasonal vegetation conditions in Western Australia". Thesis, Curtin University, 1994. http://hdl.handle.net/20.500.11937/518.
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The monitoring of continental and global scale net primary production remains a major focus of satellite-based remote sensing. Potential benefits which follow are diverse and include contributions to, and improved scientific understanding of, ecological systems, rangeland management, famine warning, agricultural commodity trading, and the study of global climate change.A NOAA-AVHRR data set containing monthly observations of green vegetation cover over a ten year period was acquired and analysed, to extract information on seasonal conditions. The data were supplied as a vegetation index, commonly known as the Normalised Difference Vegetation Index (NDVI), with a spatial resolution of approximately five km. The data set was acquired from three different satellites, and calibration problems were known to exist. A new technique was developed to estimate, and subsequently remove, the calibration bias present in the data.Monthly rainfall measurements were used as surrogate ground truth to validate the NDVI data. For regions of native vegetation, linear models relating NDVI to previous rainfall were derived, using transfer function techniques in common use in systems engineering. The models demonstrate that, in mid-latitude regions, the NDVI is a linear function of rainfall recorded over the preceding seven or eight months.Annual summaries of the image data were developed to highlight the amount and timing of plant growth. Three fundamental questions were posed as an aid to the development of the summary technique: where, when and how much? These summaries highlight the extraordinary spatial and temporal variations in plant growth, and hence rainfall, over much of Western Australia each year.Standard analysis techniques used in time series analysis, such as classical decomposition, were successfully applied to the analysis of NDVI time series. These techniques highlighted structural differences in the image data, due to land use, climatic factors and vegetation type.Overall, the results of the research undertaken in this study, using NOAA-AVHRR data in Western Australia, demonstrate that vegetation indices acquired from satellite platforms can be used to monitor continental scale seasonal conditions in an effective manner. As a consequence of these results, further research using this type of data is proposed in rangeland management and climate change modelling.
5
Roderick, Michael L. "Satellite derived vegetation indices for monitoring seasonal vegetation conditions in Western Australia". Curtin University of Technology, School of Surveying and Land Information, 1994. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=14815.
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The monitoring of continental and global scale net primary production remains a major focus of satellite-based remote sensing. Potential benefits which follow are diverse and include contributions to, and improved scientific understanding of, ecological systems, rangeland management, famine warning, agricultural commodity trading, and the study of global climate change.A NOAA-AVHRR data set containing monthly observations of green vegetation cover over a ten year period was acquired and analysed, to extract information on seasonal conditions. The data were supplied as a vegetation index, commonly known as the Normalised Difference Vegetation Index (NDVI), with a spatial resolution of approximately five km. The data set was acquired from three different satellites, and calibration problems were known to exist. A new technique was developed to estimate, and subsequently remove, the calibration bias present in the data.Monthly rainfall measurements were used as surrogate ground truth to validate the NDVI data. For regions of native vegetation, linear models relating NDVI to previous rainfall were derived, using transfer function techniques in common use in systems engineering. The models demonstrate that, in mid-latitude regions, the NDVI is a linear function of rainfall recorded over the preceding seven or eight months.Annual summaries of the image data were developed to highlight the amount and timing of plant growth. Three fundamental questions were posed as an aid to the development of the summary technique: where, when and how much? These summaries highlight the extraordinary spatial and temporal variations in plant growth, and hence rainfall, over much of Western Australia each year.Standard analysis techniques used in time series analysis, such as classical decomposition, were successfully applied to the analysis of NDVI time series. These techniques highlighted ++structural differences in the image data, due to land use, climatic factors and vegetation type.Overall, the results of the research undertaken in this study, using NOAA-AVHRR data in Western Australia, demonstrate that vegetation indices acquired from satellite platforms can be used to monitor continental scale seasonal conditions in an effective manner. As a consequence of these results, further research using this type of data is proposed in rangeland management and climate change modelling.
6
Helt, Michael F. "Vegetation identification with Lidar". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FHelt.pdf.
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7
Möller, Ingo. "Studien zur Vegetation Nordwestspitzbergens". [S.l. : s.n.], 1999. http://www.sub.uni-hamburg.de/disse/133/Disse.pdf.
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8
Schmidt, Peter A., i Dirk Wendel. "Überblick zur Vegetation Sachsens". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-77542.
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Flora und Vegetation sind Spiegelbild naturräumlicher Potenziale ebenso wie kulturbürtiger Einflüsse. Der im Rahmen einer bodenkundlichen Tagung entstandene Artikel gibt einen textlichen und kartografischen Überblick zur potenziellen natürlichen Vegetation (pnV) Sachsens. Aktuelle Vegetationsverhältnisse finden ebenso Berücksichtigung. Die Naturregionen Tief-, Hügel- und Bergland werden aus vegetationskundlicher Sicht - unter Einbeziehung aktueller Forschungen und mit Bezug auf geologische, edaphische sowie klimatische Rahmenbedingungen - charakterisiert. Regionale Besonderheiten (z. B. die Ost-West-Gliederung des Erzgebirges) werden dabei ebenso herausgestellt wie neuere Erkenntnisse zur Verbreitung von landschaftsprägenden Waldtypen (z. B. bodensaure Eichenwälder im Tiefland).
9
Smith, R. I. L. "Ecology of Antarctic vegetation". Thesis, University of Aberdeen, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.593458.
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My extensive studies throughout the maritime Antarctic allowed me to discover many new localities where the two Antarctic vascular plants (Colobanthus quitensis and Deschampsia antarctica) occur, including extending their known range to the farthest south site in the world for flowering plants. As a result of my interest in the cryptogamic flora of the maritime Antarctic, and because of my knowledge of the aquatic bryophytes of the Signy Island, I was invited to examine material of the farthest south collection of an aquatic moss by a team of American limnologists. This led to a brief review of Antarctic aquatic mosses [a related study of aquatic bryophytes from the highest Scottish lochs is referred to here, but is not included as part of the Doctorate submission]. An interesting situation has developed over the past 20 years at Signy Island. This concerns the interaction between a rapidly increasing population of fur seals (from a few dozen in 1965 to 13,350 in 1987) and the fragile and highly vulnerable plant communities. Much of the island's vegetation has been devastated or eradicated during the past five years and I have been able to quantitatively assess the changes induced by the seals by reanalysing several of precisely the same sites I studied 20 years earlier. During an ecological survey of part of Livingston Island, South Shetland Islands, and having an increasing interest in the spread of fur seals and their impact on terrestrial ecosystems, I undertood an investigation of the early history of the Antarctic fur seal industry in the 1800s and of the 'archaeological' sites (sealers' refuges) which abound on that island. My ecophysiological research included a study of the influence of growth-form on the water relations of mosses at Signy Island. Some comparable studies at a continental site are being prepared for an international symposium in Kiel, West Germany, September 1987. Several studies have been made of the chemistry of South Georgia and Signy Island plants, including one on the amount of DNA in the chromosomes of alien and native vascular species; low DNA levels in the former category of plants at South Georgia and in Europe have provided a possible explanation for the survival of certain plants under extreme climatic conditions. A review paper on plant nutrient cycling in the Antarctic and sub-Antarctic was an invited keynote presentation read at a major international symposium in South Africa. Ecological studies at both South Georgia and throughout the maritime Antarctic resulted in extensive collections of all plant groups being made. Many accounts by specialists in bryophyte and lichen taxonomy have been published based on these collections, but I have published several largely ecological papers on fungi and introduced vascular plants, including stranded trees. The combined studies of tussock grass, plant communities, the ecology and chemistry of individual native and introduced phanerogams (especially Poa annua) on South Georgia, in conjunction with a major study of the introduced reindeer on that island by another biologist, has led to a series of papers on the impact of reindeer on the vegetation. The wide spectrum of my research has allowed me to build up a high degree of first-hand knowledge and expertise in Antarctic and sub-Antarctic plant ecology, and of biological and environmental features generally. Consequently, I have written several general or popular accounts, as well as major review works. More recently I have also become involved in matters concerning conservation areas (Sites of Special Scientific Interest and Specially Protected Areas), environmental impact and conservation policy as it relates to national activities throughout the Antarctic and sub-Antarctic biomes. I co-edited a book on conservation areas in the Antarctic, writing eleven of the SPA/SSSI accounts from first-hand experience of each.
10
TEALDI, STEFANO. "River - Riparian Vegetation Interactions". Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2497016.
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The river and the riparian ecosystem are two dynamical systems which exhibit complex spatio-temporal interactions. Because of the possible implications for engineering works and environmental management, in recent times a number of studies has focused on this topic, considering both large- and small-scale problems.
Riparius is a latin word which derives from ripa (riverbank) and means 'that frequents riverbanks'. The riparian ecosystem is thus a community of individuals which lives close to the river and is regularly influenced by fresh water. Both the flora and the fauna are part of this highly dynamic community, and the research in this years has produced results for both the groups. In this thesis the attention will be focused on plants.
Riparian vegetation is of great interest because of its double role, passive and active. In the first role (i.e. the passive one) the biological activity is not considered and only the effect of vegetation morphological and mechanical characteristics on river dynamics is discussed. From this point of view vegetation merely affects the roughness, hydraulic resistance, and bank erodibility in the same manner as any a-biotic element with the same mechanical and morphological characteristics.
The active role is due to the biotic changes intrinsic to living vegetation. From this point of view, vegetation is no longer seen as a static element, but as an element with temporal and spatial dynamics, which can influence the geomorphology of the river. In fact, if the vegetation distribution along the banks changes, or the native species are substituted by exotic ones, the mechanical effects of vegetation change, leading then to possible changes of river geometry.
Riparian vegetation is closely linked to the hydrology of the river, in particular to the stochastic water level fluctuations and to the erosion/sedimentation processes. Floods and erosion/ sedimentation processes, in fact, influence the growth of plants to a great extent. Flood events are able to destroy the vegetation because they can cause physical damage, uprooting and sediment removal, anoxia and burial. The stochastic nature of floods is therefore a key point for the vegetation dynamics. In fact, the random water stage fluctuations drive the alternation of periods of exposure and submersion, which cause the alternation of growth and decay of vegetation.
Erosion/sedimentation processes are also fundamental for the vegetation dynamics, because they can cause extirpation (erosion) or provide protection and nutrients during the growth phase (sedimentation). In turn, erosion and sedimentation rates are modified by the vegetation, because the vegetation protects the site from erosion and increases hydraulic roughness, enhancing fine sediment deposition and contributing to the aggradation of the site.
In this complex scenario, in which vegetation influences and is influenced by hydrological forcings, it is important to develop analytical models able to consider all these interactions. These models can be used as tools for river management and restoration projects, in order to carefully plan the anthropic disturbances on the river and, thus, reduce the impacts on the riparian ecosystem. In fact, several works in literature report drastic changes of vegetation (shifts, invasion of exotic species in spice of native ones, reduction of biomasses etc.) and of river geometry (narrowing/widening processes, degradation/aggradation of the bed quote etc.), which perhaps could have been reduced with the use of a proper model.
The first part of this thesis is devoted to the study of the interplay between river meandering, discharge stochasticity and riparian vegetation. In particular it will be studied the impact of river sinuosity on the total vegetation biomass. In the second part of this thesis it will be studied how the coefficient of dispersion varies in presence of riparian vegetation when medium/high discharges flow in the river. In the third part of this thesis it will be analyzed how the effect of cooperation/competions impacts the distribution of the vegetation along the transect. In the fourth part of this thesis a model will be developed in order to quantitatively analyze how the construction of a dam along a river is able to influence the vegetation. In the fifth part of this thesis a model will be developed in order to quantitatively evaluate the amount of the changes in cross-section after hydrological changes.
11
Cohen, Yoav. "A comparison between vegetation indices for measuring vegetation dynamics resulting from climate variations /". [Beer Sheva] : Ben Gurion University of the Negev, 2008. http://aranne5.lib.ad.bgu.ac.il/others/CohenYoav.pdf.
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12
Cutler, Nick. "High-latitude vegetation dynamics : 850 years of vegetation development on Mt Hekla, Iceland". Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/2485.
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The overall aim of this thesis is to investigate long-term (multi-century) vegetation development in a high-latitude setting, with a particular emphasis on the emergence and persistence of spatial structure in plant communities. The spatial distribution of plants within a community influences vegetation dynamics and the functioning of terrestrial ecosystems. Knowledge of the spatiotemporal dynamics of vegetation is therefore crucial to understanding ecosystem response to disturbance, and to successful ecosystem management. Studies of spatiotemporal dynamics from high-latitude settings are rare, despite these regions being among the most sensitive to warming and subject to ongoing environmental change. The study was based on a primary succession on Mt Hekla in south-central Iceland. The chronosequence approach was used to infer 850 years of vegetation development from a suite of 14 lava flows (five of which had been disturbed by the deposition of volcanic tephra). The thesis is organised around four main research themes: 1) Trajectories of development- How do the global (i.e. non-spatial) properties of a community (e.g. species diversity) change with terrain age in a primary succession? Plant species frequency data from 12 transect surveys (each comprising 400 contiguous 10 cm x 10 cm quadrats) were used to test the predictions of classical models of primary succession; 2) Initial colonisation- How do plants first establish on newly-created terrain? Photographic surveys and point-pattern analysis were used to assess the processes by which pioneer species colonised ‘safe sites’ on lava surfaces six and fifteen years old; 3) Spatial scale and structure- How and why does the spatial structure of vegetation vary over long timescales? Vegetation and soil data from transect surveys (item 1, above) were analysed using a variety of spatial statistics, in order to test three models of spatiotemporal dynamics; 4) Temporal changes in environmental gradients- To what extent does biotic reaction feed-back into the small- (metre-) scale distribution of plants? Randomised sampling of vegetation on 42 sites was combined with continuous microclimatic monitoring to assess the changing steepness of environmental gradients, and the impact this process had on vegetation development. The analyses revealed a robust, multi-century trajectory of vegetation development on undisturbed sites. The development of vegetation on newly-emplaced flows was rapid, as colonists randomly exploited small- (millimetre) scale surface irregularities in the lava. A thick (up to 20 cm), spatially homogeneous ‘carpet’ of moss formed within 50 years of flow emplacement. Thereafter, the vegetation became progressively more structured with increasing terrain age, as patches of vegetation formed and expanded. On the oldest sites, differentiation of the vegetation according to metre-scale variations in elevation was apparent. Overall, the results emphasise the limitations of classical models of succession in high-latitude habitats and suggest widespread applicability for the nucleation model of primary succession. The study also suggests that the spatiotemporal response of vegetation to environmental gradients is mediated by short-range positive feedback. These findings have implications for modelling vegetation development on other primary substrates (e.g. glacial forelands) and the response of spatially patchy, high-latitude vegetation to future climate change.
13
Rushworth, Garry. "Late Quaternary vegetation history of Craven, Yorkshire Dales". Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/6286.
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This thesis investigates new late Quaternary vegetation records from four sites in the Craven District of the Yorkshire Dales. The chosen sites fall along an east-west transect broadly following the line of the south Craven Fault. The rationale for site selection was not based on conventional palynological considerations of potential for rich core samples, rather to provide a range of different locations within a distinct micro-region each existing in some specific proximity to known archaeological features. The logic was to attempt to get beyond broad 'natural' climatological and vegetational inferences to understand the nature and level of potential anthropogenically produced change at a local scale as a sub-set of natural change in a broader regional zone over time. The sites reveal varied vegetation histories from the Late Glacial period to the present day and all show signs of being influenced by changes in their arboreal structure at some time, although no two sites have exactly the same vegetation communities until around 5000 BP when the tree canopy is opened to allow an open grassland to dominate. The results indicate the possibility that Betula values, in particular, might indicate cooling events found in the Greenland ice cores for Greenland Interstadial 1 as well as the Pre-boreal Oscillation and the Holocene 9.3 ka BP Event. Closer chronological control of such values could help to determine whether vegetational dynamics were synchronous with fluctuations in temperature and the speed with which trees respond to severe temperature fluctuations. Various hiatuses identified during analysis of the cores may be caused by human influence on the wetlands, given that archaeological evidence from caves shows human occupation of the Craven area from the late Upper Palaeolithic onwards.
14
Freund, Anne. "Verlauf von Patienten mit infektiöser Endokarditis der linksseitigen Nativklappen und isolierten großen Vegetationen". Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-202542.
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Ziel der Studie war es zu analysieren, inwiefern eine Operation bei Patienten mit einer infektiösen Endokarditis der linksseitigen Nativklappen und keiner weiteren Operationsindikation als einer Vegetationsgröße ≥10mm, das Auftreten von systemischen Embolien, erneuten Endokarditiden und das Langzeitüberleben beeinflussen.
Dafür wurden alle Patienten, die zwischen Januar 2000 und Juni 2012 in der Klinik für Kardiologie des Herzzentrums Leipzig mit einer Linksherzendokarditis der Nativklappen und einer Vegetationsgröße ≥10mm behandelt wurden, in ein Register aufgenommen. Alle Patienten mit anderen Operationsindikationen als ihrer Vegetationsgröße wurden ausgeschlossen. Es wurde eine Langzeitkontrolle hinsichtlich definierter klinischer Ereignisse durchgeführt.
71 Patienten wurden in die Studie eingeschlossen. Die mittlere Vegetationsgrößebetrug 17±5mm. 59 Patienten wurden nach einer mittleren Zeit von 5±6 Tagen nach Beginn der Antibiotikatherapie operiert. Die übrigen 12 wurden rein konservativ
behandelt. Das mittlere Follow-up erfolgte nach 6,0±2,9 Jahren. Eine chirurgische
Behandlungsstrategie war im Vergleich zu rein medikamentöser Therapie mit einer signifikanten Erhöhung der Langzeitmortalität verbunden (p=0,03, Log-rank-Test; unadjustierte Analyse). In einem multivariaten Cox-Regressionsmodell zeigten chirurgische Behandlung, Beteiligung der Mitralklappe, Staphylokokkus aureus-positive
Blutkulturen und steigendes Alter einen Trend als unabhängige
Beeinflussungsfaktoren der Langzeitmortalität.
Ein signifikanter Unterschied zwischen den beiden Gruppen hinsichtlich
symptomatischer systemischer Embolien nach Therapiebeginn und Zahl erneuter Endokarditiden bestand nicht.
Daher scheint eine operative Behandlung von Patienten mit einer infektiösen Linksherzendokarditis der Nativklappen und großen Vegetationen ohne weitere Operationsindikationen, wie sie aktuell von europäischen und amerikanischen Leitlinien empfohlen wird, möglicherweise mit einer höheren Mortalität verbunden zu
sein.
Eine kontrollierte randomisierte Studie zur Gegenüberstellung von operativer und konservativer Behandlung dieser Subgruppe von Endokarditispatienten ist deshalb erstrebenswert.
15
Wang, Li-Fang Ph D. Massachusetts Institute of Technology. "Monte Carlo simulation model for electromagnetic scattering from vegetation and inversion of vegetation parameters". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38923.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 171-185).
In this thesis research, a coherent scattering model for microwave remote sensing of vegetation canopy is developed on the basis of Monte Carlo simulations. An accurate model of vegetation structure is essential for the calculation of scattering from vegetations, especially those with closely spaced elements in clusters. The Monte Carlo approach has an advantage over the conventional wave theory in dealing with complex vegetation structures because it is not necessary to find the probability density functions and the pair-distribution functions required in the analytic formulation and usually difficult to obtain for natural vegetation. To achieve a realistic description of the vegetation structure under consideration, two methods may be employed. One method requires the specification of the number of each type of component and the relative orientations of the components. In a structural model which incorporates this method, the detailed features can be preserved to the desired level of accuracy. This structural model is applied to two types of vegetation- --rice crops and sunflowers.
(cont.) The developed structural model for rice crops takes into account the coherent wave interactions made prominent by the clustered and closely spaced structure of rice crops, and is validated with the ERS-1 and RADARSAT data. It is utilized to interpret the experimental observations from the JERS-1 data, such as the effects of the structure of rice fields, and to predict the temporal response of rice growth. The structural model developed for sunflowers is validated using the airborne Remote Sensing Campaign Mac-Europe 91 multi-frequency and multi-polarization data acquired for sunflower fields at the Montespertoli test site in Italy. Another method to characterize vegetation structure uses growth rules. This is especially useful in modeling trees, which are structurally more complex. The Lindenmayer systems (L-systems) are utilized to fully capture the architecture of trees and describe their growth. Monte Carlo simulation results of the scattering returns from trees with different structures and at different growth stages are calculated and analyzed. The concept of the "structure factor" which extracts the structural information of a tree and and provides a measure of the spatial distribution of branches is defined, and computed for trees with different architectures.
(cont.) After study of the forward scattering problem in which the scattering coefficients are determined on the basis of known physical characteristics of the scattering objects or medium, the inverse scattering problem is considered in which the characteristics of the scattering objects or medium are to be calculated from the scattering data. In this thesis research, neural networks are applied to the inversion of geophysical parameters including soil moisture and surface parameters, sunflower biomass, as well as forest age (or equivalently, forest biomass). They are found to be especially useful for multi-dimensional inputs such as multi-frequency polarimetric scattering data. For the inversion of soil moisture and surface parameters, neural networks are trained with theoretical surface scattering models. To retrieve the sunflower biomass, neural networks are trained with the scattering returns obtained from the developed vegetation scattering model based on the Monte Carlo approach. To assess the performance of the use of experimental data to train the neural networks, the polarimetric radar data acquired by the Spaceborne Imaging Radar-C (SIR-C) over the Landes Forest in France are utilized as the training data to retrieve the forest age. Different combinations of backscattering data are used as input to the neural net in order to determine the combination which yields the best inversion result.
by L-i-Fang Wang.
Ph.D.
16
Street, Lorna Elizabeth. "Carbon dynamics in Arctic vegetation". Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5651.
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Rapid climate change in Arctic regions is of concern due to important feedbacks between the Arctic land surface and the global climate system. A large amount of organic carbon (C) is currently stored in Arctic soils; if decomposition is stimulated under warmer conditions additional release of CO2 could result in an accelerating feedback on global climate. The strength and direction of Arctic C cycle - climate feedbacks will depend on the growth response of vegetation; if plant growth increases some or all of the extra CO2 emissions may be offset. Currently the Arctic is thought to be a small net sink for CO2, the expected balance of terrestrial C sinks and sources in the future is unknown. In this thesis I explore some of the critical unknowns in current understanding of C cycle dynamics in Arctic vegetation. Quantifying gross primary productivity (GPP) over regional scales is complicated by large spatial heterogeneity in plant functional type (PFT) in Arctic vegetation. I use data from five Arctic sites to test the generality of a relationship between leaf area index (LAI) and canopy total foliar nitrogen (TFN). LAI and TFN are key drivers of GPP and are tightly constrained across PFTs in Low Arctic Alaska and Sweden, therefore greatly simplifying the task of up-scaling. I use data from Greenland, Barrow and Svalbard to asses the generality of the LAI-TFN relationship in predicting GPP at higher Arctic latitudes. Arctic ecosystems are unique among biomes in the large relative contribution of bryophytes (mosses, liverworts and hornworts) to plant biomass. The contribution of bryophytes to ecosystem function has been relatively understudied and they are poorly represented in terrestrial C models. I use ground based measurements in Northern Sweden to fill an existing data gap by quantifying CO2 fluxes from bryophytes patches in early spring and summer, and develop a simple model of bryophyte GPP. Using the model I compare bryophyte GPP to that of vascular plants before, during and after the summer growing season, finding that productive bryophyte patches can contribute up to 90 % of modelled annual GPP for typical vascular plant communities at the same site, and that the relative magnitude of bryophyte GPP is greatest in spring whilst the vascular plant canopy is still developing. Understanding how GPP relates to plant growth is important in relating remotely sensed increases in Arctic ‘greenness’ to changes in plant C stocks. I use a 13C pulselabelling techniques to follow the fate of recently fixed C in mixed vascular and bryophyte vegetation, with a focus on quantifying the contribution of bryophytes to ecosystem carbon use efficiency (CUE). I show that bryophytes contribute significantly to GPP in mixed vegetation, and act to increase ecosystem CUE. I highlight the importance of including bryophytes, which do not have roots, in aboveground: belowground partitioning schemes in C models. To further explore C turnover in bryophytes, I use the results of a second 13C labelling experiment to develop a model of C turnover in two contrasting Arctic mosses (Polytrichum piliferum and Sphagnum fuscum). I find significant differences in C turnover between Polytrichum piliferum which respires or translocates about 80 % of GPP, while Sphagnum fuscum respires 60 %. This analysis is the first to explicitly model differences in C partitioning between Arctic bryophyte species. Finally, I discuss the implications of each chapter for our understanding of Arctic C dynamics, and suggest areas for further research.
17
Quesada, carlos Alberto Nobre. "Soil Vegetation Interactions Across Amazonia". Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503277.
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Liu, David. "Flow through Rigid Vegetation Hydrodynamics". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/35068.
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Better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation. Instead of spatial averaging, this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels. Velocity data were collected with a one dimensional laser Doppler velocimeter (LDV) under single layer emergent and submerged flow conditions, and through two layers of vegetation. The effects of dowel arrangement, density, and roughness are also examined under the single layer experiments. The results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it. The region immediately behind a dowel, where the vorticity and turbulence intensity are highest, is characterized by a velocity spike near the bed and an inflection point near the top of the dowel arrays. With two dowel layers, the velocity profile in the region behind a tall dowel exhibits multiple inflection points and the highest turbulence intensities are found there.Master of Science
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Steiner, Arnold J. "Die Vegetation der Gemeinde Zermatt /". [S.l.] : [s.n.], 1999. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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DiGirolamo, Paul A. "A comparison of change detection methods in an urban environment using LANDSAT TM and ETM+ satellite imagery a multi-temporal, multi-spectral analysis of Gwinnett County, GA 1991-2000 /". unrestricted, 2005. http://etd.gsu.edu/theses/available/etd-07242006-110800/.
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Thesis (M.A.)--Georgia State University, 2005.Title from title screen. Zhi-Yong Yin, committee chair; Paul Knapp, Truman Hartshorn, committee members. Electronic text (135 p. : col. ill., col. maps)) : digital, PDF file. Description based on contents viewed Aug. 2, 2007. Includes bibliographical references (p. 125-133).
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Silva, Rui Pedro Guerreiro Duarte Rivaes. "Predicting the effects of climatic change on mediterranean riparian vegetation using a dynamic vegetation model". Master's thesis, ISA, 2010. http://hdl.handle.net/10400.5/2883.
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Mestrado em Gestão e Conservação de Recursos Naturais - Instituto Superior de AgronomiaThe present master's thesis, had as its main objective the application of a dynamic model of riparian habitats in a case study with pronounced mediterranean characteristics. he vegetation model used is based on the existence of water conditions (water height and distance to water) suitable for the development of each type of riparian vegetation in different stages of their development, modeling annually its space-time evolution. The rules underlying the model take into account the height of the flow, the shear stress and duration of flooding. The modeling of vegetation held in ArcGIS environment, bases on three general ohases: initial creation of landscape, simulation of temporal and spatial evolution of vegetation and the presentation of annual results.
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Sadler, Rohan. "Image-based modelling of pattern dynamics in a semiarid grassland of the Pilbara, Australia /". Connect to this title, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0155.
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Paula, Isabela Fernanda Moraes de. "Cobertura vegetal das regiões urbanas de Juiz de Fora - MG". Universidade Federal de Juiz de Fora (UFJF), 2017. https://repositorio.ufjf.br/jspui/handle/ufjf/5915.
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A cobertura vegetal, entendida como o conjunto das tipologias arbórea, arbustiva e rasteira, constitui um importante elemento a compor os centros urbanos em função dos diversos benefícios de cunho ecológico, social e estético que proporcionam. Nesse sentido, o conhecimento de sua ocorrência no espaço torna-se fundamental tanto para se identificar as funcionalidades destes no meio quanto para se instituir políticas ambientais que visem melhorias na sua disposição. Sendo assim, considerando a relevância deste recurso natural, esta pesquisa buscou identificar a vegetação existente nas Regiões Administrativas do município de Juiz de Fora. Os resultados obtidos demonstram uma distribuição destituída de homogeneidade, evidenciando maiores fragmentos nas áreas periféricas e reduzidos remanescentes no sentido noroeste-sudeste, revelando um processo de uso e ocupação da terra mais intenso nesses locais. Nota-se, dessa forma, a ocorrência de manchas de vegetação mais pontuais e espaçadas nesses trechos, típicas da categoria Isolated, definida pelo pesquisador Jim como dominante de áreas impermeabilizadas, enquanto nas áreas próximas as bordas dos limites, encontram-se o tipo Connected, caracterizado pela presença de verde urbano mais contíguo e de maiores extensões. Tais aspectos refletem diretamente nos resultados dos índices de cobertura vegetal obtidos, no qual a Região Centro abrange os menores valores em relação as demais. No que se refere aos espaços de integração urbana e espaços livres de construção, observa-se escassez do elemento vegetativo nesses sistemas, visto que o primeiro abrange menos de 2,1% das regiões e o segundo menos de 1,5%, o que demonstra a necessidade de melhorias nesses ambientes, de forma a contribuir mais efetivamente ao bem estar humano.
The vegetal covering, understood as a set of arboreal typology, creeper shrub, consists of an important element that composes the cities and provide a lot of befits such as ecological, social, and esthetical. In this way, the knowledge about vegetal covering throughout the cities is an important issue in order to identify its best features for communities as well as to promote environmental policies for improves the vegetal covering displacement around cities. Thus, regarding the relevance of this natural resource, the aim of this work was identify the vegetal covering that exists at administrative regions of Juiz de Fora city. On the one hand the results shown that the vegetal covering is homogeneity distributed with larges fragments at peripheral regions. On the other hand a small remaining of vegetal covering was found at northwest and southeast regions of city which reveal an intensive process of use and occupation of the ground. Thus, we found sparse and punctual vegetal stains at downtown, typical of isolated category, defined by researcher Jim as impermeable dominants areas. While at cities’ board areas, it can be found connected type vegetal covering which is characterized by continuous green urban presence with larger extension. Such issues reflect directly at vegetal covering index results we have found, in which the downtown indexes are smaller than others regions evaluated. As far as urban spaces of integration as well as building free regions are concerned we can observe scarce vegetative elements. At urban spaces of integration we find only 2,1 % of regions have vegetative elements, while at building open spaces has 1,5 % as well. Therefore, the results have shown that there are demands for improvements in these environments in order to contribute effectively for the human well-being.
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Arain, Muhammad Altaf. "Spatial aggregation of vegetation parameters in a coupled land surface-atmosphere model". Thesis, The University of Arizona, 1994. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0049_m_sip1_w.pdf&type=application/pdf.
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Islamovic, Azra. "Bumblebee (Bombus spp.) occurrence in relation to vegetation height, variation in vegetation height and flower abundance". Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-108671.
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Bumblebees are a group of valuable pollinators that are declining all over the world. The main reason is believed to be habitat loss due to the changes in agriculture. The changes in agriculture influence the structure of the vegetation and flower abundance, which are of great importance to the abundance of bumblebees. The aims of this study were to get a better understanding of bumblebees and what preferences they might have regarding vegetation height and flower abundance in semi-natural grasslands. This study is based on data collected by a Swedish national environmental monitoring program in 2006-2010. Data on twelve bumblebee species were analysed using a generalized linear model based on the dependent variables of occurrence/ non-occurrence. The target variables used in the analysis were flower abundance, vegetation height and standard deviation of vegetation height. The species-wise analyses mostly showed no or weak positive relationships between the bumblebee occurrence and the three target variables. Grouping the species-wise results into ecologically meaningful guilds and analysing them did not increase the explanatory power of flower abundance or vegetation characteristic, but vegetation height showed significant (positive) results in relation for the forest dwelling species and the species group non-parasite and parasite. The results of this study were considerably weaker than expected. Flower abundance and variation in vegetation height could not explain the occurrence of bumblebees. However, the results of this study show that vegetation height is of importance to the occurrence of bumblebees. Bumblebees in general seem to prefer a higher vegetation height. Based on the findings of this study I would recommend a low intensity of grazing in semi-natural grasslands.
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R, A. Majdaldin, B. A. Osunmadewa, E. Csaplovics i D. Aralova. "Remote sensing-based vegetation indices for monitoring vegetation change in the semi-arid region of Sudan". SPIE, 2016. https://tud.qucosa.de/id/qucosa%3A35109.
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Land degradation, a phenomenon referring to (drought) in arid, semi-arid and dry sub-humid regions as a result of climatic variations and anthropogenic activities most especially in the semi-arid lands of Sudan, where vast majority of the rural population depend solely on agriculture and pasture for their daily livelihood, the ecological pattern had been greatly influenced thereby leading to loss of vegetation cover coupled with climatic variability and replacement of the natural tree composition with invasive mesquite species. The principal aim of this study is to quantitatively examine the vigour of vegetation in Sudan through different vegetation indices. The assessment was done based on indicators such as soil adjusted vegetation index (SAVI). Cloud free multi-spectral remotely sensed data from LANDSAT imagery for the dry season periods of 1984 and 2009 were used in this study. Results of this study shows conversion of vegetation to other land use type. In general, an increase in area covered by vegetation was observed from the NDVI results of 2009 which is a contrast of that of 1984. The results of the vegetation indices for NDVI in 1984 (vegetated area) showed that about 21% was covered by vegetation while 49% of the area were covered with vegetation in 2009. Similar increase in vegetated area were observed from the result of SAVI. The decrease in vegetation observed in 1984 is as a result of extensive drought period which affects vegetation productivity thereby accelerating expansion of bare surfaces and sand accumulation. Although, increase in vegetated area were observed from the result of this study, this increase has a negative impact as the natural vegetation are degraded due to human induced activities which gradually led to the replacement of the natural vegetation with invasive tree species. The results of the study shows that NDVI perform better than by SAVI.
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Hall, Stuart. "Vegetation change and vegetation type stability in the Cape of Good Hope Nature Reserve 1966 - 2010". Bachelor's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/26385.
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Vegetation stability was investigated within the Cape of Good Hope Nature Reserve by incorporating three vegetation surveys spanning a 44 year time period. The goals of this study were to investigate changes in overall species diversity within the reserve, stability of community composition within and between sites, and which factors are influencing stability. A survey was conducted on 26 vegetation plots across the reserve. Data from this survey and two previous surveys was used to compare species diversity between time periods. Vegetation compositional similarity was also compared between sites. I tested for the effect of difference in vegetation age and soil type as predictors of vegetation groups. Results showed an overall decrease in species diversity. Analysis ofvegetation groups showed that vegetation types are mostly stable as current vegetation can be predicted by groups based on 1966 data. Vegetation is influenced significantly by fire history and soil types.
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Berglund, Mattias. "Semiautomatisk spridning av vegetation i dataspel". Thesis, University of Skövde, School of Humanities and Informatics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-43.
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Dagens spel kräver hela tiden mer resurser i en konstant växande och mer detaljerad spelvärld. Det är därför intressant att titta på alternativ till att designers manuellt placerar ut innehåll i en värld. Problemet som tas upp är om det är möjligt att kombinera generering av procedurellt innehåll i form av en skog med att låta en användare kunna påverka denna generering. Problemet delas upp i två delar där en utveckling av en arkitektur sker genom att utvärdera existerande skogsmodeller och sedan implementera arkitekturen. Slutligen sker en utvärdering av modellen genom att analysera ett antal scenarier. Resultaten visar att det är möjligt att låta en användare kunna påverka en evolvering av en skog genom att ändra egenskaper på ett specifikt område, men påverkas i stor grad av hur pass komplex skogsmodellen är. Arbetet visar att det är möjligt att enkelt kunna styra och påverka generering av procedurellt innehåll.
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Maurice, Christian. "Landfill gas emission and landfill vegetation". Licentiate thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 1998. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17271.
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Huthoff, Fredrik. "Modeling hydraulic resistance of floodplain vegetation". Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/58016.
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Walmsley, Clive Andrew. "The ecology of shingle-beach vegetation". Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525009.
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The establishment of six shingle-beaches species( Crambem aritima (sea-kale),E ryngium maritimum (sea-holly), Glauciumflavum (yellow homed-poppy), Honckenya peploides (sea sandwort), Lathyrusjaponicus (sea pea) and Rumex crispus (curled dock)) was investigated to mitigate the disturbance caused by the construction of a power station at Sizewell, Suffolk, UK. The potential for creating vegetation from container-grown plants, sown seed or the soil seed bank was examined. Shingle-beach vegetation comprising these species was successfully established using container-grown plants, whereas seeding shingle beach areas was generally unsuccessful. Mature container-grown plants were able to survive erosion or accretion, at least to some extent, because they possessed extensive root or rhizome systems which provided sufficient resources for subterranean growth, while seedlings had only a limited capacity to elongate to the new beach surface after inundation. Hernicryptophyte species were most successful in surviving disturbance; Honckenya peploides recovered from up to 0.41 m accretion or 0.26 m erosion. The monocarpic chamaephyte species, Glauciuniflavum, showed poor survival after disturbance, but successfully established from seed within one season. Seedling emergence techniques showed that there was a very limited germinable soil seed bank in June on the shingle beach compared to the neighbouring dune grassland. The seed bank was not likely to provide an adequate source of propagules for vegetation restoration. Innate hard-seed dormancy mechanisms were important in five of the six species. Dormancy reduced the potential for rapid field-establishment from seed. The use of seed stored at low temperature and humidity for 5 years showed that germination of seed, of apparently high viability, but of low vigour, was reduced because of sensitivity to non-optimal temperatures, inappropriate light conditions or low salinity concentrations. Seed germination of all species was totally inhibited by 50-100% sea-water. The establishment of vegetation was significantly influence by beach substrate composition which affected the survival, growth and fecundity of container-grown plants and seedlings emergence, survival and growth in sown plots. A mixture of shingle and sand allowed significantly greater growth in Crambe maritima, Rumex crispus and Glauciumflavum plants compared to almost pure sand substrates.
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Schofield, James Edward. "Vegetation succession in the Humber wetlands". Thesis, University of Hull, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395518.
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Flechard, Christophe R. "Turbulent exchange of ammonia above vegetation". Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243639.
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Masterman, Richard. "Vegetation effects on river bank stability". Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358028.
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Benhouhou, Salima S. "Vegetation studies in the Algerian Sahara". Thesis, University of Sheffield, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308145.
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Davies, Julia Jacqueline. "Vegetation experiments on lime spoil rehabilitation". Thesis, University of Ulster, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268592.
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Strawbridge, Fiona. "Passive microwave remote sensing of vegetation". Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242948.
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Tanino, Yukie 1980. "Aquatic gravity currents through emergent vegetation". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/26712.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (leaves 109-112).
Differential heating and cooling can generate density-driven, lateral exchange flows in aquatic systems. Despite the ubiquity of wetlands and other types of aquatic canopies, few studies have examined the hydrodynamic effects of aquatic vegetation on these currents. This study investigates the dynamics of lock-exchange flows, a particular class of density currents, propagating through rigid emergent vegetation. First, previous mathematical formulation is extended to develop theoretical models of vegetated lock-exchange flows. The regime in which stem drag is inversely proportional to velocity is considered as a special case. Lock-exchange flows were generated in a laboratory flume with rigid cylindrical dowels as model vegetation. Experimental observations were consistent with the theory. Under high stem drag or low stem Reynolds number conditions, the interface deviated from the well-documented block profile associated with unobstructed lock-exchange flows and approached a linear profile. Criteria are developed to categorize all flow conditions as inertial or non-inertial and the interface profile as linear, transitional, or non-linear, respectively, based on (a) the evolution of the velocity of the leading edge of the undercurrent and (b) the interface shape. Finally, the present model is enhanced to account for wind forcing and bed friction to better describe conditions found in nature. The theory highlights the sensitivity of currents to wind forcing.
by Yukie Tanino.
S.M.
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McIntosh, Brian S. "Rule-based modelling of vegetation dynamics". Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/12619.
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The corpus of available vegetation knowledge is characterised by its fragmented form and by the way in which relationships between different ecological quantities tend to be expressed non-quantitatively. Much of the corpus is only held informally and composed of deterministic factual or conditional statements. Despite its form, this thesis demonstrates that available ecological knowledge can be usefully employed for predictive modelling of vegetation dynamics under different conditions. The thesis concentrates on modelling Mediterranean vegetation dynamics. Using a mixture of concepts and techniques from deterministic state transition and functional attributes modelling. Qualitative Reasoning and knowledge-based systems, three ontological distinct modelling systems are developed to demonstrate the utility of available knowledge for modelling vegetation dynamics. All three systems use declarative, rule-based approaches based on first-order logic and are composed of a set of representational constructs along with a separate system for reasoning with these constructs to make predictions. A method for reasoning about change in non-quantitative model variables is developed based upon time and direction of change. This ‘temporal reasoning system’ provides a solution to the state variable problem and may offer a general way of modelling with non-quantitative knowledge. To illustrate, a different model of Mediterranean vegetation dynamics is developed and run under different conditions for each system. The capabilities and possible problems of each system in terms of ecological validity, knowledge representation and reasoning are discussed. The general utility of rule-based approaches to modelling vegetation dynamics are also discussed along with the implications of the modelling systems developed for the activities of decision-support and ecological theory development.
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Levy, Peter E. "Carbon dioxide exchange of Sahelian vegetation". Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/12411.
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Measurements of leaf and ecosystems scale CO2 flux were made at the millet, fallow and tiger bush sites at the HAPEX-Sahel Southern supersite. These were analysed in relation to biological and environmental variables. In the five species studied, leaf scale photosynthesis was strongly influenced by photosynthetic photon flux density (Q) and stomatal conductance, and was well described by the non-rectangular hyperbola model of Jarvis, Miranda and Muetzelfeldt (1985). Stem respiration was measured in two species, and increased exponentially with temperature. Stem respiration rates were higher in the wet season than in the dry season and this difference was used to separate growth and maintenance respiration. Effects of Q and sap flow on stem CO2 efflux were observed. A small number of soil respiration measurements were also made. Direct measurements of leaf area index, biomass and canopy structure were made at the millet and fallow sites. Two indirect methods of estimating leaf area index, from hemispherical photographs and measurements of transmitted Q, were used to all three sites. Together with measurements of canopy structure at each site, the measurements of leaf photosynthesis, stomatal conductance and stem soil respiration were used to parameterise two models which predict ecosystem net CO2 flux: a simple one-dimensional "big leaf" model and a complex three-dimensional model "MAESTRO". Model predictions were compared with independent ecosystem flux measurements made by eddy covariance. Generally, both models agreed well with measurements at all three sites. Differences between measurements and predictions were very small in millet and largest in tiger bush, and were attributed to the effect of canopy heterogeneity on eddy covariance measurements and the accuracy with which canopy structure parameters could be estimated.
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Gebrehiwot, Worku Zewdie. "Climate, land use and vegetation trends". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-209668.
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Land use / land cover (LULC) change assessment is getting more consideration by global environmental change studies as land use change is exposing dryland environments for transitions and higher rates of resource depletion. The semiarid regions of northwestern Ethiopia are not different as land use transition is the major problem of the region. However, there is no satisfactory study to quantify the change process of the region up to now. Hence, spatiotemporal change analysis is vital for understanding and identification of major threats and solicit solutions for sustainable management of the ecosystem. LULC change studies focus on understanding the patterns, processes and dynamics of land use transitions and driving forces of change. The change processes in dryland ecosystems can be either seasonal, gradual or abrupt changes of random or systematic change processes that result in a pattern or permanent transition in land use. Identification of these processes of change and their type supports adoption of monitoring options and indicate possible measures to be taken to safeguard this dynamic ecosystem.
This study examines the spatiotemporal patterns of LULC change, temporal trends in climate variables and the insights of the communities on change patterns of ecosystems. Landsat imagery, MODIS NDVI, CRU temperature, TAMSAT rainfall and socio-ecological field data were used in order to identify change processes. LULC transformation was monitored using support vector machine (SVM) algorithm. A cross-tabulation matrix assessment was implemented in order to assess the total change of land use categories based on net change and swap change. In addition, the pattern of change was identified based on expected gain and loss under a random process of gain and loss, respectively. Breaks For Additive Seasonal and Trend (BFAST) analysis was employed for determining the time, direction and magnitude of seasonal, abrupt and trend changes within the time series datasets. In addition, Man Kendall test statistic and Sen’s slope estimator were used for assessing long term trends on detrended time series data components. Distributed lag (DL) model was also adopted in order to determine the time lag response of vegetation to the current and past rainfall distribution.
Over the study period of 1972- 2014, there is a significant change in LULC as evidenced by a significant increase in size of cropland of about 53% and a net loss of over 61% of woodland area. The period 2000-2014 has shown a sharp increase of cropland and a sharp decline of woodland areas. Proximate causes include agricultural expansion and excessive wood harvesting; and underlying causes of demographic factor, economic factors and policy contributed the most to an overuse of existing natural resources. In both the observed and expected proportion of random process of change and of systematic changes, woodland has shown the highest loss compared to other land use types. The observed transition and expected transition under random process of gain of woodland to cropland is 1.7%, implies that cropland systematically gains to replace woodland. The comparison of the difference between observed and expected loss under random process of loss also showed that when woodland loses cropland systematically replaces it. The assessment of magnitude and time of breakpoints on climate data and NDVI showed different results. Accordingly, NDVI analysis demonstrated the existence of breakpoints that are statistically significant on the seasonal and long term trends. There is a positive trend, but no breakpoints on the long term precipitation data during the study period. The maximum temperature also showed a positive trend with two breakpoints which are not statistically significant. On the other hand, there is no seasonal and trend breakpoints in minimum temperature, though there is an overall positive trend along the study period.
The Man-Kendall test statistic for long term average Tmin and Tmax showed significant variation where as there is no significant trend within the long term rainfall distribution. The lag regression between NDVI and precipitation indicated a lag of up to forty days. This proves that the vegetation growth in this area is not primarily determined by the current precipitation rather with the previous forty days rainfall. The combined analysis showed declining vegetation productivity and a loss of vegetation cover that contributed for an easy movement of dust clouds during the dry period of the year. This affects the land condition of the region, resulting in long term degradation of the environment
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Ferreira, Carla Sofia Borges Pinto da Cruz. "Temporary ponds vegetation and dynamics:SW Portugal". Doctoral thesis, ISA, 2010. http://hdl.handle.net/10400.5/2862.
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Fernandes, Royston. "Wind erosion in presence of vegetation". Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0194.
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La poussière minérale atmosphérique résultant de l’érosion éolienne des sols affecte le système terrestre. La distribution en taille (PSD) de cette poussière joue un rôle clé dans le bilan radiatif et la chimie atmosphérique, la formation des nuages et la productivité des écosystèmes terrestres et marins. Néanmoins les modèles climatiques peinent à reproduire précisément la PSD de la poussière émise. Ceci vient de la représentation imparfaite des mécanismes d’émission de poussières et des vitesses de vent de surface associées. C’est particulièrement vrai en présence d’éléments de rugosité de surface comme la végétation en régions semi-arides. Cette thèse vise à améliorer la compréhension de l’émission de poussière en environnements semi-arides, caractérisé par des surfaces hétérogènes liées à la végétation saisonnière éparse. A cette fin, une combinaison d’expériences numériques et de terrain a été employée, en partant d’un sol nu érodable à des surfaces couvertes de végétation éparse.Une revue des schémas existants a montré des ambiguïtés dans la paramétrisation des processus influençant l’émission de poussières. Une analyse de sensibilité utilisant un modèle 1D de dispersion de poussière a démontré l’importance (i) de la PSD de la poussière à la surface et de la paramétrisation de la cohésion interparticules qui affectent la PSD de la poussière émise, et (ii) des processus de dépôt qui influencent la PSD du flux net de poussière dans la couche de surface atmosphérique. A partir de cette analyse, un nouveau schéma d’émission a été incorporé à un modèle 3D d’érosion, couplé à un modèle turbulent Large Eddy Simulation (LES), et évalué d’abord sur une surface nue sur la base de l’expérimentation WIND-O-V 2017 en Tunisie. Le modèle a ainsi été capable de reproduire la dissimilarité entre les transports turbulents de poussière et de quantité de mouvement dans la couche de surface, observée durant l’expérience. Cela signifie que poussière et quantité de mouvement ne sont pas toujours transportées par les mêmes tourbillons. Le modèle a démontré que la cause principale de cette dissimilarité est l’intermittence de l’émission de poussières, qui varie avec l’intensité du vent et le fetch.L’impact de la végétation éparse sur le flux net de poussière émis a ensuite été étudié sur la base de l’expérimentation WIND-O-V 2018, conduite sur le même site que celle de 2017. Les mesures ont été utilisées pour évaluer le modèle 3D d’érosion incluant les caractéristiques de la végétation. La comparaison entre les expérimentations 2017 et 2018 a confirmé que la végétation éparse réduit l’émission en augmentant la vitesse de frottement seuil de l’érosion, qui dépend des caractéristiques de la végétation et de la direction du vent. Au cours de l’expérimentation 2018, nous avons observé que la PSD du flux net de poussière émis variait, contrairement à 2017, avec un appauvrissement progressif en grosses particules (1.50 µm). Il s’est avéré que cet appauvrissement n’était pas lié à la présence de végétation, mais à l'épuisement du sol en grosses particules en raison de périodes d’émission plus longues sans modification de la surface, comparé à 2017. Cette absence d’influence de la végétation a été validée par la similarité entre la PSD du flux de poussière au début de l’expérimentation 2018, quand la végétation était à sa hauteur maximum, et celle de 2017 sans végétation. Et elle a été confirmée par nos simulations qui montrent (i) une re-déposition négligeable des grosses particules sur la végétation durant les émissions, et (ii) un effet négligeable de la turbulence induite par la végétation sur la PSD du flux net de poussière émis.Notre modèle 3D d’érosion apparaît comme un outil prometteur pour caractériser les émissions de poussière sur des surfaces hétérogènes représentatives des régions semi-arides et pour établir des schémas d’émission de poussières pour les modèles climatiques en fonction des propriétés de rugosité de la surfaceAtmospheric mineral dust resulting from aeolian soil erosion affects the Earth system. Their size-distribution (PSD) plays a key role on atmospheric radiation balance, cloud formation, atmospheric chemistry, and the productivity of terrestrial and marine ecosystems. However, climate models still fail to reproduce accurately the suspended dust PSD. This is explained by the poor representation of the dust emission mechanisms and the associated surface wind speed in these large-scale models. This is particularly true in the presence of surface roughnesses such as vegetation in semiarid regions. This thesis aims at improving the understanding of dust emission in semi-arid environments, characterized by heterogeneous surfaces with sparse seasonal vegetation. To this end, a combination of numerical and field experiments was employed, with investigations progressing from a bare erodible soil to surfaces with sparse vegetation.A review of the existing dust emission schemes showed ambiguities in the parametrization of the processes influencing the emitted dust. A sensitivity analysis, using a 1D dust dispersal model, demonstrated (i) the importance of surface dust PSD and inter-particle cohesive bond parametrization on the emitted dust PSD, and (ii) the importance of the deposition process on the net dust flux PSD. Based on this analysis, a new emission scheme was incorporated into a 3D erosion model, coupled with a Large Eddy Simulation (LES) airflow model, and evaluated first on a bare surface against the WIND-O-V’s 2017 field experiment in Tunisia. The model was able to reproduce the near-surface turbulent transport dissimilarity between dust and momentum observed during the experiment. This means that momentum and dust are not always transported by the same turbulent eddies. The model demonstrated that the main cause of this dissimilarity is the dust emission intermittency, which varies as a function of wind intensity and fetch.The role of sparse vegetation on the net emitted dust flux was then explored using the WIND-O-V’s 2018 experiment, conducted at the same site as the 2017 experiment. The resulting field measurements were used to evaluate the 3D erosion model, including vegetation characteristics. A comparison between the 2017 and 2018 experiments confirmed that sparse vegetation reduces dust emission by increasing the erosion threshold friction velocity, which depends on vegetation characteristics and wind direction relative to the vegetation arrangement. During the 2018 experiment, the net emitted dust flux PSD varied continuously, unlike the 2017 experiment, with a progressive impoverishment in coarse particles (1.50 μm). This impoverishment was found independent of the vegetation, and resulted from the depletion of coarse particles at the surface due to longer emission periods in 2018 without surface tillage or precipitation. This non-influence of vegetation on the dust flux PSD was validated by the similarity of the dust flux PSD at the beginning of the 2018 experiment, when the vegetation was at its maximum height, with the one of the 2017 experiment without vegetation. It was further confirmed by the simulations that demonstrated (i) negligible re-deposition of coarse particles on to vegetation during emission events, and (ii) negligible effect of the turbulence induced by the vegetation on the PSD of the net emitted dust flux.Our 3D erosion model appears as a promising tool for characterizing dust emissions over heterogeneous surfaces typical of semi-arid regions and for deriving dust emission schemes for climate models as a function of surface roughness properties
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Shannon, Debbie Anne. "Atmosphere-vegetation interactions over South Africa". Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/22109.
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Bibliography: pages 107-118.This study examines the sensitivity of the atmospheric circulation to vegetation change over South Africa in the context of the portended global warming. This is achieved using a vegetation model driven by climate change information and subsequently incorporated within a general circulation model (GCM). The stand-alone vegetation model is driven using precipitation, temperature and relative humidity derived from downscaling using artificial neural networks. The vegetation model is then run with perturbed precipitation, temperature and relative humidity from downscaled model data from lxCO₂ and 2xCO₂ GCM simulations. The resultant vegetation perturbation response to climate change is then examined and incorporated into the GCM in order to ascertain the atmospheric sensitivity to vegetation changes. The off-line results of the vegetation model indicate a moderate degree of sensitivity of the vegetation to perturbations in precipitation, temperature and relative humidity. The general trend in response to the CO₂ climate is a westwards and altitudinal shift of lowland vegetation over the eastern part of the country, and a southwards and eastwards shift of the more dryland vegetation in the west. These shifts are in accordance with expected responses, since lowland vegetation responds more to temperature changes and the dryland vegetation to precipitation changes. Nonetheless, the use of the model provides a physically justifiable scenario on which to base the GCM studies, and at a finer resolution than otherwise available. A GCM simulation with the perturbed vegetation was then performed using sea surface temperature boundary conditions for 1980 and compared to an identical GCM run without the perturbation. 1980 was chosen since this year does not represent either a strong El Niño or La Niña year. The atmospheric sensitivity to the vegetation perturbation has been examined in terms of climatic variables such as temperature, precipitation, pressure, specific humidity, horizontal divergence, and sensible and latent heat fluxes. The results show that the atmosphere is quite sensitive to relatively small vegetation changes. Atmospheric response to vegetation perturbations indicates greater sensitivity over the NW and SE regions of southern Africa. The perturbation indicates a reduction in precipitation over the SE interior, related to less moisture feeding in over the interior from the SE Indian Ocean. Wind speed changes over the adjacent ocean were also evident, and are probably related to the changes in the South Atlantic and Indian high pressures. A southwards extension of the Hadley Cell was also suggested, as well as changes in sensible and latent heat fluxes, relating to precipitation and temperature changes. It is suggested that changes may be in response to the general drying out of the country and the associated increase in aridity. This research forms the preliminary investigation for further work incorporating the atmospheric perturbation response back into driving the vegetation model in order to examine the direction of the feedback -- whether this is positive or negative in the longer term. Thus, this study has demonstrated that the atmosphere is significantly sensitive to vegetation changes over South Africa and reinforces the need for improved land surface parameterization schemes and vegetation models in general circulation models.
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Ohanyan, Vahe A. "Computer Models for Vegetation Diversity Analysis". Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1328879870.
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Borgelt, Jan. "Terrestrial respiration across tundra vegetation types". Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-132765.
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Large amounts of carbon (C) are stored in tundra soils. Global warming may turn tundra ecosystems from C sinks into sources or vice versa, depending on the balance between gross primary production (GPP), ecosystem respiration (ER) and the resulting net ecosystem exchange (NEE). We aimed to quantify the summer season C balance of a 27 km2 tundra landscape in subarctic Sweden. We measured CO2 fluxes in 37 widely distributed plots across five tundra vegetation types and in 7 additional bare soil plots, to assess effects of abiotic and biotic components on C exchange. C fluxes in bare soils were low and differed to all vegetation types. Thus, accounting for differences between bare soils and vegetated parts is crucial for upscaling a C balance using a landcover classification map. In addition, we found that both NEE and ER, varied within and across different tundra vegetation types. The C balance model for the growing season 2016 revealed a net C loss to the atmosphere. Most vegetation types acted as CO2 sources, with highest source strength in dense shrub vegetation at low elevations. The only considerable C sinks were graminoid-dominated upland meadows. In addition, we found a shift in C balance between different heath vegetation types, ranging from C source in dense deciduous shrub vegetation (Mesic Heath and Dry Heath) to C sink in low growing shrub vegetation (Extremely Dry Heath). These results highlight the importance to account for differences between vegetation types when modelling C fluxes from plot to landscape level.
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Hester, Alison Janet. "Vegetation succession under developing birch woods". Thesis, University of Aberdeen, 1988. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU010074.
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Birch readily colonizes heather moorland in the absence of regular burning, and successional changes in the dominance of various plant species take place beneath the developing woodland. Birch (unlike Calluna vulgaris and many conifers) has long been thought to have an ameliorating effect on soils. Changes such as this in association with other environmental changes accompanying the development of birch woodland can have complex and often interactive effects on the species involved in a succession of this sort. It is not known to what degree the changes in species dominance beneath developing birch can be attributed to soil changes or to other factors such as changing light levels, leaf litter, or grazing animals, for example. This thesis examines some of the species changes taking place beneath birch stands of different ages which have colonized heather moorland in north-east Scotland and attempts to elucidate some of the mechanisms controlling these species changes. (1) Examination of seed inputs revealed that this factor restricts the colonization of some, but not all, later successional species. (2) Germination of most species was unaffected by age of birch stand, but early growth of all species improved with increasing age of birch stand. (3) Results of experiments altering light intensity, nutrient availability and simulated grazing gave information on the relative importance of these factors in controlling the species changes beneath the birch stands studied. (4) The predictive ability of a Markov model in the simulation of succession under birch was shown to be limited; the use of this model did generate some interesting hypotheses about the nature of some of the processes of change operating in this successional system.
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Eklund, Carl. "Ståndortsfaktorer och vegetation : En problematiserande litteraturstudie". Thesis, Stockholms universitet, Institutionen för naturgeografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-144161.
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Ståndort är ett område där ett bestånd av en viss växt finns, ofta avses träd inom skogsproduktion. Förutsättningarna för detta, ståndortsfaktorer, återfinns i markens egenskaper (edafiska faktorer) och klimatet. Dessa påverkar därigenom växtens produktion, något som särskilt är av intresse inom skogsbruket och de skogliga vetenskaperna. Till detta kommer att växter samspelar med andra växter och organismer såsom svampar, bakterier och djur, och även den antropogena påverkan med faktorer såsom husdjursbete, atmosfäriskt nedfall och skogsproduktion har en stark inverkan på vegetationen. Utifrån att studera några av de mer kända teorierna om växtsamhällen och -strategier samt olika vinklar av ståndortsfaktorer var hypotesen att det går att få fram en problematiserande bild och hitta störfaktorer (confoundingvariabler), som kan ge felaktiga tolkningar av resultat. Ett antal kända verk inom vegetationsklassificering gicks igenom, kompletterat med stödjande litteratur. En artikelsökning genomfördes också, med kombinationer av specifika sökord med anknytning till ståndort. För att begränsa urvalet och ge en mer regional prägel på arbetet ställdes sökfiltren i artikelsökningen in på att enbart visa resultat från Skandinavien och Finland. Artiklarna delades in efter teman och behandlades efter dessa. Även om få huvudsakliga faktorer styr vegetationen finns flera variabler som lokalt har en stor betydelse, såsom snö, genetiska egenskaper och symbios med andra organismer. Dessa variabler kan vara svåra att mäta och det finns mycket på detaljnivå som är dåligt undersökt. Markanvändningar påverkar de edafiska faktorerna långt efter att brukandet ändrats eller upphört, men detta har olika stor lokal påverkan. Kvävets och kolets halter och cykler är återkommande osäkerhetsfaktorer i artiklarna, där det atmosfäriska kvävenedfallet spelar en viktig men ojämn roll, och jämförbara mätningar försvåras av skillnader i väder och klimat. Till detta kommer påverkan av markorganismer, vilka har en mycket viktig del i växternas näringsupptag, men är svår att mäta. Även om alla aspekter av en växtplats inte kan tas med bör fler felkällor tas i beaktande och modeller ha möjlighet att kalibreras mot olika teorier om växtsamhällen och -strategier. Flera faktorer som traditionellt inte räknas som ståndortsfaktorer, såsom snödjup, symbios med markorganismer och markanvändning, kan vara betydelsefulla att ta med i exempelvis modellering.A site is an area where a population of a specific plant species has its habitat, often the connotation is forestry. The prerequisites for this, the site indices (also site variables or stand variables), can be found in the characteristics of the ground (edaphic factors) as well as the climatic impact. These elements affect the growth and production, which is of interest in forestry and forest sciences. Upon this the plants interact with each other as well as with other organisms, i.e. fungi, bacteria and animals, and there is also an anthropogenic impact where factors such as livestock grazing, atmospheric deposition and forest production strongly affects the vegetation. By studying some of the more prominent theories on vegetation societies/sociologies and plant strategies, as well as different aspects of the site concept, the hypothesis was that a problematizing picture of site indices can be found and some confounding variables that can give erroneous interpretation of results. A number of major works in vegetation classification was gone through, supplemented by supporting literature. An article search was conducted to find journal articles, using combinations of specific search terms related to site indices. To narrow down the results and give a more regional touch to the thesis, the filter was set only to show results from Scandinavia and Finland. The articles were grouped into themes and handled theme-wise. Even though there are few principal factors controlling the vegetation there are a number of variables which locally can have a large impact, such as snow, genetic traits and symbiosis. These variables can be hard to measure, and a lot of things at a detailed level are poorly investigated. Land use modifies the edaphic properties long after the usage have changed or been discontinued. The amounts and cycles of nitrogen and carbon are recurrent uncertainties in the articles, where deposits of nitrogen from the atmosphere plays an important but uneven role and measurements can be hard to compare due to differences in weather and climate. Added to this, organisms in the ground have a major role in the plants’ nutrient uptake, but the effects can be hard to study. A concluding remark is that even though all aspects of a site cannot always be included more confounding variables could be taken in account and models should be able to be calibrated to different theories on vegetation societies/sociologies and plant strategies. Many factors normally not counted as site indices, i.e. snow depth, soil biota symbiosis, and land use, could be valuable to include in e.g. modelling.
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Baierle, Heinz Ullrich. "Vegetation und Flora im südwestlichen Jordanien /". Berlin [u.a.] : Cramer, 1993. http://www.gbv.de/dms/bs/toc/126235503.pdf.
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Santini, Gonzalez Bianca Ariana. "Plant functional traits and vegetation strategies". Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/12119/.
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In this thesis we tested the predictions from the CSR theory for the community membership. Predictions are that, in the absence of competition, species from all strategies (Competitors, Ruderals and Stress-tolerants) will persist in low-stress habitats, whereas in high-stress habitats, only species with Stress-tolerant traits will survive. CSR recognizes that species evolved similar traits to one universal stress. For this reason, we were interested in testing which strategies will survive in different sources of stress. Our results from field and greenhouse experiments suggest that CSR theory does not predict community membership from the initial stages of a plant life-cycle. Instead, we found that the habitat stress plays a major role in determining the species that are incorporated into a community. In this thesis we also used a trait-based approach to evaluate: 1) the relationship between key traits using annuals species, and 2) the links between genome size and phenotypic variation within species. Firstly, we studied the triangular relationship reported for seed mass and leaf area in woody species. These traits are involved in the plant reproduction strategy and plant water and energy-use. We found a triangular relationship in annuals species, suggesting that is conserved across groups (woody and annuals). We also found that the driver of this relationship is related to soil fertility. Finally, for the relationship between genome size and phenotypic variation within species, we found that larger genome species display higher variation in traits than small genome species. This can be a potential advantage in heterogeneous environments where the amount of phenotypic variation would allow the species to adapt to them.