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Vonlanthen, Corinne Maria. "Alpine plant communities : ecology and species richness /." [S.l.] : [s.n.], 2005. http://www.zb.unibe.ch/download/eldiss/05vonlanthen_c.pdf.
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Dupré, Cecilia. "Regional and local variation in plant species richness." Doctoral thesis, Uppsala universitet, Institutionen för evolutionsbiologi, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-691.
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In this thesis, I examine the variation in plant species richness along gradients of productivity and disturbance in grasslands and forest habitats in southern Sweden, and I compare the documented patterns with theoretical predictions. Moreover, I evaluate the relative importance of habitat quality and habitat configuration for the occurrence of field layer species in deciduous forests. Finally, I present a new method for the determination of the regional species pool. To examine regional and local variation in plant species richness, I gathered data on species composition in plots of different size (0.001 - 1000 m2) in three vegetation types (deciduous forests, dry grasslands and coastal meadows) in four regions of southern Sweden (Öland, Gotland, Småland and Uppland). As predicted by the species pool hypothesis, differences in small-scale species richness of deciduous forests and dry grasslands were correlated with differences in the size of the regional species pool. Moreover, among plots large-scale diversity was predictive of small-scale diversity. Species diversity showed a hump-shaped relationship with productivity in forests, and was related to environmental heterogeneity and the size of the 'habitat-specific' species pool. In the two types of grassland examined, grazed sites were richer in species than abandoned sites. Moreover, both species composition and the representation of plants with different life-history characteristics differed between grazed and abandoned sites. As predicted by the intermediate disturbance hypothesis, species richness was highest at intermediate levels of grazing in coastal meadows. However, all the above patterns were scale-dependent, and not observed at all plot sizes. The occurrence of field layer species in deciduous forests was more strongly related to habitat quality (mainly soil factors) than to habitat configuration (forest area and isolation). Across species, low seed production, clonal reproduction and habitat specificity were negatively associated with isolation.
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Dupré, Cecilia. "Regional and local variation in plant species richness /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5064-4/.
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Harral, Josephine Erica. "Experiments on resource availability and plant species richness." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415053.
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Downer, Monica Ruth. "Plant Species Richness and Species Area Relationships in a Florida Sandhill." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4030.
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Pine sandhill are integral pyrogenic communities in the southeastern United States. Though once widespread, habitat destruction, fire suppression and fragmentation have reduced the population to nearly 3%. It is important to learn as much as possible about these unique areas in order to implement best management practices to conserve and restore the existing populations of these communities.
Fire is central to the maintenance of pine sandhill communities and two conceptual hypothesis regarding burn frequency have come to light in maintaining the unique species composition and richness of these areas. The first is the Intermediate Disturbance Hypothesis which suggests that intermediate fire regime maintains species diversity. The second is the Most Frequent Fire Hypothesis suggests that these areas should be burned as frequently as fuels allow.
We used species area curves and species area relationships to answer the following questions about a pine sandhill community in the burn plot area of the University of South Florida Ecological Research Area (ERA). What are the patterns of species richness and how do they change with spatial scale? What are the factors contributing to the heterogeneity of this area and how much are they contributing? Do similarly burned areas have similar species composition? Do our results shed some light on the Intermediate Disturbance Hypothesis or Most Frequent Fire Hypothesis?
We found that physical distance contributed more to species compositional and spatial patterns than burn regime or elevation, whose effects were small. On this particular scale, the results did not support either the Intermediate Disturbance Hypothesis or Most Frequent Fire Hypothesis, as acquisition rates of species in all burn regimes were quite similar. There was no obvious pattern of increased species richness with frequent or intermediate burning.
Our results suggest a need for a dynamic plan for the conservation, preservation and management of pine sandhill communities. One must consider as many factors as possible when managing these lands, as every sandhill is unique. More research should be conducted on these ecologically sensitive and diminished areas in order to formulate best management practices to conserve, protect and restore pine sandhill in the southeastern United States.
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Williams, Brandon M. "The influence of soil heterogeneity on plant species richness." Thesis, Wichita State University, 2013. http://hdl.handle.net/10057/10650.
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Environmental heterogeneity is often cited as one of the driving mechanisms behind community species composition and diversity. However, its contribution to species composition in plant communities remains unclear because few experiments demonstrate a causal link between environmental heterogeneity and plant diversity. This is particularly true for soil manipulations despite that fact that soil is expected to provide the key resources necessary for plant growth. Here, I utilize a unique manipulation of the soil profile to create communities with spatially heterogeneous and homogeneous soil arrangements and examine the influence of soil heterogeneity on community structure, through species composition and flowering patterns, during community assembly. I employed an annual census of the assembling communities and recorded the identity and density of all species within the patches. After two years, I found that species richness was significantly higher in heterogeneous than in homogeneous plots. In the heterogeneous plots, thirteen species had higher greater establishment rates in a specific patch type representing one of the three soil strata. However, no species had greater association with the mixed stratum, comprising the homogeneous plots, than one of the heterogeneous strata. This pattern of species sorting between soil types suggests that the increased richness in heterogeneous plots is due to the increased variety of soil types comprising those communities. Alternatively, species richness in homogeneous plots, where species did not sort to distinct soils, was strongly associated with total plant density. This experiment is one of the first to provide clear, experimental evidence that fine-scale soil heterogeneity increases species richness through species sorting during community assembly.Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Biological Sciences
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Steinmann, Katharina. "Testing basic assumptions of species richness hypotheses using plant species distribution data /." Zürich, 2008. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000254735.
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Pollock, Michael Moritz. "Patterns of plant species richness in emergent and forestry wetlands of southeast Alaska /." Thesis, Connect to this title online; UW restricted, 1995. http://hdl.handle.net/1773/5518.
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Hampton, Mark Edward. "The effects of disturbance and herbivory on plant community structure, plant recruitment and species richness." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417237.
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Boag, Angela Elaine. "Spatial models of plant species richness for British Columbia's Garry oak meadow ecosystem." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46920.
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Garry oak meadow ecosystems in British Columbia are fragmented, increasingly
degraded, and have been prioritized for conservation. While distribution maps of remnant
meadow patches have been developed, the ecological integrity of plant communities in
many of these remnants remains unknown. Modeling and mapping ecological integrity
could inform conservation prioritization exercises in the region.
The primary goal of this thesis was to develop distribution models of native and exotic
plant species richness in Garry oak meadow remnants. Secondly, multiple independent
datasets were used to analyze the effects of sample size and sampling bias on the
accuracy and reliability of resulting predictive maps, which is an active area of research
in species distribution modeling. Finally, I investigated whether Terrestrial Ecosystem
Mapping (TEM) – a publicly available GIS layer of plant community associations –
provided a valid geographical extent over which to map predictions.
In Chapter 2, different datasets were found to produce different models of species
richness. However, different native richness models produced similar distribution maps,
while exotic richness maps based on different datasets were less similar. The
incorporation of spatial variables into models did not improve model fit, however
significant residual spatial autocorrelation at a broad scale was detected in some cases,
suggesting that an important environmental covariate is missing from these models.
Examples of potential missing covariates include deer density and disturbance history.
Overall, this research demonstrates that multiple independent datasets are very important
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for validating species distribution models, especially in heterogeneous landscapes.
Additionally, large sample sizes and sampling broadly across of the area of prediction
result in more robust models.
The results presented in Chapter 3 suggest that mapping predictions exclusively over
Garry oak ecosystem-classified TEM polygons is potentially overly conservative, as
species richness of native meadow species was found to be high in other TEM
classifications as well. This suggests that Garry oak meadow plant communities do not
exist solely in discreet meadow patches, and that they are dispersed throughout other
habitat types including Douglas-fir – salal forests.
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Duncan, Allison B. "Relationship between remnant size and plant species richness in the Tucson urban matrix." Thesis, The University of Arizona, 2002. http://hdl.handle.net/10150/278795.
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The Sonoran Desert surrounding Tucson, Arizona is the dominant matrix in a region undergoing a transition from desert matrix to urban matrix with little emphasis placed on preserving this native ecosystem intact. Instead, patches of desert, remnants, are cut off the desert matrix and surrounded by a variety of land uses including residential, transit, and commercial. 31 sites within the City of Tucson were surveyed and the site's plant species richness, woody cover, herbaceous cover, and disturbance percentage measured. The plants found on-site were classified into native or exotic, annual or perennial, and woody or herbaceous, and further broken down into growth form. Results indicated a significant correlation between a site's area and its percent disturbance, as well as correlations between its native vegetation and area.
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Steffan, Shawn Alan. "Biodiversity and fear ecology the cascading effects of species richness and nontrophic interactions /." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Dissertations/Spring2009/s_steffan_041709.pdf.
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Wilson, Frederick. "Factors affecting the species richness of old permanent semi-natural grasslands in North-East Scotland." Thesis, University of Aberdeen, 2003. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU173020.
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The successful management for conservation and restoration of semi-natural ecosystems may be achieved only after the factors which regulate plant biodiversity and species composition have been identified. This study investigates the floristic composition and site characteristics of old permanent semi-natural grasslands in North-east Scotland and tests using pot and field experiments the role of soil fertility in determining vascular plant species richness, relative abundance and dynamics of communities. Results from field surveys show that, of the site characteristics quantified, vascular plant species richness is most strongly correlated (negative relationship) with extractable soil phosphorus. Where species richness is high (>40 in a study stand and >17 in a 1 m2 quadrat) extractable soil phosphorus levels (determined by ammonium acetate-acetic acid/polyacrylamide solution extraction and using inductively coupled radio frequency plasma spectrometry by the atomic emission method) are consistently very low (<1.9 mg 1-1 soil) by local agricultural standards. In pot experiments using soil from a site where high species richness is maintained, the loss of forb and graminoid species from synthesised communities may be shown to increase along a nutrient gradient created by incorporating increments of phosphorus. Despite a general increase in the above ground biomass of species which survive, those with the ability to form nitrogen-fixing nodules grow to dominate the community. By comparison, a nutrient gradient created by the incorporation of potassium has little effect on the species richness of synthesised communities. At field sites where the level of extractable soil phosphorus approaches that above which species-rich semi-natural grassland communities are not found to exist, the addition of nitrogen leads to species loss through the dominance of graminoid species. This effect may be intensified by applying phosphorus.
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Pinto, Leonardo Henrique Teixeira. "Restoration of plant diversity and ecosystem functioning: effects of species richness, phylogenetic distance, functional diversity and invasive plants." PROGRAMA DE P?S-GRADUA??O EM ECOLOGIA, 2017. https://repositorio.ufrn.br/jspui/handle/123456789/23964.
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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
A biodiversidade afeta positivamente diversas fun??es ecossist?micas. No entanto, os mecanismos pelos quais a biodiversidade afeta os ecossistemas ainda s?o pouco compreendidos e requerem novos estudos experimentais destinados a identificar seus componentes. Estudos anteriores sugeriram que comunidades de plantas mais diversas podem proporcionar mais estabilidade aos ecossistemas, devido aos efeitos de complementaridade e redund?ncia. A diversidade das esp?cies de plantas pode atuar em diferentes n?veis das propriedades de um ecossistema. Um exemplo claro ? o efeito da diversidade de plantas sobre a din?mica de nutrientes nos ecossistemas terrestres. A diversidade de plants pode alterar as taxas de ac?mulo de nutrientes no solo e, tamb?m, a carga de nutrientes para os sistemas aqu?ticos. No entanto, os impactos antr?picos nos ecossistemas t?m causado a perda de habitats e, tamb?m, de biodiversidade. Tais perdas acabar?o por comprometer as fun??es dos ecossistemas e seus servi?os associados, que s?o vitais para o bem-estar humano. Portanto, o desenvolvimento de projetos de restaura??o ? fundamental para mitigar os impactos antr?picos e para a conserva??o da biodiversidade. Projetos de restaura??o oferecem a possibilidade de desenvolver um conhecimento s?lido sobre o funcionamento dos ecossistemas diante diferentes tipos de perturba??es. Para alcan?ar esse conhecimento, precisamos realizar experimentos de restaura??o baseados no conhecimento cient?fico para avaliar a variabilidade, a previsibilidade e a confiabilidade do funcionamento dos ecossistemas restaurados. Neste contexto, esta tese de doutorado ? baseada em tr?s experimentos que testaram como a diversidade de plantas e suas caracter?sticas funcionais poderiam influenciar o funcionamento dos ecossistemas restaurados. Os objetivos dessa tese foram: (i) investigar quais esp?cies de plantas e caracter?sticas funcionais s?o mais eficientes paraa reten??o de nutrientes no solo, reduzindo assim as perdas por lixivia??o e seu consequente impacto nos ecossistemas aqu?ticos; (ii) testar os efeitos da riqueza de esp?cies vegetais e da diversidade filogen?tica para o sucesso da restaura??o de uma floresta rip?ria rec?m restaurada (i.e. o sucesso foi medido como produ??o de biomassa e sobreviv?ncia das plantas); e (iii) avaliar a influ?ncia de uma esp?cie de planta invasora sobre as din?micas de nutrientes no solo e na ?gua do solo em comunidades de pastagem com diferentes n?veis de diversidade funcional. Os experimentos realizados para esta tese est?o de acordo com estudos recentes que investigam como diferentes medidas de biodiversidade e, tamb?m, diferentes fontes de estresse podem afetar o funcionamento dos ecossistemas. Os principais resultados desta tese revelam que (i) apenas uma esp?cie de planta (Mimosa tenuiflora) influenciou a limpeza da ?gua e a reten??o de nutrientes do solo. Al?m disso, tra?os funcionais relacionados ao conte?do de mat?ria seca da parte a?rea (SDMC) e ao teor de ?gua da raiz (RWC) foram mais importantes para o controle de fun??es ecossist?micas individuais relacionadas ? reten??o de ?gua e nutrientes no solo. De outro modo, somente tra?os funcionais relacionados ? produ??o de biomassa nas plantas afetaram a multifuncionalidade do ecossistema; (ii) o uso de esp?cies filogeneticamente distantes pode aumentar o sucesso da restaura??o afetando positivamente a produ??o de biomassa nas plantas; e (iii) a diversidade funcional das plantas promoveu, parcialmente, a limpeza da ?gua e, tamb?m, a fertilidade do solo em pastagens restaurados, mas n?o impediu a invas?o. Esp?cies invasoras, por sua vez, comprometem a influ?ncia da diversidade de plantas nativas na din?mica de nutrientes no solo, uma vez que afetam negativamente a produ??o de biomassa das plantas nativas. Esse efeito tem o potencial para criar um feedback positivo para novas invas?es. Tais resultados podem servir de suporte para o desenvolvimento de futuros projetos de restaura??o com ?nfase no controle de esp?cies invasoras e na restaura??o do funcionamento dos ecossistemas, uma vez que pode indicar quais esp?cies s?o mais adequadas para maximizar a fertilidade do solo e, tamb?m, a qualidade da ?gua do solo. Por fim, esta tese oferece uma contribui??o para o aprofundarmos o entendimento a respeito dos feedbacks entre plantas e solos.
Biodiversity positively affects several ecosystem functions. Nevertheless, the mechanisms by which biodiversity affects ecosystems are still poorly understood and call for new experimental studies designed to identify its underlying components. Previous studies have suggested that more diverse plant communities can provide more ecosystem stability due to complementarity and redundancy effects. Plant species diversity can act on different levels of the ecosystem properties. A clear example is the effect of plant diversity on nutrient dynamics of terrestrial ecosystems. Plant diversity can alter rates of soil nutrient accumulation and nutrient loading in aquatic systems. However, human impacts on natural ecosystems are leading to habitat and biodiversity loss. Such losses will ultimately jeopardize ecosystem functions and its associated services that are vital for human well-being. Therefore, the development of adequate restoration projects is paramount to mitigate anthropogenic impacts, while contributing to the conservation of biodiversity. Restoration projects offer the possibility to develop a solid knowledge on the functioning of ecosystems facing disturbance. For achieving this knowledge, we need to conduct theory-based restoration experiments in order to assess the variability, predictability and reliability of functioning from restored ecosystems. In this context, this PhD thesis is based on three experiments testing how plant diversity and functional traits would influence the functioning of restored ecosystems. The objectives are to investigate (i) the plant species and traits that are most efficient for retaining nutrients in the soil, thus reducing nutrient leaching losses and its consequent impact on aquatic systems; (ii) the effects of plant species richness and phylogenetic diversity on restoration success (measured as biomass production and plant survival) in a recently restored riparian forest; and (iii) the influence of an invasive alien plant species on soil and soil water nutrients in communities with different levels of functional diversity. The experiments conducted during this thesis are in accordance with recent studies that investigate how different measures of biodiversity and sources of stress could affect ecosystem functioning. The main results of this thesis reveal that (i) only one species (Mimosa tenuiflora) could influence water cleaning and soil nutrient content. Additionally, plant traits related to shoot dry matter content (SDMC) and root water content (RWC) are more important for controlling individual functions related to water and nutrient retention in the soil, while only traits related to biomass production affected ecosystem multifunctionality; (ii) the use of phylogenetically distant species can increase restoration success by positively affecting plant biomass production; and (iii) plant functional diversity partially promotes water cleaning and soil fertility in restored systems, nevertheless did not prevent invasion. In turn, invasive species disrupts the influence of plant diversity on soil nutrient dynamics by jeopardizing native plant biomass production thus, potentially, creating a positive feedback for further invasions. These results support future restoration projects focusing on invasive species control and ecosystem functions, indicating which species are most suitable for restoration to maximizing soil fertility and soil water quality. Finally, this thesis offers a contribution to the knowledge of plant-soil feedbacks.
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Van, Tonder Carlo. "Factors influencing species richness, cover and composition of vegetation on Namaqualand quartz fields." Thesis, Nelson Mandela Metropolitan University, 2006. http://hdl.handle.net/10948/630.
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Quartz fields contribute significantly to plant diversity in the Succulent Karoo biome. They are distinctly different from surrounding habitats and have high levels of plant endemism. Biological soil crusts are features of quartz field soils and fulfill a vital function in that they stabilize soils. It is important for managers of nature reserves and agricultural rangelands to know what factors influence quartz field soils and vegetation. Both stakeholders could benefit from new information that would allow for informed decision-making regarding land-use on quartz fields. The present study took place in the Namaqua National Park that contains a significant proportion of the Riethuis-Wallekraal quartz fields phytochorion. The first part of the study aimed to understand whether certain land-use activities potentially destabilize quartz field soils, which might have possible ramifications for associated biological soil crusts and vegetation. It was followed by relating variation in soil stability with species richness, cover and species composition of quartz field vegetation. Overall, positions assumed to be impacted by land-use activities had less stable soils compared to positions assumed not be impacted. Soil stability had a significant influence on species richness and cover but to a lesser degree on species composition. Quartz field vegetation was significantly influenced by soil physical and chemical properties as well as location in the quartz fields landscape. The second part of the study aimed at understanding how species richness of isolated quartz outcrops is related to their size compared to that of a mainland body of quartz outcrops. No clear species-area relationships emerged from the study. There were significant differences between isolated outcrops and mainland outcrops in substrate and vegetation composition. Findings are discussed in relation to Island Biogeography Theory.
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Hoare, David Barry. "Patterns and determinants of species richness in mesic temparate grasslands of South Africa." Thesis, Nelson Mandela Metropolitan University, 2009. http://hdl.handle.net/10948/1275.
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The aim of this study is to gain a predictive understanding of the patterns and determinants of plant biodiversity in temperate, mesic grasslands of South Africa with a primary focus on the geographical area of the Eastern Cape. From a review of the literature on hypotheses explaining diversity (Chapter 2) it was possible to formulate a number of hypotheses that could be tested to explain species richness patterns in Eastern Cape grasslands. This thesis is organised so that each main chapter deals with a specific body of theory concerning the explanation of diversity patterns. A detailed description of the study area is provided (Chapter 3), including environmental variation and a description of major vegetation patterns. A summary is provided of grassland plant community patterns, as determined by phytosociological studies in the study area. A multivariate analysis of environmental variables was undertaken to determine which variables contributed the most towards explaining environmental variation in the study area and to determine whether any variables co-vary, a possible problem for any multivariate analysis in later chapters. Altitude produced one of the strongest gradients in the study area. There were a number of variables that were correlated with altitude, most notably temperature. Rainfall co-varied partially with altitude, but there was also a strong rainfall gradient perpendicular to the altitude gradient. A description of species richness, diversity and evenness patterns at the plot scale within different grassland plant communities of the Eastern Cape is provided in Chapter 4. To determine whether the environment acts differently on different growth forms, the contribution to species richness by different major growth forms is analysed. Furthermore, since the majority of literature attempts to explain diversity in terms of environmental factors, it was necessary to analyse the relationship between species richness and various environmental variables. The results indicate that there is high variation in species richness both within and among grassland communities. Forbs make the most significant contribution to overall species richness per 100 m2, followed by grasses. Variance in richness of all species together is not significantly related to environmental variables in mesic grasslands, but is significantly related to environmental variables in semi-arid grasslands. The result of greatest interest from this chapter is the fact that richness amongst different life-forms in the same place is explained by different environmental factors, indicating that the environmental factors that affect coexistence of species have a different effect on different life-forms. A classification of all the species of the dataset into plant functional types using a multivariate approach based on functional traits was conducted (Chapter 5). The grass species were classified into 16 functional types and the forbs into 14 functional types. The functional type classification provided the opportunity for undertaking analyses to develop an understanding of 8 the contribution by niche differentiation towards promoting species richness (Chapter 6). The results provide evidence of niche differentiation in the grasslands of the study area and also that niche differentiation promotes species richness in the grasslands of the study area. It was found that higher rainfall grasslands are less structured by niche differentiation than semi-arid grasslands. A regional / historical analysis is undertaken (Chapter 7) to investigate the relationship between the regional species pool and local richness, and the relationship between local richness and phytochorological diversity. Regional richness appears to have little effect in promoting local richness in grassland plant communities of the study area except at sites where there is high local richness. This provides an indication that regional richness only promotes local richness in the absence of local limiting factors. Phytochorological diversity promotes local richness, but mostly through diversity amongst species with narrow distribution ranges. Some theories ascertain that seasonal uncertainty may provide opportunities to species that would otherwise be outcompeted and thereby promote local richness. The degree to which seasonal uncertainty and seasonality promote local richness in the Eastern Cape grasslands was therefore investigated (Chapter 8). A weak relationship exists between these variables and local species richness in grassland communities of the study area, indicating that they do not promote niche differentiation to a significant degree in the study area. It is clear that in the grasslands of the Eastern Cape, environmental limiting factors are more important in semi-arid grasslands and species interactions are more important in mesic grasslands for structuring plant communities (Chapter 9, Discussion). Regional processes do not appear to be important in structuring local communities, but the analysis undertaken in this study shows that they may be significant when factors operating at the other two levels are overcome (species interactions and environmental limiting factors.
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Oliveira, Aliane Maria de [UNESP]. "Caracterização de uma comunidade de árvores e sua infestação por lianas em uma floresta decídua." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/95081.
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Caracterização, diversidade, estrutura e estágio sucessional da comunidade de árvores de uma Floresta Estacional Decidual no Sudeste do Brasil. A composição florística, a estrutura, a diversidade e o estágio sucessional de um fragmento de floresta foram analisados nesse estudo. O trabalho foi desenvolvido no município de Votuporanga, onde o clima é considerado Aw. Foi utilizado o método de parcelas (1 ha), amostrando todos os indivíduos arbóreos com DAS 5 cm. Foram calculados os valores de freqüência, densidade e dominância (absolutos e relativos), índice de valor de importância (IVI) e os índices de Shannon-Wiener (H’) e Equabilidade (J’). A estrutura horizontal, o estágio sucessional e a formação vegetacional foram analisados. Foram amostrados 1635 indivíduos e as famílias mais ricas foram Fabaceae (17), Myrtaceae (oito), Rubiaceae (oito) e Bignoniaceae (cinco). Casearia gossypiosperma Briq. foi a espécie com o maior IVI. O índice de diversidade de Shannon-Wienner (H´) foi 2,87 nats.indivíduo-1 e a equabilidade (J) foi 0,66 . Observou-se que 93% dos indivíduos arbóreos apresentaram diâmetros entre 1 e 20 cm. Árvores pioneiras compõem 55% dos indivíduos amostrados. A predominância de indivíduos com fenologia foliar decídua (79%) determinou a classificação do fragmento como Floresta Estacional Decidual. Assim, com este trabalho foi possível identificar uma área de Floresta Estacional Decidual no noroeste do estado e oferecer conhecimento, que são essenciais, sobre a flora, a estrutura florestal e o comportamento ecológico de Florestas Estacionais Deciduais no Estado de São Paulo
Characterization, diversity, structure and successional stage of the tree community of a Seasonal Deciduous Forest in southeastern Brazil. Floristic composition, structure, diversity, and successional stage of a fragment forest have been analyzed in this study. The work was carried out Votuporanga, where the climate is considered Aw. Plot method was used (1 ha), sampling all trees 5 cm from HSD. We calculated the values of frequency, density and dominance (absolute and relative), index of importance value (IVI), the Shannon-Wiener diversity (H') and the equability (J'). The horizontal structure, the successional stage and the vegetation formation were analyzed. We sampled 1635 individuals and the richest families were Fabaceae (17), Myrtaceae (eight), Rubiaceae (eight) and Bignoniaceae (five). Casearia gossypiosperma Briq. was the species with the highest IVI. The Shannon-Wiener diversity (H') was 2.87 nats.individual-1 and the equability (J) was 0.66. It was observed that 93% of the trees individuals had diameters between 1 and 20 cm. Pioneers trees represent 55% of samples. The prevalence of individuals with deciduous leaf phenology (79%) determined the classification of the fragment as a Deciduous Seasonal Forest.Thus, this work enabled the identification an area of deciduous seasonal forest in the northwest of the state and offered essential knowledge about the flora, the forest structure and the ecology of deciduous forests in the State of São Paulo
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Petersen, Hana. "Patterns of plant species richness and diversity across two habitat types in the Upper Karoo, South Africa." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29209.
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The Nama-Karoo biome is relatively understudied in terms of its baseline biodiversity. Apart from its rich agricultural land-use history, the region is also under pressure from the development of the Square Kilometre Array, an increased demand for cleaner energy from shale gas fracking and/or other renewable energy installations, and the overarching impacts of global climate change. A reliable baseline inventory of biodiversity for the region is essential if these impacts are to be monitored and managed effectively. The main aim of this study was to relate fine-scale patterns of plant diversity and community structure to broader-scale vegetation mapping in the Karoo regions. It also investigated the role of several environmental and climatic variables as drivers of species richness, relative cover, and growth form diversity in two habitat types (i.e. plains and rocky dolerite hillslopes), and along a longitudinal environmental gradient. A pairwise floristic survey approach was implemented, using modified Whittaker plots in each habitat type at 30 sites within the shale gas exploration area in the Upper Karoo bioregion. Data were collected on species richness, relative cover, and growth form diversity of the observed vegetation. Soil samples were collected from each Whittaker plot, and climate data were obtained by point sampling from raster layers using GIS. The results showed that mean species richness was significantly higher (p < 0.01) in slope habitats than in plains habitats across the environmental gradient. Trees and woody shrubs had significantly higher species richness (p < 0.001) and relative cover (p < 0.01) in slope habitats. Low woody shrubs comprised the greatest percentage of growth form diversity in both habitat types in terms of species richness and relative cover, and were the dominant growth form across the longitudinal gradient. At the arid western extent, leaf-succulent shrubs had slightly higher relative cover (~ 25%) in slope habitats compared to other growth forms, apart from low woody shrubs. In the central regions, perennial grasses were more abundant (25 – 60%) in slope habitats, while annual grasses were more abundant (25%) in plains habitats. At the more mesic eastern end of the longitudinal gradient, perennial grasses were dominant (> 50%) in plains habitats. Cluster analysis, based on species presence data in each habitat type, showed relatively strong correspondence between plant associations in slope habitats and their respective vegetation types as currently defined. These plant associations were spatially aggregated according to their position along the environmental gradient. Little to no correspondence was found between plant associations in plains habitats and their respective vegetation types. These plant associations were interspersed with each other when plotted spatially, and occurred in a repeating pattern in plains habitats across the study area. Multiple regression models indicated that a combination of climatic and environmental variables, and soil properties significantly predicted overall species richness and relative cover of the five dominant growth forms. Habitat type commonly emerged as a significant predictor for overall species richness and relative cover. Overall dissimilarity, and dissimilarity in the relative cover of five plant functional types between plains and slope habitats, were also predicted by a combination of climatic and environmental variables, and soil properties. These predictors varied greatly between the different response variables, suggesting that different plant functional types are influenced by different drivers, depending on the habitat in which they occur. Habitat heterogeneity, coupled with local and regional variation in prevailing climate and soils, has consistently emerged as an important driver of plant species richness and relative cover in global drylands research. Measuring richness and diversity within habitats requires a high sampling resolution in both plot size and number. This study has shown that sampling at the 0.1 ha scale (or larger) captures a representative sample of richness and diversity within a given habitat type in the Nama-Karoo biome, where low woody shrubs (< 60 cm tall) are the dominant growth form. In the current vegetation map of South Africa, the vegetation types for the Upper Karoo bioregion are coarse, and hence give the impression of homogeneity in what is in reality a relatively heterogenous landscape. Fine-scale baseline biodiversity data such as are presented in this study may improve the resolution of the existing vegetation map, as well as inform better conservation and management practices in economically important and biologically diverse rangelands in the Nama-Karoo biome, prior to future developments in the region.
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Johnson, Catherine E. "Role of Plant Species Richness in Green Roof Plots on the Quantity and Quality of Stormwater Runoff." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397734513.
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Haig, April Raissa. "The effect of habitat fragmentation on lichen and plant species richness of Niagara Escarpment cliffs in Ontario, Canada." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24475.pdf.
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Medinski, Tanya. "Soil chemical and physical properties and their influence on the plant species richness of arid South-West Africa." Thesis, Stellenbosch : University of Stellenbosch, 2007. http://hdl.handle.net/10019.1/2157.
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Thesis (MScConsEcol (Conservation Ecology and Entomology)--University of Stellenbosch, 2007.Understanding the drivers and mechanisms of changes in plant richness is a basis for making scientifically sound ecological predictions and land use decisions. Of the numerous factors affecting plant richness, soil has a particularly large influence on the composition and structure of terrestrial flora. Infiltrability is one of the most important factors determining soil moisture, and therefore is of particular interest in semi-arid ecosystems, where water is one of the most limiting resources. Other soil properties, such as clay + silt content, electrical conductivity (EC) and pH may also influence plants. Heterogeneity of these properties creates niches with specific conditions, which in turn affects spatial distribution of plants. An understanding of the relationships between plant richness and soil properties is, however, incomplete. The present study has two main foci. Firstly, relationships between plant richness and soil infiltrability, clay + silt, EC and pH (H2O) were investigated, and secondly, due to the strong influence of infiltrability on plant richness, further investigations were undertaken to improve the understanding of the role of particle size fractions, EC of the soil solution and exchangeable sodium percentage (ESP) on infiltrability. This study only concentrated on the surface 2 cm thick soil layer (known as pedoderm).
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O'Brien, Eileen M. "Climate and woody plant species richness : analyses based upon southern Africa's native flora with extrapolations to subsaharan Africa." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670313.
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Hancock, Christopher Nigel. "Factors affecting the physiognomy and species richness of plant communities of valleys of the Darling Plateau, Western Australia." Thesis, Hancock, Christopher Nigel (2002) Factors affecting the physiognomy and species richness of plant communities of valleys of the Darling Plateau, Western Australia. PhD thesis, Murdoch University, 2002. https://researchrepository.murdoch.edu.au/id/eprint/51804/.
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Native vegetation along and near watercourses on the Darling Plateau, east of Perth, Western Australia was studied in order to identify the key environmental parameters affecting structure and species richness. Measurements were taken of vegetation height, cover and species richness, together with groundwater levels and a range of edaphic parameters.
Floristic data were used to sort releves into community types. One upland, three riparian margin and four riparian plant community types were identified. The greatest degree of floristic and environmental change across the valley floor occurred between the inner riparian margin and the riparian zone proper. At this point substantial increases in soil moisture and nutrients coincided with a change to a dense but species poor riparian community. Differences between riparian community types reflected differences in summer water availability along each of the watercourses, and therefore differences in the length of the growing season.
The crown size, girth and height of eucalyptus peaked in the riparian margin at the down-slope limit of Eucalyptus wandoo. The shrub stratum increased in height from the lower valley slopes and across the valley floor, peaking as Melaleuca thickets in the riparian zone where groundwater levels remained elevated into early summer. Vegetation cover as a whole increased from upland to riparian habitats, primarily in response to increasing soil moisture and penetrability or 'softness'. The perennial component increased with summer soil moisture and penetrability and decreased with pH, while the cover of annuals was inversely related to perennial cover. Tree and shrub cover increased with the duration of groundwater elevation, as did ground cover, though there was still an inverse relationship between tree/shrub cover and ground cover.
Species richness and life form diversity declined from upland, through riparian margin to riparian vegetation. Upland sites featured a mix of phanerophytes, chamaephytes, hemicryptophytes: sedges, geophytes and therophytes, while riparian sites were dominated by only phanerophytes and sedges. The decline in total species richness was correlated with increasing moisture, soil fertility and plant cover. Trends in species richness differed between plant life forms. The smaller life forms in particular were increasingly excluded as one moved from upland to riparian habitats, leaving sedges and phanerophytes to dominate. Although there were strong correlations between alpha species richness and some abiotic environmental parameters, these would have influenced species richness at the scale of species pools, rather than the releve (25m2) scale. Biotic factors may influence species richness at both the species pool and the releve scales. A conceptual model has been presented to better focus any further studies of species richness. In it, the types of factors liable to affect species richness are summarised, along with the level (regional species pool vs releve) at which each factor acts. The concept of a coexistence coefficient, i.e. a measure of what proportion of the species pool may coexist within a quadrat/releve, is discussed.
Seasonal comparisons of tissue moisture content and xylem pressure potentials indicated that riparian plants on perennial watercourses did not experience a reduction in tissue moisture or xylem pressure over summer, i.e. they 'avoided' summer drought. On the other hand, riparian plants on seasonal watercourses did experience drops in tissue moisture or xylem pressure over summer. Together with the hydrological data, these data indicate that the type of riparian community supported at any site depends on the amount of water available through summer, and the ability of species to tolerate summer drought.
The study underscored the overriding importance of hydrology in determining the structure and diversity of vegetation in valleys of the Darling Plateau. It showed that seasonal hydrology, as it affects vegetation, can be viewed in at least two ways - namely the degree of soil saturation/waterlogging in winter vs the amount of water available over summer. Hydrological regimes affect species distributions in different ways. These may be direct, as when species are precluded by waterlogging or summer drought or indirect, as when elevated soil moisture in summer produces a thick shrub cover, which in turn prevents the growth of minor species.
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Lejon, Anna G. C. "Ecosystem response to dam removal." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-55586.
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This thesis aims to improve our understanding of how riverine ecosystems respond to dam removal. Riverine and particularly riparian ecosystems are among the most variable and important features of all landscapes. They connect landscape elements both longitudinally and laterally, and are governed by processes such as flooding, erosion and deposition that create dynamic, diverse and heterogeneous habitats. In fact, riparian zones are among the world’s most species-rich habitats. Worldwide there are millions of dams that fragment stream and river systems, regulate flows and degrade ecosystems. Dams impact freshwater, marine and terrestrial ecosystems and threaten biodiversity by disrupting organism movements and energy flows in the landscape. An important upstream effect of dams is inundation of habitats and development of new shorelines around impounded areas. Effects downstream of dams are mainly caused by changed hydrological regimes and retention of organic and inorganic materials in reservoirs, leading to reduced transport and dispersal of for example seeds to reaches downstream. The removal of dams create expectations that biota will eventually recover. We have studied a number of dam removal projects in Sweden. Our experimental results showed that following dam removal, newly exposed soils in former impoundments were rapidly colonized by pre-removal species. Their species richness increased slightly with time and their species composition indicated a slow change towards that in the reference site. In addition, the vegetation in formerly impounded areas showed a direction of change from lentic riparian plants (high proportion of aquatics) towards lotic ones, consisting of native perennials typical of free-flowing streams. We also found that the apprehensions that former impoundments would turn into pools of mud did not come true; in fact, a process towards more pristine channel morphology was observed. After removal there was erosion and downstream transport of sediment. We found only minor effects on macroinvertebrate communities. For example, a few species decreased over the years, suggesting that dam removal in itself might cause a temporary disturbance. This highlights the importance of long-term studies after dam removal, and also the importance of comparisons with pre-removal conditions and stretches unaffected by dams. Thorough documentation of executed dam removal projects and distribution of the results and experiences are tremendously important in the planning process of future decommissioning projects. Also, our experiences have taught us that in order to attain a successful dam removal it is important to involve stakeholders such as non-governmental organizations and local inhabitants in the process.
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Zinko, Ursula. "Plants go with the flow : predicting spatial distribution of plant species in the boreal forest." Doctoral thesis, Umeå : Ekologi och geovetenskap, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-315.
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Oliveira, Aliane Maria de. "Caracterização de uma comunidade de árvores e sua infestação por lianas em uma floresta decídua /." Botucatu : [s.n.], 2011. http://hdl.handle.net/11449/95081.
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Orientador: Andréia Alves RezendeBanca: Maria Tereza Grombone Guaratini
Banca: Roque Cielo Filho
Resumo: Caracterização, diversidade, estrutura e estágio sucessional da comunidade de árvores de uma Floresta Estacional Decidual no Sudeste do Brasil. A composição florística, a estrutura, a diversidade e o estágio sucessional de um fragmento de floresta foram analisados nesse estudo. O trabalho foi desenvolvido no município de Votuporanga, onde o clima é considerado Aw. Foi utilizado o método de parcelas (1 ha), amostrando todos os indivíduos arbóreos com DAS 5 cm. Foram calculados os valores de freqüência, densidade e dominância (absolutos e relativos), índice de valor de importância (IVI) e os índices de Shannon-Wiener (H') e Equabilidade (J'). A estrutura horizontal, o estágio sucessional e a formação vegetacional foram analisados. Foram amostrados 1635 indivíduos e as famílias mais ricas foram Fabaceae (17), Myrtaceae (oito), Rubiaceae (oito) e Bignoniaceae (cinco). Casearia gossypiosperma Briq. foi a espécie com o maior IVI. O índice de diversidade de Shannon-Wienner (H') foi 2,87 nats.indivíduo-1 e a equabilidade (J) foi 0,66 . Observou-se que 93% dos indivíduos arbóreos apresentaram diâmetros entre 1 e 20 cm. Árvores pioneiras compõem 55% dos indivíduos amostrados. A predominância de indivíduos com fenologia foliar decídua (79%) determinou a classificação do fragmento como Floresta Estacional Decidual. Assim, com este trabalho foi possível identificar uma área de Floresta Estacional Decidual no noroeste do estado e oferecer conhecimento, que são essenciais, sobre a flora, a estrutura florestal e o comportamento ecológico de Florestas Estacionais Deciduais no Estado de São Paulo
Abstract: Characterization, diversity, structure and successional stage of the tree community of a Seasonal Deciduous Forest in southeastern Brazil. Floristic composition, structure, diversity, and successional stage of a fragment forest have been analyzed in this study. The work was carried out Votuporanga, where the climate is considered Aw. Plot method was used (1 ha), sampling all trees 5 cm from HSD. We calculated the values of frequency, density and dominance (absolute and relative), index of importance value (IVI), the Shannon-Wiener diversity (H') and the equability (J'). The horizontal structure, the successional stage and the vegetation formation were analyzed. We sampled 1635 individuals and the richest families were Fabaceae (17), Myrtaceae (eight), Rubiaceae (eight) and Bignoniaceae (five). Casearia gossypiosperma Briq. was the species with the highest IVI. The Shannon-Wiener diversity (H') was 2.87 nats.individual-1 and the equability (J) was 0.66. It was observed that 93% of the trees individuals had diameters between 1 and 20 cm. Pioneers trees represent 55% of samples. The prevalence of individuals with deciduous leaf phenology (79%) determined the classification of the fragment as a Deciduous Seasonal Forest.Thus, this work enabled the identification an area of deciduous seasonal forest in the northwest of the state and offered essential knowledge about the flora, the forest structure and the ecology of deciduous forests in the State of São Paulo
Mestre
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Levy, Foster, and Elaine S. Walker. "Vascular Flora of the Rocky Fork Tract, Tennessee, USA, and Its Use in Conservation and Management." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etsu-works/709.
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A flora of the 3800 ha Rocky Fork Tract in northeast Tennessee produced 749 species of which 19 were on the Tennessee Rare Plant List and 34 were on the Cherokee National Forest Species Viability List with 87 county records from Greene County and 217 from Unicoi County. Rare species were particularly numerous in the Cyperaceae and Orchidaceae. The tract serves as a refuge for several regionally uncommon species by supporting either large populations or metapopulations of these species. Exotic species comprised 15% of the flora and were most common in the Fabaceae and Poaceae. The most unique habitat was a heath bald dominated by Rhododendron catawbiense with abundant Xerophyllum asphodeloides in the herbaceous layer. While species richness was relatively high compared to regional sites of comparable area, diversity was limited by the absence of high elevation spruce-fir communities and the paucity of wetlands.
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Gerstner, Katharina Verfasser], Ralf [Akademischer Betreuer] [Seppelt, and Jürgen [Akademischer Betreuer] Dengler. "The global distribution of plant species richness in a human-dominated world : [kumulative Dissertation] / Katharina Gerstner ; Ralf Seppelt, Jürgen Dengler." Halle, 2016. http://d-nb.info/1116951657/34.
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Esther, Alexandra. "Investigating mechanisms maintaining plant species diversity in fire prone Mediterranean-type vegetation using spatially-explicit simulation models." Phd thesis, Universität Potsdam, 2010. http://opus.kobv.de/ubp/volltexte/2010/4463/.
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Fire prone Mediterranean-type vegetation systems like those in the Mediterranean Basin and South-Western Australia are global hot spots for plant species diversity. To ensure management programs act to maintain these highly diverse plant communities, it is necessary to get a profound understanding of the crucial mechanisms of coexistence. In the current literature several mechanisms are discussed. The objective of my thesis is to systematically explore the importance of potential mechanisms for maintaining multi-species, fire prone vegetation by modelling. The model I developed is spatially-explicit, stochastic, rule- and individual-based. It is parameterised on data of population dynamics collected over 18 years in the Mediterranean-type shrublands of Eneabba, Western Australia. From 156 woody species of the area seven plant traits have been identified to be relevant for this study: regeneration mode, annual maximum seed production, seed size, maximum crown diameter, drought tolerance, dispersal mode and seed bank type. Trait sets are used for the definition of plant functional types (PFTs). The PFT dynamics are simulated annual by iterating life history processes.
In the first part of my thesis I investigate the importance of trade-offs for the maintenance of high diversity in multi-species systems with 288 virtual PFTs. Simulation results show that the trade-off concept can be helpful to identify non-viable combinations of plant traits. However, the Shannon Diversity Index of modelled communities can be high despite of the presence of ‘supertypes’. I conclude, that trade-offs between two traits are less important to explain multi-species coexistence and high diversity than it is predicted by more conceptual models.
Several studies show, that seed immigration from the regional seed pool is essential for maintaining local species diversity. However, systematical studies on the seed rain composition to multi-species communities are missing. The results of the simulation experiments, as presented in part two of this thesis, show clearly, that without seed immigration the local species community found in Eneabba drifts towards a state with few coexisting PFTs. With increasing immigration rates the number of simulated coexisting PFTs and Shannon diversity quickly approaches values as also observed in the field. Including the regional seed input in the model is suited to explain more aggregated measures of the local plant community structure such as species richness and diversity. Hence, the seed rain composition should be implemented in future studies.
In the third part of my thesis I test the sensitivity of Eneabba PFTs to four different climate change scenarios, considering their impact on both local and regional processes. The results show that climate change clearly has the potential to alter the number of dispersed seeds for most of the Eneabba PFTs and therefore the source of the ‘immigrants’ at the community level. A classification tree analysis shows that, in general, the response to climate change was PFT-specific. In the Eneabba sand plains sensitivity of a PFT to climate change depends on its specific trait combination and on the scenario of environmental change i.e. development of the amount of rainfall and the fire frequency. This result emphasizes that PFT-specific responses and regional process seed immigration should not be ignored in studies dealing with the impact of climate change on future species distribution.
The results of the three chapters are finally analysed in a general discussion. The model is discussed and improvements and suggestions are made for future research. My work leads to the following conclusions:
i) It is necessary to support modelling with empirical work to explain coexistence in species-rich plant communities.
ii) The chosen modelling approach allows considering the complexity of coexistence and improves the understanding of coexistence mechanisms.
iii) Field research based assumptions in terms of environmental conditions and plant life histories can relativise the importance of more hypothetic coexistence theories in species-rich systems. In consequence, trade-offs can play a lower role than predicted by conceptual models.
iv) Seed immigration is a key process for local coexistence. Its alteration because of climate change should be considered for prognosis of coexistence. Field studies should be carried out to get data on seed rain composition.Feuer geprägte, mediterrane Vegetationstypen, wie sie im Mittelmeerraum und Süd-West Australien zu finden sind, gelten als globale „hotspots“ für Pflanzendiversität. Um sicher zu stellen, dass Managementprogramme zum Erhalt dieser hoch diversen Pflanzengesellschaften zielgerichtet beitragen, ist ein profundes Verständnis der wesentlichen Koexistenzmechanismen notwendig. In der aktuellen Literatur werden verschiedene Mechanismen diskutiert. Das Ziel meiner Doktorarbeit ist es, die Bedeutung der Mechanismen für den Erhalt der artenreichen, feuergeprägten Vegetation anhand eines Modells systematisch zu untersuchen. Das von mir dafür entwickelte Modell ist räumlich-explizit, stochastisch und regel- und individuenbasiert. Es ist unter Zuhilfenahme von Daten zu Populationsdynamiken parametrisiert, die über 18 Jahre im Mediterranen Buschland von Eneabba Westaustraliens gesammelt wurden. Anhand von 156 Arten sind sieben für meine Studie relevante Pflanzeneigenschaften identifiziert wurden: Regenerationsart, jährlich maximale Samenproduktion, Samengröße, maximaler Durchmesser, Trockentoleranz, Ausbreitungsart und Samenbanktyp. Kombinationen der Eigenschaften bilden funktionelle Pflanzentypen (PFTs), deren jährliche Dynamik über Lebenszyklusprozesse im Modell simuliert wird. Der erste Teil meiner Arbeit präsentiert die Studie zur Bedeutung von „trade-offs“ für den Erhalt der hohen Diversität in artenreichen Systemen. Die Simulationsergebnisse mit 288 virtuellen PFTs zeigen, dass das „trade-offs“-Konzept für die Identifizierung nicht-lebensfähiger Kombinationen von Pflanzeneigenschaften hilfreich sein kann. Allerdings kann der Shannon-Diversitäts-Index der modellierten Pflanzengesellschaft trotz der Anwesenheit von „Supertypen“ hoch sein. Ich schlussfolgere, dass „trade-off“ zwischen zwei Eigenschaften weniger wichtig für die Erklärung der Koexistenz von vielen Arten und hoher Diversität sind, als es durch konzeptionelle Modelle vorhergesagt wird. Viele Studien zeigen, dass Sameneintrag aus dem regionalen Samenpool essenziell für den Erhalt lokaler Artendiversität ist. Es gibt allerdings noch keine systematischen Studien zur Zusammensetzung des Samenregens artenreichen Systemen. Die Ergebnisse der Simulationsexperimente im zweiten Teil meiner Arbeit machen deutlich, dass ohne Sameneintrag die lokale Pflanzengesellschaft Eneabbas sich in eine Richtung entwickelt, in der nur wenige PFTs koexistieren. Mit steigender Samenimmigrationsrate erreicht die Anzahl an koexistierenden PFTs und die Shannon-Diversität schnell die Werte, die auch im Feld gefunden werden. Der regionale Sameneintrag kann also als Erklärung zur Struktur lokaler Pflanzengesellschaften dienen. Seine Zusammensetzung sollte jedoch in zukünftigen Studien berücksichtigt werden. Im dritten Teil meiner Doktorarbeit präsentiere ich Analysen zur Sensibilität der PFTs von Eneabba vorhergesagte Klimaszenarien und der Auswirkungen auf die Samenimmigration. Die Ergebnisse zeigen deutlich, dass Klimaänderungen das Potential haben, die Anzahl an ausgebreiteten Samen der meisten Eneabba PFTs zu verändern. Die Entscheidungsbaum-Analyse veranschaulicht, dass die Reaktion auf Klimaänderung PFT-spezifisch ist. In den Eneabba hängt die Sensitivität der PFTs gegenüber klimatischen Veränderungen von den PFT-spezifischen Eigenschaftskombinationen und vom Klimaszenarium ab, d.h. von der Entwicklung der Regenfallmenge und der Feuerfrequenz. Dieses Ergebnis betont, dass PFT-spezifische Reaktionen und die klimabedingten Änderungen in der Samenimmigration in Studien zum Einfluss von Klimaänderungen auf die zukünftige Artenverteilung berücksichtigt werden sollten. Die Ergebnisse aus den drei Kapiteln werden in der allgemeinen Diskussion zusammengeführt und analysiert. Das Modell wird diskutiert und Verbesserungen und Vorschläge für weitere Forschung aufgezeigt. Meine Arbeit führt zu folgenden Schlussfolgerungen: i) Es ist notwendig, empirische Arbeit und Modellierung zu kombinieren, um Koexistenz in artenreichen Systemen zu erklären. ii) Durch den gewählten Modellansatz kann die Komplexität von Koexistenz erfasst und das Verständnis vertieft werden. iii) Auf Felddaten basierende Annahmen bezüglich Umweltbedingungen und Lebenzyklus können zur Relativierung der Bedeutsamkeit von Mechanismen führen. So können Trade-offs eine geringere Rolle spielen, als konzeptionelle Modelle nahe legen. iv) Samenimmigration ist ein Schlüsselprozess für lokale Koexistenz. Deren Änderung aufgrund von Klimawandel sollte für Prognosen zu Artenvorkommen berücksichtigt werden. Feldstudien sollten durchgeführt werden, um die Datenlücken zur Samenregenzusammensetzung zu füllen.
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Day, Nicola J. "Two decades of vegetation change across tussock grasslands in New Zealand's South Island." Master's thesis, Lincoln University. Bio-Protection and Ecology Division, 2008. http://theses.lincoln.ac.nz/public/adt-NZLIU20080304.145252/.
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New Zealand's South Island tussock grasslands have been highly modified by human activities, including burning, grazing and introductions of exotic plants for pastoralism. Studies suggest that tussock grasslands are degraded, in that native species have declined, and exotic species have increased in both diversity and abundance. These trends are primarily thought to be related to the impacts of grazing and subsequent grazing removal. Few studies have assessed long-term changes that have occurred in tussock grasslands, and those that have are generally limited to one particular location. This thesis aimed to investigate temporal changes in community structure in tussock grasslands, and relate these changes to environmental variables and land tenure. Data were used from 90 permanently-marked vegetation transects, which were set up on 19 geographically widespread properties in areas of tussock grassland across Canterbury and Otago in the South Island of New Zealand. The transects were on land in both conservation and pastoral tenure. Each transect was 100 m, and consisted of 50 0.25 m² quadrats. The transects were measured between 1982 and 1986 (first measurement), were re-measured between 1993 and 1999 (second measurement) and again between 2005 and 2006 (third measurement). A total of 347 vascular species were observed over the 90 transects and three measurement times. Species richness declined between the first and second measurements (first time interval), and increased between the second and third measurements (second time interval), at both the small (quadrat) and large (transect) scales. Both native and exotic species declined in mean quadrat species richness during the first time interval, and then increased during the second time interval. Changes in mean quadrat species richness were similar on transects in both conservation and pastoral tenure. Multivariate analysis of species' occurrences in quadrats identified a long gradient in species composition for these 90 transects. Four key plant communities were identifed along this gradient and differed in their mean elevation: (1) Highly-modified pastoral community, (2) Short-tussock grassland community, (3) Tall-tussock grassland community, (4) Alpine mat-forming species community. A detailed investigation into temporal changes that occurred on 53 transects that occurred in short- and tall-tussock grassland communities showed that changes in species composition were not consistent over time. Transects on different properties changed in species composition by different amounts. Specifically, in ordination space, transects on two properties changed in composition significantly more than transects on one other property. The property that a transect was on also affected the way that it changed in composition, i.e. native species were more likely to have increased on transects on some properties. Transects in conservation tenure did not change in species richness or composition differently from those in pastoral tenure. Considering that many native plants in tussock grasslands are relatively slow-growing, and that these areas have been grazed and burned for more than a century, we may expect it to be some time before we can detect differences in vegetation dynamics on conservation land from that on pastoral land. The changes in the community structure of these tussock grasslands were related to a combination of environmental factors, such as soil chemistry, climate, and management factors. This study has allowed greater understanding of vegetation change in tussock grasslands, and demonstrates the importance of long-term ecological monitoring in making reliable and accurate predictions about landscape-scale changes in tussock grassland community structure.
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Flint, Andrew R. "The biodiversity of the Wealden ghyll woodlands : species richness, abundance and distribution patterns in a rare and fragmented habitat." Thesis, University of Brighton, 2014. https://research.brighton.ac.uk/en/studentTheses/77f93fe9-19d0-4c2f-863d-b12e5edec87d.
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The Wealden ghyll woodlands are associated with unique plant assemblages that include nationally rare bryophyte species with oceanic affiliations. The identification and monitoring of this type of 'priority' habitat, recognised as important in terms of regional and national biodiversity, is a central facet of the UK Biodiversity Action Plan (UKBAP). Despite the acknowledged importance of ghyll woodlands for non-vascular plant species, previous studies attempting to examine and characterise the ghyll woodlands have neglected to include these bryophyte communities. This research identifies and characterises the Wealden ghyll woodlands through an examination of the spatial and temporal distributions of bryophyte and flowering plant species. The research also seeks to provide baseline data against which biodiversity levels can monitored. In order to identify and contextualise the importance of ghyll woodland in terms of regional biodiversity, survey data was collected from other types of ancient woodland throughout the region for comparative analysis. The study involved the collection of species and environmental data from a total of 1440 random quad rats from 60 survey sites situated throughout the Weald, as well as the use of archive survey data collected during two 20 year periods (1951-1970 and 1976-1995). A number of statistical approaches including general linear modelling, ANOSIM, MannWhitney U and Spearman rank correlation analysis were used to identify the environmental correlates of spatial and temporal changes in species distributions. Spatial analysis indicated that ghyll woodland is restricted to the stream valleys themselves which were significantly richer in bryophyte and flowering plant species than the surrounding woodlands. NVC classifications assigned to the ghylls indicated the presence of 'oceanic' plant communities that are associated with damp, humid microclimatic conditions. A number of authors have explained the presence of oceanic bryophytes within the ghylls as being the result of a damp, humid microclimate present within the stream valleys. However, the study found no significant differences between climatic conditions within the ghyll valleys and those in the surrounding ancient woodlands. ANOSIM analysis indicated that community composition was influenced by site substrate, with clay and sandstone ghyll woodlands containing significantly different plant communities. Chi-squared analysis identified a temporal increase in the ratio of oceanic bryophytes and ancient woodland indicator flowering plant species during the study period. Analysis of Ellenberg indicator values indicated a move towards more shadetolerant plant communities within the ghyll woodlands. The patchily distributed ghyll woodlands were examined for signs of habitat fragmentation through genetic analysis of the bryophyte Conocephalum conicum (Great Scented Liverwort) using the random amplification polymorphic DNA technique (RAPD). Wright's fixation index (FST) and Nei 's coefficient of gene variation (GST) both indicated a loss of genetic diversity characteristic of genetic isolation. A Mantel test based on Nei 's genetic distance values indicated that the genetic isolation observed was not correlated with the geographical distance between populations. The study indicated that temporal changes are occurring in the composition of ghyll woodland plant communities and that bryophyte populations are displaying symptoms of genetic isolation. The study illustrates the importance of some form of monitoring program if the biodiversity value of these sites is to be maintained.
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Larouche, Martine. "Effects of past land use and landscape context on plant species composition and richness in woodlots of an agricultural landscape in Québec." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119667.
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The forest transition occurring in developed countries, including northeastern North America and western Europe, led to an emergence of secondary forests that fueled research about past land-use legacies on biodiversity. Past land-use has been shown to lower plant species richness, especially that of forest herb species. A few studies have also considered landscape configuration around secondary forests, either in the present-day or during the early period of old field colonization. My study examines the effects of both past land-use and past landscape context on species composition and richness in a 2046 km2 landscape dominated by agriculture in the Montérégie in southwestern Québec. Using historical topographical maps from the 1860s and 1910s, and a forest map from the 1990s, I analyzed the evolution of forest cover across the landscape and used an Affinity Propagation algorithm to cluster forest patches with similar land-use and configuration history. I then tested the effects of past land use and landscape context (surrounding forest proportion) on species composition and richness in 52 study sites using nonmetric multidimensional scaling analysis and correlations. Results show that landscape context in the past, and especially in the 1910s within a 200m buffer around study sites, is correlated with both current species composition and richness. Hence, forest patches that had a low forest cover around them in the past have a lower total, endozoochorous and anemochorous species richness and greater epizoochorous species richness than forest patches that were surrounded by a greater amount of forest in the past. As for past land use, this variable does not have a strong effect on plant species composition and richness. Other variables like soils, surficial deposits or recent forest management intensity do not affect total species richness and composition in study sites except for tree species, likely because of maple syrup production. My conclusions can be useful for forest protection and conservation by helping to prioritize forest patches to protect based on past landscape context. The results also suggest that the quality of forest patches can be enhanced by creating ecological corridors connecting patches, thereby increasing the number of surrounding seed sources.La transition forestière ayant lieu dans les pays développés, incluant le nord-est de l'Amérique du Nord et l'Europe de l'Ouest, a conduit à l'émergence de forêts secondaires, lesquelles ont alimenté la recherche sur les legs de l'utilisation passée des terres sur la biodiversité. Il a été démontré que l'utilisation passée du territoire peut appauvrir la richesse en espèces végétales et spécialement en herbacées forestières. Quelques études ont également considéré la configuration du paysage autour de parcelles forestières, soit à l'époque actuelle ou durant la période de colonisation des terres abandonnées. La présente étude se penche sur les effets de l'utilisation passée du territoire et du contexte paysager passé (proportion du couvert forestier environnant) sur la composition et la richesse en espèces végétales dans un paysage de 2046 km2 dominé par l'agriculture en Montérégie, au sud-ouest du Québec. Utilisant des cartes topographiques historiques des années 1860 et 1910 et une carte forestière des années 1990, j'ai analysé l'évolution du couvert forestier sur ce territoire et utilisé l'algorithme Affinity Propagation pour regrouper les parcelles forestières ayant une histoire d'utilisation du territoire et de contexte paysager similaires. J'ai ensuite testé les effets de l'utilisation passée des terres et du contexte paysager passé sur la composition et la richesse en espèces végétales de 52 parcelles forestières en utilisant une analyse de gradation non métrique multidimensionelle ainsi que des corrélations. Les résultats montrent que le contexte paysager passé, et particulièrement dans les années 1910 à l'intérieur d'un rayon de 200 mètres autour des sites d'étude, est corrélé à la composition et à la richesse en espèces végétales actuelles de ces sites. Ainsi, des parcelles forestières ayant eu un couvert forestier faible autour d'elles dans le passé contiennent moins d'espèces végétales au total, moins d'endozoochores et d'anémochores et plus d'épizoochores que des parcelles forestières entourées d'un plus grand couvert forestier dans le passé. L'utilisation passée du territoire n'a, quant à elle, pas d'effets importants sur la composition et la richesse en espèces végétales. D'autres variables telles les sols, les dépots de surface ou l'intensité de l'aménagement forestier récent n'affectent pas la composition ni la richesse en espèces végétales dans les sites d'étude sauf pour les espèces d'arbres, probablement en raison de la production de sirop d'érable. Les conclusions de cette étude peuvent être utiles à des fins de protection et de conservation de la forêt. Ainsi, elles pourraient aider à prioriser les parcelles forestières à protéger en se basant sur la proportion de couvert forestier autour d'elles dans le passé. Les résultats de cette étude suggèrent également que la qualité des boisés peut être améliorée en créant des corridors écologiques connectant les parcelles, augmentant par le fait même les sources de graines autour d'elles.
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Heimann, Juliane [Verfasser], Wolfgang W. [Akademischer Betreuer] Weisser, Günter [Akademischer Betreuer] Köhler, and Klaus [Akademischer Betreuer] Reinhold. "Generalist insect herbivore performance in dependence of plant species richness, composition and quality / Juliane Heimann. Gutachter: Wolfgang W. Weisser ; Günter Köhler ; Klaus Reinhold." Jena : Thüringer Universitäts- und Landesbibliothek Jena, 2012. http://d-nb.info/1028799012/34.
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Shah, Parita Raj. "Evaluation of Digital PCR (dPCR) for the Quantification of Soil Nitrogen Turnover Bacteria in Wetland Mesocosms in Response to Season, Fertilization, and Plant Species Richness." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/87580.
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Excess nutrients from nonpoint sources are an ongoing problem that is expected to worsen as population and fertilizer usage rise. Conventional centralized treatment systems are not well suited to address nonpoint source pollution. More distributed best management practices (BMPs) like constructed wetlands are a promising alternative and have been widely implemented in the US since the 1970's. Constructed wetlands are multi-functional systems that can effectively store and transform harmful contaminants using primarily natural processes. However, the removal of pollutants like nitrogen by wetlands is highly variable, likely due to a combination of factors such as plant species-specific assimilation behavior, the effects of plant communities on microbial diversity and function, and variable nitrogen inputs. In this study, the effect of plant species richness (i.e., number of plant species in a system) and seasonal nutrient loading (i.e., nitrogen fertilization) on the microbial community responsible for regulating nitrogen turnover in wetland mesocosm soils was investigated. The chip-based QuantStudio 3D digital PCR (QS3D dPCR) system was used to quantify ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), comammox, anammox, and denitrifiers. Principal component analysis (PCA) was used to identify dominant patterns in the microbial community and nitrogen species. Resampling-based analysis of variance (ANOVA) was used to assess statistical significance of any observed differences caused by nitrogen fertilization or plant species richness. Results indicated that fertilization or season, which was convolved with fertilization, was the dominant factor influencing the microbial community in the study environment (27% variance explained), as indicated by the disparate clustering of fall (fertilized) and spring (unfertilized) samples about principal component 1 (fall: negative PC1, spring: positive PC1). Because unplanted unfertilized controls sampled in November clustered within the season in which they were collected rather than with other unfertilized samples collected in May, season may have influenced microbial community shifts more than fertilization for unplanted systems. This finding should be interpreted cautiously, however, given the small number of unplanted unfertilized controls (N = 2) and the absence of similar controls in the planted systems. The most abundant bacterial groups detected in May (November) were AOB, nirK, anammox, and Nitrospira spp. NOB (AOB, anammox, Nitrospira spp. NOB, and nosZ). The effects of plant species richness were more nuanced, with greater richness significantly impacting the abundance of only a subset of bacterial groups (i.e., the nitrifying bacteria AOB, Nitrospira spp. NOB, and comammox, but not the denitrifying bacteria). Different relationships between richness and microbial abundance were observed in different seasonal nutrient loadings (i.e., interaction effects between richness and fertilization were detected for some bacterial groups).MS
As global population continues to rise, fertilizer application is becoming more commonplace in order to meet increasing agricultural demand. Fertilizers supply nutrients like nitrogen that, in excess, can negatively affect water quality. Since conventional treatment systems are largely impractical to control such diffuse, nonpoint sources of pollution, more distributed best management practices (BMPs) like constructed wetlands are a promising alternative. Several important nitrogen transformations occur within wetlands, of which soil microbial communities have a significant influence over. For instance, nitrifying bacteria can transform ammonia into nitrate and denitrifying bacteria can transform nitrate into atmospheric nitrogen. Constructed wetlands are designed to mimic these complex, dynamic processes, and can be manipulated for more effective nitrogen pollution control. However, the removal of pollutants like nitrogen by wetlands is highly variable, likely due to a combination of factors such as plant species-specific assimilation behavior, the effects of plant communities on microbial diversity and function, and variable nitrogen inputs. In this study, the effects of plant species richness (i.e., number of plant species in a system) and seasonal nutrient loading (i.e., nitrogen fertilization) on several types of nitrifying and denitrifying bacteria in wetland mesocosm soils were investigated. Digital polymerase chain reaction (dPCR) was used to quantify bacterial abundance. Principal component analysis (PCA) was used to identify dominant patterns within the data and resampling-based analysis of variance (ANOVA) was used to assess statistical significance of any observed differences caused by fertilization, season, and/or plant species richness. Results indicated that fertilization or season, which was convolved with fertilization, wasthe dominant factor influencing the microbial community in the study environment. The effects of plant species richness were more nuanced, with greater richness significantly impacting the abundance of only a subset of bacterial groups (i.e., the nitrifying bacteria AOB, Nitrospira spp. NOB, and comammox, but not the denitrifying bacteria).
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Lilley, Patrick Ledford. "Determinants of native and exotic plant species diversity and composition in remnant oak savannas on southeastern Vancouver Island." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/243.
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Many regional and local factors can influence the distribution of native and exotic species in ecological communities. I examined the regional- and local-scale determinants of native and exotic vascular plant species richness and composition in a highly fragmented oak savanna ecosystem on southeastern Vancouver Island. In sharp contrast to most reported results, I found a negative relationship between native and exotic richness at the regional scale, and no relationship at the local scale. Two extrinsic factors, surrounding road density and climate, best explained the regional-scale relationship by each affecting natives and exotics in opposite ways. Road density and climate were also the dominant predictors of native and exotic composition at the regional scale. Patterns in the patch occupancy of individual species confirmed the importance of these factors but I found that low surrounding road densities and cool, wet conditions predicted the presence of many natives and the absence of many exotics. Environmental factors explained variation in richness and composition at the local scale, but these factors were different for natives and exotics. My results suggest that natives and exotics respond to roads and climate in fundamentally different ways. Roads increase both exotic propagule pressure and disturbance, which may facilitate exotic invasion. In contrast, disturbance from roads may increase the likelihood of local extinction for particular natives. Differing climatic preferences within the native and exotic species pools may also partially explain the observed patterns. There was no evidence that native diversity directly affects exotic diversity (or vice versa). Surprisingly, I found that connectivity was not an important predictor of richness or composition despite the high degree of habitat fragmentation in this ecosystem.
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Schetter, Timothy Andrew. "A Multiscale Spatial Analysis of Oak Openings Plant Diversity with Implications for Conservation and Management." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1334089503.
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Bergström, Elin. "Växtartrikedomens svar på restaurering av hävdade gräsmarker : En litteraturstudie." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-178830.
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En av de naturtyper med flest antal växtarter i världen är hävdade gräsmarker som är präglade av traditionell skötsel. Denna naturtyp har minskat kraftigt i area och för att förhindra framtida artutdöenden är restaureringsåtgärder viktiga. Syftet med denna rapport var att med hjälp av vetenskapliga publikationer undersöka vilken effekt restaurering av före detta hävdade gräsmarker i norra och centrala Europa har på växtartrikedomen. Mer specifikt undersöktes effekten av olika restaureringsmetoder på totala antalet arter, arttätheten och artsammansättningen. Utöver detta undersöktes vilka faktorer som påverkar möjligheten till restaurering. Resultatet tyder på att restaurering med bete eller slåtter är mest framgångsrik av de olika undersökta metoderna. Restaurering med bete eller slåtter visade sig kunna ha en positiv effekt på totala antalet arter, arttätheten och artsammansättningen. Enbart rensning av träd och buskar var inte en långsiktigt hållbar metod för restaurering eller bevarandet av artrikedomen eller arter associerade med hävdade gräsmarker. Det finns många faktorer som påverkar möjligheten till restaurering och alla är inte entydiga. Något som kan vara intressant att vidare utforska är vilken betydelse de olika artrikedomsmåtten och artsammansättningen har för att kunna optimera restaureringsprojekt. Förutom att restaurering av hävdade gräsmarker både kan bidra till att utöka Natura 2000-nätverket och uppfylla de globala målen, ger det oss mängder med ekosystemtjänster och bevarande av kulturlandskap.
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Broshot, Nancy Ellen. "The Effects of Urbanization and Human Disturbance Upon Plant Community Structure and Bird Species Richness, Diversity, and Abundance in a Natural Forested Area (Forest Park) in Portland, Oregon." PDXScholar, 1999. https://pdxscholar.library.pdx.edu/open_access_etds/3962.
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The effects of urbanization and continual human disturbance on the plant and avian communities of Forest Park and forested lands surrounding Portland, Oregon, were studied. I examined characteristics of plant and avian communities at 25 sites, 24 which were in Forest Park and surrounding areas and one which was in the Ancient Forest Preserve (old-growth stand) northwest of Forest Park. Data were analyzed using multiple regression, ANOV A, and Bonferonni/Dunn. Seven variables were selected representing different urbanization gradients. An additional covariable coded for the old-growth stand, allowing it to be used as a control.
Many tree variables, especially those related to shade-tolerant species, were positively correlated with both the distance from downtown Portland and the number of houses in the surrounding area, and negatively correlated with the distance from the nearest forest edge; however, many shrub and herbaceous variables were negatively correlated with the distance from downtown Portland. Species diversity for herbaceous and shrub species was greater at more urban sites, but diversity of trees was lower at more urban sites. There were significantly more non-native species of plants in the city section. I found significantly fewer saplings and small trees, especially shade-tolerant species, in the section of Forest Park closest to downtown Portland, although tree mortality was positively correlated with distance from Portland.
Summer bird data revealed significant increases in the abundances of urban and edge species at more urban sites, with concomitant reductions in forest species. There were significantly more ground gleaning birds and short distance migratory species. I also found a significantly greater abundance of birds in the old-growth stand during the winter. This increase was positively correlated with the depth of snow in the nearby Cascade Mountains.
My results indicate that Forest Park is apparently progressing in a normal successional pattern with the exception of the city section. The reduction in shade tolerant saplings and small trees in the city section suggest that rate of succession has been slower at more urban sites. Avian data suggest that urbanization affects bird species abundance and guild composition in the more urban areas.
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Schmiedel, Inga Verfasser], Heike [Akademischer Betreuer] Culmsee, Erwin [Akademischer Betreuer] Bergmeier, Christoph [Akademischer Betreuer] Leuschner, Renate [Akademischer Betreuer] Bürger-Arndt, Susanne [Akademischer Betreuer] [Bögeholz, Hermann [Akademischer Betreuer] Behling, and Markus [Akademischer Betreuer] Hauck. "Vascular plant species richness at the landscape scale: Patterns and processes / Inga Schmiedel. Gutachter: Erwin Bergmeier ; Christoph Leuschner ; Renate Bürger-Arndt ; Susanne Bögeholz ; Hermann Behling ; Markus Hauck. Betreuer: Heike Culmsee." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://d-nb.info/1072550598/34.
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Ström, Lotta. "Effects of climate change on boreal wetland and riparian vegetation." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-43811.
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Models of climate change predict that temperature will increase during the 21th century and the largest warming will take place at high northern latitudes. In addition to warming, predictions for northern Europe include increased annual precipitation and a higher proportion of the precipitation during winter falling as rain instead of snow. These changes will substantially alter the hydrology of rivers and streams and change the conditions for riverine communities. The warming is also expected to result in species adjusting their geographic ranges to stay within their climatic tolerances. Riparian zones and wetlands are areas where excess water determines the community composition. It is therefore likely that these systems will be highly responsive to alterations in precipitation and temperature patterns. In this thesis we have tested the predicted responses of riparian vegetation to climate-driven hydrologic change with a six year long transplant experiment (I). Turfs of vegetation were moved to a new elevation with shorter or longer flood durations. The results demonstrate that riparian species will respond to hydrologic changes, and that without rare events such as unusually large floods or droughts, full adjustment to the new hydrological regime may take at least 10 years. Moreover, we quantified potential effects of a changed hydrology on riparian plant species richness (II) and individual species responses (III) under different climate scenarios along the Vindel River in northern Sweden. Despite relatively small changes in hydrology, the results imply that many species will become less frequent than today, with stochastic extinctions along some reaches. Climate change may threaten riparian vegetation along some of the last pristine or near-natural river ecosystems in Europe. More extensive loss of species than predicted for the Vindel River is expected along rivers in the southern boreal zone, where snow-melt fed hydrographs are expected to be largely replaced by rain-fed ones. With a seed sowing experiment, we tested the differences in invasibility between open wetlands, forested wetlands and riparian zones (IV). All six species introduced were able to germinate and survive in all habitats and disturbance levels, indicating that the tested wetlands are generally invisible. Germination was highest in open wetlands and riparian zones. Increasing seed sowing density increased invasion success, but the disturbance treatments had little effect. The fact that seeds germinated and survived for 2 to 3 years in all wetland habitats indicates that wetland species with sufficiently high dispersal capacity and propagule pressure would be able to germinate and establish here in their respective wetland type. Our results clearly demonstrate that a changed climate will result in substantial changes to functioning, structure and diversity of boreal wetland and riparian ecosystems. To preserve species rich habitats still unaffected by dams and other human stressors, additional protection and management actions may have to be considered.
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Bagaria, Morató Guillem. "Time lags in plant community assembly after forest encroachment into Mediterranean grasslands: drivers and mechanisms." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/295705.
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La pèrdua, fragmentació i transformació dels hàbitats representen una gran amenaça per a la biodiversitat en els ecosistemes terrestres d'arreu del món, desencadenant tant extincions com colonitzacions amb un resultat incert en la composició i la riquesa d'espècies. Els retards de diverses dècades, coneguts com a deute d'extinció i crèdit de colonització, són habituals després dels canvis en els usos del sòl. No obstant, hi ha una manca d'estudis que abordin l'ensamblatge de comunitats tenint en compte tant el deute d'extinció pels especialistes de l'hàbitat previ com el crèdit de colonització pels especialistes del nou hàbitat. L'objectiu d'aquesta tesi és, per tant, abordar les causes i els mecanismes dels efectes diferits del canvi en l'hàbitat i el paisatge sobre les comunitats vegetals en prats calcaris semi-naturals en ambients mediterranis des d'una aproximació inclusiva, tenint en compte tant els canvis en la riquesa com en la composició d'espècies i els seus retards potencials. El deute d'extinció i el crèdit de colonització han estat quantificats després de diverses dècades de canvis en l'hàbitat, i les seves causes han estat investigades (Capítol 1). Amb l'objectiu de desentrellar els processos que hi ha darrere els canvis de la comunitat, s'han investigat els patrons i causes de les extincions i colonitzacions d'espècies que ja s'han donat, a través dels dos components de la β-diversitat: recanvi d'espècies i diferències de riquesa (Capítol 2). D'altra banda, el paper dels atributs de les plantes com a mediadors de l'extinció d'espècies de l'hàbitat previ (Capítol 3), i els mecanismes poblacionals i individuals del retard en l'extinció d'un dels especialistes de prat més freqüents (Aphyllanthes monspeliensis; Capítol 4) han estat abordats després del canvi en l'hàbitat. Els estudis s'han dut a terme a les muntanyes del sud de Catalunya (nord-est de la Península Ibèrica), on la forestalització s'ha donat com a conseqüència de la reducció en la pastura durant la segona meitat del segle XX. Tot i que han passat més de 50 anys des de l'inici d'aquest procés de forestalització dels prats, s'ha detectat un important deute d'extinció per als especialistes de prat i crèdit de colonització per als especialistes de bosc. El deute d'extinció també ha estat confirmat per l'especialista de prat A. monspeliensis, ja que la seva abundància depèn de la connectivitat passada però no de l'actual. A més a més, un efecte rescat des dels prats circumdants i un lent decaïment vegetatiu i reproductiu després del deteriorament de l'hàbitat han estat identificats com a mecanismes que afavoreixen el deute d'extinció. El crèdit de colonització de les plantes de bosc, al seu torn, probablement es manté per una limitació de la dispersió. Tot i que la riquesa ha canviat poc després de la forestalització, sí que s'ha donat un elevat recanvi d'espècies per al conjunt de la comunitat, fruit d'extincions i colonitzacions idiosincràtiques dels especialistes de prat i de bosc, respectivament. No obstant, mentre la fragmentació de l'hàbitat ha afectat negativament alguns especialistes de prat, no s'ha trobat un paper important dels atributs de les plantes en la mediació de les extincions per a aquest grup. S'espera que la pèrdua generalitzada d'espècies de prat i el guany generalitzat d'espècies de bosc, que resulten del pagament del deute d'extinció i el crèdit de colonització, continuïn a l'àrea d'estudi fins i tot en el cas que no avancés el procés de forestalització.Habitat loss, fragmentation and transformation are major threats for biodiversity in terrestrial ecosystems worldwide, driving both species extinctions and colonisations with an uncertain outcome on species composition and richness. Time lags of several decades, known as extinction debt and colonisation credit, often occur after land-use change events. Nevertheless, there is a lack of studies addressing community assembly taking into account both extinction debt for habitat specialists of the former habitat and colonisation credit for habitat specialists of the new habitat. The aim of this thesis is, therefore, to address the drivers and mechanisms of time-lagged effects of habitat and landscape change on plant communities in semi-natural Mediterranean calcareous grasslands from a comprehensive approach, taking both changes in species richness and composition and their potential time lags into account. Extinction debt and colonisation credit are quantified after several decades of habitat change, and their drivers are investigated (Chapter 1). In order to disentangle the processes behind community change, the patterns and drivers of species extinctions and colonisations that already occurred are investigated through the two components of β-diversity: species replacement and richness differences (Chapter 2). Moreover, the role of plant traits in mediating extinctions of species of the former habitat (Chapter 3), and the population and individual-level mechanisms of extinction delay for one of the most frequent grassland specialists (Aphyllanthes monspeliensis; Chapter 4) are assessed after habitat change. The studies were conducted in the southern mountains of Catalonia (northeastern Iberian Peninsula), where forest encroachment occurred following grazing reduction during the second half of the 20th century. Although more than 50 years elapsed since the beginning of forest encroachment into these grasslands, both an important extinction debt for grassland specialists and colonisation credit for forest specialists are detected. Extinction debt was also confirmed for the grassland specialist A. monspeliensis, since its abundance depends on historical but not current connectivity. In addition, a rescue effect from surrounding grasslands and a slow vegetative and reproductive decay after habitat deterioration were identified as mechanisms enhancing extinction debt. Colonisation credit of forest plants, in turn, was probably maintained by dispersal limitation. Although species richness changed little after forest encroachment, high species replacement for the whole community occurred, resulting from idiosyncratic grassland specialists' extinctions and forest specialists' colonisations. However, while habitat fragmentation negatively affected some grassland specialists, no clear role of plant traits was found in mediating extinctions of this group. A generalised loss of grassland species and gain of forest species, resulting from the payment of extinction debt and colonisation credit, is expected to continue in the studied area even if no further forest encroachment occurs.
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Pajunen, A. (Anu). "Willow-characterised shrub vegetation in tundra and its relation to abiotic, biotic and anthropogenic factors." Doctoral thesis, University of Oulu, 2010. http://urn.fi/urn:isbn:9789514261138.
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Abstract
Deciduous shrubs form the tallest type of vegetation in arctic-alpine areas and are important for ecosystem function. In the southern part of the Eurasian tundra zone, willows (Salix spp.) are the most common species in the shrub layer. In the alpine areas of Northern Fennoscandia, willow shrubs are characteristic to areas between tree line and treeless tundra heaths. Vertical structure and composition of willow-characterized tundra vegetation is affected by a variety of ecological factors including climate and herbivory. In turn, the abundance of the willow canopy affects understory species in several ways that still remain inadequately understood.
In this PhD work I describe compositional differentiation of willow-characterized vegetation by using a large data set spanning from north-western Fennoscandia to the Yamal Peninsula in north-western Siberia. I studied environmental factors affecting willow-characterized vegetation and willow growth by using correlative analyses. The factors under investigation were latitude, distance from the sea, depth of thaw, position in the slope, industrial disturbance and reindeer grazing. In addition, I examined the relationships between the shrub biomass estimate and composition and species richness of understory vegetation. The effects of reindeer grazing on vegetation in an alpine forest-tundra ecotone were studied experimentally using reindeer-proof exclosures.
I found that willow-characterized vegetation is floristically variable and comprises at least eight vegetation types. The most abundant willow thickets typically have a forb-rich understory. The growth of willow increased along with increasing summer temperatures. However the height of willow was more determined by distance from the sea, thaw depth and slope position. Reindeer grazing decreased the abundance of willow and changed the composition of understory vegetation. In addition, industrial activities were detected to have destructed shrub vegetation and turned it into graminoid-dominated vegetation. Shrub canopies facilitated forbs but decreased the cover of all the other groups including dwarf shrubs, bryophytes and lichens. The species richness of vegetation decreased along with increasing shrub abundance.
My study shows that arctic-alpine willow vegetation is more diverse than previously thought. There is a predictable relationship between summer temperatures and willow growth. However, the results also show that there are many factors, both physical and anthropogenic, that are likely to complicate this pattern. Most important of these counteracting effects are industrial activities and reindeer grazing. In the areas where shrubs grow in abundance, the species richness of understory vegetation is likely to decrease and forbs are likely to replace other tundra species.
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Orihuela, Rodrigo Leonel Lozano. "Diversidade e abundância de hemiepífitos em um gradiente altitudinal na Floresta Atlântica no Sul do Brasil." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/26288.
Full textAbstract:
O objetivo principal deste trabalho foi identificar os principais fatores abióticos e bióticos correlacionados com a distribuição da abundância e riqueza de hemiepífitos primários, secundários e lianas rizo-escandentes, sinúsias que carecem de estudos, em um gradiente altitudinal na Floresta Atlântica sul-brasileira. Alocamos 15 unidades amostrais no total (de 400 m2 cada), distribuídas nas porções inferior (200 - 250 m a.n.m.), média (380 - 430 m) e superior (670 - 720 m) de um gradiente altitudinal no nordeste do Rio Grande do Sul. Amostramos em cada parcela a abundância de cada espécie, a porcentagem de árvores colonizadas por cada sinúsia e as seguintes variáveis explanatórias: abertura do dossel, composição do solo e densidade de árvores com DAP ≥ 5 e 20 cm; e para cada cota altitudinal, a temperatura e precipitação média anual. Utilizamos modelos lineares generalizados para analisar a influência das variáveis na abundância das sinúsias. Encontramos que as variáveis climáticas (precipitação e temperatura) foram as principais variáveis explanatórias relacionadas com variação na abundância e riqueza das três sinúsias analisadas. As distintas formas de vida apresentaram diferenças na intensidade da resposta às variáveis. Foi registrado um aumento de quatro vezes na abundância de hemiepífitos secundários e de praticamente duas vezes para lianas rizo-escandentes, entre a porção inferior e a superior do gradiente, correlacionando-se positivamente com o aumento da precipitação e umidade. A riqueza total de espécies apresentou um decréscimo na porção superior do gradiente, que foi correlacionado ao decréscimo da temperatura. Os resultados encontrados corroboram trabalhos anteriores, com outros grupos vegetais e animais, que afirmam que as variáveis climáticas são as preditoras de primeira ordem da distribuição das espécies e reforçam a necessidade de se analisar distintas formas de vida, pois estas tendem a responder de modo distinto aos fatores ambientais.The main aim of this study was to analyze the major abiotic and biotic factors correlated with distribution, abundance and richness of primary and secondary hemiepiphytes and root-climbing lianas along an altitudinal gradient of the South Brazilian Atlantic Forest. Fifteen 400-m² square sample plots within three altitudinal levels at the slope of Serra Geral in north-eastern Rio Grande do Sul were defined. Abundance of all species, the percentage of host trees colonized by each synusia, and explanatory variables canopy openness, soil composition and tree density with DBH ≥ 5 and ≥ 20 cm were recorded for each sample plot. Mean annual air temperature and rainfall were recorded for each altitudinal level. Climatic variables (precipitation and temperature) were the main explanatory variables related with the variation in abundance and richness in the three synusiae studied. The three life forms showed different intensities in their response to these variables. The abundance of secondary hemiepiphytes increased up to four times from the lower to upper altitudinal levels, while root-climbing lianas increased almost twice in the same direction, following an increase in precipitation and humidity. Total species richness decreased toward the upper level of the gradient correlated with lower temperatures and colder winter months. Our results corroborate previous studies on other taxonomic groups, which indicate that climatic variables are first-order predictors for species distribution and reinforce the importance to study different life forms, because these may respond in distinct ways to environment factors.
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Bedecarrats, Alain. "Les peuplements végétaux issus de l'ensemencement des pistes de ski dans les Alpes du Nord : structure et dynamisme." Grenoble 1, 1988. http://www.theses.fr/1988GRE10071.
Full textAbstract:
Les groupements issus de l'enherbement au moyen de melanges de graines de varietes d'especes herbacees commercialisees (dont principalement festuca rubra, festuca ovina, phleum pratense, lolium perenne, trifolium repens, trifolium hybridum, lotus corniculatus) des zones terrassees lors de la construction des pistes de ski evoluent tres rapidement en fonction des configurations des milieux. Leur etude dans les domaines du montagnard superieur a l'alpin inferieur sur des terrains pauvres en calcium et a bon equilibre textural situes aux menuires et a val thorens en savoie fait ressortir: que jusqu'au subalpin moyen et sur des sols a bon potentiel edaphique (soit que les sols initialement en place ont ete faiblement decapes, soit que des apports importants en matiere organique et en elements mineraux ont ete realises ou que des dispositifs de piegeage des elements fins ont ete installes), ils constituent des formations fermees: ces groupements se stabilisent par modification dynamique: au cours d'une phase juvenile (pendant les trois premieres periodes de vegetation) ils sont composes par les especes introduites et quelques ruderales; au cours d'une phase de transition apparaissent des especes autochtones de premiere installation: au cours de la phase de maturation la contribution specifique et la richesse specifique des especes spontanees provenant pour partie des groupements vegetaux environnants augmentent fortement: pour les stations fortement terrassees et/ou a tres haute altitude, les recouvrements observes sont faibles
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Lindgren, Jessica. "Small remnant habitats : Important structures in fragmented landscapes." Doctoral thesis, Stockholms universitet, Institutionen för naturgeografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-148653.
Full textAbstract:
The world-wide intensification of agriculture has led to a decline in species richness due to land use change, isolation, and fragmentation of natural and semi-natural habitats in agricultural and forestry landscapes. As a consequence, there is a current landscape management focus on the importance of green infrastructure to mitigate biodiversity decline and preserve ecosystem functions e.g. pollination services and pest control. Even though intensification in agriculture has been ongoing for several hundreds of years, remnant habitats from earlier management practices may still be remaining with a surprisingly high plant richness. Preserving these habitats could help conserving plant species richness in agricultural landscapes, as well as other organisms that are dependent on plants for food and shelter. In this thesis I focus on two small remnant habitats; midfield islets and borders between managed forest and crop field in southeastern Sweden. In the past, both habitats were included in the grazing system and therefore often still have remnant population of grassland specialist species left today. I have used these two remnant habitats as model habitats to investigate the effect of landscape factors and local factors on species richness of plants, flower morphologies and plants with fleshy fruits. Additively, I analysed the effect of surrounding landscape and local openness on the functions; pollination success, biological pest control of aphids and seed predation on midfield islets. One of my studies showed that spatial distribution and size of the habitat affected plant species richness. Larger habitat size and higher connectivity between habitats increased species richness of plants in the habitats. Openness of the habitats was shown to be an important factor to increase species richness and richness of flower morphologies, both on midfield islets and in forest borders. Even though midfield islets had the highest species and morphology richness, both habitat types are needed for habitat complementary as forest borders have more plants with fleshy fruits and a higher richness of plant species that flowers in spring/early summer. It was also shown that a more complex forest border, not just with gaps in the canopy, but also with high variation in tree stem sizes increases plant species richness in the field layer. The conclusion is that by managing small remnant habitats to remain or become more semi-open and complex in their structure, would increase species richness of plants, grassland specialist species, and flower morphologies. It would also increase some ecosystem functions as seed predation and biologic pest control of aphids are more effective close to trees. If both midfield islets and forest borders would be managed to be semi-open, the area and connectivity of semi-open habitat would increase in the agricultural landscape, which may also improve pollination success as the connectivity between populations has a possibility to increase. Grassland specialist species are clearly abundant in the small remnant habitats. As the decline of semi-natural grasslands is causing a decline in grassland specialists’ species, not only plants, I recommend that small remnant habitats are included in conservation and management plans and strategies to improve habitat availability and connectivity for grassland species in agricultural landscapes.Research funder Ekoklim. Project:4339602.
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.
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Li, Yuanzhi. "Structure et dynamique d'occupation de l'espace fonctionnel à travers des gradients spatiaux et temporels." Thèse, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/11615.
Full textAbstract:
Les modèles d'occupation de niche au sein des communautés locales, la variabilité spatiale de la biodiversité le long des gradients environnementaux du stress et des perturbations, et les processus de succession végétale sont plusieurs sujets fondamentaux en écologie. Récemment, l'approche basée sur les traits est apparue comme un moyen prometteur de comprendre les processus structurant les communautés végétales et cette approche a même été proposée comme méthode pour reconstruire l'écologie communautaire en fonction des traits fonctionnels. Par conséquent, lier ces thèmes fondamentaux en utilisant une lentille fonctionnelle devrait nous donner un aperçu de certaines questions fondamentales en écologie et sera l'objectif principal de ma thèse. En général, mon projet de doctorat vise à étudier les structures de l'occupation de l'espace fonctionnel dans les gradients spatio-temporels. Plus précisément, l'objectif du chapitre 2 est (i) d'étudier les modèles d'occupation de la niche fonctionnelle en calculant trois métriques clés de niche (le volume total de niche fonctionnelle , le chevauchement des niches fonctionnelles et le volume de niche fonctionnel moyen) des communautés pauvres en espèces aux communautés riches en espèces et (ii) de déterminer le principal facteur de la structure observée de l'occupation de la niche fonctionnelle dans les communautés végétales du monde entier. Dans le chapitre 3, je vise à prédire et à expliquer la variation de la richesse en espèces selon les gradients de stress et de perturbation, en reliant le modèle d'équilibre dynamique et l'occupation de la niche fonctionnelle en fonction du cadre développé au chapitre 2. L'objectif du chapitre 4 est de tester expérimentalement l’application d'une méthode d'ordination CSR évaluée globalement en fonction de trois traits de feuilles (surface foliaire, teneur en matière sèche des feuilles et surface foliaire spécifique) dans les études locales. Enfin, l'objectif du chapitre 5 est de tester expérimentalement les hypothèses qui concilient les points de vue déterministes et historiquement contingents de la succession végétale, en étudiant la variation des divergences taxonomiques et fonctionnelles entre les communautés selon des gradients de stress et de perturbation.
L'étude globale (chapitre 2) est basée sur une collection de 21 jeux de données, couvrant les biomes tropicaux et tempérés, et se compose de 313 communautés végétales représentant différentes formes de croissance. Les études locales (chapitre 3, 4 et 5) sont basées sur le même système expérimental constitué de 24 mésocosmes présentant différents niveaux de stress et de perturbation. L'expérience a commencé en 2009 avec le même mélange de graines de 30 espèces herbacées semées sur les 24 mésocosmes et s'est terminée en 2016. Nous avons permis la colonisation naturelle de graines de la banque commune de graines de sol et de l'environnement pendant la succession de sept ans. Dix traits ont été mesurés sur cinq individus (échantillonnés directement à partir des mésocosmes) par espèce par mésocosme en 2014 (chapitre 3 et 4). Un autre ensemble de traits (16 traits, y compris certains traits qui ne pouvaient pas être mesurés directement dans les mésocosmes), ont été mesurés au niveau de l'espèce (valeurs moyennes des traits) pour les 34 espèces les plus abondantes (certaines espèces disparues dans les mésocosmes) au cours des sept Ans, en les regroupant séparément pour une saison de croissance.
Au chapitre 2, nous avons constaté que les communautés étaient plus diverses en termes fonctionnels (une augmentation du volume fonctionnel total) dans les communautés riches en espèces et que les espèces se chevauchaient davantage au sein de la communauté (augmentation du chevauchement fonctionnel), mais ne divisaient pas plus finement l'espace fonctionnel (aucune réduction du volume fonctionnel moyen). En outre, le filtrage de l'habitat est un processus répandu qui conduit à la caractérisation de l'occupation de niche fonctionnelle dans les communautés végétales. Dans le chapitre 3, nous avons trouvé un modèle similaire d'occupation de niche fonctionnelle sur un système expérimental avec une taille spatiale communautaire constante et un effort d'échantillonnage des traits, qui, avec le chapitre 2, nous a fourni une image plus complète et plus solide de l'occupation de niche fonctionnelle dans les communautés végétales. De plus, nous avons réussi à relier le modèle de l'occupation de la niche fonctionnelle et le modèle d'équilibre dynamique et avons constaté que le filtrage concurrentiel était le processus dominant qui détermine le mode d'occupation de la niche fonctionnelle et la richesse des espèces le long du stress et de la perturbation des gradients. Au chapitre 4, nous fournissons un soutien empirique à une méthode d'ordination CSR calibrée globalement en montrant une relation entre l'abondance relative d'espèces en croissance dans les mésocosmes ayant différents niveaux de fertilité du sol et mortalité indépendante de la densité et leur classification CSR. Au chapitre 5, nous avons montré que la succession d'installations au cours de sept ans dans ces mésocosmes était plus déterministe d'un point de vue fonctionnel, mais plus historiquement contingent d'un point de vue taxonomique et que l'importance relative de la contingence historique a diminué à mesure que l'environnement devenait plus stressé ou perturbé.
En conclusion, les structures de l'occupation de l'espace fonctionnel dans (le volume fonctionnel total, le chevauchement fonctionnel et le volume fonctionnel moyen, les Chapitre 2 et 3) ou entre les communautés locales (dissimilarité fonctionnelle, chapitre 5) sont déterministes plutôt que neutres (ou contingence historique ). Les espèces tolératrices de stress sont plus avantagées dans les mésocosmes moins fertiles tandis que les espèces rudérales sont plus avantagées dans les mésocosmes avec plus de mortalité indépendante de la densité.Abstract : The patterns of niche occupancy within local communities, the spatial variability of biodiversity along environmental gradients of stress and disturbance, and the processes of plant succession are several fundamental topics in ecology. Recently, the trait-based approach has emerged as a promising way to understand the processes structuring plant communities and has even been proposed as a method to rebuild community ecology based on functional traits. Therefore, linking these fundamental themes through a functional lens should give us more insight into some basic questions in ecology and will be the main objective of my thesis. Generally, my PhD project is to investigate the structures of functional space occupancy along both spatial and temporal gradients. Specifically, the objective of Chapter 2 is to investigate the patterns of functional niche occupancy by calculating three key niche metrics (the total functional niche volume, the functional niche overlap and the average functional niche volume) from speciespoor communities to species-rich communities and to determine the main driver of the observed pattern of functional niche occupancy across plant communities worldwide. In Chapter 3, I aim to predict and explain the variation of species richness along gradients of stress and disturbance, by linking the dynamic equilibrium model and functional niche occupancy based on the framework developed in Chapter 2. The objective of Chapter 4 is to experimentally test the application of a globally calibrated CSR ordination method based on three leaf traits (leaf area, leaf dry matter content and specific leaf area) in local studies. Finally, the aim of Chapter 5 is to experimentally test the hypotheses reconciling the deterministic and historically contingent views of plant succession, by investigating the variation of taxonomic and functional dissimilarities between communities along gradients of stress and disturbance. The global study (Chapter 2) is based on a collection 21 trait datasets, spanning tropical to temperate biomes, and consisting of 313 plant communities representing different growth forms. The local studies (Chapter 3, 4 and 5) are based on the same experimental system consisting of 24 mesocosms experiencing different levels of stress and disturbance. The experiment started in 2009 with the same seed mixture of 30 herbaceous species broadcast over the 24 mesocosms and ended in 2016. We allowed natural colonization of seeds from the common soil seed bank and from the surroundings during the seven-year succession. Ten traits were measured on five individuals (sampled directly from the mesocosms) per species per mesocosms in 2014 (Chapter 3 and 4). Another set of traits (16 traits including some traits that were not able to measured directly in the mesocosms) were measured at the species level (species mean traits values) for the 34 most abundant species (some species disappeared in the mesocosms) over the seven years, by regrowing them separately for one growing season. In Chapter 2, we found communities were more functionally diverse (an increase in total functional volume) in species-rich communities, and species overlapped more within the community (an increase in functional overlap) but did not more finely divide the functional space (no decline in average functional volume). Moreover, habitat filtering is a widespread process driving the pattern of functional niche occupancy across plant communities. In Chapter 3, we found a similar pattern of functional niche occupancy on an experimental system with a constant community spatial size and trait-sampling effort, which together with Chapter 2 provided us a more comprehensive and robust picture of functional niche occupancy across plant communities. In addition, we succeeded in linking the pattern of functional niche occupancy and the dynamic equilibrium model and found that habitat filtering was the dominant process determining the pattern of functional niche occupancy and species richness along the gradients stress and disturbance. In Chapter 4, we provide empirical support for a globally calibrated CSR ordination method by showing a relationship between the relative abundance of species growing in mesocosms having different levels of soil fertility and density-independent mortality and their CSR classification. In Chapter 5, we showed that plant succession over seven years in these mesocosms was more deterministic from a functional perspective but more historically contingent from a taxonomic perspective, and that the relative importance of historical contingency decreased as the environment became more stressed or disturbed. In conclusion, the structures of functional space occupancy within (the total functional volume, the functional overlap and the average functional volume; Chapter 2 and 3) or between local communities (functional dissimilarity, Chapter 5) are deterministic rather than neutral (or historical contingency). Stress-tolerators were more favored in high stress communities, while ruderals are more favored in high disturbed mesocosms (Chapter 4).
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Köchy, Martin, and Sven Bråkenhielm. "Separation of effects of moderate N deposition from natural change in ground vegetation of forests and bogs." Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/1662/.
Full textAbstract:
The effect of moderate rates of nitrogen deposition on ground floor vegetation is poorly predicted by uncontrolled surveys or fertilization experiments using high rates of nitrogen (N) addition. We compared the temporal trends of ground floor vegetation in permanent plots with moderate (7–13 kg ha−1 year−1) and lower bulk N deposition (4–6 kg ha−1 year−1) in southern Sweden during 1982–1998. We examined whether trends differed between growth forms (vascular plants and bryophytes) and vegetation types (three types of coniferous forest, deciduous forest, and bog). Trends of site-standardized cover and richness varied among growth forms, vegetation types, and deposition regions. Cover in spruce forests decreased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs cover decreased faster with low deposition. Cover of bryophytes in spruce forests increased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs and deciduous forests there was a strong non-linear increase with moderate deposition. The trend of number of vascular plants was constant with moderate and decreased with low deposition. We found no trend in the number of bryophyte species. We propose that the decrease of cover and number with low deposition was related to normal ecosystem development (increased shading), suggesting that N deposition maintained or increased the competitiveness of some species in the moderate-deposition region. Deposition had no consistent negative effect on vegetation suggesting that it is less important than normal successional processes.
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Aksamit, Dawn N. "Exotic Invasive Plants on Private Woodlands of Virginia: Effects on forest composition, structure, and wildlife habitat." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/30975.
Full textAbstract:
Exotic invasive plants have become a significant issue in the Southeastern United States for private landowners. These plants possess characteristics that allow for rapid growth and easy adaptation to many growing conditions, often outcompeting native vegetation and altering wildlife habitat, especially in disturbed areas. Disturbance, including access roads, trails, harvest sites, powerline corridors, and fence rows, is common on private land. Private landowners are often left to combat these problems without many monetary or expertise resources that are available to federal lands. Three field sites, each in a different physiographic province in Virginia, were surveyed for exotic invasive populations and sampled with nested overstory, understory, and regeneration plots and wildlife point intercept transects using paired plots during the summers of 2006 and 2007. Species richness of the overstory and understory did differ, but native percent understory cover and sapling density remained unchanged. Tree density and forest basal area were reduced with presence of exotic invasive plants. Regeneration diversity and density decreased in areas of exotic plant invasion. Eastern cottontail habitat suitability increased with the presence of exotic invasive plants. Suitability of habitat for the gray squirrel, downy woodpecker food, black-capped chickadee reproduction, and eastern wild turkey cover declined with the occurrence of exotic invasive plants. Twenty three of thirty seven total invasive plots were within twenty feet of a disturbance area. Continual assessment of impacts will help provide a better understanding of the nature of exotic invasive plants to landowners and may help them to manage and prevent plant invasions.Master of Science
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Guthrie, Ruth J. "Patterns of invertebrate distribution and abundance on Cordyline australis in human-modified landscapes." Diss., Lincoln University, 2008. http://hdl.handle.net/10182/1235.
Full textAbstract:
Fragmentation of forest habitat by urban and rural development has had profound effects on the distribution and abundance of many native species; however, little is known about the ecological processes driving patterns in community structure (species richness and composition) of host-specialised herbivores in modified habitats. I examined patterns in community structure of 9 specialist and 19 generalist invertebrate herbivores of cabbage trees (Cordyline australis Laxmanniaceae) across a highly-modified landscape. I found that, although species richness of specialists was highest in forest sites, the majority of host-specialised species were not restricted to forest habitats and were as widespread as many generalists. In terms of site occupancy, only two specialist and four generalist species were rare. I show that patterns of species occupancy and abundance reflect differing susceptibility to habitat modification, with landscape-level variation an important predictor of abundance for nearly all species. When species occurrences and life history traits were considered I did not find strong evidence for the importance of dispersal ability, which suggests that habitat variability had a stronger organising effect on the community. In a replicated common garden experiment, I found distinct regional patterns in the community structure of the specialist invertebrates occurring on different phylogenetic groups of C. australis. In contrast, community structure of generalist herbivores did not differ significantly among host genotypes. I speculate these patterns are due to historical changes in the distribution of cabbage trees in the Southern phylogenetic region that caused specialised herbivores to become locally adapted on populations of low genetic diversity following expansion after the last glacial maximum. However, this consistent selection pressure did not occur in the Northern region where C. australis habitat has been more consistently available over the past tens of thousands of years, reflected in higher host genetic diversity. This study has advanced our understanding of the patterns in community structure of an indigenous, host-specialised fauna in a highly modified and fragmented urban and rural landscapes.
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Schwoertzig, Eugénie. "Contribution des corridors fluviaux à la dynamique de la biodiversité végétale urbaine." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAH005/document.
Full textAbstract:
L'écologie urbaine, qui a émergé depuis une trentaine d'années, s'intéresse notamment à l'étude de la biodiversité et du fonctionnement des écosystèmes en ville. Ce travail de thèse porte plus particulièrement sur l'analyse de l'écosystème "corridor fluvial", et son rôle dans la dynamique des communautés végétales en fonction d'un gradient d'urbanisation. Les corridors fluviaux assurent en effet une connexion structurelle entre la ville et la campagne, et leur conservation en milieu urbain implique d'en comprendre précisément la fonctionnalité écologique. L'objectif de ce travail est donc de mettre en évidence l'effet du gradient d'urbanisation sur la composition et la structure des communautés végétales le long d'un cour d'eau et de vérifier si l'existence en ville de corridors fluviaux contribue efficacement à la dispersion et à la rapidité de colonisation des milieux adjacents. Deux cours d'eau, la Bruche et l'hydrosystème Rhin Tortu - Ziegelwasser, ont été étudiés dans leur partie aval la plus urbaine au sein de l'Eurométropole de Strasbourg. [...]Urban ecology, which has emerged over the last thirty years, focused in particular on studying thebiodiversity and on functioning of ecosystems in cities. This work explores urban riparian corridors and their rolein the dynamic of plant communities based on a gradient of urbanization. Indeed, riparian corridors provide astructural connection between the city and the countryside, and their conservation involves preciselyunderstanding their ecological functionality. The objectives of this work are to highlight the effect of the urbanization gradient on the composition and structure of plant communities along a river to determine whether the existence of urban riparian corridors effectivelycontributes to the colonization of adjacent areas. Two rivers, the Bruche and the Rhin Tortu - Ziegelwasser, arestudied in their most urban downstream part in the metropolitan area of Strasbourg, eastern France. [...]