Relevant bibliographies by topics / Plant species assemblage

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  2. Dissertations / Theses
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Academic literature on the topic 'Plant species assemblage'

Author: Grafiati
Published: 14 March 2023

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Journal articles on the topic "Plant species assemblage"

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Vitt, Dale H., Melissa House, and Jeremy A. Hartsock. "Sandhill Fen, an initial trial for wetland species assembly on in-pit substrates: lessons after three years." Botany 94, no. 11 (November 2016): 1015–25. http://dx.doi.org/10.1139/cjb-2015-0262.

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Open-pit mining of oil sands removes wetland plant communities from the landscape. Sandhill Watershed, located on Syncrude Canada’s oil sands lease, is the first reclamation of a complex watershed that includes a 17 ha central wetland designed to develop into a rich fen. Here we sample the vegetation after three years. Of the 124 plant species recorded, 48% are peat-forming species, including 24 bryophyte species. We identified, using ordination techniques, four plant assemblages that vary in abundance of peat-forming plants. Each assemblage occurs in a spatially distinct area of Sandhill Fen, forming vegetation zones that are closely associated with height of water table. The plant assemblage distributed in the wettest areas has abundant marsh species. The assemblages in the driest areas of the fen have large numbers of upland and weed species and few species characteristic of fens. In between is a species assemblage with an abundance of species characteristic of natural peat-forming habitats. Two key findings are: water levels control spatial distributions of species assemblages, and non-peat-forming plant species are abundant and a concern for the establishment of peat-forming wetlands. Future designs should include plans for a number of interconnected site types such as marshes, fens, and riparian areas.
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Fansong, Meng. "Middle Triassic lycopsid flora of South China and its palaeoecological significance." Journal of Palaeosciences 45 (December 31, 1996): 334–43. http://dx.doi.org/10.54991/jop.1996.1253.

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In recent years, a flora characterized by Lycopsida has been found from the Middle Triassic Badong Formation in Yangtze Gorge area, China, and may be subdivided into two plant assemblages, i.e., Anisian, Pleuromeia, marginulata-Annalepis sangzhiensis assemblage and Ladinian Annalepislatiloba-Scytophyllum assemblage. Of them, the former assemblage, containing 18 genera and 30 species, is one of the typical floras of the tidal flat in the world during Anisian. In addition, the character and ecology of the Anisian plant assemblage are emphatically discussed in this paper.
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Van-Silva, Wilian, Andrei Guimarães Guedes, Priscila Lemes de Azevedo-Silva, Fernanda Francisca Gontijo, Rosana Silva Barbosa, Gustavo Ribeiro Aloísio, and Flávio César Gomes de Oliveira. "Herpetofauna, Espora Hydroelectric Power Plant, state of Goiás, Brazil." Check List 3, no. 4 (November 1, 2007): 338. http://dx.doi.org/10.15560/3.4.338.

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We provide a checklist of the herpetofaunal assemblage from Espora Hydroelectric Power Plant region (UHE Espora), southwestern of the state of Goiás, Brazil. Representatives of 32 amphibian and 71 reptile species were obtained during faunal monitoring and faunal rescue programs carried out in the study area. The obtained species list and distribution records are here discussed in an attempt to improve the still limited knowledge on Cerrado herpetofaunal assemblages.
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CALDARA, ROBERTO, DAVIDE SASSI, and IVO TOŠEVSKI. "Phylogeny of the weevil genus Rhinusa Stephens based on adult morphological characters and host plant information (Coleoptera: Curculionidae)." Zootaxa 2627, no. 1 (September 27, 2010): 39. http://dx.doi.org/10.11646/zootaxa.2627.1.3.

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A phylogenetic analysis of the species belonging to the weevil genus Rhinusa Stephens, 1829 (Coleoptera: Curculionidae: Curculioninae: Mecinini) was carried out. Rhinusa weevils feed on plants of the closely related families Scrophulariaceae and Plantaginaceae. Based on a cladistic analysis of six outgroup and 33 ingroup taxa, and 39 adult morphological and 8 ecological characters, eight well supported species groups and two monobasic groups belonging to three separate and more inclusive assemblages were recognized. The first assemblage (A) includes nine species belonging to two groups (R. bipustulata and R. tetra groups), whereas the second and third assemblages (B and C) include a total of 14 species belonging to two groups (R. antirrhini and R. linariae groups) and six groups (R. pilosa, R. herbarum, R. neta, R. vestita, R. mauritii and R. melas groups), respectively. Two of the three main assemblages (A and B) are well supported as monophyletic entities, whereas the third assemblage (C) has weak support contingent in part upon the exclusion of host plant associations. Assemblage A includes all species living on species of Scrophulariaceae, with two groups occurring on two closely related plant genera, Scrophularia (R. bipustulata group) and Verbascum (R. tetra group), respectively. The other two assemblages include species living exclusively on species of the family Plantaginaceae, tribe Antirrhineae. These patterns suggest a well conserved and phylogenetically congruent association among the weevils and their hosts. Optimizing host plant preferences onto the morphological phylogeny indicates that feeding on Plantaginaceae was the plesiomorphic condition for the genus Rhinusa. In general there are no strict relationships between groups of weevils and their specific feeding habits; however, species of the R. antirrhini group are all feeding on seed capsules. In contrast, in other groups the larvae of closely related species display significant variations in host plant parasitism. Some species of the R. tetra group feed on seed capsules whereas others are stem borers. In turn, certain species of the R. neta group feed on seed capsules yet others are inquilines of gall forming species of Rhinusa. The latter habit is present in multiple convergent groups such as the R. linariae and R. pilosa groups.
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Kooyman, Robert M. "Traits and gradients influence the canopy position of small-statured rain forest trees." Australian Journal of Botany 60, no. 8 (2012): 735. http://dx.doi.org/10.1071/bt12195.

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Plant height determines a species’ position in the canopy and regulates access to light. Shifts in trait values for assemblages (plots) arrayed along abiotic gradients can reflect changes in species composition, and shifts in species trait values. Multivariate analysis was used to quantify the relationship of assemblage-level floristic composition to environmental gradients. Species trait values for maximum height, leaf area, seed size and wood density were quantified for woody species in the assemblage samples, and partitioned into within- and among-assemblage components to enable trait correlations to be identified, including in relation to abiotic gradients. Assemblages in upslope topographic positions had lower height, smaller leaves and higher wood density. Across the assemblages, shifts in species composition, decreasing canopy height and the position of smaller trees in the canopy were all linked to decreasing soil depth in upslope topographic positions. Regardless of stand height, the canopy position of most main canopy dominants remained largely unchanged in response to shifts in environmental gradients. In contrast, shorter-stature tree species retained height along the gradient and subsequently shifted from the subcanopy to the canopy as soil depth and site (plot) canopy height decreased. Within a community, height and position in the canopy can shift under differing environmental conditions.
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Wellman, Charles. "A land plant microfossil assemblage of Mid Silurian age from the Stonehaven Group, Scotland." Journal of Micropalaeontology 12, no. 1 (August 1, 1993): 47–66. http://dx.doi.org/10.1144/jm.12.1.47.

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Abstract. Land plant microfossils recovered from the Stonehaven Group near Stonehaven, Scotland comprise sporomorphs (cryptospores and miospores) and plant fragments (tubular structures and cuticle-like sheets). A new species of hilate cryptospore, Hispanaediscus lamontii sp. nov., is proposed. The sporomorph assemblage indicates a late Wenlock, or possibly earliest Ludlow age and is interpreted as accumulating in a continental environment. The new age constraint suggests that the Stonehaven Group is not in continuous succession with overlying “Lower Old Red Sandstone” deposits and should be treated separately. The assemblage provides important information regarding the composition of Mid Silurian continental plant microfossil assemblages and indicates that the vegetation comprised few taxa and was cosmopolitan.
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Lee, Philip. "The impact of burn intensity from wildfires on seed and vegetative banks, and emergent understory in aspen-dominated boreal forests." Canadian Journal of Botany 82, no. 10 (October 1, 2004): 1468–80. http://dx.doi.org/10.1139/b04-108.

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This paper compares seed and vegetative banks, and the emergent understory in unburned, lightly burned, and intensely burned patches within an aspen-dominated boreal forest in northeastern Alberta, Canada. Propagule banks were measured immediately after the fire, while the understory was surveyed 2 years later. Seedling and shoot emergence techniques were used to assess the abundance and assemblage of species within seed and vegetative banks. Median seed density was ordered unburned > lightly burned = intensely burned patches. A cumulative index of vegetative bank abundance was ordered unburned > lightly burned > intensely burned patches. Species assemblages were significantly different amongst burn intensities for seed banks and emergent understory. Vegetative bank assemblages were significantly different between unburned and burned patches but not between lightly and intensely burned patches. Furthermore, seed and vegetative bank assemblages within each burn intensity were also significantly different. Indicator species analysis suggested that all significant differences were due largely to broad assemblage differences rather than a few unique species. Ordination with nonmetric multidimensional scaling correspondence analysis separated seed and vegetative banks, and emergent understory along two axes (88.8% of the total variation). The first axis (50.3% of the total variation) indicated that the unburned and lightly burned species assemblages were more similar to the vegetative bank, while the intensely burned patches were more similar to the seed bank. The second axis (38.5% of the total variation) placed vegetative banks closer to emergent vegetation than seed banks.Key words: seed bank, bud bank, vegetative bank, aspen, boreal, fire.
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Naeem, Shahid, Katarina Håkansson, John H. Lawton, M. J. Crawley, Lindsey J. Thompson, and Katarina Hakansson. "Biodiversity and Plant Productivity in a Model Assemblage of Plant Species." Oikos 76, no. 2 (June 1996): 259. http://dx.doi.org/10.2307/3546198.

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Bourceret, Amélia, Corinne Leyval, François Thomas, and Aurélie Cébron. "Rhizosphere effect is stronger than PAH concentration on shaping spatial bacterial assemblages along centimetre-scale depth gradients." Canadian Journal of Microbiology 63, no. 11 (November 2017): 881–93. http://dx.doi.org/10.1139/cjm-2017-0124.

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At centimetre scale, soil bacterial assemblages are shaped by both abiotic (edaphic characteristics and pollutants) and biotic parameters. In a rhizobox experiment carried out on planted industrial soil contaminated with polycyclic aromatic hydrocarbons (PAHs), we previously showed that pollution was distributed randomly with hot and cold spots. Therefore, in the present study, we investigated the effect of this patchy PAH distribution on the bacterial community assemblage and compared it with that of root depth gradients found in the rhizosphere of either alfalfa or ryegrass. Sequencing of 16S rRNA amplicons revealed a higher bacterial diversity in ryegrass rhizosphere and enrichment in specific taxa by the 2 plant species. Indeed, Bacteroidetes, Firmicutes, and Gammaproteobacteria were globally favored in alfalfa, whereas Acidimicrobiia, Chloroflexi, Alpha-, and Betaproteobacteria were globally favored in ryegrass rhizosphere. The presence of alfalfa created depth gradients of root biomass, carbohydrate, and pH, and actually shaped the bacterial assemblage, favoring Actinobacteria near the surface and Gemmatimonadetes and Proteobacteria at greater depths. Contrarily, the bacterial assemblage was homogeneous all along depths of the ryegrass root system. With both plant species, the PAH content and random distribution had no significant effect on bacterial assemblage. Globally, at centimeter scale, bacterial community assemblages were mostly shaped by soil physical and chemical depth gradients induced by root growth but not by patchy PAH content.
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Bernardes, Carolina, and Flávia Regina Capellotto Costa. "Environmental variables and Piper assemblage composition: a mesoscale study in the Madeira-Purus interfluve, Central Amazonia." Biota Neotropica 11, no. 3 (September 2011): 83–91. http://dx.doi.org/10.1590/s1676-06032011000300006.

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This study aimed to determine the effects of canopy openness, litter depth, soil cation content and texture on Piper assemblage composition at a mesoscale. Piper assemblage composition and environmental variables were inventoried in 41 0.125 ha (250 × 5 m) plots placed in a terra firme forest located in the Madeira-Purus interfluve, Central Amazonia. Ordination of the 41 plots by Non-metric Multidimensional Scaling (NMDS) in one dimension captured 58% of the floristic variation and was used as the response variable in multiple regression models. Environmental variables explained 39% of the variation in Piper assemblage composition, which was significantly related to litter depth, soil texture and canopy openness, but not to the cation content. Effects of edaphic components on plant assemblage structure have been reported for different plant groups, however the strong effect of litter depth at a mesoscale had not yet been demonstrated. We suggest that litter depth variation not only influences the structure of Piper assemblages, but also of other plant groups at a mesoscale, as this environmental variable has a direct or indirect effect on species germination and establishment.
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Dissertations / Theses on the topic "Plant species assemblage"

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Glaeser, Lilyan C. "Established Plant Physiological Responses and Species Assemblage Development during Early Fen Reclamation in the Alberta Oil Sands." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1757.

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Reclamation of the boreal landscape, including both wetlands and uplands integrated into complex watersheds, has presented a challenge over the past decade with few attempts. Relevant today is wetland/peatland reclamation on reclaimed landscapes positioned on saline sand deposits left on ‘in-pits’ from open pit oil sands mining. The study site for the following questions was an experimental watershed, Sandhill Fen, located north of Fort McMurray, Alberta. Part of the reclamation challenge lies in choosing characteristic species that are tolerant of conditions present on the reclaimed landscape. Species need to both survive harsh environmental conditions and facilitate succession from mineral-based wetlands (marshes) to peat-based ones (fens).Beckmannia syzigachne is a species associated with rich fens in boreal Alberta but its potential to tolerate the given conditions of an open pit mine has yet to be explored. Thus the first question investigated was: How does Beckmannia syzigachne, respond to stress inherent in open pit mines, specifically sodium and soil wetness? Once plants are established, their success and health can be assessed by their physiological responses to the inherent conditions of an open pit mine and further compared to naturally occurring reference populations, called benchmarks, associated with boreal wetlands and peatlands.Carex aquatilis, Scirpus atrocinctus, and Triglochin maritima are three species naturally occurring or strong associated with rich fens and have established on an open pit reclamation site. The second question investigated was: how do Carex aquatilis, Scirpus atrocinctus, and Triglochin maritima physiologically respond to the soil moisture, sodium in the soil, and conductivity of the reclamation site and compare to benchmark populations? Given the large size and isolation from the natural landscape, revegetating the reclamation site may be difficult. Many species have begun to naturally colonize a reclamation site and the assemblage of species and how they might change affect the progression of fen reclamation is unknown. The third question investigated was: what does the early assemblage of species on a reclamation site consist of and do the species give indications of successional trajectory toward a peat-forming wetland? Lastly, active management of the reclamation site can have a great effect on the trajectory of the established species. Actively planting specific assemblages could assist in the trajectory of succession by encouraging the proliferation of desirable species and hindering the establishment of undesirable species. Planting assemblages of high diversity could be more beneficial than planting monocultures. Thus the last question investigated was: does the planting of diverse assemblages effect the establishment of desirable and undesirable species on a reclamation site? Overall, the investigation of these questions revealed some interesting results and concluded strong recommendations for ongoing and future fen reclamation of open pit mines. Beckmannia syzigachne shows decreased morphological and physiological performance with higher sodium concentrations, but tolerates the expected soil wetness and sodium concentrations of the reclamation site, Sandhill Fen. Carex aquatilis, Scirpus atrocinctus, and Triglochin maritima had very strong physiological relationships with percent soil moisture, but weak or no relationships with sodium in the soil or soil water electrical conductivity, and responded similarly to benchmark populations. Soil moisture may be the most important factor during the early development of an open pit reclamation site, as the different assemblages of species found at Sandhill Fen was strongly tied the percent soil moisture, the wetter the soil, the more desirable species were abundant. After one year, it does not appear planting diverse assemblages has nearly a strong effect on the species abundances as soil moisture does. Sandhill Fen serves as a model for future reclamation of fens on oil sands and these experiments have shown soil moisture is an important abiotic factor that requires attention and manipulation if fen reclamation is to be successful on open pit mines. Overall, at Sandhill Fen the establishment and proliferation of desirable species is a positive observation and the physiological responses similar to natural populations bodes well for the success of fen reclamation.
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BONARI, GIANMARIA. "DIFFERENT HABITAT AND TAXA: VARIOUS APPROACHES AND THEIR IMPLICATIONS FOR A LONG-SIGHTED MANAGEMENT AND CONSERVATION." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1010508.

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The thesis starts in the continental context of the White Carpathians Protected Landscape Area and UNESCO Biosphere Reserve (Czech Republic), a protected area famous for its grasslands with the globally highest fine-scale plant species richness. The effects of management on species richness and composition of both plants and animals were tested in relation to different management practices (mowing, grazing, abandonment and mixed management) for several years at several sites, clarifying the disagreements that have occurred among conservationists and practitioners to date. The thesis continues with a focus on the Mediterranean context. Here, the distribution patterns of understorey assemblages of coastal pine stands on sand dunes were studied, given the scarcity of literature due to scholarly disdain. Using more than a hundred plots along Italian coastlines in different pine forest types, community similarity and specificity was assessed in order to provide lacking management clues. Subsequently, focusing on a pine forest stand located in Southern Tuscany, the thesis aimed to solve another pivotal question, namely by investigating the concordance of species assemblages between vascular plants, oribatid mites and soil chemical properties with special attention to the role of vegetation structure (i.e. tree, shrub and herbaceous cover) for biological components. This part provides new answers about congruence among communities and following appropriate management practices to be fulfilled for communities. The last part, performed along a wide range of Tuscan coasts, deals with one of the most extreme habitats in the Mediterranean basin: coastal dunes. Here, the understanding of the response of plant species to soil factors was estimated. This provides concrete proposals for the effective conservation of coastal habitats.
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Gross-Camp, Nicole D. "Dispersion of large-seeded tree species by two forest primates primate seed handling, microhabitat variability, and post-dispersal seed fate /." [Yellow Springs, Ohio] : Antioch University, 2009. http://www.ohiolink.edu/etd/view.cgi?acc_num=antioch1233073947.

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Thesis (Ph. D.)--Antioch University New England, 2008.
Title from PDF t.p. (viewed Feb. 19, 2009). "A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Environmental Studies at Antioch University New England 2008"--The title page. Advisor: Beth A. Kaplin, Ph. D. Includes bibliographical references (p. 122-123).
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Fraser, Michael 1957. "Effects of natural vegetation, fire and alien plant invasion on bird species assemblages in mountain fynbos of the southwestern Cape Province, South Africa." Master's thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/8423.

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Bibliography: leaves 148-160.
The effects on birds of fine-scale differences in plant species assemblage and vegetation structure, and of two major disturbance factors (woody alien plant infestation and fire), were investigated in Mountain Fynbos at two sites in the southwestern Cape Province, South Africa. Three associated processes were also studied. These were the relative importance of three animal taxa as seed predators following fire, the extent to which an indigenous bird species ate alien Acacia cyclops fruits, and potentially dispersed its seeds, and the number of nectarivorous birds which visited an isolated nectar resource. Avian responses to fire in Mountain Fynbos varied according to season, locality and burning regime. Recently and cleanly burnt fynbos at a flat, low altitude, coastal site supported a distinctly non-fynbos avifauna, characterized by relatively large-bodied, ground-feeding, opportunistic species.
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Jaunatre, Renaud. "Dynamique et restauration d’une steppe méditerranéenne après changements d’usages (La Crau, Bouches-du-Rhône, France)." Thesis, Avignon, 2012. http://www.theses.fr/2012AVIG0324/document.

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La restauration écologique a été identifiée comme une approche permettant notamment de ralentir la perte de biodiversité et de maintenir tous les biens et services issus de cette biodiversité desquels dépend le bien être de notre civilisation actuelle. Cette restauration des écosystèmes se base sur des connaissances provenant à la fois de l'écologie des communautés et de l’écologie de la restauration. Les objectifs de la thèse sont donc de comprendre la dynamique d’une steppe méditerranéenne après changements d’usage ainsi que la mise en oeuvre de techniques qui pourraient être appliquées à la restauration de cet écosystème après une perturbation anthropique sévère. La thèse a pour objet d'étude la steppe méditerranéenne de la plaine de Crau, et notamment d’anciennes cultures pour étudier la recolonisation spontanée après perturbation et le projet de réhabilitation à grande échelle de Cossure pour les expérimentations sur les techniques de restauration. En ce qui concerne la dynamique après une perturbation anthropique exogène sévère, nous avons confirmé la faible résilience de la communauté végétale steppique à la fois à moyen (30-40 ans) et long terme (150 ans), tandis que les paramètres du sol et le taux d'infestation des mycorhizes sont résilients sur le long terme. En outre, nous avons confirmé le rôle joué par les trois filtres dans la recolonisation des communautés végétales. En ce qui concerne la steppe de la Crau, la recolonisation est déterminée en premier par le filtre abiotique, puis par le filtre de dispersion et enfin par le filtre biotique. Compte tenu de la faible résilience de la communauté, nous avons testé plusieurs techniques de restauration appliquées à grande échelle au sein du projet de réhabilitation de Cossure: le semis d’espèces nurses, l'étrépage de sol, le transfert de foin et le transfert de sol. Afin d'évaluer l'efficacité des techniques de restauration, nous avons développé des indices pour mesurer « l 'intégrité » de la structure de la communauté permettant de distinguer les abondances inférieures des abondances supérieures par rapport à la communauté de référence. Les meilleurs résultats ont été obtenus avec le transfert du sol, suivi par l’étrépage de sol, puis le semis d’espèces nurses et enfin le transfert de foin. Ces résultats ont toutefois confirmé la difficulté de restaurer totalement la communauté végétale steppique. Les recherches menées au sein de cette thèse montrent que les connaissances actuelles en matière de restauration écologique permettent de restaurer au moins partiellement certaines composantes de cet écosystème, mais suggèrent de mettre un maximum de moyens pour la conservation in situ des habitats naturels plutôt que de devoir les restaurer après qu'ils aient été détruits
Ecosystem restoration has been identified as one approach to slow down the loss of biodiversity and to protect all the biodiversity-based goods and services from which humankind benefits. Restoration feeds from knowledge coming from both community ecology and restoration ecology. The objectives of the thesis are to provide insights on both the dynamics of a mediterranean steppe after changes in land-use and the implementation of techniques which could be applied to restore this ecosystem after severe anthropogenic disturbances. The thesis takes as a study object the La Crau Mediterranean steppe, and especially former cultivated fields to study the recovery after cultivation and the Cossure large scale rehabilitation project to experiment rehabilitation and restoration techniques. Concerning dynamics after severe exogenous anthropogenic disturbances, we confirmed the low resilience of the steppe plant community both at mid- (30-40 years) and long-term (150 years) while the resilience of soil parameters and mycorrhizal infestation rate are effective on the long-term. Moreover we confirmed the role played by the three filters in the plant community recovery and found that for the La Crau steppe, this is firstly driven by the abiotic filter, then by the dispersion filter and finally by the biotic filter. Given this low resilience, we tested several restoration techniques applied at large-scale within the Cossure rehabilitation project: nurse species seeding, topsoil removal, hay transfer and soil transfer. In order to assess the efficiency of restoration techniques we developed indices to measure the community structure integrity, disentangling lower and higher abundances compared to the reference. The best results were obtained with soil transfer, followed by topsoil removal, then nurse species seeding and finally hay transfer. The research conducted for this thesis shows that current knowledge in ecological restoration makes it possible to restore at least partially some La Crau ecosystem components, but ought to lead us to understand the importance of in situ conservation of natural habitats as a better alternative to restore them after they were destroyed
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Vleminckx, Jason. "The influence of soil factors and anthropogenic disturbances on tree species assemblages in central African forests." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209100.

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La diversité végétale exceptionnelle des forêts tropicales a toujours suscité une part d’incompréhension chez les scientifiques qui tentent de comprendre les processus à l’origine de cette diversité, ainsi que les mécanismes expliquant les changements spatiaux de composition spécifique. Une des clés de ce dernier mystère résiderait dans l’influence de la différentiation des niches écologiques, mais aussi de la dispersion limitée des graines et d’événements stochastiques (purement aléatoires et non prévisibles). La niche d’une espèce contraint celle-ci à s’établir dans un habitat présentant des gammes de conditions bien délimitées en termes de propriétés du sol (disponibilité en nutriments et toxicité de certains éléments) et d’intensité lumineuse. Par exemple, certaines espèces sont plus tolérantes à l’ombrage (espèces « sciaphiles ») que d’autres qui ne peuvent s’établir que dans des trouées forestières offrant suffisamment de lumière (espèces « héliophiles »). En Afrique centrale, les communautés d’arbres sont aujourd’hui en grande partie composées de ces espèces dites « héliophiles », alors que les ouvertures forestières naturelles sont rares. Il est fortement suspecté que la dominance de ces espèces soient la conséquence de trouées générées par l’homme qui, jusqu’au début de la période coloniale (vers 1900), occupait de vastes surfaces de forêt où il pratiquait l’agriculture sur brûlis. Cependant, peu d’études ont jusqu’à présent déterminé dans quelle mesure ces pratiques agricoles ont influencé la composition spécifique des forêts à l’échelle régionale comme à l’échelle locale.

L’objectif du présent travail est de faire la lumière sur l’impact de ces perturbations humaines mais aussi plus généralement sur l’influence relative de la niche écologique des espèces d’arbres par rapport à d’autres facteurs (dispersion limitée et facteurs stochastiques) sur leur distribution spatiale. Pour cela nous avons utilisé des données botaniques et environnementales provenant d’inventaires réalisés dans une forêt tropicale située en République Démocratique du Congo (quatre transects parallèles mesurant chacun 500 à 600 m de long), ainsi que des données similaires complémentées d’inventaires anthracologiques (estimation de la quantité de charbons de bois dans le sol, utilisée comme indicateur de feux passés d’origine anthropique) récoltées dans trois régions du sud du Cameroun (208 parcelles de 0,2 ha chacune).

Les données récoltées nous ont permis de mettre en évidence un impact significatif des propriétés physico-chimiques du sol sur la composition en espèces d’arbres. Plus précisément, nous avons pu constater une différence floristique marquée entre deux habitats très contrastés (sol sableux vs. sol argileux, Rép. Dém. Du Congo), et cela à une échelle spatiale locale (< 1 km²) où l’on pensait que de l’influence des facteurs stochastiques et de dispersion limitée étaient prépondérante. Mes analyses ont également démontré que cette différence était plus marquée pour les arbres de la canopée que pour les arbres des strates inférieures (« sous-canopée »), ce qui est sans doute lié au fait que de nombreux individus de la sous-canopée sont composés de juvéniles régénérant la canopée, parmi lesquels de nombreux arbres subissent une exclusion compétitive en cours (brouillant ainsi les signaux d’association espèce-habitat).

À une échelle spatiale beaucoup plus large cette fois (de 5 à 100 km, inventaires du Sud Cameroun), nous avons démontré que la diversité floristique était également influencée de manière significative par l’hétérogénéité spatiale de propriétés abiotiques du sol, notamment par les concentrations en (i) certains nutriments essentiels pouvant présenter des valeurs potentiellement limitantes (K, Mg, Ca et P) ainsi qu’en en (ii) élements pouvant être présents en quantités toxiques (Al et Mn). Cependant, alors que le signal environmental a été clairement détecté à l’échelle communautaire, seule les abondances d’une minorité d’espèces (< 15%) ont répondu significativement à la variation des conditions de sol. En outre, le nombre de réponses significatives a augmenté avec l’échelle d’observation ainsi qu’avec le degré d’hétérogénéité environnementale et/ou floristique. Pour mettre en évidence cet effet du sol, nous avons introduit une nouvelle approche permettant de tester la fraction d’une analyse de partition de variance correspondant à la part de variation floristique expliquée par l’effet de conditions édaphiques spatialement structurées (co-variation entre effets spatiaux et édaphiques), en combinant l’analyse de partition de variance avec des vecteurs propres de Moran (« Moran’s eigenvector maps ») et des translations toroïdales. Bien que cette méthode nous ait permis de déterminer si la fraction en question était significative, nous avons également mis en doute son interprétation habituelle suggérant que cette fraction représente une structure floristique directement induite par des structures spatiales de conditions de sol. Grâce à des simulations de populations végétales liées à des propriétés environnementales, nous avons mis en évidence que la valeur de la fraction étudiée ne semble finalement pas influencée par le degré de structuration spatiale des conditions environnementales, remettant donc en question l’utilité de l’analyse de partition de variance pour inférer des effets de processus écologiques sous-jacents sur la distribution spatiale des espèces d’arbres.

Enfin, les données floristiques et anthracologiques du Sud Cameroun ne nous ont pas permis de démontrer statistiquement l’hypothèse que les perturbations humaines passées sont en partie responsables de la dominance actuelle des espèces héliophiles. L’absence de corrélation significative entre l’abondance relative de ces espèces et la quantité de charbons de bois dans le sol peut s’expliquer par le fait que la majorité de ces charbons (60%) étaient trop vieux (1500 à 3000 ans) pour refléter des perturbations ayant influencé la diversité végétale présente.

Les conclusions générales de ma thèse de doctorat soutiennent que la niche écologique des espèces d’arbres des forêts tropicales africaines contribue de manière significative à déterminer leur assemblage dans l’espace, mais aussi que ces effets de niche dépendent fortement du contexte environnemental étudié ainsi que de l’échelle spatiale d’observation. Ce travail lève donc en partie un voile sur l’écologie des écosystèmes forestiers d’Afrique centrale qui restent largement méconnus par rapport à ceux d’Asie du Sud-Est et des régions néotropicales.


Doctorat en sciences, Spécialisation biologie végétale
info:eu-repo/semantics/nonPublished

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Morzaria, Luna Hem Nalini. "Determinants of plant species assemblages in the Californian marsh plain : implications for restoration of ecosystem function /." 2005. http://catalog.hathitrust.org/api/volumes/oclc/62308418.html.

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Wetherill, Karen R. "Structure, function, and analysis of Coleoptera and Heteroptera assemblages on two species of hazelnut in Oregon." Thesis, 2000. http://hdl.handle.net/1957/33209.

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The European hazelnut, Corylus avellana L., was imported into the U.S. in the late 1800's and is now grown throughout the Willamette Valley in Oregon. A native species of hazelnut, C. cornuta Marshall, is a common shrub found in forested areas of the Pacific Northwest. Foliage of both C. avellana and C. cornuta was sampled using beating sheets. The objectives of the study were as follows: 1. To compile a complete list of the Coleoptera and Heteroptera fauna of both species of hazelnut. 2. To determine the amount of overlap across host plants. 3. To measure arthropod abundance and species diversity within functional groups across a forest-edge-orchard gradient. 4. To use ordination techniques to determine where peak abundance of individual taxa occur along the forest-edge-orchard gradient. One hundred and thirty-two species of Coleoptera and forty-nine species of Heteroptera were identified on Hazelnut foliage. The most abundant Heteroptera in the orchards studied is a newly introduced mirid predator, Malacocoris chlorizans (Panzer). There is a great deal of overlap between the two hazelnut species. Most differences are attributed to rare species. Diversity and abundance of predaceous Coleoptera and Heteroptera were severely hindered by IPM management practices, involving insecticide usage, within the orchards. However, the organic orchards retained high levels of diversity and abundance of predaceous Coleoptera and Heteroptera in the centers of the orchards. The organic orchards had higher diversity of phytophagous Coleoptera and Heteroptera as compared to IPM orchards, but the abundance of those insects was not different between the IPM and organic orchards. The ordinations of the Coloeptera data show that the peak abundances of individual species often shift along the forest-edge-orchard gradient over time and that the organic orchards retain peak abundances of predaceous Coleoptera even in late season. The ordinations of the Heteroptera data show that several mirid predators are at their peak abundances within the orchards of both IPM and organic orchards.
Graduation date: 2000
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Books on the topic "Plant species assemblage"

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Wilsey, Brian J. Conservation and Restoration of Grasslands. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198744511.003.0008.

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Conservation programs alter herbivore stocking rates and find and protect the remaining areas that have not been plowed or converted to crops. Restoration is an ‘Acid Test’ for ecology. If we fully understand how grassland systems function and assemble after disturbance, then it should be easy to restore them after they have been degraded or destroyed. Alternatively, the idea that restorations will not be equivalent to remnants has been termed the ‘Humpty Dumpty’ hypothesis—once lost, it cannot be put back together again. Community assembly may follow rules, and if these rules are uncovered, then we may be able to accurately predict final species composition after assembly. Priority effects are sometimes found depending on species arrival orders, and they can result in alternate states. Woody plant encroachment is the increase in density and biomass of woody plants, and it is strongly affecting grassland C and water cycles.
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Moffett, Lisa. The Archaeobotany of Late Medieval Plant Remains. Edited by Christopher Gerrard and Alejandra Gutiérrez. Oxford University Press, 2018. http://dx.doi.org/10.1093/oxfordhb/9780198744719.013.63.

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This chapter considers the application of archaeobotany to the later medieval period in Britain with reference to selected sites. The strengths and weaknesses of methods and evidence are explained. The most common plants remains are cereals but fruit and nuts are also found in abundance, some being imported species. Vegetables and herbs are generally poorly preserved. Some of the richest assemblages come from wet deposits in ports and may include exotics or from towns where possible thatch and industrial remains are known. Elite sites such as castles, manors, and monasteries sometimes also have abundant plant remains but the evidence from lower-status rural sites can be absent or difficult to recognize. Key concerns for the future include the limited scope of many commercial archaeological investigations, the need to exploit the archaeobotanical evidence more fully other than as a source of information about diet, and the importance of collaborative work between archaeobotanists and historians.
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Wetherill, Karen R. Structure, function, and analysis of Coleoptera and Heteroptera assemblages on two species of hazelnut in Oregon. 2000.

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Lézine, Anne-Marie. Vegetation at the Time of the African Humid Period. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.530.

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An orbitally induced increase in summer insolation during the last glacial-interglacial transition enhanced the thermal contrast between land and sea, with land masses heating up compared to the adjacent ocean surface. In North Africa, warmer land surfaces created a low-pressure zone, driving the northward penetration of monsoonal rains originating from the Atlantic Ocean. As a consequence, regions today among the driest of the world were covered by permanent and deep freshwater lakes, some of them being exceptionally large, such as the “Mega” Lake Chad, which covered some 400 000 square kilometers. A dense network of rivers developed.What were the consequences of this climate change on plant distribution and biodiversity? Pollen grains that accumulated over time in lake sediments are useful tools to reconstruct past vegetation assemblages since they are extremely resistant to decay and are produced in great quantities. In addition, their morphological character allows the determination of most plant families and genera.In response to the postglacial humidity increase, tropical taxa that survived as strongly reduced populations during the last glacial period spread widely, shifting latitudes or elevations, expanding population size, or both. In the Saharan desert, pollen of tropical trees (e.g., Celtis) were found in sites located at up to 25°N in southern Libya. In the Equatorial mountains, trees (e.g., Olea and Podocarpus) migrated to higher elevations to form the present-day Afro-montane forests. Patterns of migration were individualistic, with the entire range of some taxa displaced to higher latitudes or shifted from one elevation belt to another. New combinations of climate/environmental conditions allowed the cooccurrences of taxa growing today in separate regions. Such migrational processes and species-overlapping ranges led to a tremendous increase in biodiversity, particularly in the Saharan desert, where more humid-adapted taxa expanded along water courses, lakes, and wetlands, whereas xerophytic populations persisted in drier areas.At the end of the Holocene era, some 2,500 to 4,500 years ago, the majority of sites in tropical Africa recorded a shift to drier conditions, with many lakes and wetlands drying out. The vegetation response to this shift was the overall disruption of the forests and the wide expansion of open landscapes (wooded grasslands, grasslands, and steppes). This environmental crisis created favorable conditions for further plant exploitation and cereal cultivation in the Congo Basin.
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Jim Dine: Entrada Drive-Special Edition. Steidl, 2006.

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Book chapters on the topic "Plant species assemblage"

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Kotanen, Peter M. "Direct and indirect effects of herbivores influencing plant invasions." In Plant invasions: the role of biotic interactions, 226–40. Wallingford: CABI, 2020. http://dx.doi.org/10.1079/9781789242171.0226.

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Abstract Non-native plants rarely escape damage by herbivores. Instead, upon arrival in a new region, they begin to acquire new enemies, replacing those they have lost during their migration. These herbivores can include both natives to the new region and species that have themselves been accidentally or deliberately introduced from elsewhere, potentially including examples originating from the invader's original range. Shifts of new enemies from other hosts can occur over a range of timescales, depending in part on whether evolutionary change is required, but are likely to be faster for plants that are widespread and phylogenetically related to a herbivore's original host, and faster for generalist herbivores than for specialists. The occurrence of herbivores is not necessarily uniform across an invader's range; instead, they may be less diverse or abundant in host populations that are geographically or ecologically marginal, though existing evidence is mixed. Collectively, these new suites of herbivores can affect the growth and fitness of invaders, both directly by damaging them and indirectly by attacking their competitors. Studies comparing the demographic consequences of herbivory for successful vs unsuccessful invaders may help to clarify how often such impacts limit invasiveness. The view that an invader enters 'enemy-free' space is inaccurate; instead, persistence and spread of non-native plants often may be affected by the novel and changing assemblage of herbivores that they acquire within their new distribution.
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Catalano, Chiara, Salvatore Pasta, and Riccardo Guarino. "A Plant Sociological Procedure for the Ecological Design and Enhancement of Urban Green Infrastructure." In Future City, 31–60. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-75929-2_3.

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AbstractUrban green infrastructure could represent an important mean for environmental mitigation, if designed according to the principles of restoration ecology. Moreover, if suitably executed, managed and sized, they may be assimilated to meta-populations of natural habitats, deserving to be included in the biodiversity monitoring networks. In this chapter, we combined automatised and expert opinion-based procedures in order to select the vascular plant assemblages to populate different microhabitats (differing in terms of light and moisture) co-occurring on an existing green roof in Zurich (Switzerland). Our results lead to identify three main plant species groups, which prove to be the most suitable for the target roof. These guilds belong to mesoxeric perennial grasslands (Festuco-Brometea), nitrophilous ephemeral communities (Stellarietea mediae) and drought-tolerant pioneer species linked to nutrient-poor soils (Koelerio-Corynephoretea). Some ruderal and stress-tolerant species referred to the class Artemisietea vulgaris appear to fit well with local roof characteristics, too. Inspired by plant sociology, this method also considers conservation issues, analysing whether the plants selected through our procedure were characteristic of habitats of conservation interest according to Swiss and European laws and directives. Selecting plant species with different life cycles and life traits may lead to higher plant species richness, which in turn may improve the functional complexity and the ecosystem services provided by green roofs and green infrastructure in general.
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Bolch, Erik A., Maria J. Santos, Christiana Ade, Shruti Khanna, Nicholas T. Basinger, Martin O. Reader, and Erin L. Hestir. "Remote Detection of Invasive Alien Species." In Remote Sensing of Plant Biodiversity, 267–307. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-33157-3_12.

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AbstractThe spread of invasive alien species (IAS) is recognized as the most severe threat to biodiversity outside of climate change and anthropogenic habitat destruction. IAS negatively impact ecosystems, local economies, and residents. They are especially problematic because once established, they give rise to positive feedbacks, increasing the likelihood of further invasions and spread. The integration of remote sensing (RS) to the study of invasion, in addition to contributing to our understanding of invasion processes and impacts to biodiversity, has enabled managers to monitor invasions and predict the spread of IAS, thus supporting biodiversity conservation and management action. This chapter focuses on RS capabilities to detect and monitor invasive plant species across terrestrial, riparian, aquatic, and human-modified ecosystems. All of these environments have unique species assemblages and their own optimal methodology for effective detection and mapping, which we discuss in detail.
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Silva, Luís, Flavie Le Jean, José Marcelino, and António Onofre Soares. "Using Bayesian Inference to Validate Plant Community Assemblages and Determine Indicator Species." In Modeling, Dynamics, Optimization and Bioeconomics II, 445–61. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-55236-1_21.

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Hui, Cang, Pietro Landi, and Guillaume Latombe. "The role of biotic interactions in invasion ecology: theories and hypotheses." In Plant invasions: the role of biotic interactions, 26–44. Wallingford: CABI, 2020. http://dx.doi.org/10.1079/9781789242171.0026.

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Abstract Changes in biotic interactions in the native and invaded range can enable a non-native species to establish and spread in novel environments. Invasive non-native species can in turn generate impacts in recipient systems partly through the changes they impose on biotic interactions; these interactions can lead to altered ecosystem processes in the recipient systems. This chapter reviews models, theories and hypotheses on how invasion performance and impact of introduced species in recipient ecosystems can be conjectured according to biotic interactions between native and non-native species. It starts by exploring the nature of biotic interactions as ensembles of ecological and evolutionary games between individuals of both the same and different groups. This allows us to categorize biotic interactions as direct and indirect (i.e. those involving more than two species) that emerge from both coevolution and ecological fitting during community assembly and invasion. We then introduce conceptual models that can reveal the ecological and evolutionary dynamics between interacting non-native and resident species in ecological networks and communities. Moving from such theoretical grounding, we review 20 hypotheses that have been proposed in invasion ecology to explain the invasion performance of a single non-native species, and seven hypotheses relating to the creation and function of assemblages of non-native species within recipient ecosystems. We argue that, although biotic interactions are ubiquitous and quintessential to the assessment of invasion performance, they are nonetheless difficult to detect and measure due to strength dependency on sampling scales and population densities, as well as the non-equilibrium transient dynamics of ecological communities and networks. We therefore call for coordinated efforts in invasion science and beyond, to devise and review approaches that can rapidly map out the entire web of dynamic interactions in a recipient ecosystem.
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Hettinger, Ned. "Understanding and Defending the Preference for Native Species." In The International Library of Environmental, Agricultural and Food Ethics, 399–424. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-63523-7_22.

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AbstractThe preference for native species, along with its concomitant antipathy toward non-natives, has been increasingly criticized as incoherent, obsolete, xenophobic, misanthropic, uncompassionate, and antithetical to conservation. This essay explores these criticisms. It articulates an ecological conception of nativeness that distinguishes non-native species both from human-introduced and from invasive species. It supports, for the most part, the criticisms that non-natives threaten biodiversity, homogenize ecological assemblages, and further humanize the planet. While prejudicial dislike of the foreign is a human failing that feeds the preference for natives, opposition to non-natives can be based on laudatory desires to protect natural dimensions of the biological world and to prevent biological impoverishment. Implications for our treatment of non-native, sentient animals are explored, as well as are questions about how to apply the native/non-native distinction to animals that share human habitats and to species affected by climate change.
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Ali, M. M., K. J. Murphy, and V. J. Abernethy. "Macrophyte functional variables versus species assemblages as predictors of trophic status in flowing waters." In Biology, Ecology and Management of Aquatic Plants, 131–38. Dordrecht: Springer Netherlands, 1999. http://dx.doi.org/10.1007/978-94-017-0922-4_19.

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Resende, Tales Carvalho, and Avenir Geradine Meikengang. "Regional cooperation for the conservation of biodiversity in the Congo Basin forests: Feedback on actions carried out in the TRIDOM-TNS landscapes." In Managing Transnational UNESCO World Heritage sites in Africa, 135–45. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-030-80910-2_12.

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AbstractBiodiversity does not adhere to political boundaries. Globally, more than 50% of all terrestrial species have a range that crosses an international border. This includes more than 50% of all mammals, 25% of all amphibians and almost 70% of all birds. Of the threatened species, over 20% had a transboundary range (Mason et al., 2020). Covering a total area of more than 1.5 million km2 in six Central African countries (Cameroon, Gabon, Equatorial Guinea, Central African Republic, Republic of Congo and Democratic Republic of Congo), the so-called Congo Basin forests are the second largest tropical forest in the world after the Amazon Basin. They form the most diverse assemblage of plants and animals in Africa, and are home to some 10,000 species of plants, 1,000 birds, 700 fish and 400 mammals, including many iconic species such as forest elephants, lowland gorillas and chimpanzees. Currently, almost 15% of the total forest area of the Congo Basin has protected area status. The management of these protected areas is now based on a new paradigm: the landscape conservation approach. Twelve landscapes have been identified as priorities in the Congo Basin because of their relative taxonomic importance, overall integrity, and the resilience of the ecological processes they represent. Among these landscapes, the TRIDOM (Trinational Dja-Odzala-Minkébé) (Cameroon, Congo and Gabon) and TNS (Trinational Sangha) (Cameroon, Congo and Central African Republic) stand out as hosting the majority of the last remaining forest elephants, lowland gorillas and chimpanzees in Central Africa. The presence of four of the eight natural World Heritage sites in the Congo Basin forests testifies to the exceptional importance of these two contiguous transboundary landscapes. This article will review the evolution of regional cooperation for the conservation of biodiversity in the Congo Basin forests by providing feedback on actions carried out in the TRIDOM and TNS landscapes.
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Godinho, Francisco, Julie Charmasson, Atle Harby, António Pinheiro, and Isabel Boavida. "Hydropeaking Impact Assessment for Iberian Cyprinids: Hydropeaking Tool Adaptation." In Novel Developments for Sustainable Hydropower, 135–45. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-99138-8_12.

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AbstractHydropeaking negatively affects fish assemblages, but knowledge gaps still constrain our ability to rank and mitigate the impacts of different hydropower operation regimes at particular power plants. This is especially relevant for species and rivers for which the effects of hydropeaking are less investigated, such as the Iberian cyprinids and Mediterranean rivers. Therefore, a recently developed hydropeaking tool to systematically assess hydropeaking impacts on salmonids has been adapted for Iberian cyprinids within the research project FIThydro. The general tool framework developed for the salmonids was kept for the cyprinids, with the combined use of factors describing the physical effects and indicators of fish vulnerability to assess hydropeaking impact. An initial set of effect and vulnerability factors was developed for Iberian cyprinids. In addition, preliminary thresholds were established for each indicator to account for different levels of impact of hydropeaking on the focus taxa. The proposed factors/indicators and thresholds were critically reviewed by experts on Iberian cyprinids ecology and Mediterranean rivers functioning, and a final set of effect and vulnerability factors was established. The final factors retained most of the ones proposed for salmon, but included new ones, particularly for vulnerability.
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Boeken, Bertrand, and Yarden Oren. "Linking Species Diversity and Landscape Diversity." In Biodiversity in Drylands. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780195139853.003.0016.

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Ecologists generally agree that species diversity is linked to landscape features (Pickett and White 1985, Glenn et al. 1992, Wiens et al. 1993, Rosenzweig 1995, Hoagland and Collins 1997, Ritchie and Olff 1999). We present a conceptual framework for connecting species diversity and landscapes by showing how changes in species assemblages and changes in landscape structure coincide. We focus on the dynamics of the mutual relationship between (1) the frequency of occurrence of the various landscape mosaic components (patches) and their properties in terms of abiotic conditions, resource availabilities, and structural features, and (2) the occurrence and abundance of the species of an assemblage within and among these components. Although we use examples of assemblages of annual plants in semiarid shrubland, we stress the generality of our approach and its applicability to many other groups of organisms and landscapes. Most ecologists would also agree that there are connections between the observations that (1) individuals and populations of organisms are affected by environmental heterogeneity in the landscape, (2) species assemblages (or communities) consist of populations (or parts of them), and (3) changes in the landscape affect species assemblages, and vice versa. In this chapter we explore this often intuitive relationship explicitly. Our basic premise is that species assemblages are collections of populations interacting with the heterogeneity of the landscape. We use the term “assemblage” to preclude assumptions about interactions and proximity or encounters among the organisms. Simple presence in the sampled landscape is the criterion for belonging to an assemblage; the landscape mosaic is an assemblage of patches, which, like species, may or may not interact. We assume that the landscape is heterogeneous, comprising a mosaic of distinct patches, which can be distinguished by some patch property. Our approach does not require a particular size or kind of landscape, but its scale and structure and the definition of patches have to be relevant for the distribution of the organisms whose diversity we study. In this chapter we discuss the functional connection between the dynamics of landscapes and of species assemblages.
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Conference papers on the topic "Plant species assemblage"

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Soler, Rosina, Gimena Bustamante, and Paula Blazina. "Manipulating mammal herbivory in South Patagonia forests: effects on plant species assemblage, survival and short-term growth response of <em>Nothofagus antarctica</em> seedlings." In The 1st International Electronic Conference on Forests — Forests for a Better Future: Sustainability, Innovation, Interdisciplinarity. Basel, Switzerland: MDPI, 2020. http://dx.doi.org/10.3390/iecf2020-07959.

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Artoni, Alessio, and Massimo Guiggiani. "Revisiting Plane-Generated Gear Tooth Surfaces: A Novel Design Perspective." In ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/detc2015-47327.

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The teeth of ordinary spur and helical gears are generated by a (virtual) rack provided with planar generating surfaces. The resulting tooth surface shapes are a circle-involute cylinder in the case of spur gears, and a circle-involute helicoid for helical gears. Advantages associated with involute geometry are well known: in particular, the motion transmission function is insensitive to center distance variations, and contact lines (or points, when a corrective surface mismatch is applied) evolve along a fixed plane of action, thereby reducing vibrations and noise emission. As a result, involute gears are easier to manufacture and assemble than non-involute gears, and silent to operate. A peculiarity of their generation process is that the motion of the generating planar surface, seen from the fixed space, is a rectilinear translation (while the gear blank is rotated about a fixed axis): the component of such translation that is orthogonal to the generating plane is the one that ultimately dictates the shape of the generated, envelope surface. Starting from this basic fact, we set out to investigate this type of generation-by-envelope process and to profitably use it to explore new potential design layouts. In particular, with some similarity to the basic principles underlying conical involute (or Beveloid) gears, but within a broader scope, we propose a generalization of these concepts to the case of involute surfaces for motion transmission between skew axes (and intersecting axes as a special case). Analytical derivations demonstrate the theoretical possibility of involute profiles transmitting motion between skew axes through line contact and, perihaps more importantly, they lead to apparently novel geometric designs featuring insensitivity of transmission ratio to all misalignments within relatively large limits. The theoretical developments are confirmed by various numerical examples.
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Reports on the topic "Plant species assemblage"

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Mawassi, Munir, Baozhong Meng, and Lorne Stobbs. Development of Virus Induced Gene Silencing Tools for Functional Genomics in Grapevine. United States Department of Agriculture, July 2013. http://dx.doi.org/10.32747/2013.7613887.bard.

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Grapevine is perhaps the most widely grown fruit crop. To understand the genetic make-up so as to improve the yield and quality of grapes and grape products, researchers in Europe have recently sequenced the genomes of Pinot noir and its inbred. As expected, function of many grape genes is unknown. Functional genomics studies have become the major focus of grape researchers and breeders. Current genetic approaches for gene function studies include mutagenesis, crossing and genetic transformation. However, these approaches are difficult to apply to grapes and takes long periods of time to accomplish. It is thus imperative to seek new ways for grape functional genomics studies. Virus-induced gene silencing (VIGS) offers an attractive alternative for this purpose and has proven highly effective in several herbaceous plant species including tomato, tobacco and barley. VIGS offers several advantages over existing functional genomics approaches. First, it does not require transformation to silence a plant gene target. Instead, it induces silencing of a plant gene through infection with a virus that contains the target gene sequence, which can be accomplished within a few weeks. Second, different plant genes can be readily inserted into the viral genome via molecular cloning and functions of a large number of genes can be identified within a short period of time. Our long-term goal of this research is to develop VIGS-based tools for grapevine functional genomics, made of the genomes of Grapevine virus A (GVA) from Israel and Grapevine rupestris stem pitting-associated virus (GRSPaV) from Canada. GVA and GRSPaV are members of the Flexiviridae. Both viruses have single-stranded, positive sense RNA genomes, which makes them easy to manipulate genetically and excellent candidates as VIGS vectors. In our three years research, several major breakthroughs have been made by the research groups involved in this project. We have engineered a cDNA clone of GVA into a binary vector that is infectious upon delivery into plantlets of micropropagated Vitis viniferacv. Prime. We further developed the GVA into an expression vector that successfully capable to silence endogenous genes. We also were able to assemble an infectious full-length cDNA clones of GRSPaV. In the following sections Achievements and Detailed description of the research activities, we are presenting the outcome and results of this research in details.
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