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1
Gubsch, Marlén. "Plant species and functional group responses to changes in plant community diversity and composition : functional traits, species interactions and resource use /". [S.l.] : [s.n.], 2009. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18342.
Testo completo
2
Barbarasch, Bruce Michael. "Effects of surrounding land use on plant species composition in urban forest fragments". PDXScholar, 2005. https://pdxscholar.library.pdx.edu/open_access_etds/4130.
Testo completoAbstract (sommario):
As human development occurs in forested areas, forests become fragmented into small islands in a matrix of urban land uses. This study examined the effect of surrounding urban land uses on the native and exotic plant species found on the edges of forest fragments in the Portland, OR metropolitan region.
3
Fribley, Laura A. "Woody plant species composition in forest fragments at Muscatatuck National Wildlife Refuge". Virtual Press, 2006. http://liblink.bsu.edu/uhtbin/catkey/1339145.
Testo completoAbstract (sommario):
Several invasive woody plants grow in forest fragments at Muscatatuck National Wildlife Refuge in Seymour, Indiana. The objective of this study was to determine what woody species were growing in two upland forests and to assess the level of dominance that invasive species had in these areas. The variables of depth into the forest and directional aspect were also considered. Thirty-two belt transects were sampled and 54 woody species were found, including six invasive species: Ailanthus altissima (tree-ofheaven), Berberis thunbergii (Japanese barberry), Elaeagnus umbellata (autumn olive), Lonicera japonica (Japanese honeysuckle), Lonicera maackii (amur honeysuckle), and Rosa multiflora (multiflora rose). Importance values were calculated as an indicator of relative species dominance. Detrended Correspondence Analysis and Cluster analysis suggested that the invasive species were grouped on the forest edge transects; aspect was not found to be a determinant in where invasive species grew. Correlation coefficients demonstrated a significant difference between transect depth and the following variables at both forests: woody species density per transect, invasive species dominance, Elaeagnus umbellata density per hectare, and Lonicera japonica dominance. Rosa multiflora was one of the three most dominant understory species in both forests; on the edge transect, it was one of the top two. Soil temperatures were also measured at each transect, but no consistent trends were found within the data. In light of resources available, it is suggested that land managers focus on controlling Rosa multiflora and Ailanthus altissima.Department of Natural Resources and Environmental Management
4
Snyder, Keirith A. 1967. "Patterns of plant species diversity and composition in a semi-arid riparian ecosystem". Thesis, The University of Arizona, 1995. http://hdl.handle.net/10150/278513.
Testo completoAbstract (sommario):
Understanding plant community structure is fundamental to successful restoration and conservation of riparian ecosystems. High plant species diversity is often cited as an important characteristic of riparian areas. Graphical summaries, principal components analysis, and analysis of variance were used on species composition and abundance data to determine community patterns in riparian areas and surrounding uplands. Woody plant composition varied with relative elevation above the primary channel, but herbaceous composition appeared unaffected by proximity to the riparian area. Alpha diversity indices, richness, Shannon's H', and Simpson's D, were not always higher within the riparian area. Alpha diversity of woody plants demonstrated no consistent pattern, however vertical structural diversity was highest near the stream. Herbaceous plants showed increased diversity in floodplain sites and decreased diversity in hillslopes sites, suggesting that topographical profile influenced diversity. Herbaceous richness was better predicted from overstory characteristics than herbaceous biomass and environmental variables.
5
Bauer, Robert Benjamin. "Mob stocking effects on herbage nutritive value, herbage accumulation, and plant species composition". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/73914.
Testo completoAbstract (sommario):
Mob stocking is a variation of rotational stocking known for restricting a large number of animals to a small area before being moved to new grass after a few hours. This method allows a long (90-day) recovery period but was hypothesized to diminish the nutritional value of herbage relative to continuous and rotational stocking with lesser stocking density at similar stocking rates. This thesis summarizes two studies conducted in Blacksburg and Raphine, and in Steeles Tavern, VA, respectively, at a single beef cattle stocking rate of 12 animal unit months per hectare live body weight. The objectives were to: (1) compare the yield and nutritional value of herbage in pastures managed with three stocking methods, termed mob, rotational, and continuous stocking; (2) compare the abundance of seeded clover species among the stocking methods; and (3) estimate the nutritional value of herbage that is consumed by beef cattle during mob stocking using extrusa sampled from esophageally-cannulated animals. Analysis of standing herbage during two years produced several important findings. Although standing herbage mass was significantly greater in mob stocked pastures at Blacksburg and Raphine, aboveground net primary productivity in 2014 did not differ significantly among mob, rotational, and continuous stocking at any of the project locations. Herbage nutritive value did not differ significantly among stocking methods over two years at Blacksburg and Raphine; however, herbage from mob stocked pastures at Steeles Tavern contained significantly greater concentrations of crude protein in September and October relative to herbage from continuous- and rotationally-stocked pastures at those times. Differences in herbage mass likely contributed to significant differences in establishment of seeded clovers: red clover [Trifolium pratense L. Cinnamon Plus] establishment was similar among stocking methods but white clover [Trifolium repens L. Will] establishment was greater in continuously stocked pastures than mob and rotationally stocked pastures. Hand-clipped samples collected at Blacksburg in September 2014 significantly underestimated the crude protein content of the herbage selected by the steers, although the concentrations of fiber constituents in herbage did not differ significantly between clipped samples and esophageal samples. Although the nutritive value of the herbage on offer did not generally differ among stocking methods at this stocking rate, diet selected was at times less nutritious during mob stocking than continuous and rotational stocking methods. At this stocking rate, stocking method had less influence on pastures than seasonal variation in weather and plant maturity.Master of Science
6
Garratt, Iain Michael Ronald. "The assessment of variable buffer zones to manage rocky ridges in Johannesburg, Gauteng / I.M.R. Garratt". Thesis, North-West University, 2006. http://hdl.handle.net/10394/18.
Testo completo
7
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.
Testo completoAbstract (sommario):
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.
8
Mangan, Scott A. "Importance of the species composition of arbuscular mycorrhizal fungi to tropical tree seedlings". [Bloomington, Ind.] : Indiana University, 2007. 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:3243802.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2007.Title from PDF t.p. (viewed Nov. 18, 2008). Source: Dissertation Abstracts International, Volume: 67-12, Section: B, page: 6842. Adviser: James D. Bever.
9
Wright, Gabrielle A. Wright. "WHITE-TAILED DEER BROWSE PREFERENCE FOR AN INVASIVE SHRUB, AMUR HONEYSUCKLE, DEPENDS ON WOODY SPECIES COMPOSITION". Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami1510834316256772.
Testo completo
10
Hammond, Daniel N. Jr. "Characterization of Vascular Plant Species Composition and Relative Abundance in Southern Appalachian Mixed-Oak Forests". Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36614.
Testo completoAbstract (sommario):
Eight study sites were established in mid-elevation, south aspect, mixed-oak forests in the Ridge and Valley and Allegheny Mountain physiographic provinces of Southwestern Virginia and West Virginia to address questions concerning the variability in species composition, richness, and relative abundance of vascular plant species in those communities. All forest strata were sampled using a nested plot design. Variability in species richness and species composition was found to be high. Total species richness values ranged from 84 to 273, and Sorrenson's Coefficient of Similarity index values indicated that approximately 46, 38, and 51 percent of the species in the overstory, mid-story, and herb stratum were the same among sites, respectively. However, despite differences in composition and richness, K-S tests revealed significant differences in the distribution of ranked relative abundance only in the mid-story at two sites. Differences did occur in the relative abundance of twelve growth form categories. While tree seedlings and perennial herbs dominated, on average, woody vines and fern species represented substantial coverage on sites in the Allegheny Mountains. Correlations among forest strata were weak. The greatest amount of variation in species richness was attributiable to the standard deviation of a forest site quality index (FSQI), which was thought to represent the variation in microtopography across each site. The lack of correlation and high variability in plant species richness and composition, despite similarities in topographic characteristics, reinforce the inherent weaknesses involved with using the chronosequence approach to studying ecological responses in the Southern Appalachian mixed-oak region. Future remeasurement and long term monitoring of these study sites, following the implementation of silvicultural manipulations, will provide the information needed to make inference on the effects of forest management practices on Southern Appalachian mixed-oak forests.Master of Science
11
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.
Testo completoAbstract (sommario):
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.
12
Miller, Helen. "Plant ecology of lowland Alnus Glutinosa woodlands : the management implications of species composition, requirements and distribution". Thesis, Aston University, 2012. http://publications.aston.ac.uk/16442/.
Testo completoAbstract (sommario):
Wet woodlands have been recognised as a priority habitat and have featured in the UK BAP since 1994. Although this has been acknowledged in a number of UK policies and guidelines, there is little information relating to their detailed ecology and management. This research, focusing on lowland Alnus glutinosa woodlands, aimed to address this data paucity through the analysis of species requirements and to develop a methodology to guide appropriate management for this habitat for the benefit of wildlife. To achieve these aims data were collected from 64 lowland Alnus glutinosa woodlands and a review of the literature was undertaken to identify species associated with the target habitat. The groundflora species found to be associated with lowland Alnus glutinosa woodland were assessed in relation to their optimal environmental conditions (Ellenberg indicator values) and survival strategies (Grime CSR-Strategy) to determine the characteristics (Characters of a Habitat; CoaHs) and range of intra-site conditions (Niches of a Habitat; NoaH). The methodologies, using CSR and Ellenberg indicator values in combination, were developed to determine NoaHs and were tested both quantitatively and qualitatively at different lowland Alnus glutinosa sites. The existence of CoaHs and NoaHs in actual sites was verified by detailed quadrat data gathered at three Alnus glutinosa woodlands at Stonebridge Meadows, Warwickshire, UK and analysed using TWINSPAN and DCA ordination. The CoaHs and NoaHs and their component species were confirmed to have the potential to occur in a particular woodland. Following a literature search relating to the management of small wet woodlands within the UK, in conjunction with the current research, broad principles and strategies were identified for the management of lowland Alnus glutinosa woodland. Using the groundflora composition, an innovative procedure is developed and described for identifying the potential variation within a particular site and determining its appropriate management. Case studies were undertaken on distinct woodlands and the methodology proved effective.
13
Phillips, Samantha Elizabeth. "Composition of the Community of Small Mammals in the Great Basin Desert". BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6961.
Testo completoAbstract (sommario):
Small mammals are a keystone guild in arid ecosystems; often exhibiting top-down control of the diversity and structure of plant communities. However, changing climate, shifting fire regimes, and the invasion of exotic plants are modifying the structure of arid systems. Environmental changes in these arid systems are likely altering small mammal communities, and therefore, their ecological role. We examined two aspects of the community composition of small mammals in the Great Basin: changes in community composition since large scale sampling of the region began in 1930, and the current population of a sensitive species of small mammal, the dark kangaroo mouse (Microdipodops megacephalus). In Chapter 1, we compared diversity and composition of present day small mammal communities to communities sampled between the years of 1930 and 1980. We sampled 234 historical locations across the eastern Great Basin region during the summers of 2014 and 2015. Our results indicated that diversity, richness, and evenness of small mammals in the Great Basin have declined significantly over the last century (P=0.002, P=0.03, P=0.002). The relative abundance of generalist species has increased, while specialist species have declined (P<0.001, P<0.001). Also, community composition at each site has changed significantly over the past century. Alterations in the community structure of small mammals may have cascading implications for the future of the Great Basin ecoregion. In Chapter 2, we conducted a region-wide survey for the dark kangaroo mouse in western Utah. Four teams sampled 232 locations across western Utah during the summers of 2014-2015. Of the 232 sites sampled, only 5 sites resulted in dark kangaroo mouse captures, totaling 15 individuals. These results could indicate a state-wide population decline for this species, both compared to historic population levels and to the populations surveyed less than ten years ago. The rapid decline may be a result of habitat degradation associated with invasive plant species and increasing fire frequency, the effects of which are exacerbated by the dark kangaroo mouse's life history as an ecological specialist. Unless large-scale habitat restoration and preservation is conducted for remaining populations, it is likely the dark kangaroo mouse will continue to decline within the state.
14
Steinman, Alexis. "Assessment of Wetland Water Quality and Plant Species Composition across the Rural, Peri-Urban, and Urban Gradient". Thesis, North Dakota State University, 2017. https://hdl.handle.net/10365/28381.
Testo completoAbstract (sommario):
The Prairie Pothole Region, specifically eastern North Dakota, has experienced intense disturbance from agricultural demands and urban sprawl. This study assessed wetlands across the rural, peri-urban, and urban gradient to determine the impacts of urbanization on water quality and vegetation composition. Thirty wetlands were randomly selected and compared based on land use type and the impervious to pervious surface ratio within one mile of each wetland. Water quality samples were taken in 2015 and 2016, and a vegetation assessment was completed at all wetlands. Results indicate disturbance from urbanization impacts wetland water quality and vegetation composition. Rural wetland water quality and vegetation significantly differ from both peri-urban and urban wetlands, whereas peri-urban and urban wetland water quality and vegetation do not differ. Information from this study is useful to wetland professionals across the globe as urban development and sprawl continue to impact wetlands.
15
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.
Testo completoAbstract (sommario):
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.
16
Goedhart, Christian Leonard. "Influence of osmotic stress, ethanol, and a substituted pyridazinone, BAS 13-338, on the growth and lipid composition of two Chlorella species". Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53634.
Testo completoAbstract (sommario):
Chlorella vulgaris and Chlorella pyrenoidosa were compared relative to their abilities to grow at osmotic potentials of -0.1, -0.5, -1.0, -1.5, -2.0 MPa, [polyethylene glycol(PEG)-induced], and for osmotically-induced changes in lipid composition. C. vulgaris growth was inhibited as osmotic potentials decreased, while C. pyrenoidosa growth was moderately inhibited at -2.0 hPa. C. vulgaris produced increasing concentrations of triglycerides and sterol esters and decreasing levels of polar lipids and sterols as osmotic concentrations increased. Polar lipids, triglycerides, and sterols declined in C. pyrenoidosa while steryl esters remained constant. Ratios of free sterols to polar lipids were 10-fold greater in C. pyrenoidosa and were unaffected by reduced osmotic potentials. In C. vulgaris the sterol to polar lipid ratio declined.
Decreasing osmotic potentials in a continuous culture of C. vulgaris, lowered cell lipid concentration, and had no effect on chlorophyll concentrations. The greatest decrease occurred as the osmotic potential decreased from -0.1 to -0.5 HPa. Decreasing osmotic potential caused the phospholipid concentrations to decline. Saturation of triglycerides and free fatty acids increased and decreased, respectively, while polar lipids remained fairly constant. However, the sterol to phospholipid ratio increased as the osmotic potential was lowered.
BAS 13-338 (4-chloro-5-(dimethylamino)-2-phenyl-5- 3(2H)pyridazinone) had no effect on C. vulgaris resistance to osmotic stress, but caused growth inhibition as concentrations increased. However, BAS 13-338 was effective in decreasing growth inhibition of C. vulgaris grown in inhibitory levels of ethanol. BAS 13-338 had differing effects on the lipid composition of C. vulgaris when grown in PEG at an osmotic potential of -1.5 MPa compared to -0.1 MPa with 0.33% ethanol. The greatest effects were observed in the ethanol treatments where the qualitative composition of precursor sterols increased as the level of BAS 13-338 increased.
This investigation confirmed the important role of lipids in responding to environmental stress through observations of lipid responses to osmotic stress and by manipulation of lipid concentrations using BAS 13-338. Resistance to ethanol inhibition but not osmotic inhibition was achieved in the investigation.Ph. D.
17
Wender, Bryan William. "The impacts of seven silvicultural alternatives on vascular plant community composition, structure, and diversity in the southern Appalachians". Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/35653.
Testo completoAbstract (sommario):
The effects of seven silvicultural prescriptions were examined one full growing season post-treatment on five sites in the Ridge and Valley, Cumberland Plateau, and Allegheny Plateau of Virginia and West Virginia. Prescriptions were (1) control, (2) understory control with herbicide, (3) group selection, (4) high-leave shelterwood, (5) low-leave shelterwood, (6) leave tree, and (7) clearcut. The effects of each treatment on the vascular plant community were characterized by changes in species diversity, species composition, exotic species richness, Raunkiaer's life-forms, and growth-forms. Pre-treatment, baseline data, and a randomized block design ensured the precision of post-treatment comparisons. High-disturbance treatments (i.e., low-leave shelterwood, leave tree, clearcut) exhibited lower tree-stratum species richness than unharvested treatments. Prescriptions had no effect on shrub-stratum richness. Compared to the control, woody, herb-stratum richness was higher in harvested treatments. Non-woody herb-stratum richness was unaffected. No differences in herb-stratum species diversity were detected using Shannon's (exp H') or Simpson's (1/D) indices. Non-woody species richness per 2-ha treatment plot was significantly higher than the control for high-disturbance treatments. Pre- vs. post-treatment species composition was least similar for high-disturbance treatments, as measured by qualitative and quantitative community similarity indices. Exotic woody species richness was unaffected by treatment; however, non-woody exotic species were more prevalent in high-disturbance treatments. Hemicrytophytes replaced phanerophytes as the most important life-form for harvested treatments. Therophytes were more important in harvested treatments, while the proportion of cryptophtes and chamaephytes did not change in response to treatments. Tree and shrub growth-forms were less dominant in harvested treatments, while graminoids and annual/biennial forbs were more important for high-disturbance treatments. These data represent only the initial results of a long-term study designed to examine plant-community response to silviculture for one harvest rotation length. Long-term results will aid in devising management strategies that address concerns for biodiversity without devaluing traditional resource demands.Master of Science
18
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/.
Testo completoAbstract (sommario):
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.
19
Cheng, Zhiqiang. "Ecology of urban lawns the impact of establishment and management on plant species composition, soil food webs, and ecosystem functioning /". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1187031808.
Testo completo
20
Daye, Desalegn Desissa. "Fragmented forests in south-west Ethiopia : impacts of land-use change on plant species composition and priorities for future conservation". Thesis, Bangor University, 2012. https://research.bangor.ac.uk/portal/en/theses/fragmented-forests-in-southwest-ethiopia--impacts-of-landuse-change-on-plant-species-composition-and-priorities-for-future-conservation(c44a2d3f-12b7-431c-bf7e-ce835da79b13).html.
Testo completoAbstract (sommario):
There is major concern internationally, and specifically in the Ethiopian afromontane biodiversity hotspot, about the impact of forest habitat fragmentation on biodiversity conservation. This study assessed the effect of land-use change on land-cover pattern, forest patch spatial structure and consequent effects on plant species richness and composition in two areas of southwest Ethiopia: Illubabor and the Gamo highlands of Gamo Gofa. Land-use change analysis was conducted on three sites, I (1500-2000 m altitude) and II and III (1878-2422 m altitude), each of 47,648 ha, in Illubabor and one area of 66,765 ha in the Gamo highlands. Two Landsat images from the years 1986 and 2000 and one Spot image from 2007 covering Illubabor and two Landsat images from 1995 and 2010 covering most of the Gamo highlands study area were analysed. The change in area, number, shape and edge density of patches of each land-cover class were quantified between the years. Field sampling of woody plants was conducted in plots within 30 forest patches in Illubabor stratified between the three sites, and ten in the Gamo highlands stratified between sacred groves and non-sacred forests. Information on local knowledge, cultural association, institutions, practices and threats of the sacred groves was obtained by interviewing 24 of their traditional custodians. The landscape pattern in both Illubabor Zone and Gamo highlands has changed rapidly over 20 years. In highland areas there has been a rapid conversion of forest to farm, settlement and grazing land. At lower altitude forest cover has been retained but it has been degraded by its use for understorey coffee cultivation. The area and number of forest patches has decreased while patch shape and edge density has increased. In Illubabor forests' woody plant species richness was higher in the lower altitude site I (70.8±9.2) than in sites 11 (50.9±6.3) and III (54.3±4.9), with little difference in the shape of their species accumulation curves. Species composition also differed between site I and sites II and III; altitude and disturbance were more strongly associated with this difference than were patch size, shape and edge density. There was little difference in tree density or basal area amongst the sites. Within forest patches, tree basal area was higher in the patch interior (96.8±9.4 m2 ha-l) than in the edge zone (77.2±15.3 m2 ha-1), however total tree density did not differ significantly. The interior forest had twice the density of trees taller than 22 m and a higher density of small trees (5-14.9 cm DBH) than the edge. Tree species richness did not differ significantly between the two habitats, however including shrubs and vines total woody species richness was higher in the edge (69.3±5.9) than interior (52±3.5) forest. While the upper canopy of interior forest was dominated by species with a wide habitat distribution range, it also had a higher abundance of forest-habitat specialist species than the edge. Species with a distribution associated with forest-margins were, as expected, more abundant in the edge habitat. No association was found between tree density, basal area or height in both habitat types and any fragmentation variables (patch size, shape or edge density) or environmental variables (rainfall, altitude or cumulative disturbance). However, edge habitat basal area was negatively associated with disturbance. Shrub, vine and geophytic angiosperm herb species composition differed between forest edge and interior habitats. Species richness of vascular epiphytes was higher in interior (28.9±1.8) than edge (13.6±1.4) habitat, as was their individual density (114.5±6.5 and 42.7±3.7 respectively), which was associated with the density of large DBH trees. Epiphyte density was not associated with any fragmentation variables, rainfall or altitude, however in the edge habitat it was negatively associated with disturbance. Species composition varied between the two habitats, with forest-habitat distribution species, which tended to have herbaceous stems and leaves, being more abundant in the interior habitat. However, the same three epiphyte species were dominant in both habitats, and species with succulent stems and leaves or woody stems had similar abundance in both. Geophytic fern species richness was higher in interior (29.4±1.8) than edge (22.1±1.4) habitat, as was individual density (104±22.3 and 59.8±13.7 respectively). Species with forest-habitat distribution, those with creeping or erect rhizomes and those with tufted fronds were more abundant in the interior, while generalist distribution species and those with spaced fronds showed no difference. In the Gamo highlands, sampled woody plant species richness and diversity were higher in sacred groves than in non-sacred forests, however, the species accumulation curve showed no difference between the two categories of forest. Their species composition differed and the sacred groves had a higher proportion of species endemic to Ethiopia (12.5%) than the non-sacred forests (9.2%). Two national conservation priority species, Cordia africana and Hagenia abyssinica, were only recorded in the sacred groves, and one IUCN red list species, Prunus africana, was more abundant there. Mean basal area was significantly higher in the sacred groves (1.55±0.45 m2 ha-1) than the non-sacred forests (1.28±0.41) as was tree seedling density (1111.7±393.2 ha-1 and 476.8±87.3 ha-1 respectively) but not sapling density. In conclusion, forests in southwest Ethiopia are undergoing a high rate of fragmentation and degradation. The resulting loss of forest interior core habitat is associated with a loss of biodiversity, especially of vulnerable forest-specialist species of woody plant, vascular epiphyte and geophytic fern. Nonetheless, the remaining small forest patches do still have high biodiversity value and they should be made a high conservation priority. In the Gamo highlands these small patches are generally sacred sites with high cultural value, however they have recently come under high levels of threat which risks loss ofbiocultural diversity. Their conservation through strengthening of traditional community institutions is a high priority.
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Gustavsson, Eva. "Grassland plant diversity in relation to historical and current land use /". Uppsala : Dept. of Ecology, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/2007106.pdf.
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22
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.
Testo completoAbstract (sommario):
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.
23
Heimann, Juliane [Verfasser], Wolfgang W. [Akademischer Betreuer] Weisser, Günter [Akademischer Betreuer] Köhler e 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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24
Vujnovic, K. "Small-scale plant species composition and diversity in relation to environmental and disturbance factors in fescue grasslands of the aspen parkland of Alberta". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ34430.pdf.
Testo completo
25
Richmond, Douglas Scott. "Influence of Endophytic Perennial Ryegrass, Lolium perenne L., on the population density of two insects and plant species composition in mixed Turfgrass Swards /". The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488187049542887.
Testo completo
26
Isherwood, Ewan. "The Effect of Contemporary Hydrologic Modification on Vegetation Community Composition Distinctness in the Florida Everglades". FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/1027.
Testo completoAbstract (sommario):
The historic Everglades Ridge and Slough landscape maintained regularly spaced and elevated sawgrass ridges interspersed among exposed deeper-water sloughs; however, widespread but irregular hydrologic modification has degraded much of this landscape patterning. My study assessed the effects of hydrologic modification on vegetation community distinctness within the Ridge and Slough landscape through sampling species composition at fine-scales along a hydrologic gradient to measure the magnitude of segregation of species among patch types. The results show that vegetation community and topographic variation degradation is widespread, with distinctness differences proceeding and possibly being driven by topographic variation loss. Vegetation responses to past hydrologic regime modifications are likely affected by temporal lags; however, vegetation distinctness regeneration may also be hindered by a vegetatively homogeneous alternative stable state. Hydrologic regime restoration is critical for Ridge and Slough patterned landscape reestablishment, but management targets are complicated by vegetation response lags and possibly alternative stable states.
27
Ruggles, Thomas Alan. "Plant communities on reclaimed surface mines in Northeast Ohio: Effects of succession and nitrogen-fixing autumn olive". Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1574681631819824.
Testo completo
28
Ložytė, Aurelija. "The influence of agri-environmental measures based grassland management on grassland plant communities". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140526_082518-10331.
Testo completoAbstract (sommario):
Grassland is an important component of agrarian landscape, performing wide range of ecological, economic and social functions. Long-term changes of the conditions of habitats, determined by human economic activities, influence the state of grassland plants. Rural Development Programme for Lithuania 2007–2013 sets measure to preserve biological diversity of grassland. The purpose of it is to reduce negative anthropogenic effect on grassland plant communities using the EU funds. Having researched the differences of grassland plant diversity and economic value, influenced by different intensity economic activities, the main objective of this paper is to evaluate the efficiency of EU regulated, agri-environmental measures based, grassland management methods in small farming sector of Lithuania. The research, involving the assessment of the number of plant species, diversity of plant families, distribution of relative plant abundance, and dominance of plant species in plant communities in grassland managed traditionally and according to the requirements of agri-environmental farming, showed that both types of grassland had similar plant communities. Such conclusion was drawn from the analysis of Jaccard and Sörensen similarity coefficients. The difference of plant adaptation to soil dampness, acidity, and nutrition was not statistically significant in grasslands of both types. Most of the plants in grassland researched were mesophytes; soil acidity was not a determining factor to... [to full text]Pievos yra svarbus agrarinio kraštovaizdžio komponentas, atliekantis įvairias ekologines, ekonomines ir socialines funkcijas. Ilgalaikiai augaviečių sąlygų pokyčiai, kuriuos lemia žmogaus ūkinė veikla, įtakoja pievų augalų būklę. Lietuvos kaimo plėtros 2007–2013 m. programoje numatyta priemonė pievų biologinės įvairovės išsaugojimui, kurios tikslas panaudojant ES lėšas mažinti neigiamą antropogeninį poveikį pievų augalų bendrijoms. Ištyrus pievų augalijos įvairovės ir ūkinės vertės skirtumus, sąlygotus skirtingos ūkinės veiklos intensyvumo, šio darbo tikslas įvertinti reglamentuotų, ES agrarinės aplinkosaugos priemonėmis paremtų, pievų tvarkymo metodų efektyvumą smulkiuose Lietuvos ūkiuose. Atliktas tyrimas parodė, kad įvertinus augalų rūšių skaičių, augalų šeimų įvairovę, augalų rūšių santykinio gausumo pasiskirstymą, dominuojančias augalų rūšis tradiciniais ir agrarinės aplinkosaugos reikalavimus atitinkančiais ūkininkavimo metodais tvarkomose pievose, nustatyta, kad jose augo panašios augalų bendrijos. Tai parodė ir Žakaro bei Sörensen bendrumo koeficientų reikšmės. Abiejų tipų pievose rastų augalų rūšių prisitaikymo prie dirvožemio drėgmės, rūgštingumo, turtingumo maisto medžiagomis rodiklių reikšmės statistiškai reikšmingai nesiskyrė. Pievų augalų bendrijose vyravo mezofitai, daugumai augalų rūšių dirvožemio rūgštingumas buvo neįtakojantis veiksnys, pievoms būdingi mezooligotrofiniai ir mezotrofiniai žolynai. Tyrimas parodė, kad biologinės įvairovės apsaugai palankus... [toliau žr. visą tekstą]
29
Petersen, Ute [Verfasser], Johannes [Akademischer Betreuer] Isselstein, Christoph [Akademischer Betreuer] Leuschner e Teja [Akademischer Betreuer] Tscharntke. "Effects of agricultural management and manipulated plant species composition of permanent grassland on productivity and sward structure / Ute Petersen. Gutachter: Johannes Isselstein ; Christoph Leuschner ; Teja Tscharntke. Betreuer: Johannes Isselstein". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1043718567/34.
Testo completo
30
Ehnes, James W. "The influences of site conditions, age and disturbance by wildfire or winter logging on the species composition of naturally regenerating boreal plant communities and some implications for community resilience". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ31975.pdf.
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31
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.
Testo completoAbstract (sommario):
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.
32
Lindgren, Åsa. "Effects of herbivory on arctic and alpine vegetation". Doctoral thesis, Stockholm University, Department of Botany, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-6746.
Testo completoAbstract (sommario):
The distribution of plant species and functional traits in alpine and arctic environments are determined by abiotic conditions, but also by biotic interactions. In this thesis, I investigate interactions among plants and herbivory effects on plant community composition and plant functional traits in three different regions: Swedish Lapland, Beringia (USA/Russia) and Finnmark (Norway). Reindeer grazing was found to be extensive in southern Lapland and had limited effects on plant community composition and seedling germination. However, reindeer presence was found to influence plant functional traits, particularly in the subalpine birch forest. Tall herbs were lower and had lower SLA when reindeer were present, while small herbs showed an opposite pattern. The contrasting effects on the two herb groups are probably explained by a competitive release for small herbs when the tall herbs are suppressed by reindeer. Rodents had the largest relative impact on plant community composition in southern Lapland and this is consistent with the study from Finnmark, where rodents heavily affected dwarf shrubs on predator-free islands. With no predators present, vole densities increased profoundly and almost depleted some dwarf shrub species. These results support the idea that small mammals in arctic and alpine tundra are controlled by predators (i.e. top-down). However, a decrease in the nutritional quality in a sedge after defoliation gives support for the idea that small mammals are regulated by plant quality (i.e. bottom-up). In Beringia, small and large herbivores differed in the relation to plant community composition, since large herbivores were related to species richness and small herbivores were related to plant abundance. Plant functional traits were related only to large herbivores and standing crop of vascular plants.
33
Küchenmeister, Frank [Verfasser], Johannes [Akademischer Betreuer] Isselstein, Klaus [Akademischer Betreuer] Dittert e Nicole [Akademischer Betreuer] Wrage-Mönnig. "Sustainable grassland herbage production under drought stress - the role of plant species number and functional group composition / Frank Küchenmeister. Gutachter: Johannes Isselstein ; Klaus Dittert ; Nicole Wrage-Mönnig. Betreuer: Johannes Isselstein". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/104441460X/34.
Testo completo
34
Karlík, Petr [Verfasser], e Peter [Akademischer Betreuer] Poschlod. "How is the age of an anthropogenic habitat - calcareous grasslands - affecting the occurrence of plant species and vegetation composition - a historical, vegetation and habitat ecological analysis. / Petr Karlík ; Betreuer: Peter Poschlod". Regensburg : Universitätsbibliothek Regensburg, 2019. http://d-nb.info/1200209036/34.
Testo completo
35
Ložytė, Aurelija. "Agrarinės aplinkosaugos priemonėmis paremtų tvarkymo metodų įtaka pievų augalų bendrijoms". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140526_082534-19976.
Testo completoAbstract (sommario):
Pievos yra svarbus agrarinio kraštovaizdžio komponentas, atliekantis įvairias ekologines, ekonomines ir socialines funkcijas. Ilgalaikiai augaviečių sąlygų pokyčiai, kuriuos lemia žmogaus ūkinė veikla, įtakoja pievų augalų būklę. Lietuvos kaimo plėtros 2007–2013 m. programoje numatyta priemonė pievų biologinės įvairovės išsaugojimui, kurios tikslas panaudojant ES lėšas mažinti neigiamą antropogeninį poveikį pievų augalų bendrijoms. Ištyrus pievų augalijos įvairovės ir ūkinės vertės skirtumus, sąlygotus skirtingos ūkinės veiklos intensyvumo, šio darbo tikslas įvertinti reglamentuotų, ES agrarinės aplinkosaugos priemonėmis paremtų, pievų tvarkymo metodų efektyvumą smulkiuose Lietuvos ūkiuose. Atliktas tyrimas parodė, kad įvertinus augalų rūšių skaičių, augalų šeimų įvairovę, augalų rūšių santykinio gausumo pasiskirstymą, dominuojančias augalų rūšis tradiciniais ir agrarinės aplinkosaugos reikalavimus atitinkančiais ūkininkavimo metodais tvarkomose pievose, nustatyta, kad jose augo panašios augalų bendrijos. Tai parodė ir Žakaro bei Sörensen bendrumo koeficientų reikšmės. Abiejų tipų pievose rastų augalų rūšių prisitaikymo prie dirvožemio drėgmės, rūgštingumo, turtingumo maisto medžiagomis rodiklių reikšmės statistiškai reikšmingai nesiskyrė. Pievų augalų bendrijose vyravo mezofitai, daugumai augalų rūšių dirvožemio rūgštingumas buvo neįtakojantis veiksnys, pievoms būdingi mezooligotrofiniai ir mezotrofiniai žolynai. Tyrimas parodė, kad biologinės įvairovės apsaugai palankus... [toliau žr. visą tekstą]Grassland is an important component of agrarian landscape, performing wide range of ecological, economic and social functions. Long-term changes of the conditions of habitats, determined by human economic activities, influence the state of grassland plants. Rural Development Programme for Lithuania 2007–2013 sets measure to preserve biological diversity of grassland. The purpose of it is to reduce negative anthropogenic effect on grassland plant communities using the EU funds. Having researched the differences of grassland plant diversity and economic value, influenced by different intensity economic activities, the main objective of this paper is to evaluate the efficiency of EU regulated, agri-environmental measures based, grassland management methods in small farming sector of Lithuania. The research, involving the assessment of the number of plant species, diversity of plant families, distribution of relative plant abundance, and dominance of plant species in plant communities in grassland managed traditionally and according to the requirements of agri-environmental farming, showed that both types of grassland had similar plant communities. Such conclusion was drawn from the analysis of Jaccard and Sörensen similarity coefficients. The difference of plant adaptation to soil dampness, acidity, and nutrition was not statistically significant in grasslands of both types. Most of the plants in grassland researched were mesophytes; soil acidity was not a determining factor to... [to full text]
36
Broders, Kirk Dale. "Seed and Seedling Disease of Corn and Soybean in Ohio: The Role of Fusarium graminearum, Pythium species diversity, fungicide sensitivity, Pythium community composition, and soil properties in disease severity". Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1228096392.
Testo completo
37
Hess, Manon. "Restauration écologique des communautés végétales après éradication d'espèces invasives : Rôle de la dynamique de colonisation et des effets de priorité Using limiting similarity to enhance invasion resistance: theoretical and practical concerns Priority effects: Emerging principles for invasive plant species management Giving recipient communities a greater head start and including productive species boosts early resistance to invasion". Thesis, Avignon, 2020. http://www.theses.fr/2020AVIG0357.
Testo completoAbstract (sommario):
Les plantes invasives posent d’importants problèmes environnementaux et de santé publique, et leur contrôle est aujourd’hui un défi majeur. Elles rencontrent des conditions particulièrement favorables après des perturbations conduisant à une suppression du couvert végétal. La mise en place d’un couvert végétal séquestrant rapidement ces ressources parait alors une réponse probante pour réduire l’invasion. Néanmoins, les caractéristiques des communautés nécessaires pour exercer une résistance efficace dans les premières phases d’installation sont encore peu connues.Je me suis intéressée à deux mécanismes qui pourraient influencer la résistance à l’invasion des communautés végétales herbacées lors des premiers stades d’installation après une perturbation majeure, que sont (1) la ‘limiting similarity’, impliquant que la coexistence d’espèces partageant la même niche écologique est limitée par l’exclusion compétitive, et (2) les effets de priorité, qui surviennent lorsque l’installation d’une espèce affecte la performance ou la survie d’une espèce arrivant par la suite. L’examen de la littérature confirme que l’application de la ‘limiting similarity’ pour lutter contre les plantes invasives est complexe et n’a, jusqu’à aujourd’hui, fait preuve d’efficacité. Intégrer les effets de priorité aux méthodes de contrôle des plantes invasives après une perturbation semble d’avantage prometteur. Une des stratégies consiste en la mise en place d’un couvert végétal exerçant de forts effets de priorité négatifs, diminuant le succès d’installation des plantes invasives. Deux expérimentations en serre ont été réalisées à cet effet, visant à jouer sur les effets de priorité de la communauté native receveuse afin d’en comprendre l’implication dans la résistance à l’invasion. Dans une première expérimentation, le temps d’avance de la communauté receveuse sur l’arrivée de trois espèces invasives (i.e. Ambrosia artemisiifolia, Bothriochloa barbinodis et Cortaderia selloana), la composition en espèces et la densité des semis ont été manipulés. Une meilleure résistance à l’invasion a été observée lorsque les communautés produisent une forte biomasse aérienne, cette dernière étant associée à la présence d’espèces productives. Retarder l’arrivée des espèces invasives a également réduit le succès d’invasion, mais ceci uniquement lorsque la production de biomasse était suffisamment importante. Une seconde expérimentation a porté sur l’influence de l’identité de la première espèce installée dans la communauté receveuse ainsi que l’ordre de semis des espèces (semis simultané de la communauté ou séquentiel) sur la structuration de la communauté et les conséquences sur sa résistance à l’invasion par A. artemisiifolia. Des différences minimes dans la dynamique de colonisation de la communauté receveuse a substantiellement affecté sa structure, sa production de biomasse, la concentration du sol en nutriments, ainsi que sa résistance précoce à l’invasion. Le semis séquentiel a généralement diminué la résistance à l’invasion par rapport au semis simultané de l’ensemble de la communauté. Les espèces installées en premier ont généré des effets de priorité d’intensité variable, vraisemblablement par le biais de la compétition racinaire, impactant l’invasibilité.En conclusion, la dynamique de colonisation a considérablement influencé le succès d'invasion par le biais de différences de production de biomasse et de préemption des ressources. Les effets de priorité des communautés récemment établies et la résistance à l'invasion associée pourraient être améliorés en (1) maximisant le temps d’avance à la communauté receveuse par rapport aux espèces invasives, (2) introduisant des espèces capables de produire rapidement de la biomasse et de préempter les ressources du sol, et (3) évitant le semis séquentiel, en particulier lorsque les premières espèces installées sont des espèces productives fixatrices d'azoteInvasive plant species cause serious environmental and sanitary issues and their control is today a major challenge. Disturbances involving vegetation removal and an increase in resource availability offer particularly favorable conditions for invasive plant colonization. Establishing a plant cover rapidly sequestering resources could be a relevant strategy to limit invasion. However, little is known about the characteristics enabling newly established communities to exert strong invasion resistance, especially in the early growth stages.In this thesis, I focused on two potential determinants of invasion resistance of herbaceous plant communities in the early growth stages after a major disturbance, which are (1) the concept of limiting similarity, stating that the coexistence of species sharing the same ecological niche is limited by competitive exclusion, and (2) priority effects, which occur when the establishment of a species affects the performance or survival of later arriving species. The application of limiting similarity to control invasive plants appears complex, ineffective and unsuitable for the most common situations. In contrast, integrating priority effects into invasive plant management strategies seems more promising. One strategy consists in restoring a plant cover exerting strong negative priority effects, decreasing the success of subsequent invasive plant establishment. In two greenhouse experiments, I explored the role of priority effects in early invasion resistance. In a first experiment, I manipulated species composition, sowing density and the elapsed time between community sowing and invasion by Ambrosia artemisiifolia, Bothriochloa barbinodis and Cortaderia selloana. A higher invasion resistance was observed when communities produced a high aboveground biomass, which was associated with the presence of productive species. Delaying invasive species arrival also decreased invasion success, but only if it allowed a sufficient increase in biomass production. A second experiment investigated how the identity of the first native colonizer (one of two grasses: Dactylis glomerata and Lolium perenne, or one of two legumes: Onobrychis viciifolia and Trifolium repens) and the timing of species establishment (synchronous vs. sequential sowing) influenced the structuration of the recipient community and its resistance to invasion by A. artemisiifolia. Small differences in assembly history of the recipient community substantially affected community structure, biomass production, soil nutrient content, as well as early invasion resistance. Sequential sowing generally decreased invasion resistance compared with a synchronous sowing. Early colonizers generated priority effects of variable strength most likely via belowground competition, which affected A. artemisiifolia’s invasion success. A prior establishment of the N-fixing legume T. repens particularly boosted A. artemisiifolia’s performance. In conclusions, this thesis work highlights the inadequacy of revegetation strategies based on limiting similarity and reveals promising perspectives of manipulating assembly history and priority effects for designing invasion resistant communities. Assembly history significantly influenced early invasion success by inducing differences in biomass production and resource preemption by the recipient community. Priority effects of newly established communities and associated invasion resistance could be enhanced by (1) giving as much time advance as possible to the recipient community over invasives, (2) introducing species displaying an ability to rapidly produce biomass and preempt soil resources, or (3) avoiding sequential sowing especially when early colonizers are nitrogen-fixing, productive species
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Conley, Gary D. "Examining the Cover and Composition of the Successional Vegetation Mosaic of Pre-SMCRA Mined Landscapes in Southeast Ohio". Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1357751096.
Testo completo
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Soest, Francien van. "Factors determining location and species composition of wet grasslands in Southwest England /". Utrecht : Royal Dutch Geographical Society [u.a.], 2005. http://www.loc.gov/catdir/toc/fy0710/2007385399.html.
Testo completo
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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.
Testo completoAbstract (sommario):
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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Baril, Lisa Marie. "Change in deciduous woody vegetation, implications of increased willow (Salix spp.) growth for bird species diversity, and willow species composition in and around Yellowstone National Park's Northern range". Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/baril/BarilL1209.pdf.
Testo completoAbstract (sommario):
Deciduous woody vegetation (DWV) in Yellowstone's northern range is a rare, but important habitat type. Including willow, alder, aspen, and cottonwood, DWV was limited in height and areal extent since the early 1900s. Since the mid-1990s; however, DWV has increased in height and areal extent in some locations. Previous studies regarding DWV change have focused on quantifying change in vegetation growth in areas of limited extent and none have quantified increased DWV growth at the scale of the landscape. Furthermore, no studies have evaluated the implications for increased growth of DWV for wildlife in the region or how DWV species themselves may influence rates of growth. In this thesis I evaluate change in DWV within wetland and riparian areas using aerial photographs from 1991 and 2006. I also investigate how an increase in willow, the dominant component of DWV in the region, has likely influenced bird diversity. Finally, since willow species vary with respect to genetic limitations on growth and reproduction that in turn may influence observed patterns of growth; I examine willow species composition across the northern range. Results of the air photo interpretation revealed a 170% increase in DWV. Most plots that increased did so by recruitment rather than densification; however, DWV was difficult to detect below 100 cm indicating that the number of plots increasing by recruitment may have been overestimated. Bird community variables were examined in three willow growth conditions: height suppressed, recently released, and previously tall (tall prior to observed increase in growth). I found that willow structure generally increased in complexity from structurally simple height suppressed willows to structurally complex previously tall willows and that this allowed for greater bird richness, abundance, diversity, and the abundance of several willow dependent bird species. I also found that willow species composition was similar and diverse between the released and previously tall condition, but that the suppressed condition was dominated by a singe species. I conclude that increased DWV has allowed for greater bird diversity in the northern range and that increased willow growth in the suppressed condition may be influenced by species composition there.
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Sabol, Thomas David. "Effects of Western Juniper (Juniperus occidentalis) removal on avian species composition in shrub-steppe habitat in south-central Oregon". View full-text version online, 2005. http://soda.sou.edu/awdata/060221a1.pdf.
Testo completoAbstract (sommario):
Thesis (M.S.)--Southern Oregon University, 2005."A thesis submitted to the Department of Biology of Southern Oregon University in partial fulfillment of the requirements for the degree of Master of Science in Environmental Education." Includes bibliographical references (p. 36-50) Also available via Internet as PDF file through Southern Oregon Digital Archives: http://soda.sou.edu. Search Bioregion Collection.
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Salie, K. (Khalid). "The contribution of riparian vegetation to the species composition of the Jonkershoek Valley in Stellenbosch, South Africa". Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/49790.
Testo completoAbstract (sommario):
Thesis (MSc)--University of Stellenbosch, 2003.ENGLISH ABSTRACT: Many authors express the value of riparian vegetation in terms of the function and number of species per unit area. Although riparian vegetation is confined to narrow bands of plants along watercourses, kloofs and gullies, it is a specialised habitat for many species. To determine the contribution of riparian vegetation to the species richness of the Jonkershoek Valley, Western Cape Province, South Africa, a checklist was compiled, by referring to past research and to the PRECIS national database for the South African flora for a list of species recorded from the area. A total of 1 743 taxa and 108 families were included in this list for the Valley. Specific characteristics were attributed to each of the 1 743 species on the basis of characters determined from the literature. Analysis of these data indicates that woody perennial shrubs with sclerophyll leaves are the representative plant type for the study area as a whole. The specialist structural description of a riparian species in the Jonkershoek Valley is: an unbranched woody perennial phanerophyte of a height between 2.0-8.0 m with microphyllous sclerophyilleaves. This group contributes 63% towards the riparian flora. Riparian habitats occupy only 2.5% of the total study area but contribute 26% of the vascular plants. The riparian communities of the Santa Monica Mountains (USA) cover 0.7% of that mountain study area and provide a habitat for 20.5% of the total vascular plants of the area. Both areas, therefore, show a similar level of diversity. This remarkable species richness of riparian zones is consistent with that found in other riparian communities i.e. Sweden and France. The study area was sampled by means of relevés arranged along 53 transects through the main stem and it's tributaries. A total number of 139 relevés were recorded which were used to identify, characterise and describe the riparian communities. Eight vegetation units, consisting of two groups, three communities, two subcommunities and one form, were described. The one group described the riparian communities while the other described a seepage community. The bigger groups exhibit environmental properties over a broader spectrum, while smaller groups exhibit characteristic environmental properties. The vegetation is found to represent a continuum rather than discreet entities. Many indicator species are encountered in the communities. Because of the characteristic canopy-understorey physiognomy of riparian vegetation, many communities are interspersed, making it difficult to delineate discreet community boundaries. The vegetation of the riparian zone of the Eerste River in the Jonkershoek Valley, is relatively pristine. Thirty-six species not native to the Valley were included in the checklist of which only four were recorded during the phytosociological study.
AFRIKAANSE OPSOMMING: Verskeie skrywers beklemtoon die kosbaarheid van rivieroewerplantegroei in terme van hul funksie en aantal spesies per oppervlakeenheid. Alhoewel rivieroewerplantegroei beperk is tot 'n noue band van plante langs waterweë, klowe en skeure, is dit 'n gespesialiseerde habitat vir baie spesies. Om die bydrae wat rivieroewerplantegroei tot die spesie-rykheid van die Jonkershoekvallei, Wes-Kaapprovinsie, Suid-Afrika te bereken, is 'n spesieslys saamgestel uit vorige studies en 'n PRECIS nasionale databasis vir die Suid-Afrikaanse flora waaruit 'n lys saamgestel is van spesies wat aangeteken is vir die area. 'n Totaal van 1 746 taxa uit 108 families is ingesluit in die plantelys. Vir elk van die 1 743 spesies, is spesifieke karakters uit die literatuur bepaal. 'n Analise hiervan dui aan dat die verteenwoordigende plant van die Jonkershoekvallei as gehele studie area 'n houtagtige, meerjarige struik met sklerofil blare is. Die spesialis strukturele beskrywing van 'n plant vir die Jonkershoekvallei is as volg: 'n onvertakte houtagtige meerjarige fanerofiet met 'n hoogte van 2.0-8.0 m met mikrofilliese sklerofil blare. Hierdie groep dra tot 63% by tot hierdie flora. Rivieroewer habitatte beslaan slegs 2.5% van die totale studie area, maar het tot 26% tot die vaatplante bygedra. Die Santa Monica Berge (VSA) se rivieroewerplantegroei bedek 0.7% van die bergagtige studie area en voorsien 'n habitat vir 20.5% van die vaatpplante. Beide gebiede toon dieselfde mate van diversiteit. Hierdie uitstaande spesiesrykheid is in lyn met wat gevind is in ander rivieroewergemeenskappe bv. in Swede en Frankryk. Die studie area is gemonster deur relevés wat uitgemerk is langs 53 transekte deur die hoofstroom en die sytakke. 'n Totaal van 139 releves is gemonster wat gebruik is om die gemeenskappe te identifiseer, karaktifiseer, en te beskryf. Agt plantegroei-eenhede, bestaande uit twee groepe, drie gemeenskappe, twee subgemeenskappe en een vorm, is beskryf. Die een groep beskryf rivieroewergemeenskappe terwyl die ander groep "n gemeenskap in die syfersone beskryf. Die groter groepe het wyer omgewingseienskappe getoon, terwyl die kleiner groepe spesifieke eienskappe toon. Dit is vasgestel dat die plantegroei eerder "n kontinuum voorstel as diskrete eenhede. Dit het tot gevolg dat dit moeilik is om die grense van gemeenskappe uit te wys. Vele indikatorspesies is aangetref. Die plantegroei van die rivieroewer van die Eersterivier in die Jonkershoeksvallei, kan beskryf word as relatief onversteurd. Ses-en-dertig spesies wat nie eie aan die Vallei is nie, is ingesluit in die spesieslys waarvan vier tydens die fito-sosiologiese studie aangeteken is.
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Sheldon-Sayer, Lynne. "The vegetation of Maud Island, Marlborough, New Zealand". Lincoln University, 2006. http://hdl.handle.net/10182/1707.
Testo completoAbstract (sommario):
Maud Island (Te Hoiere - "a long paddle or mighty pull") is a moderately sized island of 309 hectares, located in the Pelorus Sound (41°, 02 'S, 173° 54 'E) Marlborough, at the north-east end of the South Island of New Zealand. It has a long history of human modification and impacts since its colonisation by Maori and early Europeans. The vegetation of Maud Island has been studied in the 1980's and again in the early 1990's. The objectives of this study were to (1) describe how the vascular plant communities vary in species composition across Maud Island, (2) determine which environmental factors are important predictors of the variation in species composition of Maud Island plant communities, and (3) describe the pattern of succession of the plant communities on Maud Island over the last twenty years. In this 2001 study, I comprehensively sampled the vegetation on Maud Island using a Reconnaissance Description Procedure in a total of 158 plots across the island and compared these results to previous descriptions. I also retook photos at permanent photo points to provide a visual comparison of vegetation change. In total, 219 plant species were identified; 177 species occurred within the plots and 42 additional species were observed while walking around the coastline and walking tracks. Six dominant plant species occurred in over 70% of the plots. They were Pteridium esculentum, Pseudopanax arboreus, Hebe stricta var. stricta, Melicytus ramiflorus, Ozothamnus leptophylla and Coprosma robusta. Two-Way Indicator Species Analysis resulted in the description of eight different plant communities on the island. Detrended correspondence analysis showed a high degree of turnover in species composition among these communities. Canonical correspondence analysis showed that slope and moisture were particularly important predictors of variation in plant species composition. The environmental factors that best predicted to variation communities were slope, moisture, and a gradient in historical disturbance. Comparisons of present and past vegetation maps and photos (ground and aerial) showed, in terms of the successional pathways of the vegetation on Maud Island, that over time, the vegetation is reverting from short stature grassland and scrub to predominantly forest scrub and young secondary forest.
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De, Lacy Peter James Gerard. "Woody species composition and congregant appreciation of the cultural and spiritual services provided by cemeteries and church gardens in Grahamstown, South Africa". Thesis, Rhodes University, 2015. http://hdl.handle.net/10962/d1016401.
Testo completoAbstract (sommario):
Urbanization has increased rapidly throughout the world. The densification of urban areas has greatly reduced the number of natural areas occurring within the urban environment as well as impacting the ecosystem services that these areas provide. Urban greening and sustainable practices have been advocated as a means to once again provide the urban population with ecosystem services. Sacred natural areas that occur in surrounding forest, temple and cemetery sites have been known harbour a variety of biological diversity, as well as provide people with a number of cultural and spiritual benefits. Much of the literature on sacred natural sites comes from rural or eastern countries, leaving a large gap in the knowledge pertaining to information on these sites in both developed nations as well as urban areas. The aim of this study was to determine the abundance and composition of woody species, as well as the spiritual and cultural significance of sacred natural sites in Grahamstown. This study defined a sacred urban area as any form of garden surrounding a church, temple or mosque, as well as cemeteries. It looked at a total of 28 church gardens, one Hindu garden, one Mosque garden and five cemeteries in Grahamstown, South Africa. For each site the area was calculated and a tree and shrub inventory was done for all individuals above 1.5 m tall. Church/cemetery age, denomination and appearance were recorded as well as soil samples collected. An ordination of the data was done to summarize the community data, relating the community variation to environmental gradients. Questionnaires were completed by congregants who attended a religious building with a garden, as well as those that were not surrounded by a garden. These questionnaires were used to determine the cultural, spiritual and aesthetic value of trees and the sacred area, as well as the perceived and felt benefits that these areas provide. Those that were completed by congregants without gardens looked to find out whether or not it was believed that these areas would improve their experiences. There was an average plant density of 106.1 woody plants per hectare, with a total of 139 different species encountered. Of these, 56 percent were exotic species. This is slightly lower than that of studies done elsewhere in the world, but may be due to the omission of non-woody ornamentals and lawn species in this study. Of the top 11 most frequently occurring species, only two were indigenous. There was generally low similarity between plant assemblages found at the different sites. A significantly positive relationship was found between site size and woody plant basal area as well as the total number of woody plants. Site age and religious denomination had little influence on woody plant density, basal area, species richness or woody plant abundance. Congregants stated that a garden surrounding a religious building improved both their spiritual and aesthetic experiences. Stated spiritual and aesthetic experience was significantly influenced by basal area, while abundance significantly influenced stated aesthetic experience. Greenery was therefore important to many of the congregants, however, the species that were present were less influential. A greater sample size from a variety of religions and sacred areas within urban environments throughout the world would prove to be an interesting comparison for future research.
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Teske, Johanna Kavanagh. "Connecting the Dots: Investigating Planet Formation and Composition Through Observations of Carbon and Oxygen Species in Stars, Disks, and Planets". Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/318831.
Testo completoAbstract (sommario):
What physical processes and sources of material contribute to exoplanet compositions? Specifically, what roles do the protoplanetary disk composition and structure, and host star abundances play in the different stages of planet formation? In this thesis, beginning with a brief literature review in Chapter 2, I trace oxygen and carbon species through these stages to inform how, when, and where planets form. In Chapter 3 I describe a study of the molecular emission from the warm inner disks of T Tauri stars, where terrestrial planets likely form. I report moderate correlations between HCN emission strength and both stellar accretion rate (measured from UV or optical excess emission associated with accretion) and X-ray luminosity. These correlations point towards accretion related processes being an important source of disk atmosphere heating, and suggests that efficient H₂O formation and/or UV dissociation of N₂ (both also associated with higher stellar accretion rates) may aid in the production of HCN. Studies following mine have further connected the abundance of HCN versus H₂O to the growth and migration of planetesimals in the disk, which helps control the formation of both giant and terrestrial planets. I shift to an already-formed exoplanet in Chapter 4, where I present optical photometry of the best-observed transiting super-Earth GJ 1214b with the goal of constraining the short-wavelength slope of its transmission spectrum. Most previous observations suggested a flat spectrum from the near-IR to the optical, corresponding to a low-scale-height, high-molecular-weight atmosphere. My observations are in general agreement with these findings, keeping the "door open" for a H₂O-rich atmosphere for GJ 1214b, which other published g-band observations appeared to contradict. Chapters 5-7 of my thesis focus on measuring stellar abundances, particularly C/O ratios, in transiting (mostly) hot Jupiter exoplanet host stars from high resolution optical spectroscopy. Host star abundances may indicate the precursor materials present in the disk and available for incorporation into planets. In hot Jupiters, the C/O ratio affects the partitioning of C in the major observable molecules, making C and O diagnostic of temperature structure and composition. I also demonstrate that extra caution is necessary in deriving carbon and oxygen abundances, especially for cool and metal-rich stars. Though exoplanetary C/O ratios are still uncertain, the more precise abundance analysis possible right now for their host stars can help constrain their formation environments and current compositions. I summarize my graduate school research in Chapter 8, and discuss the next steps I will take in my postdoctoral career.
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DeGomez, Tom, e Melanie Lenart. "Management of Forests and Woodlands (Climate Change and Variability in Southwest Ecosystems Series)". College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006. http://hdl.handle.net/10150/146920.
Testo completoAbstract (sommario):
4 pp.This is part of a series of publications on climate change and forests/woodlands
Climate change may have dramatic effects on Arizona's forests and woodlands. Wildfires and insects may become of greater concern. Plant species will likely shift in elevation to adapt to the warming conditions.
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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.
Testo completoAbstract (sommario):
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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Xu, Jun. "Quality evaluation of Dendrobium species based on the analysis of multiple components". Thesis, University of Macau, 2010. http://umaclib3.umac.mo/record=b2454978.
Testo completo
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Monona, Ewumbua Menyoli. "Evaluating Standard Wet Chemistry Techniques and NIR Spectroscopic Models for Determining Composition and Potential Ethanol Yields of Multi-Species Herbaceous Bioenergy Crops". Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/29855.
Testo completoAbstract (sommario):
Herbaceous perennials represent a considerable portion of potential biomass feedstocks available for the growing bioenergy industry. Their chemical composition and biomass yields, which are important in determining ethanol potential on an area and mass basis, vary with plant variety and type, environment, and management practices. Therefore, a study was conducted to assess the variability of lignin and carbohydrate content, biomass yields, and theoretical ethanol yields on an area basis among different herbaceous perennial species combinations grown in Minot (2008) and Williston (2008, 2009, and 2010), North Dakota (ND). After wet chemistry compositional analysis was done, the carbohydrate contents
were used to determine theoretical ethanol potential on a mass basis. Using the dry-matter yield, the theoretical ethanol yield on an area basis was also calculated for these biomass species. Total carbohydrate content for the biomass samples in Williston and Minot varied from 45 to 61% dry basis. Analysis of Variance (ANOVA) at a= 0.05 showed that carbohydrate content varied between years and environments. Also an interaction plot shows that no biomass species had consistently higher or lower carbohydrate content in the different environments. Switchgrass (Panicum vigatum L.) grown as single species or together with other perennial grasses had higher dry-matter yield and theoretical ethanol
yield potential in Williston irrigated plots while mixtures containing intermediate or tall wheatgrass species (Thinopyrum spp.) produced better yields in Minot non-irrigated plots. Variability in theoretical ethanol yield on a mass basis (3.7% coefficient of variation (CV) in Williston and 9.7% CV in Minot) was much less than the variability in dry-matter yields (27.5% CV in Williston and 14.8% CV Minot). Therefore, biomass production is much more important than composition in choosing species to grow for ethanol production.
Recently, many studies have focused on developing faster methods to determine biomass composition using near infrared (NIR) spectroscopy. Other NIR models have been developed on single biomass feedstocks but a broad-based model for mixed herbaceous perennials is yet to be developed. Therefore, NIR calibration models for lignin, glucan, and xylan were developed with 65 mixed herbaceous perennial species using a DA 7200 NIR spectrometer (950 - 1,650 nm) and GRAMS statistical software. The models for lignin and xylan had R(2) values of 0.844 and 0.872, respectively, upon validation and are classified as
good for quality assurance purposes while glucan model had an R(2) of 0.81 which is considered sufficient for screening. The R(2) and the root mean square error of prediction (RMSEP) results showed that it is possible to develop calibration models to predict chemical composition for mixed perennial biomass when compared with results for models developed for single feedstock by Wolfrum and Sluiter (2009) and Liu et al. (2010). Studying the variability in predicting constituents using NIR spectroscopy over time (hours and days), it was observed that the average CV was between 1.4 to 1.6%. The average CV
due to repacking (presentation) alone was 1.3%. The CVs for NIR predictions ranged between 1.4 to 5.7% while for wet chemistry ranged between 3.8 to 13.5%; hence, NIR predictions were more precise than wet chemistry analysis.