A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg 1992. / The aim of the study was to develop understanding of the relationships between vegetation types of the grassland biome of South Africa and the environment, with an emphasis on structural and functional characteristics. The grassland biome in South Africa has traditionally been divided into 'pure' grasslands, assumed to be climatically determined, and 'false' grasslands of recent anthropogenic origin. A review of literature from several disciplines including palaeobotany, archaeology, ecology and biogeography indicates that this is not a valid distinction. It is clear that the distribution of the grassland biome as a whole is poorly understood, but the general correlation between the distribution of biomes and climate elsewhere in the world suggests that this warrants more detailed investigation. A water balance approach was used to develop climatic incices that both predict the distribution of grasslands, and are easy to interpret biologically. The indices are the mean. number of days per annum when moisture is available for plant growth, tbe mean temperature on days when moisture is available for plant growth (wet season temperature),. and the mean temperature when moisture is not available for plant growth (dry season temperature). Based on these three.indices the grassland biome in South Africa call be distinguished from neighbouring biomes. The fynbos and succulent karoo biomes have rainfall in winter. The grassland, nama-karoo and savanna biomes have' rainfall in summer. The forest biome experiences rainfall throughout the year. Of the summer rainfall biomes, the quantity of water available in the grassland biome b greater than in the nama-woo, similar to savanna, but less than forest. Grasslands experience cooler dry season temperatures than savannas. The localised distribution of woody plants within the. grassland biome suggests that it is the effect of climate on the fire regime that may be of overriding importance h'l determining the distribution of the biome as a whole. Woody elements are restricted to sites that are either protected from fire, or experience fires of lower intensity than sites that support- grassland, The unifying feature of the grassland biome is its proneness to fire. The presence of a warm, moist season promotes plant production and leads to a high standing crop close to the ground. The prolonged dry season causes vegetation to dry out annually, rendering it flammable. More arid biomes have plants more widely spaced, making it difficult for fire to spread. In more mesic biomes where rainfall is less sea.sonal than in the grasslands or savannas, fuels do not dry out sufficiently to ignite, A number of additional climatic features may promote burning in the grassland biome, It has the highest lightning density of all South Africa's biomes. 'tVarm, dry 'berg' winds desiccate fuels and 1 omote burning in the more mesic grasslands, The 'curing' of the grass sward due to dry season frost and temperature drop is important in establishing early dry season flammability. Savanna trees are fire tolerant, but they appear sensitive to the cold temperatures prevaient in the grassland biome in. the dry season, The relationship between the distribution of functional characters of grassland plants and environmental conditions was investigated. The distincrion between sweetveld, mixed veld and sourveld was recognised as one of the most Important functional features of South Africa's grasslands, The distribution of these vegetation types was examined in detail. Sweetveld occurs In warm, dry areas; sourveld in cool, moist areas. There Is overlap between these tyP.Js that Is dependant on soil nutrient status. Sweetveld that occurs in climatic conditions that would be expected to support mixed veld and sourveld, is on soils derived from basic parent material, including basalt, dolerite, gabbro and norite. Similarly, sourveld that occurs in areas that climatically would be expected to support sweetveld, is on soils derived from acid parent material such as sandstone and quartzite .. Soil nutrients that are most highly correlated to the occurrence of these three veld types are phosphoms availability and an index of nitrogen mineralization potential. 'l'here is an increase in bot; available phosphorus and the index of readily mineralizable nitrogen from sourveld to mixed veld to sweetveld. These features am inc01).10111tedinto a conceptual model that relates the distribution of these grassland types to carbon and nitrogen metabolism, with the role of phosphorus either similar to nitrogen, or else it may act indirectly by affecting the. rate of nitrogen mineralization, Nitrogen mineralization OCcursat lower water availability than carbon assimilation, and its temperature optimum is higher than that of carbon assimilation. Where nitrogen mineralization is favoured ielative to carbon assimilation, sweetveld is likely to (}C(.1\Xr. Where carbon assimilation is. favoured relative to; nitrogen mineralization, sourveld is likely to occur ....Soil texture affects the balance between these two processes in the degree to wm.r;h it protects soil organic matter, and thereforv the size of the nitrogen and ph_QSPllO_rOll.S pools. Changes in the rlj,stribution of South Africa's b~\omesfor a scenario of climate change are predicted using the biome model developed in this study. This illustrates the value of developing predictive models. / MT2017

Semi-natural grasslands are among the most threatened habitats in Europe, endangered mainly by cessation of former management practices and conversion into other types of land use. Extensive research has been carried out in European grasslands in last decades, to explain origins of diversity and to provide guidelines for its conservation. However, the very slow response of perennial plants to landscape changes often impedes to accurately evaluate why species occur just where they occur and not elsewhere. Abandoned fields are perceived as potential habitats for species from declining grasslands. Indeed, many species are able to spontaneously colonise abandoned fields, but many other species are absent from communities that develop there. An important question remains what limits their successful establishment. By answering this question, we can gain also important insights into factors determining species distribution in grasslands because colonization of recently abandoned fields by grassland species is the ongoing process which is not obscured by historical changes in landscape structure. The very basic aim of this thesis was to evaluate the status quo of dry grassland plants in fields abandoned in last two decades. And in the second step, to identify what are the main constrains of successful...

Past extensive changes in land use have resulted in fragmentation of species habitats. Changes in landscape structure have provoked discussion about the prospects of species of fragmented habitats in the future agricultural landscape. Landscape dynamics of plant species is basically a result of extinction and colonization rates. Many studies have confirmed the former expectation that a number of habitats suitable for a plant species in a landscape stay unoccupied. The differences in species distribution and proportion of suitable habitats occupied by a given species are hypothesized to be due to the area and isolation of suitable habitats and colonization and survival ability of a given species. To understand species dynamics in a changing landscape, first we have to reveal the relationships between the distribution of species and their proportion of occupied habitats, habitat age, habitat configuration and species colonization and survival ability. After the complete understanding of the determinants of species dynamics we will be able to predict reliably species prospect in the future. The very basic aim of this thesis was to reveal the determinants of landscape dynamics of dry grassland species in terms of their distribution and frequency in the landscape. The importance of correct identification...

Aj Many different methods are used to protect nature. Recently, however, the Earth Remote Sensing (RS) methods have come to the fore. An indisputable advantage is the ability to apply acquired data from RS in the GIS environment and to combine them easily with other important data about studied areas. To evaluate the change in the status of grassland Natura 2000 habitats, a manual assessment of the change of vegetation cover from orthophoto maps was chosen. In the GIS tools were used to analyses the changes in cover of target habitats in selected administrative areas of four municipalities in the Šumava NP between years 2004 and 2015. Differences in the enlargement of the built-up areas of four studied municipalities as a whole and the losses of target habitats due to development activities were studied. The results are compared with the results of similar monitoring conducted in the Krkonoše NP. Key words: Management of protected areas, secondary grasslands, rare habitats, succession, biodiversity

O manejo do pastejo tem grande influência sobre produtividade animal a pasto, resposta à adubação e longevidade da pastagem, seja em sistemas adubados ou não adubados. É necessário conhecer o manejo do pastejo mais adequado para cada sistema. Neste estudo em Piracicaba SP, Brasil, foram analisadas respostas de Panicum maximum cv. Tanzânia adubado (A) e não adubado (NA), à manejos do pastejo com interrupção da rebrota aos 95% de interceptação luminosa (I.L.) e três severidades de desfolha (alturas de resíduo de 20cm, 30cm, e 50cm). As pastagens adubadas receberam 572 kgN.ha-1, 472 kgK2O.ha-1 e 230 kgP2O5.ha-1, e as pastagens não adubadas não receberam nenhum tipo de fertilização. O pastejo foi realizada por bovinos. O delineamento foi o de blocos completos casualizados, com 6 tratamentos (A20, A30, A50, NA20, NA30 e NA50) e 5 repetições, totalizando 30 unidades experimentais (piquetes) de 400 m² cada. O período de avalições foi de julho de 2010 a março de 2011. Não foi possível atingir 95% de I.L. nos tratamentos NA20 e NA30, que tiveram entrada aos 91% e 89% respectivamente, nos demais tratamentos a entrada dos animais ficou entre 94% e 96% de I.L.. O intervalo entre pastejos do tratamento NA50 foi de 130 dias, e dos tratamentos adubados 90d, 29d e 17d, para os períodos de inverno primavera e verão respectivamente. Não houve diferença de alturas de entrada nos tratamentos não adubados (91cm). A altura de entrada do tratamento A50 foi maior que ás dos tratamentos A30 e A20 (74cm x 56cm e 50cm respectivamente). A massa de forragem em pré pastejo variou entre 3596 e 9518 kgMS.ha-1, apresentando maior proporção de material morto e menor proporção de folhas nos resíduos de 50cm. A massa seca total em pós pastejo foi maior quanto maior a altura de resíduo (1224, 1926 e 5556 kgMS.ha-1 para os resíduos de 20cm, 30cm e 50cm respectivamente). A massa seca de folhas verdes em pós pastejo foi maior nos resíduos de 50cm (248, 470 e 1616 kgMS.ha-1 para os resíduos de 20cm, 30cm e 50cm respectivamente). A proporção de folhas no resíduo não variou entre alturas nos tratamentos adubados (28%), mas foi decrescente conforme reduções no resíduo dos não adubados (34%, 22% e 13% nos resíduos de 50cm, 30cm e 20cm respectivamente). O acúmulo total dos tratamentos adubados e não adubados foi de 19514 e 8897 kgMS.ha-1 respectivamente. O acúmulo dos pastos adubados foi de 3204, 7484 e 9703 kgMS.ha-1 no inverno, primavera e verão respectivamente. A proporção de perdas em relação ao cúmulo foi maior nos resíduos de 50cm em relação aos de 20cm e 30cm (46% x 30% e 29% respectivamente). A densidade populacional de perfilhos foi de 672 e 521 perfilhos.m-2 em pastos adubados e não adubados respectivamente. A infestação por plantas invasoras foi maior nos resíduos de 20cm, independentemente da adubação. É possível que o manejo do pastejo mais adequado seja de alturas pré e pós pastejo mais altas sem adubação, e mais baixas com adubação intensiva. / In pasture based production systems, grazing management has great influence over productivity, responses to fertilization and pasture longevity. There may be differences between best ways of managing the grazing process in tropical grasses under different fertility conditions. The aim of this study was to analyze the effects of defoliation severity associated with defoliation frequency based in light interception (95%) over Panicum maximum cv. Tanzânia grasslands under hi and low fertilization. The experiment was conducted at São Paulo State University, Piracicaba SP Brazil. Treatments were factorial combinations of 2 fertility conditions, fertilized (F) and unfertilized (UF) grasslands and 3 defoliation intensities (20cm, 30cm and 50cm post grazing heights). Fertilized treatments received 572 kg N.ha-1, 472 kg K2O.ha-1 e 230 kg P2O5.ha-1, and unfertilized didnt receive any kind of fertilization. Beef cattle steers were used as defoliation agents. Treatments were distributed among the 30 experimental units (400 m² paddocks) according to a complete and randomized block design, with 6 treatments (F20, F30, F50, NF20, NF30 and NF50) and 5 replications. The evaluation period was from July, 2010 to March 2011. Unfertilized treatments with the lower post grazing heights (20cm and 30cm) could not reach 95% of light interception due to it leaves morphology (upright) and small tiller population. Grazing intervals were the same among fertilized treatments in the summer (17 days). Pasture height in the moment that it achieved 95% of light interception were higher for the unfertilized grasslands, and for the higher post grazing treatments. Smaller post grazing heights were related with greater leaf and less dead material proportion in the pre grazing forage mass. There was no effect of the residual heights over the leaf proportion in the post grazing mass considering the fertilized pastures. Lower defoliation intensities were related with bigger proportions of forage losses due to grazing process. Fertilized treatments produced 19514 kg of DM.ha-1 while the unfertilized treatments produced 8897 kg of DM.ha-1 in 198 days, and there was no influence of residual heights over this characteristic. Tiller densities were affected only by fertilization and not by the grazing intensity. However, the grazing intensity had effect in to the weed appearance.

Made available in DSpace on 2015-03-05T16:19:36Z (GMT). No. of bitstreams: 0 Previous issue date: 26 / UNISINOS - Universidade do Vale do Rio do Sinos / A constante degradação ambiental, em especial a fragmentação de hábitat, tem levado a alterações nas populações de mamíferos em todo o mundo. No Campo de Instrução de Santa Maria (CISM), Santa Maria, Estado do Rio Grande do Sul/Brasil, isto não é diferente, onde a colonização humana trouxe tanto a perda quanto a fragmentação. Na região, os Campos Sulinos e da Mata Atlântica formam uma paisagem onde fragmentos de Floresta Estacional Decidual são circundados por áreas de campos, atualmente usados para pecuária, agricultura e manobras militares. Neste estudo avaliei o uso de fragmentos florestais e áreas de campo por mamíferos, abordando freqüência de ocorrência, riqueza, diversidade e abundância de registros em três tipos de hábitats grandes fragmentos (FG) > 193 ha, pequenos fragmentos (PE) entre 18 e 47 ha e áreas de campos (CA). Estabeleci grades de armadilhas com seis armadilhas de pegadas, iscadas com banana, bacon e "gland lure". Em cada série bimestral de amostragens revisei as armadilhas a cada quatro dias, registrando as pegadas encontradas em cada armadilha. Houve um total de seis séries de amostragens entre ago/04 e jul/05, onde obtive um total de 364 registros de grupos de mamíferos (formado por um ou mais espécies da mesma família). Mazama sp. usa grandes fragmentos mais frequentemente que canídeos (Pseudalopex gymnocercus e Cerdocyon thous) que são mais generalistas no uso de hábitat. Os grandes fragmentos mostraram maior riqueza (FG = 9, PE = 7 e CA = 3), diversidade e abundância de registros que os outros tipos de hábitats. Entretanto, há diferenças significativas apenas nas amostragens de Nov-Dez/2004 e Jan-Fev/05, os quais os valores de P foram 0,031 e 0,022 para riqueza e abundância. Para diversidade os valores de P foram 0,042 e 0,010 nos mesmos meses. Estas diferenças ocorreram apenas entre grandes fragmentos de áreas de campo. Os resultados indicaram que grandes áreas de florestas têm uma elevada riqueza, principalmente quando comparada a áreas de campos. Além da importância das grandes áreas de florestas para os mamíferos, ficou evidente também o valor que as áreas de campos possuem, por abrigar espécies mais associadas a áreas campestres. No CISM, mesmo com a alteração das áreas de campo e dos fragmentos de Floresta Estacional Decidual, os resultados mostram o peso de diferentes hábitats no conceito de diversidade beta (dissimilaridade entre hábitats). Um manejo apropriado das áreas de campo seria importante para a conservação de mamíferos em ambos biomas, Floresta Atlântica e Pampas. / The constant environmental degradation, in special the habitat fragmentation, has leading to alterations in mammal populations around de world. Into the Campos de Instrução de Santa Maria (CISM), Santa Maria, State of Rio Grande do Sul/Brazil, it is not different, since the human colonization has led to habitat loss and fragmentation. In this region the Campos Sulinos (southern grasslands) and Atlantic forest, form a landscape where fragments of Deciduous Seasonal Forests are surrounded by grasslands now used for cattle-raising, agriculture, and military activities. In this study I evaluated utilization of forest fragments and grassland by mammals, focusing on their frequency of occurrence, richness, diversity, and abundance in three types of habitats (large forest fragments (FG) - > 193 ha, small forest fragments (PE) between 18 and 47 ha, and open areas (CA). I established "trapping" grids with six footprint traps, baited with banana, bacon and "gland lure". For each bi-monthly trapping session I revised the traps every four days after setting them, recording all footprints found. For a total of six trapping sessions between Aug/04 and Jul/05, where I obtained 364 records of mammal groups (formed for one or more species of the same family). Mazama sp. deers use large fragments more frequently whereas the canids (Pseudalopex gymnocercus and Cerdocyon thous) were more generalist in habitat use. The larger fragments showed higher richness (FG=9; PE=7 and CA=3), diversity and abundance of records than the other areas. However, there are significant differences only in the samplings of Nov-Dez/2004 and Jan-Feb/05, which the P values were 0,031 and 0,022 for richness and abundance. For the diversity the values of P were 0,042 and 0,010 in the same months. These differences occurred only between large fragments (FG) and grasslands (CA). Results indicated that large forested areas harbour a higher richness, mainly when compared to the grasslands. Larger forest fragments are important for mammals, but in our study grasslands shelter characteristic species of such areas, increasing beta diversity. In the CISM, even with the relatively high disturbance of the grasslands and Deciduous Seasonal Forest, the results showed the importance of different habitats into the idea of beta diversity (dissimilarity between habitats). A proper management of these areas would be important for mammal conservation of both Atlantic Forest and Campos Sulinos.

Made available in DSpace on 2017-07-21T18:13:38Z (GMT). No. of bitstreams: 1 Karine Dalazoana.pdf: 6220855 bytes, checksum: 0017548277dde01ea05c3897cffbb272 (MD5) Previous issue date: 2010-02-08 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / In the present, the ecosystems‟ fragmentation is considered one of the main causes of the biodiversity loss in natural environments. The remaining native grassland (Estepe Gramíneo-Lenhosa) in Parana State has been suffering hard human pressure, especially due to the expansion of activities as agriculture, animal production and forestation. The Campos Gerais National Park maintains an important portion of these natural grassland ecosystems relatively well conserved. Comprehending the functional organization of this landscape is fundamental for its management, in both ways, as in conservation as much as in restoring destroyed areas. Therefore, this study aims to characterize the special heterogeneity of the grassland matrix by the boundaries of the Campos Gerais National Park, to comprehend its spacial organization and its functional relations. Moreover, it has been made analysis of the landscape‟s composition and structure based on maps, describing the physical characteristics of the area, followed by floristic and vegetation structure researches. There were 481 fragments identified, 54.5% of the Devonian Scarp in the Park is by native grassland. There is a predominance of Stricto Sensu Grasslands (Dry Grasslands), followed by the Wet Grasslands besides the Rocky Grasslands. The floristic research showed high vegetal diversity, with many endemic, rare and endangered species. The sample sufficiency was fixed between 14 and 18 meters, depending on the environmental conditions of the fragment. The landscape appears to be low to moderate diverse, with an similarity distribution of fragments (E = 0.91), with a lack of dominance (DOM = 0.10). The shape indices and circularity and fractal dimension revealed fragments varying from isogeometrical to slight linear. The analyzes of proximity and neighborhood showed a favorable context to connectivity and to the biological flow of species, once a great portion of the grassland fragments (about 78.6%) having neighbors until 100 meters far. So, larger fragments are source areas while the smaller ones are ecological stepping-stones and those more linear perform as corridors. For the generalist species, the grassland fragments of the Campos Gerais National Park seems to be connected, otherwise, for the restrictive species it is necessary future studies. There is a high susceptibility of edge related to the water flow, specially the Wet Grasslands. Management of the grassland areas is necessary to promote its natural regeneration, guarantying the conservation of fauna and flora, minimizing the human pressures and its consequent reducing biodiversity. / Atualmente a fragmentação de ecossistemas pode ser considerada uma das principais causas da perda de biodiversidade em ambientes naturais. Os campos nativos (Estepe Gramíneo-Lenhosa) remanescentes no estado do Paraná vem sofrendo forte pressão antrópica, principalmente com a expansão das atividades agro-silvo-pastoris. O Parque Nacional dos Campos Gerais abriga uma parcela significativa destes ecossistemas campestres naturais relativamente bem conservados. A compreensão da organização funcional desta paisagem é integrante fundamental para sua gestão, tanto no sentido de conservação quanto de recuperação de áreas já degradadas. Para tanto, esse trabalho tem por objetivo caracterizar a heterogeneidade espacial da matriz campestre nos limites do Parque Nacional dos Campos Gerais, visando compreender sua organização espacial e suas relações funcionais. Deste modo, foram realizadas análises de composição e estrutura da paisagem sobre mapeamentos descrevendo as características físicas da área, seguidos de levantamentos florísticos e de estrutura de vegetação. Foram identificados 481 fragmentos, sendo que 54,5% da área da Escarpa Devoniana no PNCG é constituída por campos nativos. Verificou-se a predominância da Estepe Stricto Sensu, seguida pela estepe higrófila e refúgios vegetacionais rupestres. O levantamento florístico revelou elevada diversidade vegetal, com a presença de diversas espécies endêmicas, raras e ameaçadas. A suficiência amostral para estudos de comunidades campestres fixou-se entre 14 e 18m, dependendo das condições ambientais do fragmento. A paisagem revela-se baixa a moderadamente diversificada, apresentando uma distribuição igualitária de fragmentos (E = 0,91), com ausência de dominância (DOM = 0,10). Os índices de forma, circularidade e dimensão fractal revelaram fragmentos que variam de isogeométricos a pouco linearizados. As análises de proximidade e vizinhança revelaram um contexto favorável à conectividade e ao fluxo biológico de espécies, com grande parcela dos fragmentos campestres (cerca de 78,6%) possuindo vizinhos em distâncias de até 100m. Nesta perspectiva, fragmentos maiores prestam-se ao papel de áreas-fonte enquanto os menores enquadram-se como trampolins ecológicos e aqueles mais lineares na condição de corredores. Para espécies generalistas os fragmentos de campo do Parque Nacional dos Campos Grais parecem estar conectados, contudo, para espécies restritivas necessita-se mais estudos. Há grande suscetibilidade de borda com relação aos fluxos hídricos, em especial com relação à Estepe Higrófila. É necessário que haja o manejo das áreas de campo nativo com o intuito de promover a sua regeneração natural, assegurando a preservação das espécies vegetais e animais de modo a minimizar as pressões antrópicas exercidas e conseqüente perda de biodiversidade.

Ecossistemas campestres encontram-se fortemente impactados por conversão de hábitat e por espécies exóticas invasoras. É necessário restaurar os ecossistemas campestres ao redor do globo. Entretanto, para os ecossistemas campestres brasileiros há poucas experiências de restauração e precisamos testar a viabilidade de técnicas normalmente empregadas em outros lugares. O objetivo deste estudo foi testar diferentes combinações de técnicas para restauração de campos invadidos por Urochloa decumbens nos Campos Sulinos, sul do Brasil. Combinaram-se duas técnicas de controle da espécie invasora (aplicação de herbicida e remoção superficial de solo) e duas técnicas de introdução de espécies nativas (transposição de feno e semeadura direta). Foram estabelecidos oito blocos em um experimento bifatorial no Morro Santana, Porto Alegre, combinando dois fatores e cada um com três tratamentos (duas técnicas mais o controle). A cobertura de vários grupos de espécies, riqueza de espécies e composição de espécies foram avaliadas por análises de variância, e então também por análise de coordenadas principais. Adicionalmente, a relação entre a cobertura da invasora e das espécies nativas foi investigada. As técnicas de controle da invasora mostraram-se eficientes tanto na redução da cobertura da espécie, como em permitir a entrada de espécies nativas na comunidade. Comparando as duas técnicas, aplicação de herbicida pareceu ser melhor do que a remoção superficial de solo, pois parcelas que tiveram a aplicação tiveram menor cobertura da invasora e maior riqueza de espécies. Já as técnicas de introdução de espécies mostraram-se insuficientes para adicionar espécies nativas na comunidade para competir com U. decumbens. Padrões de composição de espécies diferiram entre os tratamentos. Técnicas de controle do invasor diferiram grandemente do seu controle, que foi dominado por U. decumbens. Uma clara relação existe entre a cobertura da invasora e a presença e cobertura de espécies nativas. Então o controle da espécie invasora é fundamental para uma maior recuperação da vegetação. Entretanto, os resultados aqui apresentados correspondem a apenas oito meses após a finalização da implementação do experimento, e ações futuras de manejo na área deverão combinar novamente o controle da invasora com introdução de espécies nativas. / Grasslands ecosystems are strongly impacted by land use and invasive species. It is necessary restore these ecosystems around the world. However, there are few experiences with ecological restoration for the Brazilian grasslands and we need to test the viability of techniques normally used in others grasslands ecosystems. The aim of this study was to test different combinations of techniques to the ecological restoration of grasslands invaded by Urochloa decumbens in Campos, Southern Brazil. We combine two techniques to control the invasive species (herbicide application and topsoil removal) and two techniques to introduce native species (hay transfer and direct sowing). We established nine blocks in a bi-factorial experiment on Morro Santana, Porto Alegre, Rio Grande do Sul, combining two factors and each one with three treatments (two techniques plus the control). The coverage of various groups of species, species richness, and species composition were evaluated by variance analyses, and the later also by a principal ordination analysis. Additionally, the relation between invader coverage and native species was investigated. Both techniques to control invasive species have shown to be efficient to reduce the coverage of the invasive species, as well as to allow the arrival of native species. Specifically comparing them, the herbicide application seems to be a better treatment than the topsoil removal, once plots with herbicide had lower invasive species coverage and higher species richness. However, the species introduction techniques failed efficiently to add native species to the community composition and to compete with U. decumbens. Species composition patterns differed among the treatments. The invader control techniques greatly differed from their control, which was dominated by U. decumbens. A clear relationship exists between the invader coverage and the presence and coverage of native species. Thus, the control of the invasive species is fundamental to further vegetation recovery. Nevertheless, results here presented correspond to just eight months from the experiment implantation and future monitoring and management actions on the area should combine once more the control of the invasive species and the introduction of native species.

No description available.

Une assurance indicielle est proposée en réponse à l'augmentation des sécheresses impactant les prairies. Elle se base sur un indice de production fourragère (IPF) obtenu à partir d'images satellitaires de moyenne résolution spatiale pour estimer l'impact de l'aléa dans une zone géographique définie. Le principal enjeu lié à la mise en place d'une telle assurance réside dans la bonne estimation des pertes subies. Les travaux de thèse s’articulent autour de deux objectifs : la validation de l'IPF et la proposition d'amélioration de cet indice. Un protocole de validation est construit pour limiter les problèmes liés à l'utilisation de produit de moyenne résolution et au changement d’échelle. L'IPF, confronté à des données de référence de différentes natures, montre de bonnes performances : des mesures de production in situ (R² = 0,81; R² = 0,71), des images satellitaires haute résolution spatiale (R² = 0,78 - 0,84) et des données issues de modélisation (R² = 0,68). Les travaux permettent également d'identifier des pistes d'amélioration pour la chaîne de traitement de l'IPF. Un nouvel indice, basé sur une modélisation semiempirique combinant les données satellitaires avec des données exogènes relatives aux conditions climatiques et à la phénologie des prairies, permet d'améliorer la précision des estimations de production de 18,6 %. L’ensemble des résultats obtenus ouvrent de nombreuses perspectives de recherche sur le développement de l'IPF et ses potentiels d'application dans le domaine assurantiel. / An index-based insurance is provided in response to the increasing number of droughts impacting grasslands. It is based on a forage production index (FPI) retrieved from medium resolution remote sensing images to estimate the impact of hazard in a specific geographical area. The main issue related to the development of such an insurance is to obtain an accurate estimation of losses. This study focuses on two objectives: the FPI validation and the improvement of this index. A validation protocol is defined to limit problems attached to the use of medium resolution products and scaling issues in the comparisons process. FPI is validated with different data: ground measurements production (R² = 0.81; R² = 0.71), high resolution remote sensing images (R² = 0.78 - 0.84) and modelled data (R² = 0.68). This study also points out areas of improvement for the IPF chain. A new index, based on semi-empirical modeling combining remote sensing data with exogenous data referring to climatic conditions and grassland phenology, allows improving production estimation accuracy by 18.6%. Results of this study open several new research perspectives on FPI development and its potential practical application.