Dissertations / Theses on the topic 'Plant communitie'
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Swedo, Barbara L. "Plant-microbe associations controls on soil bacterial community structure and consequences for aboveground plant communities /." [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337259.
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Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2008.Title from PDF t.p. (viewed on Jul 28, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7260. Adviser: Heather L. Reynolds.
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Iglesias, Maria Claudia. "Spacial patterns of the genders in Dioecius plant species." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65458.
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Foy, Elizabeth Christina. "Riparian vegetation and forest structure of two unregulated tributaries, compared to the regulated Snake River, Grand Teton NP, WY." Thesis, Montana State University, 2008. http://etd.lib.montana.edu/etd/2008/foy/FoyE1208.pdf.
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The dynamic nature of rivers shapes riparian plant communities, and changes to the flow regime can have profound effects on these diverse ecosystems. To examine how riparian plant communities of the dam-regulated Snake River in Grand Teton National Park, WY respond to hydro-geomorphological factors, I studied the vegetation of two unregulated tributaries, Pacific Creek and Buffalo Fork, in relation to the main river. I considered three perspectives in this analysis. In chapter 2, I examined hydro-geomorphological processes shaping riparian vegetation in naturally flowing systems, by evaluating 15 environmental variables, and determining which were most related to vegetation. Using cluster analysis, I identified six distinct communities. I described environmental conditions associated with each community, using the unconstrained ordination technique NMDS, coupled with generalized additive models (GAMs). Community types occur on characteristic geomorphologic landforms. Depth to gravel, soil texture, pH, distance to bankfull channel, and elevation above water are all related to vegetation, and interact to determine where community types occur. In my third chapter, I compared the vegetation of the unregulated tributaries to the Snake River, as a means of assessing dam effects. Species richness per plot is higher on the tributaries, despite higher overall richness on the Snake River. Through the use of NMDS ordination and clustering techniques, I found the composition of the upper section of the Snake River, immediately below the dam, to be distinct. However, this section is naturally more incised, and the lower sections of the river do not seem to be influenced, suggesting dam impacts on vegetation are minimal. Environmental variables related to vegetation composition include elevation above water, depth to gravel, and geomorphological landform. In chapter 4, I compared age class distributions of spruce and cottonwoods across river sections, and found no evidence for a late-successional trend on the regulated river, versus unregulated tributaries. Age distribution is related to geomorphological landform, and browing also influences forest structure through root coppicing. Forest understory communities are structured by cottonwood age.
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Carlyle, Cameron Norman. "Interacting effects of climate change and disturbance on grassland plants and plant communities." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42269.
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Grasslands are threatened by urbanization, agricultural conversion, over-grazing, tree-encroachment, and invasive plants. Simultaneously, climate change acts on all levels of biological organization, from entire communities to the physiology of individuals. The environmental stresses induced by climate change have the potential to interact with human-caused disturbance, but the response of plants to these stresses and disturbances, and how they may interact, are not well known. To conserve grasslands it is critical to know which types of grassland and which plant species will be most affected. To understand the mechanisms of change at the ecosystem level it is necessary to study the response at lower levels of biological organization. Using a variety of approaches I studied the potentially interacting effects of stress (primarily reduced water availability) and disturbance (plant biomass removal) on different levels of biological organization. I ran a 4-year field experiment in which I manipulated water availability, temperature and clipping in three different grassland types. I found complex plant community structure and biomass response; treatments often interacted but the different grassland types had their own particular responses. As part of this experiment I monitored the effects of treatments on soil moisture and temperature and found that the effects are generally consistent with expectations, but treatments do not act exclusively or independently on target variables. In addition to stress and disturbance, competition is a key process structuring grasslands. In the greenhouse, I examined how plant competition is affected by stress and disturbance. I found that the interpretation of how competition is affected is dependent on the way competition is measured. Some measures of competition showed reduced competition across stress and disturbance gradients, but other measures showed no change. Finally, I examined the root traits of 18 species of grass in the greenhouse in response to reduced water availability. I found significant variation in traits among species, maintenance of trait hierarchies across environments and little evidence of plasticity, except for root: shoot ratio. Overall, stress, disturbance and their interactions are important in influencing individual plant performance, competition, structuring plant communities, and ecosystem function.
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Binney, Elizabeth P. "Comparative analysis of community and population levels of organization in the rare grass, Achnatherum hendersonii." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ27107.pdf.
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Boughton, Elizabeth Hermanson. "Understanding plant community composition in agricultural wetlands context dependent effects and plant interactions /." Orlando, Fla. : University of Central Florida, 2009. http://purl.fcla.edu/fcla/etd/CFE0002678.
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Laxton, Emma. "Relationship between leaf traits, insect communities and resource availability." Thesis, Electronic version, 2005. http://hdl.handle.net/1959.14/483.
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Thesis (PhD)--Macquarie University, Division of Environmental and Life Sciences, Dept. of Biological Sciences, 2005.Bibliography: p. 178-203.
Introduction -- Study sites -- Leaf characteristics and resource availability -- Insect herbivory and resource availability -- Insect communities and resource availability -- Influence of resource availability on recovery from herbivory -- Conclusions.
This project used the resource availability hypothesis (Coley et al., 1985) as a framework for investigating the relationship between resource availability (as defined by soil nutrients), leaf traits, insect herbivore damage and insect community structure. According to the hypothesis, plants from low resource environments should be better-defended, have longer leaf lifespans and slower growth rates than plants from higher resource environments. Higher resource plant species are expected to suffer higher levels of herbivory and recover faster from herbivory than low resource plant species (Coley et al. 1985). A corollary to this hypothesis is that plants from higher resource sites should support greater densities of insect herbivores than low resource species. Comparisons between high and low resource sites were made in terms of: (i) leaf traits of mature and immature leaves; (ii) phenology of leaf maturation; (iii) herbivore damage in the field and laboratory; (iv) diversity and abundance of herbivorous insect fauna; and (v) ability to recover from herbivory.
Mode of access: World Wide Web.
243 p. ill., maps
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Palisaar, Jaan. "The floodplain meadows of Soomaa National Park, Estonia vegetation - dispersal - regeneration /." Connect to this title online, 2006. http://www.opus-bayern.de/uni-regensburg/volltexte/2006/705/.
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Gosper, Carl R. "Consequences of weed invasion and control on plant-bird interactions and bird communities." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20050221.155953/index.html.
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Zuefle, Marion E. "The impact of non-native woody plants on the native herbivorous insect community of northern Delaware." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 75 p, 2006. http://proquest.umi.com/pqdweb?did=1163239621&sid=7&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Patrick, L. Brian. "Fertilization and plant litter effects on the plant and epigeal arthropod communities." [Kent, Ohio] : Kent State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1259588844.
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Thesis (Ph.D.)--Kent State University, 2009.Title from PDF t.p. (viewed April 14, 2010). Advisor: Mark W. Kershner. Keywords: biodiversity; nitrogen; fertilization; plant litter; trophic dynamics; epigeal community. Includes bibliographical references.
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Coulter, Celeste Tina. "Vegetation response to seasonality of prescribed fire and postfire seeding following mechanical fuel-reduction treatments in oak-chaparral communities of southwestern Oregon /." View full-text version online through Southern Oregon Digital Archives, 2008. http://soda.sou.edu/awdata/081119z1.pdf.
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Thesis (M.S.)--Southern Oregon University, 2008.Includes bibliographical references (p.135-142 ). Also available via Internet as PDF file through Southern Oregon Digital Archives: http://soda.sou.edu. Search Bioregion Collection.
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Viketoft, Maria. "Soil nematode communities in grasslands : effects of plant species identity and diversity /." Uppsala : Dept. of Ecology, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/200748.pdf.
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Leung, Pui-chi. "Exotic plant invasion of upland plant communities in Hong Kong, China." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36632442.
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Berglund, Linda. "Disturbance, nutrient availability and plant growth in phenol-rich plant communities /." Umeå : Dept. of Forest Vegetation Ecology, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/s327.pdf.
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Leung, Pui-chi, and 梁佩芝. "Exotic plant invasion of upland plant communities in Hong Kong, China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36632442.
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Cameron, Duncan Drummond. "A role for differential host resistance to the hemiparasitic angiosperm, Rhinanthus minor L. in determining the structure of host plant communities?" Thesis, University of Aberdeen, 2004. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=238495.
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This study describes the effect of the root hemi-parasitic angiosperm Rhinanthus minor on the structure of the communities in which it lives and seeks to elucidate a mechanism through which the parasite acts to effect these changes in the community. Field manipulations reveal that R. minor suppressed the growth of grasses and legumes in a newly sown meadow whilst promoting the forbs within one growing season. In contrast the removal of R. minor from mature meadow plots did not influence their composition. After an additional growing season the parasite did not further influence the composition of the new meadows but removal did begin to benefit the biomass of mature plots. In isolation the parasite caused most damage to grasses whilst leaving legumes and forbs undamaged. Moreover, the parasite performed worst in terms of growth and photosynthesis when attached to the forbs. Consequently the parasite was able to moderate intra-specific competition between grasses and forbs. I thus hypothesised that forbs were able to prevent the parasite form abstracting resources where as grasses could not. Tracer experiments using isotopically e5N) labelled potassium nitrate confirmed this hypothesis showing that more of the resources taken up by the host were stolen by the parasite from grasses than from forbs. There was much variability in the translocation of resources from the legume studied. The reasons underlying the differential uptake of resources were highlighted using histological studies which showed that all of the forbs possessed successful resistance mechanisms to the parasite whilst no successful resistance was observed in the grasses or legumes. Two different resistance mechanisms were observed in the forbs; hypersensitive cell-death at the host-parasite interface and host lignification. I therefore propose that differential host resistance may underlie this parasite's community level effects as forbs possess a resistance capacity that other potential hosts do not.
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Rosenfeld, Kristen Marie Wentworth Thomas R. Suiter Dale William. "Ecology of Bird Island, North Carolina an uninhabited, undeveloped barrier island /." Connect to this title online, 2004. http://www.lib.ncsu.edu/theses/available/etd-07122004-185722/.
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Erickson, Heather E. "Nitrogen and phosphorus availability, ecosystem processes and plant community dynamics in boreal wetland meadows /." Thesis, Connect to this title online; UW restricted, 1994. http://hdl.handle.net/1773/5590.
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Vannier, Nathan. "The clonal plant microbiota : assembly rules, heritability and influence on host phenotype." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1B027/document.
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Les plantes vivent en association avec une grande diversité de microorganismes qui forment son microbiota. Ce microbiote fournit des fonctions clés qui influencent tous les aspects de la vie d'une plante, de l'établissement à la croissance jusqu'à la production. Cette thèse a pour intention de déterminer les règlent d'assemblage du microbiote et ses conséquences pour le phénotypel l'adaptation et l'évolution des plantes. Pour atteindre cet objectif nous avont utilisé différentes approches expérimentales comprenant des plantes clonales comme organismes modèles ainsi que des mésocosmes prairiaux pour analyses à l'échelle des communautés. Nos résultats ont démontré i) que les Champignons Mycohiziens à Arbuscules induisent d'important es variations phénotypiques pour les traits des plantes clonales impliqués dans l'exploration de l'espace et l'exploitation des ressources. Ces changements dépendent de l'identité des symbiontes et altèrent les capacités des plantes à développer des réponses plastiques à l'hétérogénéité environnementale. ii) Les plantes ont évolué un méchanisme permettant la transmission d'une partie de leur microbiote a leur descendance, assurant la qualité de leur habitat. iii) Le contexte spécifique des communautés de plantes est un facteur majeur structurant l'assemblage du microbiota des plantes à échelle locale. L'abondance de certaines espèces de plante dans le voisinage d'une plante cible augmente ou diminue la diversité de son microbiote, déterminant in fine ses performances. De manière générale, cette thèse démontre l'importance des organismes symbiotiques dans la compréhension de l'adaptation et de l'évolution des plantesPlants live in association with a wide diversity of microorganisms forming the microbiota. The plant microbiota provides a variety of key functions that influence many aspects of plant's life comprising establishment, growth and reproduction. The present thesis aims at determining the assembly rules of the plant microbiota and its consequences for plant phenotype, adaptation and evolution. To fulfill this objective, we used different experimental approaches using either clonal plants as model organisms or grassland mesocosms for community-wide analyses. Our results demonstrated i) that Arbuscular Mycorrhizal Fungi induce important phenotypic variations in clonal plants traits involved in space exploration and resources exploitation. These changes depended on the identity of the symbionts and altered the plants ability to produce plastic responses to environmental heterogeneity. ii) Plants have evolved a mechanism allowing the transmission of a part of their microbiota to their progeny, ensuring thus their habitat quality. iii) The plant community context is a major factor structuring local plant microbiota assembly. Particular plant species identity in the neighborhood increase or decrease the microbiota diversity and ultimately determine the focal plant performance. This thesis overall demonstrates the importance of symbiotic microorganisms in the understanding of the plant adaptation and evolution. From the knowledges acquired we developed a novel understanding of symbiotic interactions in clonal plants by extending the holobiont theory to the meta-holobiont theory
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Bush, Catherine Dana. "Native seed mixes for diverse plant communities." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28920.pdf.
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Cervantes, Peredo Luis Manuel. "Effects of Hemiptera on successional plant communities." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362367.
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Allan, Caroline Elizabeth. "Nitrogen fixation in riverine wetland plant communities." Thesis, University of Glasgow, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297033.
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Sutton, Julian James. "On the dynamics of annual plant communities." Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235530.
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Shaw, Rosalind F. "Plant-herbivore interactions in montane willow communities." Thesis, University of Aberdeen, 2006. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU212664.
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This project investigated the impacts of browsing by large herbivores on all aspects of the life cycle of montane willows, using Salix arbuscula L. (Mountain Willow) as the main model species. S. arbuscula was found to be almost entirely insect pollinated, although the levels of wind pollination varied between populations. The density of nearby male plants had a positive effect on fruit set in both insect and wind pollinated catkins, but the effect was stronger in wind-only pollinated catkins. In insect pollinated catkins, catkin characteristics such as length and total number of flowers were most important in determining fruit set. Browsing was found to have both direct and indirect negative impacts on seed production in S. arbuscula, which was also highly variable between years. Direct effects included reduction of the number of inflorescences produced by browsing removal of the previous year's growth, on which most inflorescences are found. There were fewer inflorescences found per shoot on browsed plants, suggesting that browsing also reduces inflorescence production via resource limitation. Lower numbers of inflorescences per plant led to fewer pollinator visits and resulted in reduced seed production, particularly in years of poor overall production. Seed and early seedling survival were found to be strongly limited by microsite availability, as both S. arbuscula and S. lapponum required bare ground for germination and early survival. Slugs were found to have a negative impact on seedlings during the first season of growth, where as small mammals (bank voles) had a negative effect one the seedlings were larger. Growing in disturbed microsites may also favour seedling establishment through reducing the likelihood of slug and small mammal predation.
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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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Siegwarth, Mark. "Zen and the Art of Plant Communities." University of Arizona (Tucson, AZ), 2012. http://hdl.handle.net/10150/556788.
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Madgwick, Genevieve. "Long term changes in aquatic plant communities in English lowland lakes." Thesis, University of Stirling, 2009. http://hdl.handle.net/1893/2270.
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This thesis looks into the use of historical macrophyte records to assess long term changes in macrophyte communities in lakes and potential reasons for these changes. In particular it uses historical records to assess changes in macrophyte communities in the Norfolk Broads and West Midland Meres, two sets of lowland, eutrophic lakes in England. It provides a critical examination of the use of historical records, highlighting some of the constraints common to such data such as variations in recording effort, and bias in species recording and site selection. Having acknowledged these issues we then go on to develop a robust way to interpret such data, using a “change index” based on species persistence over the last 200 years within individual lakes. Species with high change index values, which represented species which had persisted or increased within the lake districts, were those known to be characteristic of eutrophic lakes. Conversely species with low index scores, which had declined in both the broads and meres over the last 200 years, included species associated with less fertile conditions but also a selection of typically eutrophic species. Averaging of change index scores in present day survey data served to identify the historically least changed lakes and to rank lakes in order of degree of botanical change over the last century. We then analysed the ecological basis of the change index in order to better understand the processes behind the decline of some species and survival of others in the Norfolk Broads and West Midland Meres. Functional groups determined from morphological and regenerative traits displayed significant differences in change index values in both groups of lakes, but declining taxa occurred across a wide range of plant growth forms. Non-hierarchical clustering of species based on their ecological preferences, obtained from published literature, resulted in groups with distinct change index values, indicating that changes in the status of species could be partly explained by these preferences. Of these, trophic preference was consistently the most important, with species of less fertile habitats consistently experiencing the greatest declines. However, some characteristically eutrophic species have also declined significantly, particularly in the broads. In these cases increasing loss of shallow water, low energy habitats in the broads, or loss of fluctuating water levels and less alkaline backwaters in the meres, appear to have been contributory factors. In addition to the change index approach, we also used historical records at a site level to complement palaeolimnological analysis and investigate the change in macrophyte community composition and structure at Barton Broad, Norfolk. Sediment samples were extracted from the bottom of the broad and analysed for sub-fossil remains and pollen of macrophytes. The historical records and palaeolimnological analysis combined showed that early communities did not consist entirely of low growing, oligotrophic and mesotrophic species as previously thought, but in fact comprised a mixture of these and other more characteristically high nutrient species associated with taller, or free-floating growth habit. As eutrophication progressed throughout the last century, the community was increasingly dominated by these latter growth forms. Diversity was maintained, however, since encroaching reedswamp generated a mosaic of low energy habitats which supported a range of species unable to withstand the hydraulic forces associated with more open water habitat. When the reedswamp disappeared in the 1950s, many of the dependent aquatic macrophytes also declined resulting in widespread macrophyte loss. The thesis demonstrates not just the complexities of using historical records, but also ways in which these can be overcome to make useful observations about macrophyte community change and lake ecological integrity to inform conservation and lake management, both on a site and lake district level.
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Finyom, Cyprien William Bopda. "Characterisation of the endophytic bacterial communities associated with South African sorghum plants: looking for potential plant growth-promoting endophytes." Thesis, University of Western Cape, 2012. http://hdl.handle.net/11394/3431.
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>Magister Scientiae - MScThe term endophyte is used to define all microorganisms that, during a part of their life cycle, colonize the internal tissues of a plant host. Many endophytes have been found to promote plant growth by acting either as biocontrol agents, biofertilizers or phytohormone producers. This study aimed to characterise the endophytic microbial community diversity associated with sorghum farmed in South Africa. Members of any common endophytic bacterial species identified during the study might in future studies be developed to improve sorghum production. Sorghum tissues (roots, shoots, stems) were sampled in three South African provinces (Free State, Limpopo and North West), each site being characterised by the use of different agricultural practices. Denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) analyses were used to characterise the endophytic bacterial communities. The analysis clearly demonstrated that the endophytic bacterial community structure in the three sorghum tissue types differed, suggesting that endophyte colonization is tissue-specific. The endophytic bacterial community structure is quite similar in each tissue when comparing the populations present in the sampling sites. In the sorghum endophytic microbial communities, common bacterial species were identified using molecular tools: The cyanobacterium Synechococcus and Staphylococcus saprophyticus were identified in the root samples. Pantoea sp., Erwinia sp., Enterobacter sp. and Klebsiella sp. were found in all shoot samples. Nocardia fluminea, Bacillus cereus and Microbacterium sp. were isolated as common shoot endophytic bacteria. This study defines, for the first time, the endophytic bacterial species associated with South African sorghum plants. These common endophytic bacterial species can be used to enhance the yield of sorghum crops.
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Trentanovi, Giovanni. "Vascular plant species diversity in fragmented secondary plant communities: a landscape ecology approach." Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3421745.
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Landscape ecology has been defined in a variety of different ways, but the common theme is the study of the ecological effects of ecosystem spatial patterning. Since the long history
of landscape alteration has created novel systems with unknown dynamics, new tools are necessary to understand, manage and restore human dominated landscapes, preventing the loss of biodiversity. Among all, habitat fragmentation is the main process which affects biodiversity
especially in human dominated landscapes.
This thesis is based on three research papers concerning the evaluation of plant species diversity in fragmented and secondary plant communities. Moreover, the effect of natural
reforestation process on biodiversity of secondary plant communities was investigated through a review paper. Focusing in each paper on different specific objectives due to the variability of landscape context and habitat type, the overall goal of this work was to detect spatial and
management components influencing vascular plant species diversity. Through the different tools and methodologies used in each case study, we want to demonstrate the great applicability and versatility of landscape ecology approach both in theory and practice.
The analyses were conducted on three fragmented secondary plant communities, i.e. meadow-pastures (Paper II), recent secondary woodlands (Paper III) and hedgerows (Paper IV),
scattered in a dominant matrix type. Paper III was done during the collaboration with the Technische Universität of Berlin (Department of Ecology) during my research period abroad.
The case studies were conducted both at patch and at landscape level, considering actual field data and management variables of the secondary plant communities surveyed (patch level) and the analysis of landscape asset around (landscape level). The latter was performed by GIS
analysis. Regression models were used to relate plant species diversity to spatial and management variables.
The survival of species depends on landscape dynamics and on spatial plant community configuration (Paper I). More specifically, where environmental site condition and management variables have not impact on secondary community variability and they did not differ between
the surveyed communities, plant species diversity can be deeply influenced by spatial variables (Paper II and III). On the contrary, where management variables have a strong effect on secondary community alteration, i.e. in agrarian hedgerows, this effect is independent from the
landscape assets of the different surveyed sites (Paper IV).
In general, the integrative methods used by the “landscape ecology approach” allowed us to quantify in a holistic way complex natural-cultural patterns and processes on different time-space scales that influenced vascular plant species diversity.L’ecologia del paesaggio studia l’influenza dei pattern spaziali sui flussi di specie. La continua frammentazione ed alterazione delle fitocenosi in paesaggi antropizzati rende necessario comprendere le dinamiche delle comunità vegetali che caratterizzano il paesaggio antropizzato, cercando di evitare il più possibile la perdita di diversità biologica che spesso è conseguenza di tali trasformazioni. La mia tesi è basata su tre articoli di ricerca riguardanti l’analisi della diversità della flora vascolare in fitocenosi secondarie e frammentate. In un lavoro di review invece, è stato analizzato l’effetto della riforestazione spontanea su fitocenosi secondarie a seguito dell’abbandono delle pratiche agricole. Ciascun lavoro è stato caratterizzato da specifici obiettivi, adattati in base alla variabilità del paesaggio e del tipo di fitocenosi secondaria indagata. Ciononostante, l’obiettivo comune di questa tesi è stato quello di esaminare l’influenza delle variabili di paesaggio e gestionali sulla variabilità della flora vascolare, tramite l’utilizzo di metodologie e strumenti propri dell’ecologia del paesaggio. Le analisi sono state effettuate in tre fitocenosi secondarie e frammentate, i.e. pascoli (Paper II), neoformazioni boschive (Paper III) e siepi rurali (Paper IV), inserite all’interno di differenti matrici paesaggistiche. Il terzo caso di studio (Paper III) è stato sviluppato in collaborazione con la Technische Universität di Berlino durante il mio periodo di dottorato all’estero. Le analisi sono state effettuate sia a livello di patch che di paesaggio, considerando quindi congiuntamente i rilievi floristici e le variabili gestionali (livello di patch) e l’analisi dell’assetto paesaggistico attorno alle fitocenosi indagate (livello di paesaggio). Le analisi di paesaggio sono state effettuate tramite strumenti GIS. Vari modelli di regressione sono stati utilizzati per mettere in relazione la diversità di specie vascolari con le variabili di paesaggio e gestionali. La sopravvivenza delle specie dipende profondamente dalle dinamiche del paesaggio e dalla sua configurazione spaziale (Paper I). Più nello specifico, nei casi di studio in cui le variabili stazionali e gestionali sono ininfluenti o omogenee in tutti i siti, la diversità di specie vascolari è profondamente influenzata dalle variabili spaziali (Paper II e III). Dove invece la gestione altera sostanzialmente l’equilibrio della fitocenosi, l’effetto è indipendente dalle variabili di paesaggio (Paper IV). In generale, i principi ed i metodi dell’ecologia del paesaggio che sono stati utilizzati nei casi di studio presentati, hanno permesso di quantificare precisamente i processi e le dinamiche che influenzano la diversità di specie vascolari a differnti scale spaziali e temporali.
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Hunter, Dakota. "Invasive Species Research in Compensatory Wetland Mitigation: Investigating Plant Community Composition and Environmental Correlates with Three Invasive Plants." W&M ScholarWorks, 2019. https://scholarworks.wm.edu/etd/1563899036.
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Invasive plant species can alter natural communities and degrade ecosystem function, yet the factors influencing species invasion are poorly understood. Understanding how environmental factors affect plant invasion on compensatory wetland mitigation sites would allow wetland managers to approach invasive species management using a proactive approach (prior to invasion), thus minimizing the likelihood of invasive plants colonizing the system and degrading ecosystem function. In Chapter 1, I introduce the concepts and relevant literature used repeatedly in my project. In Chapter 2, I examine which key environmental factors are associated with altered plant community structure and invasive species prevalence on compensatory wetland mitigation sites. In Chapter 3, I look further into the plant community assemblage at each of my study sites and examine differences in the plant community at varying levels of invasive plant prevalence. For this study, Arthraxon hispidus (small carpet grass), Microstegium vimineum (Japanese stilt grass), and Typha spp. (cattail) were selected as representative invasive plants due to their abundance on non-tidal wetland mitigation sites, as well as their relative differences in ecological tolerance for environmental conditions (e.g., light availability or flooding). Within populations of these species, transects consisting of five 4m2 plots were established on 34 wetland mitigation sites within the Coastal Plain and Piedmont physiographic provinces in Virginia. Along transects, plots were randomly assigned to locations that captured the gradient from completely invaded (invasive species dominant) to uninvaded (invasive species absent or nearly so). For each plot, vegetation abundance data, soil samples, and canopy imagery were obtained for analysis. In Chapter 2, Canonical Correspondence Analysis (CCA) reveals iron, phosphorus, calcium, carbon:nitrogen ratio, canopy cover, and hydrology as correlates with variation in plant community composition across the invasion gradient. In Chapter 3, Spearman rank correlation results show no significant relationship between native species richness and invasive species abundance for any of the three species examined. Further analysis using Sørensen indices of similarity and species accumulation curves corroborate this result. Further study is required to determine causality in the relationships between invasive species and environmental variables, but results demonstrate the need for function-based criteria regarding invasive species management on compensatory wetland mitigation sites. Current standards encourage the use of non-specific herbicides, which may increase the risk of damaging native plant communities and perpetuating the cycle of disturbance and re-invasion on wetland mitigation sites.
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Marteinsdóttir, Bryndís. "Plant community assembly in grazed grasslands." Doctoral thesis, Stockholms universitet, Institutionen för ekologi, miljö och botanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-102185.
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Species assembly into local communities from the surrounding region can be caused either by species failure to reach the site (i.e. seed limitation) or to establish (i.e. establishment limitation). The aim of this thesis was to investigate plant species assembly and to determine the relative importance of different factors in that process. In a cultivated landscape in southeast Sweden, plant community assembly was studied in grazed ex-arable fields. Community assembly from the surrounding region into the local community was explored using trait-based null models and seed sowing and transplanting experiments. The influence of local environmental factors and landscape history and structure on community assembly was also studied. In addition, differences in species assembly between ex-arable fields and semi-natural grasslands were explored. Seed limitation was the strongest filter on local community assembly. Only a fraction (36%) of species in a region dispersed to a local site and adding seeds/transplants increased species establishment. Species abundance at the regional scale, species dispersal method and seed mass strongly influenced which species arrived at the local sites. Establishment limitation also affected the assembly. Of species arriving at a site 78% did establish, seedling survival was low and which species established was influenced by species interactions, local environmental conditions and stochastic events. In addition, landscape structure that determined the species richness in the regional species pool influenced the local assembly. The comparison between assembly in ex-arable fields and semi-natural grasslands indicated that the main cause of difference in species assembly between them was difference in their age. The main conclusion of this thesis is that regional processes are more important than local factors in determining plant community assembly.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted. Paper 5: Manuscript.
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Thiet, Rachel Kay. "Soil microbial community pattern and process : impacts on vascular plant communities in three ecosystems of high conservation value /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486459267521939.
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Ratcliffe, Sophia Emma Thirza. "Competition and coexistence in experimental annual plant communities." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/11515.
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Gaudet, Connie Lee. "Competition in shoreline plant communities: A comparative approach." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6516.
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I tested the general hypothesis that competitive ability is an important determinant of pattern in shoreline plant communities. Specifically I tested four predictions generated from this general hypothesis: (1) the competitive performance of plant species is related to their distribution along natural gradients of fertility and standing crop; (2) the competitive performance of plant species is related to measurable plant traits; (3) the competitive performance of plant species is not significantly affected by changing nutrient supply; and (4) there is an "evolutionary trade-off" between nutrient stress tolerance of species and competitive performance that underlies the distribution of species along natural gradients of fertility and standing crop. These questions were posed at a broad, multi-species scale using comparative measures of competitive performance, stress tolerance, and morphology from over 40 shoreline plant species, and field distribution data from several natural shoreline communities in Ontario, Nova Scotia and Quebec. Results showed that the experimentally determined measure of the relative competitive performance of a species was significantly correlated with its position along natural gradients of fertility and standing crop; and with simple measurable plant traits, in particular above-ground biomass (r$\sb{\rm s}$ = 0.92; p .0001). Results also showed that the competitive performance of species under high and low nutrient conditions was significantly correlated after two growing seasons (r$\sb{\rm s}$ = 0.76; P .001); and that stress tolerance, measured as the relative biomass production of species under low nutrient conditions, was inversely correlated with competitive performance (r = $-$0.62, p .005).
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Lee, Harold Thomas. "The effects of eutrophication on wetland plant communities." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6673.
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The first two parts of this study are concerned with a natural field project in which I measured specific plant traits, community state variables, species frequencies, and soil fertility in a large scale comparative study of eight Great Lakes wetlands. I asked the following questions: (1) Are there measurable, quantifiable differences between wetlands--with respect to plant traits, community state variables and fertility, and (2) Are there empirical relationships between plant traits/community state variables and fertility variables. Significant differences between four productive and four unproductive wetlands were found across all the plant traits, except rhizome diameter, all the community state variables and all the fertility variables, except nitrogen. Productive wetlands had lower species richness and were taxonomically distinct from unproductive wetlands. I found that total phosphorus was the most important independent variable and that the most important dependent variables were plant height, standing crop, and species richness. I ran a large outdoor screening experiment bioassaying 40 wetland plants, at two fertility levels, to measure a trait I call 'biomass sensitivity'. I found that all species produced more biomass in the fertile treatment. By comparing species according to the proportional 'biomass sensitivity' (P($\Delta$B)) trait, that is the proportional change in biomass between high and low nutrients, I find there are no differences between species. (Abstract shortened by UMI.)
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DeSandoli, Lisa Ann. "Restoration of plant communities to red-burned soils." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44301.
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Fire, natural or anthropogenic, is a common occurrence in the open forests and grasslands of Western North America. The effects of fire on soil and vegetation depend largely on the soil temperatures and the residence time of the burn. Generally, the more severe the fire, the more significant the changes are to soil and vegetation. The relationship between the most severe fires, or where the soil has been oxidized to a red colour, and invasive species is unknown. Resource availability may increase on these soils, leading to favourable conditions for invasive species, or the disturbance may be so severe that nothing is able to grow indefinitely.
I performed two studies to investigate the relationship between invasive species and red-burned soil. To reduce the threat of interface fires near Kamloops, BC, excess timber was harvested, piled and burned on site (pile burning), created multiple burn scars denuded of vegetation and large areas of red soil. In the first study, I investigated soil nutrient flux differences between red-burned and unburned soil using ion-exchange resin technology. I also investigated three restoration methods to control invasive species: the addition of agronomic or native seed, the addition of arbuscular mycorrhizal fungi (AMF) inoculum, and the addition of soil cover. Non-native species cover was high on red soil 2 years post-burn, which may be linked to measured increased nutrients. Only the addition of agronomic seed was successful at suppressing non-native species cover.
The second study compared the growth of native, agronomic and invasive species on unburned and red-burned soil in a greenhouse study. Soil was collected in the field and transferred to a greenhouse. Treatments were soil burning, AMF, and watering. Burning increased aboveground biomass for the native species. AMF addition increased invasive species aboveground biomass for the invasive species, but decreased biomass for agronomic and native species. Watering increased aboveground biomass for the agronomic and invasive species.
The findings here suggest that pile burning creates areas that are susceptible to colonization of non-native species. Restoration efforts should be directed at these sites as soon as possible to ameliorate the effects of invasive species colonization.
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Newton, Erika Lucie. "Plant-herbivore interactions in natural Brassica oleracea communities." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/72253.
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Co-evolutionary interactions between plants and herbivores are suggested to be the driving force behind the high diversity observed in plant secondary metabolites. These compounds play an important role in herbivore resistance mechanisms in many plant species. An individual plant can produce and store a number of structurally different secondary compounds. Variation in plant chemical profiles is commonly observed within and between natural populations across a wide range of taxa, yet the ecological importance of this variation is still a major question in the area of plant-herbivore interactions. In this thesis I use wild cabbage (Brassica oleracea var. oleracea) plants in twelve naturally established populations to investigate plant-herbivore interactions mediated by structural variation in aliphatic glucosinolates, a class of secondary metabolites produced by the Brassicaceae. Overall, the results showed that several herbivore species respond to the genetically determined variation in glucosinolate profile, indicating that the structure of the local herbivore community can be influenced by variation in plant defence chemistry. In addition, the direction of herbivore responses to different plant chemical phenotypes differed between species. A finer scale study which focused on the interactions between an herbivore and aliphatic glucosinolate variation supported the general trend observed in the large scale study. Glucosinolate profile was also found to have an impact on plant seed set. The findings show that glucosinolate profiles may be under selection in these natural plant populations and provide some support for the role of herbivores in the maintenance of secondary metabolite diversity.
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Johnston, Mark A. "Rabbit grazing and the dynamics of plant communities." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/11781.
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Stonehouse, Amanda L. "The flora and plant communities of Botany Glen." Virtual Press, 2003. http://liblink.bsu.edu/uhtbin/catkey/1266033.
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Botany Glen, The James S. Wilson Memorial Sanctuary, is an 18 hectare (45 acre) forested tract located in Grant County, Indiana, adjacent to the Mississinewa River. Botany Glen is an important natural area in east central Indiana due to its relatively small size and high diversity.The flora documents 331 species and varieties of vascular plants representing 241 genera and 90 families; 158 species are recorded for the first time in Grant County. Of the 331 species listed, 67 (or 20%) are exotic. Most of these exotics have failed to penetrate the interior of the forest.Permanent monitoring plots were established in dry upland forest, floodplain forest and secondary successional forest. Data were collected from overstory, understory and herbaceous plant layers in these plots. Analysis of these data and information from the floristic inventory were utilized to describe the structure and composition of three primary plant communities. Baseline data and procedures were established for future study of this property.Department of Biology
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Jeffs, Christopher. "Natural enemies and the diversity of plant communities." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:49c80db9-6590-4e06-b86f-24d225046969.
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The processes that determine the structure of plant communities are of considerable practical and theoretical interest. Natural enemies such as herbivores, seed predators and pathogens provide one potentially important influence on plant diversity. I investigated the effects of natural enemies on plant diversity in two contrasting, species-rich plant communities (tropical forests in Panama and temperate grasslands in the UK), focusing on pre-dispersal seed predation by insects, and the mortality of seeds and seedlings caused by soil fungi. In Panama I found that pre-dispersal insect seed predators generate significant levels of mortality in multiple tropical tree species, with high heterogeneity in predation rates among individuals and at different forest sites. Insect seed predators were highly host-specific, consistent with a role in enhancing plant diversity. At Upper Seeds, a calcareous grassland site in the UK, I used manipulative experiments to show that soil fungi increase the diversity of plants propagating from soil seed banks. A parallel experiment in Panama, mimicking germination under light gap conditions, revealed differential effects of fungi among sites, with fungicide treatment appearing to increase the diversity of propagated seedlings at some sites but reducing it at others. These results suggest that the influence of soil fungi on pre-emergence mortality can alter plant diversity, even when post-emergence mortality from fungal pathogens is limited. In Panama, I also tested whether enemy-mediated mortality increases with rainfall, potentially contributing to the positive regional correlations widely observed between precipitation and plant diversity. In contrast to predictions, neither pre-dispersal insect seed predation nor the influence of soil fungi on seedling recruitment were affected significantly by site humidity, or (for soil fungi) with experimentally manipulated soil moisture levels. Overall, my results provide evidence that pre-dispersal seed predators and soil fungi can affect plant recruitment and diversity at early life stages, with potential consequences for the community structure of adult plants.
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Gauthier, Marie-Eve. "Restoring peatland plant communities on mineral well pads." Master's thesis, Université Laval, 2014. http://hdl.handle.net/20.500.11794/25320.
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Les tourbières sont largement représentées dans la région boréale de l'Alberta, mais peu est connu sur la restauration de plates-formes de forage localisées en milieux tourbeux. Deux expériences de terrain ont testées la provenance du matériel végétal (bog, écotone bog-peupleraie, fen dominé par saules-Cyperacées, riche fen arbustif, riche fen forestier) à réintroduire sur différents substrats (sciure, loam argileux, mélange sciure-loam, tourbe, microtopographie) sur d’anciennes plates-formes. Nos résultats montrent que les communautés de tourbières peuvent s’établir sur un sol minéral après transfert d’une couche muscinale. Le type de communauté végétale où les propagules sont récoltées est un facteur déterminant au succès des bryophytes à s’établir. Un amendement en tourbe facilite l’établissement des plantes. La technique de transfert de mousse est une approche prometteuse pour la restauration de fens sur plateformes pétrolières. Nous recommandons une mise à l’échelle pour tester la validité de ces méthodes de réintroduction de végétation de manière mécanisée.Peatlands are largely represented in the boreal region of Alberta but little is known about their restoration on well sites. The goal of this study is to compare plant communities and substrates in order to recover peatland vegetation. Two field experiments tested which plant communities (bog, bog-aspen ecotone, willow-sedge fen, shrubby rich fen, treed rich fen) would best regenerate on different substrate (sawdust, clay loam, mix sawdust-clay, peat, surface roughness). We found that peatland communities can establish on mineral soil after propagules transfer using the moss layer transfer technique (MLTT). The choice of plant community, where the propagules are harvested is key to bryophytes establishment. Peat amendment facilitated the plants establishment. The MLTT is a promising approach to restore fen plants on well sites. We recommend a scale-up experiment for a whole well site to test the validity of MLTT within pad removal techniques.
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Hansel, James R. "INFLUENCE OF URBANIZATION ON WOODY RIPARIAN PLANT COMMUNITIES." Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1113852536.
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Parker, John. "Plant-herbivore interactions consequences for the structure of freshwater communities and exotic plant invasions /." Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11182005-131013/.
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Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2006.Mark E. Hay, Committee Chair ; Julia Kubanek, Committee Member ; Joseph Montoya, Committee Member ; J. Todd Streelman, Committee Member ; David M. Lodge, Committee Member. Includes bibliographical references.
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Parker, John D. "Plant-herbivore interactions : consequences for the structure of freshwater communities and exotic plant invasions." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/9460.
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Invasive exotic species threaten native biodiversity, alter ecosystem structure and function, and annually cost over $100 billion in the US alone. Determining the ecological traits and interactions that affect invasion success are thus critical for predicting, preventing, and mitigating the negative effects of biological invasions. Native herbivores are widely assumed to facilitate exotic plant invasions by preferentially consuming native plants and avoiding exotic plants. Here, I use freshwater plant communities scattered broadly across the Southeastern U.S. to show that herbivory is an important force driving the ecology and evolution of freshwater systems. However, native consumers often preferentially consume rather than avoid exotic over native plants. Analyses of 3 terrestrial datasets showed similar patterns, with native herbivores generally preferring exotic plants. Thus, exotic plants appear defensively nave against these evolutionarily novel consumers, and exotic plants may escape their coevolved, specialist herbivores only to be preferentially consumed by the native generalist herbivores in their new ranges. In further support of this hypothesis, a meta-analysis of 71 manipulative field studies including over 100 exotic plant species and 400 native plant species from terrestrial, aquatic, and marine systems revealed that native herbivores strongly suppressed exotic plants, while exotic herbivores enhanced the abundance and species richness of exotic plants by suppressing native plants. Both outcomes are consistent with the hypothesis that prey are susceptible to evolutionarily novel consumers. Thus, native herbivores provide biotic resistance to plant invasions, but the widespread replacement of native with exotic herbivores eliminates this ecosystem service, facilitates plant invasions, and triggers an invasional meltdown. Consequently, rather than thriving because they escape their co-evolved specialist herbivores, exotic plants may thrive because their co-evolved generalist herbivores have stronger negative effects on evolutionarily nave, native plants.
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CaraDonna, Paul James, and Paul James CaraDonna. "Temporal Ecology of a Subalpine Ecosystem: Plant Communities, Plant-Pollinator Interactions, and Climate Change." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/620860.
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Ecological systems are inherently dynamic, and a primary way in which they are dynamic is through time. Individual organisms, populations, communities, species interactions, and ecosystem functions all follow a temporal progression from the past, to the present, and into the future. This temporal progression can occur over the course of minutes, hours, days, weeks, months, years, decades, or various other timescales. In this sense, temporal dynamics are an intrinsic property of all biological systems. In fact, one of the most prominent signals of recent global climate change is the significant change in the timing of biological events for a diversity of organisms. In light of this widespread pattern, there is a renewed interest in understanding the multifaceted importance of time in ecology. In this dissertation, I investigate the temporal ecology of a subalpine ecosystem, specifically focusing on flowering plant communities and plant-pollinator interactions. I examine the temporal dynamics of this system over multiple decades in response to ongoing climate change as well as over shorter time scales within a growing season. Using a 39-year record of flowering phenology, I show that species-specific shifts in the timing of flowering in response to climate change can substantially reshape a subalpine plant community over this time period. Community phylogenetic analyses reveal that these changes are largely independent of evolutionary history. Using a laboratory experiment, I show that the timing of an important harsh abiotic event-low temperatures that cause frost damage to plants-can differentially affect flowering plant species, with implications for plant demography, community structure, and interactions with pollinators. Finally, I show that plant-pollinator interactions exhibit substantial within-season temporal turnover, and that this temporal flexibility of plant-pollinator interactions from one week to the next is consistent and predictable across years. Taken together, this dissertation provides a multifaceted investigation of the temporal ecology of plant communities and plant-pollinator interactions, revealing the important consequences of ecological timing at short-term and longer-term scales.
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Prins, Natalie. "The restoration of riparian plant communities following alien plant clearing in the Western Cape." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/6164.
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Bibliography: leaves 102-118.Few of the riparian zones of the Western Cape Province, South Africa, can still be described as 'natural', as many, if not all, have been impacted upon in one way or another. They are, therefore, frequently disturbed environments that are highly susceptible to invasion by alien plants. the vegetation of riparian zones controls the flow of water, nutrients and sediments into streams. Plan communities in these habitats are often rish in species, and serve as corridor facilitating the movement of organisms.
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Bennett, Lindsay. "Invasive plant removal strategies and native plant community recovery in Ontario, Canada." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41240.
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The introduction and spread of invasive species are of major conservation concern. Invasive plant species are hypothesized to impact the population dynamics of native flora, including species at risk (SAR), and may disrupt the functioning of the plant communities which they invade. Some native plant populations may be more vulnerable due to pre-existing factors such as fragmented habitat, poor competitive nature, and/or limited geographical ranges. Because of this, the presence of one or more invasive species is frequently cited as a leading cause of at-risk species decline. However, the actual evidence for this link is weak and the mechanisms are unclear. In this study, I aimed to (1) determine the effect of invasive management schemes on the recovery of native plant communities and to (2) examine the role of factors such as method of removal and duration of invasive removal at two conservation areas in southern Ontario. After 12 candidate study areas were surveyed, two were chosen for the study (for logistical reasons). Specifically, pairs of ‘control’ and ‘invasive’ removal sites were established at St. Williams Conservation Reserve, near Turkey Point Provincial Park, ON (N = 10) and Bruce Peninsula National Park, ON (N = 8) through May - August 2018. Plots were surveyed for native and invasive plant species richness and abundance using transect methods. I found a significant difference in the abundance of native and invasive plants between control and treatment plots at St. Williams Conservation Reserve and Bruce Peninsula National Park, although the trends were in the opposite direction. Neither site had a significant difference in plant diversity between treatment types. I discuss my findings in light of the differences in land use history and management at the two areas and their implications for invasive removal schemes to manage for native plant conservation.
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Morris, Michael Roger. "The contribution of spawning pacific-salmon to nitrogen fertility and vegetation nutrition during riparian primary succession on an expansive floodplain of a large river." Diss., [Missoula, Mont.] : The University of Montana, 2008. http://etd.lib.umt.edu/theses/available/etd-09302008-151352/.
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Potdar, Madhukar Vishwanathrao. "Interference in monocultures and mixtures of orchardgrass (Dactylis glomerata L.) and timothy (Phleum pratense L.)." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/27510.
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Interference among plants involves responses of plants to their environment as modified by the presence and/or growth of neighbouring plants. An important theme of research on plant interference is the relationship between plant population density and measures of plant growth or agricultural yield. An experiment on plant interference was performed in which plots of two important forage species, orchardgrass (Dactylis glomerata L.) and timothy (Phleum pratense L.), were grown at different total population densities and mixture proportions. Measures of plant growth and yield were taken at five separate harvests during one growing season.
The analysis of variance indicated that primary and derived measures of growth and yield generally were strongly affected by the three main experimental factors: time, total population density and mixture proportions. Best subset multiple regression analysis, using Mallow's CP criterion, helped to define which experimental factors and interactions were related closely to plant responses. Both of these analytical methods indicated that the main effects of experimental factors were often significant, while interactions among factors were less prominent. The best subset models were different in structure for different response variates, however, indicating that plant responses varied when different measures of growth were considered.
Models were developed which provided an effective description of yield-density responses in monocultures and mixtures when interference was strong. Model parameters were used to compare the relative strengths of intraspecific and interspecific interference in each species. The higher-yielding species, timothy, exerted stronger interference, both within and between species than orchardgrass. Interference was significant early in growth and intensified with increasing population density. The parameters of the yield-density models were also used to assess differential yield responses in the mixtures. Net overyielding occurred in most mixtures because overyielding in timothy was not fully offset by underyielding in orchardgrass. The greatest yield advantage occurred in mixtures containing orchardgrass and timothy in proportions of 2:1.
The dynamics of plant growth were followed using methods of plant growth analysis. Absolute growth rate, relative growth rate, unit leaf rate and crop growth rate were among the growth indices showing strong responses to interference. Interference seemed to disturb the time course of growth in a complex way. Allometric relationships between dry weight per plant and either leaf area per plant or tiller number per plant were also affected by interference. The species differed in their allometric responses, and the relationships between allometry and different treatment factors also varied.Land and Food Systems, Faculty of
Graduate