Au cours de la première moitié de l’Holocène les conditions climatiques, eustatiques et anthropiques connaissent de nombreuses et importantes modifications. Parmi celles-ci, les données. Parmi celles-ci, les données régionales relatives au quart nord-ouest du bassin méditerranéen révèlent plusieurs variations pluriscalaires et significatives des conditions d’humidité ainsi que des températures. Parallèlement, la hausse du niveau marin enregistre des vitesses très élevées et la région de l’arc Liguro-Provençal voit l’installation des premières communautés agro-pastorales de la culture « Impressa », en l’occurrence dès le début du 6ème millénaire cal. BCE. Afin de qualifier la réponse de la végétation alluviale côtière, entre la fin du 8ème et le 5ème millénaire, face à l’évolution de ces conditions, l’analyse pollinique à haute résolution de deux séquences sédimentaires alluviales (bassin du Loup et de la Cagne) à été réalisée. Grâce à une approche pluridisciplinaire (carpologie, ostracologie, sédimentologie…) et méthodologique inédite (analyse du transport pollinique fluviatile) les résultats montrent une évolution précise des écosystèmes végétaux côtiers et alluviaux. Au sein de cette évolution, la remontée du niveau marin joue un rôle fondamental comme en témoigne l’expansion littorale des aulnaies marécageuses. Le forçage climatique joue également un rôle important. Les étés plus humides du 6ème millénaire participe à la diffusion du sapin à basse altitude, alors que l’augmentation de la fréquence des sécheresses estivales enregistrées à partir du 5ème millénaire favorise le développement d’une végétation sclérophylle à bruyère arborescente. La néolithisation de la région participe également au façonnage des paysages littoraux. La récurrence du type pollinique Cerealia (gr. Hordeum) dès les premières décennies du 6ème millénaire atteste de l’importance des plaines alluviales côtières dans l’économie de production des premiers groupes néolithiques. / This study investigates the impact of climate and sea level changes and the anthropogenic perturbations on the alluvial vegetation in the Mediterranean French coastal plains during the early to mid Holocene. Between 7000 and 3700 BCE, the combination of different type of regional proxy records reveal significant changes in the humid conditions and temperatures. These records also reveal rapid sea level changes and the first Neolithic settlement (5800 caL. BCE) in Southeastern France (« Impressed ware culture »). High resolution pollen data from two cores sampled in the alluvial plains of the Cagne and the Loup Rivers enable to study the vegetation responses to these changes. Thisstudy employed a pluridisciplinary approach (carpology, study of ostracods, sedimentology…) and developed a new ethodology for the assessment of the fluvial pollen transport. The results reveal a significant connection between the vegetation structure from the coastal area and the sea level changes. This relationship explains the alder expansion in the swamp area. Moreover the results also reveal the effects of the humid summer conditions on the vegetation dynamics and explain the spruce expansion during the sixth millennium BCE as well as the expansion of the sclerophyllous vegetationduring the fifth millennium BCE. The impact of the Neolithic agriculture on the alluvial land cover started with the first ecades of the sixth millennium BCE. Thanks to the frequencies of the pollen grains of cereals (Hordeum gr.) and the pollen vidence of forest decline between 6000 and 3700 BCE, the results show the significance of the Mediterranean coastal area in the Neolithic economy.

En structure, le bois est soumis à des sollicitations différentes dont les principales sont physiques, mécaniques et environnementales. Lorsque ces sollicitations sont couplées, le comportement mécanique du bois devient difficile à appréhender. L’objectif de cette thèse est de mettre en évidence, via un protocole de suivi de l’évolution de la flèche, l’impact des variations des conditions climatiques sur la durée de vie en structure des poutres de bois. Le travail s’articule essentiellement autour de deux grands axes principaux, un protocole expérimental spécial et une approche analytique basée sur la résistance des matériaux (RDM) de l’évolution de la flèche d’une poutre entaillée en ambiance non contrôlée. Le dispositif prend en compte : les processus de fissuration du bois, notamment de l’ouverture et de la propagation de la pointe d’une fissure se propageant linéairement depuis le droit de l’entaille, jusqu’à la rupture totale de la poutre ; le suivi des paramètres climatiques que sont la température, l’humidité relative du milieu et les variations de l’humidité interne des poutres testées. Les résultats obtenus montrent qu’une humidification entraine une augmentation de la flèche relative et un séchage génère un départ de fissures pouvant conduire à une rupture de la poutre. Le modèle analytique de l’évolution de la flèche d’une poutre entaillée en ambiance non contrôlée, est tiré des hypothèses classiques de la théorie des poutres de Timoshenko et de l’ensemble des résultats expérimentaux obtenus. Il prend en compte les processus de fissuration, les variations de son humidité interne et l’intensité du chargement qui lui est appliqué. Le modèle représente assez bien les comportements instantané et différé de la poutre induits par les chargements mécanique et environnementaux. / In structure, wood is subjected to different loadings, where the principals are physical, mechanical and environmental. The coupling of these different loadings, make the understand of the mechanical behaviour of wood difficult. The aim of this thesis is to highlight, through a protocol for monitoring the evolution of the deflection, the impact of the conditions of climatic variations on the lifetime of timber of the notched beams. The work is essentially based around two major axes highlighting, respectively, a new experimental devices and a new analytical approach of the following of the evolution of the beam deflection, in outdoor conditions. The experimental device takes into account: the monitoring of the evolution of the notched-beam deflection; the cracking processes of wood, in particular the following of its initiation, the opening and the propagation of the tip of crack which appeared, on the notched-beam until its collapse; the monitoring of the climatic parameters such as temperature, the environmental relative humidity and the variations of the moisture content of the beams during the test. The results show that the variations of these climatic parameters favour the acceleration of the wood aging process in the structure. The analytical model of the evolution of the deflection of a notched beam, shown in this work, is based on the classical hypotheses of Timoshenko’s beam theory and all the experimental results obtained. It takes into account the cracking processes of notched-beam, the variations of its moisture content and the intensity of the loading applied on the beam.

Submitted by Maicon Juliano Schmidt (maicons) on 2015-04-18T15:33:42Z No. of bitstreams: 1 Roberta da Cruz Piuco.pdf: 5094425 bytes, checksum: b68193551bc07bd504e42c0ebcc4e3e5 (MD5) / Made available in DSpace on 2015-04-18T15:33:42Z (GMT). No. of bitstreams: 1 Roberta da Cruz Piuco.pdf: 5094425 bytes, checksum: b68193551bc07bd504e42c0ebcc4e3e5 (MD5) Previous issue date: 2013-11-21 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPQ – Conselho Nacional de Desenvolvimento Científico e Tecnológico / UNISINOS - Universidade do Vale do Rio dos Sinos / INCT-APA - Instituto Nacional de Ciência e Tecnologia Antártico de Pesquisas Ambientais / Programa Antártico Brasileiro / SECIRM - Secretaria Interministerial para os Recursos do Mar / MMA - Ministério do meio Ambiente / O pinguim-papua (Pygoscelis papua) reproduz a partir de 46°S a 65°S. Apesar de sua ampla distribuição são consumidores costeiros e não migratórios, possuem um alto nível de filopatria e as populações estão restritas a ilhas de reprodução e faixas de forrageamento e apresentam variações contrastantes entre populações. Esta tese tem como objetivos: 1) avaliar as respostas do tamanho da população reprodutiva de pinguim-papua de acordo com fatores climáticos em Stinker Point, Ilha Elefante; 2) identificar o dimorfismo sexual de tamanho em caracteres morfométricos em adultos reprodutores de pinguins-papua em Stinker Point, Ilha Elefante, comparando-se com a técnica de sexagem molecular. Além disso, verificar a variação morfométrica da espécie em três locais do Arquipélago das Shetlands do Sul e comparar com dados da literatura e 3) quantificar um tipo potencial de assimetria em pinguins-papua nas ilhas Elefante e Rei George, caracterizando seus níveis assimétricos como uma forma de avaliar a qualidade do ambiente. A população reprodutiva de pinguim-papua respondeu significativamente ao Índice de Oscilação Antártica e à anomalia de temperatura durante o início do período reprodutivo. Provavelmente pelas variações climáticas extremas interferirem na decisão dos indivíduos de reproduzir ou não em um determinado ano. Na avaliação do dimorfismo sexual, através de medidas morfométricas, o comprimento do bico foi a medida de maior dimorfismo sexual (5,3%) e classificou corretamente 76,7% das aves, sendo em média as fêmeas maiores que os machos. Dentre as medidas morfométricas analisadas, todas apresentaram diferenças entre os locais do Arquipélago das Shetlands do Sul e Península Antártica. Dada a pouca acurácia das funções discriminantes na sexagem e as diferenças das medidas morfométricas conforme a área geográfica de pinguim-papua, é preciso ter cautela ao classificar indivíduos com base em uma única avaliação, de forma que a sexagem molecular apresentou melhor resultado. Quanto ao tipo de assimetria, os níveis observados refletem um padrão de assimetria flutuante (AF), porém sem diferença significativa. A ausência de altos níveis de AF indica que não há níveis cumulativos suficientes de estresses ambientais que pudesse causar distúrbios fisiológicos e alterar a homeostase do desenvolvimento normal nesta espécie na Antártica. / Gentoo penguin (Pygoscelis papua) breed from 46ºS to 65ºS. Despite its wide distribution are inshore consumers and non-migratory, have a high level of philopatry and populations are restricted to island breeding and foraging ranges and shown variations contrasting among populations. This thesis aims to: 1) to evaluate the breeding population size responses of the Gentoo penguin according to climate factor at Stinker Point, Elephant Island; 2) to identify the sexual dimorphism of size in the morphometric characteristics of male and female adult Gentoo penguins at Stinker Point, Elephant Island, compared with the technique of molecular sexing. Furthermore, to verify morphometric variation of the specie at three sites f the South Shetlands Archipelago and compare with literature data and 3) to quantify one kind of potential asymmetry in Gentoo penguins, breeding at Elephant and King George Islands and attempt to characterize their extremes of variation as a way of evaluating the current living quality of the environment. The breeding population size of Gentoo penguin responded significantly to the Antarctic Oscillation Index and the temperature anomaly during the early reproductive period. Probably by extreme climatic variations affecting the decision on breeding or skipping breeding in a given year. In the assessment of sexual dimorphism using morphometric characters, the bill length was the larger measure of sexual dimorphism (5.3%) and correctly classified 76.7% of the birds, were found females larger than males. Among the morphometric measurements analyzed, all showed differences among the sites of the South Shetlands Archipelago and Antarctic Peninsula. Given the limited accuracy of the discriminant function sexing and differences of these morphometric measurements according to the geographical area of Gentoo penguin, is necessary have caution to classify individuals based on a single assessment, so that the molecular sexing presented best result. For the type of asymmetry, the levels of asymmetry reflect a fluctuating asymmetry (FA) pattern, however no significant difference. Absence of high levels of observed FA in our study led us to think it indicates there are not sufficient cumulative levels of environmental stresses such that they might cause physiological disturbances and alter the homeostasis of normal development in this species in Antarctica.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / It is certain that most of Brazilian highways are under unfavorable conditions of trafficability. Technological developments led to a large increase in load capacity of trucks, resulting in higher impacts on the highways. Another factor to be considered in this degradation process of pavements is climatic variations, very common in Brazil. Among many types of defects found on Brazilian highways, one deserves special attention, the fatigue cracking. Aiming to investigate this problem, this study aimed to study the fatigue phenomenon in laboratory for asphalt mixture used in the field (Av. Hélvio Basso, Santa Maria-RS) and evaluate in laboratory its possible improvement using polymer modified binder before to fatigue performance at three different temperatures: 10°C, 25°C and 35°C. Three asphalt mixtures were prepared in the la, two conventional binder used in the monitored section (CACAMPO asphalt content in the field, and CALAB 50/70 asphalt content obtained in laboratory dosage), and a third polymer modified binder with (CALAB 60/85-E). Mixtures reproduced in the laboratory were prepared according to the Marshall methodology and the materials were characterized according to traditional experiments. For all mixtures, the volumetric parameters were determined, stability, fluency, adhesion, Indirect Tensile Streght, Total Resilience Moduli and performance to fatigue by indirect tensile stress under controlled mode. These last three were held at the three test testing temperatures. In the laboratory, it was evident the improvement in thermal susceptibility properties and stability of the mixture by using the modified binder polymer, providing a blend less susceptible to variations in temperature and stable at high temperatures. The results obtained in the laboratory demonstrated the superiority of the mixture CALAB 60/85 E, for the three temperatures studied, with emphasis on the destructive tests at the higher temperature. The rigidity of the mixtures, measured by the resilience module, showed little influence by the use of the modified binder, however, showed very different behavior with variation in temperature. Regarding the fatigue performance, the modified blends proved to be far superior than the conventional mix, ensuring an increase in service life for the three temperatures studied, specially for the temperature of 35°C. The temperature variation of the test proved to be very crucial in the fatigue performance of the asphalt mixture, which is inversely proportional to the temperature increase. At the end of the study, it is concluded that the use of polymer modified binders for can be a great option to improve the performance of asphalt mixtures against the fatigue rupture mechanism and it can be used successfully in regions with large temperature variations. Thus, it is possible to ensure an increase in the service life of the asphalt layer and therefore to the pavement as a whole. / É notório que grande parte das rodovias brasileiras encontram-se em condições desfavoráveis de trafegabilidade. A evolução tecnológica permitiu um grande aumento da capacidade de carga dos caminhões, refletindo em maiores solicitações nas rodovias. Outro fator a ser considerado neste processo degradativo dos pavimentos são as variações climáticas, muito presentes no Brasil. Dentre tantos tipos de defeitos encontrados nas rodovias brasileiras, um deles merece destaque especial, a degradação por fadiga. Com intuito de investigar tal problema, o presente trabalho teve como propósito estudar o fenômeno de fadiga em laboratório para uma mistura asfáltica utilizada em campo (Av. Hélvio Basso, Santa Maria-RS) e avaliar, em laboratório, a sua possível melhora pelo uso de ligante modificado por polímero perante o seu desempenho à fadiga, em três temperaturas distintas: 10°C, 25°C e 35°C. Foram preparadas em laboratório três misturas asfálticas, duas com o ligante convencional utilizado no trecho monitorado (CACAMPO, teor de asfalto de campo, e CALAB 50/70, teor de asfalto obtido em dosagem de laboratório) e uma terceira, com ligante modificado por polímero (CALAB 60/85-E). As misturas foram preparadas conforme a Metodologia Marshall e os insumos foram caracterizados de acordo com ensaios tradicionais. Para todas as misturas, determinram-se os parâmetros volumétricos, estabilidade, fluência, adesividade, Resistência à Tração indireta, Módulo de Resiliência total e desempenho à fadiga por tração indireta à tensão controlada. Estes três últimos foram realizados nas três temperaturas de ensaio. Em laboratório, ficou evidente a melhora das propriedades de suscetibilidade térmica e estabilidade da mistura pelo uso do ligante modificado por polímero, proporcionando uma mistura menos suscetível às variações de temperatura e mais estável a temperaturas elevadas. Os resultados obtidos em laboratório demonstraram a superioridade da mistura CALAB 60/85-E, para as três temperaturas analisadas, com ênfase para os ensaios destrutivos à temperatura mais elevada. A rigidez das misturas, medida pelo Módulo de Resiliência, mostrou-se pouco influenciável pela utilização do ligante modificado, porém, apresentou comportamentos bem distintos com a variação da temperatura. Quanto ao desempenho à fadiga, as misturas modificadas apresentaram-se muito superiores às convencionais, garantindo um incremento na vida de serviço para as três temperaturas analisadas, sendo este, mais evidente para a temperatura de 35°C. A variação da temperatura de ensaio mostrou-se bastante determinante no desempenho à fadiga das misturas asfálticas, sendo este, inversamente proporcional ao aumento de temperatura. Ao término do estudo, conclui-se que o emprego de ligantes modificados por polímero pode ser uma ótima opção de melhora do desempenho de misturas asfálticas frente ao mecanismo de ruptura por fadiga, podendo ser utilizado com sucesso em regiões que apresentam grandes variações térmicas. Desta forma, garantindo um incremento na vida de serviço do revestimento asfáltico e consequentemente ao pavimento como um todo.

L’empreinte des activités humaines sur les milieux naturels commence à se faire sentir avec la révolution néolithique, il y a quelques 10.000 ans, aux débuts de l’Holocène. Dans le cadre de l’ANR PaléoSyr/PaléoLib et à partir d’archives sédimentaires prélevées dans différents contextes environnementaux (côtier, lacustre et fluviatile/marais), le but de ce travail est de mettre en évidence l’évolution des changements paléoenvironnementaux pour chaque site et d’en évaluer la part relevant respectivement des fluctuations climatiques et des activités humaines, afin de mieux comprendre la relation Homme- Environnement-Climat à l’Holocène. L’étude de ces différents contextes paléoenvironnementaux permet de contraindre temporellement le développement des premières influences humaines sur leur milieu naturel, et de préciser leur mode d’action, à l’aide de marqueurs biotiques (pollen) et abiotiques du sédiment. Les principales fluctuations environnementales enregistrées soulignent les hétérogénéités régionales de réponse aux forçages climatiques et permettent ainsi d’affiner nos connaissances aux échelles locale et régionale / The first sizeable consequences of human activities on the natural environment are thought to have taken place during the Neolithic revolution, at the beginnings of the Holocene, about 10,000 years ago. The aim of this study is to assess the respective role of climate fluctuations and human activities on the evolution of different environmental contexts (coastal, lake and fluvial / swamp) during this interval using sedimentary and palynological records, and hence improve our understanding of Human-Environment-Climate relationships during the Holocene. The study of these different paleoenvironmental settings through the use of both biotic (pollen) and abiotic (sediment geochemistry) markers allow to constrain the temporal development of the first human influences on the natural environment, and to determine their various modes of action (e.g. pastoralism, cultivation). The sequence of environmental changes reconstructed in this study hence highlights profound regional heterogeneities in the response of the studied areas to climatic and anthropic forcing and thus have important implications for our knowledge of the environment-human relationships at the local and regional scales

PhD (Agricultural Economics) / Department of Agricultural Economics and Agribusiness / Climate change is a global phenomenon that has been of great concern and its tackle is of outmost importance for food security among other things. In response to climate change adaptation, the study intended to determine awareness of climate change, its critical determinants and impacts among farmers, particularly emerging farmers. The study also investigated socio-economic characteristics of farmers that play a vital role in selection of various adaptive strategies, furthermore, institutional factors that contributed in emerging farmers’ decision to either adapt or not to climate change were also investigated. The main aim of the study was to develop a model that could be used in future to enhance adaptation to climate change through various identified adaptive strategies in Limpopo province of South Africa. The study was conducted in five districts of Limpopo province, namely: Capricorn, Mopani, Sekhukhune, Vhembe and Waterberg. The study made use of structured questionnaire to collect data from 206 emerging farmers. A two-stage cluster sampling technique was employed to select participants of the study. Statistical Package for the Social Sciences (SPSS; version 25, 2017) was used to analyse the data; cross-tabulation, multinomial and binary logistic models were used for analysis. Preliminary descriptive statistics results from cross-tabulation indicated that farmers were aware of climate change; had noted various critical determinants of climate change and were aware of impacts of climate change during production seasons between 2014 and 2018. Using Multinomial Logit model, further analysis indicated that there are socio-economic characteristics that significantly influenced selection of various adaptive strategies among farmers. Variables that significantly influenced selection of various adaptive strategies were household size, farming experience, formal education, occupation, gender and monthly on-farm income. The study also discovered that institutional factors such as accessing different kinds of extension services, securing source of support and accessing climate change information such as weather forecast, positively and significantly influence farmers’ decision to adapt to climate change. Recommendations of the study were that there should be capacity building in a form of training programmes that promote climate change awareness as farmers need to be capacitated to enable them to take strategic decisions on a daily basis. Furthermore, it was also recommended that training of farmers should target illiterate farmers and farmer without off-farm occupation and specific needs of farmers should be taken into consideration when initiating adaptation initiatives as adaptation to climate change is best monitored at farm level. The study also recommended that various stakeholders such as community of practice, climatologists, and agro-meteorologists should provide various support to emerging farmers to improve farmers’ resilience towards climate change through adaptation. / NRF

La modélisation dynamique des systèmes écologiques constitue une méthode incontournable pour comprendre,prédire et contrôler la dynamique des écosystèmes semi-naturels, qui fait intervenir des processuscomplexes. Le principal objectif de cette thèse est de développer un modèle permettant de simuler la dynamiqueà moyen terme de la végétation herbacée dans les prairies permanentes, en tenant compte à lafois de la productivité et de la biodiversité. Les prairies sont des réservoirs présentant une forte biodiversitévégétale, qui soutiennent de nombreux services écosystémiques. Sur le plan agricole, cette importantediversité contribue à la qualité de la production fourragère, et de plus, elle permet une plus grande résistancede la végétation face à des changements climatiques (réchauffement moyen, vagues de chaleur etde sécheresse).Pourtant, cette notion clé de biodiversité n’est que faiblement prise en considération dans la modélisationde l’écosystème prairial : elle est souvent absente ou alors présente sous une forme très simplifiée. Enréponse à ces considérations, ces travaux de thèse présentent la construction d’un modèle de successionbasé sur des processus, décrit par un système d’équations différentielles ordinaires, qui représente ladynamique de la végétation aérienne des prairies tempérées. Ce modèle intègre les principaux facteursécologiques impactant la croissance et la compétition des espèces herbacées, et peut s’ajuster à n’importequel niveau de diversité, par le choix du nombre et de l’identité des espèces initialement présentes dansl’assemblage. Ce formalisme mécaniste de modélisation nous permet alors d’analyser les relations qui lientdiversité, productivité et stabilité, en réponse à différentes conditions climatiques et différents modes degestion agricole.[...]Ces résultats soulignent alors le besoin de prendre en compte le rôle clé joué par la biodiversité dansles modèles de l’écosystème prairial, de par son impact sur le comportement des dynamiques simulées.De plus, pour rendre correctement compte des interactions au sein de la végétation, le nombre d’espècesconsidéré dans le modèle doit être suffisamment important. Enfin, nous comparons les simulations devégétation de ce modèle à des mesures issues de deux sites expérimentaux, la prairie de fauche d’Oensingen,et le pâturage de Laqueuille. Les résultats de ces comparaisons sont encourageants et soulignentla pertinence du choix et de la représentation des processus écologiques clés qui composent ce modèlemécaniste.Ce travail de thèse propose donc un modèle, en total adéquation avec les besoins actuels en terme demodélisation de l’écosystème prairial, qui permet de mieux comprendre la dynamique de la végétationherbacée et les interactions entre productivité, diversité et stabilité. / Dynamic modelling of ecological systems is an essential method to understand, predict and control thedynamics of semi-natural ecosystems, which involves complex processes. The main objective of this PhDthesis is to develop a simulation model of the medium- and long-term dynamics of the herbaceous vegetationin permanent grasslands, taking into account both biodiversity and productivity. Grasslandecosystems are often hot spots of biodiversity, which contributes to the temporal stability of their services.On an agricultural perspective, this important biodiversity contributes to the forage quality, andbesides, it induces a higher ability of the vegetation cover to resist to different climatic scenarios (globalwarming, heat and drought waves).However, this key aspect of biodiversity is only poorly included in grassland models : often absent ofmodelling or included in a very simple form. Building on those considerations, this PhD work exposes thewriting of a process-based succession model, described by a system of Ordinary Differential Equationsthat simulates the aboveground vegetation dynamics of a temperate grassland. This model implementedthe main ecological factors involved in growth and competition processes of herbaceous species, and couldbe adjust to any level of diversity, by varying the number and the identity of species in the initial plantcommunity. This formalism of mechanistic models allows us to analyse relationships that link diversity,productivity and stability, in response to different climatic conditions and agricultural management.In mathematical grassland models, plant communities may be represented by a various number of statevariables, describing biomass compartments of some dominant species or plant functional types. The sizeof the initial species pool could have consequences on the outcome of the simulated ecosystem dynamicsin terms of grassland productivity, diversity, and stability. This choice could also influence the modelsensitivity to forcing parameters. To address these issues, we developed a method, based on sensitivityanalysis tools, to compare behaviour of alternative versions of the model that only differ by the identityand number of state variables describing the green biomass, here plant species. This method shows aninnovative aspect, by performing this model sensitivity analysis by using multivariate regression trees. Weassessed and compared the sensitivity of each instance of the model to key forcing parameters for climate,soil fertility, and defoliation disturbances. We established that the sensitivity to forcing parameters ofcommunity structure and species evenness differed markedly among alternative models, according tothe diversity level. We show a progressive shift from high importance of soil fertility (fertilisation level,mineralization rate) to high importance of defoliation (mowing frequency, grazing intensity) as the sizeof the species pool increased.These results highlight the need to take into account the role of species diversity to explain the behaviourof grassland models. Besides, to properly take into account those interactions in the grassland cover, theconsidered species pool size considered in the model needs to be high enough. Finally, we compare modelsimulations of the aboveground vegetation to measures from two experimental sites, the mowing grasslandof Oensingen, and the grazing grassland of Laqueuille. Results of these comparison are promising andhighlight the relevance of the choice and the representation of the different ecological processes includedin this mechanistic model.Thus, this PhD work offers a model, perfectly fitting with current needs on grassland modelling, whichcontribute to a better understanding of the herbaceous vegetation dynamics and interactions betweenproductivity, diversity and stability.